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RR-0-5430-P3 - CTIS - University of Texas at El Paso

1. 1 cm i I I I Es 00 C n T 1 1 1 13 13 13 IRI imik 2 11 5e 1 MC 96 2160 2340 2160 2150 MC P 96 16 80 18 20 16 80 E 4 1 54 1 1890 2 4 70 0 i 1 Back Save Results Figure 5 3 Cost Benefit Results for the Remediation Strategies 40 REFERENCE e AASHTO 2002 AASHTO Design Guide 2002 NCHRP 1 37 The Mechanistic Empirical Design Guide Federal Highway Administration e Abd El Halim A O Haas R and Chang W A 1983 Geogrid Reinforcement of Asphalt Pavements and Verification of Elastic Layer Theory TRB Research Board Record No 949 pp 55 65 Basma A A Tuncer E R 1991 Effect of Lime on Volume Change and Compressibility of Expansive Clays Transportation Research Board TRR No 1296 Washington DC pp 54 61 e Bell D O and Wright S G 1991 Numerical Modeling of the Response of Cylindrical Specimens of Clay to Drying FHWA TX 92 1195 e Bell F G 1996 Lime Stabilization Of Clay Minerals And Soils Engineering Geology 42 pp 223 237 e Cicoff G A and Sprague C J 1991 Permanent Road Stabilization Low Cost Pavement Structures and Lightweight Geotextiles Transportation Research Record 1291 pp 294 310 e Croft J B 1967 The Influence of Soil Mineralogical Composition on Cement Stabilization Geotechnique vol 17 London En
2. To proceed to the REMEDIATION module the user needs to click the Determine Remediation Strategies button in the bottom right of the screen The REMEDIATION module is presented in Chapter 4 ExSPRS Expert System for Pavement Remediation Strategies September 2006 Version 1 0 EVALUATION module This section is used to perform both structural and performance evaluation checks on the pavement section Additional Evaluation Information Required Evaluation Checks Outcome Longitudinal Graph 27 Bar B 26 i E 5 d E 40 50 60 FO a 30 100 Distance from shoulder towards centerline in Determine Remediation Strategies Figure 3 4 Longitudinal Cracking Check Graphical Result 17 18 CHAPTER 4 REMEDIATION MODULE In this chapter the following items are discussed as used in the REMEDIATION module o Alternative ways to consider for overcoming structural inadequacy and performance problems o Description of each alternative on how to improve the pavement system In the REMEDIATION module six modification strategies grouped into two categories are available for consideration 1 To improve subgrade strength and stiffness and 2 To minimize moisture variation induced swell shrink problems ExSPRS will recommend appropriate methods to consider from either or both categories following the logic flowchart shown in Figure 4 based on the evaluation results Figure 4 1 Logic Flowchart of Reco
3. I 3 Geosyntethics Tensile strength Ib 600 Cost 5 234 4 Decreasing Clay Content Depth ir 12 o Cost LEY 0 7 I 5 Deep Dynamic Compaction Proctor 95 Cost 5 5 Moisture Control h c Mex Fanny Barrier film thickness n 044 Cost 5 reu le d Dramage baprosement Culvert diameter hz l Cost LF 2050 spaceing ft 500 Sloped section gentle Cost 5 n15 Yoon Vagetation emerat Big tree diameters nifi to of big trees to be removed per mile TN Ma of trees less to 400 Cost Ea 10 35 than 12 per acre s Hardwoods D to 25 Roadside width for smaller trees 19 Cost acre 2750 00 Modified Input Original Stabilization Geosyuntethics Moisture Content LIndercut amp Dynamit Decreasing clay BEEN a Backfill Compaction corntert Mr nptimum iksi 30 o X X 4 X m25 X 8 22 Mrwetiksi 45 50 14 9 PI 200 OMS 96 MOD HEN ipsi Soil Class u e to m 2 P 25 d az in ho e Qu h 347142 400 Fatigue 1 057 1 206 1 606 1 185 1057 1 057 1 085 E millions Ruting millions Design C in Design B 0 021 0 021 0 027 4 LT i s um Gy dm G3 4 bo Ci my
4. NOT INTENDED FOR CONSTRUCTION BIDDING OR PERMIT PURPOSES Yaqi Wanyan MSCE Enrique Portillo Imad Abdallah MSCE Soheil Nazarian PhD PE 66495 Table of Content CHAPTER 1 INTRODUCTION mute ee cu S LUE 1 l 1 SYSTEM REQUIREMENT AND INSTALLATION RN 2 1 2 DESCRIPTION PROGRAM 5554 a E NT UN eMe EE D CHAPTER 2 INPUT MODULE eren pe eed a eee ee Vasa tee 7 2s BASIC NP e ae ee NE er M EIE y 22 EVALUATION OPTIONS INPUT se reto aee leitete Md 9 PACEM A A 11 CHAPTER 3 EVALUATION MODULE 2 icivtessas vcektui ee eese ence an 13 3 1 EVALUATION OPTIONG 2ccsccccscoccsceccscsccscscscscsecscsscscaccscsceecscescscesescascscacescscscsceees 13 3 26 EVALUATION CHECKS 15 CHAPTER 4 RE VER DTA TION MODULE anua 19 4 1 REMEDIATION STRATEGIES FOR CONSIDERATION cccccececcececcececcsceccscecscscessscecescecesees 20 4 2 DETAILS OF REMEDIATION STRATEGIES TO CONSIDER c cccescccecsceccccecscecescsceceececesees 20 CHAPTER 5 COST BENE ETE MODULE id 33 de COST ANALYSIS ASSUMP LIONS bsec bene eost ceu biles 33 SN 30 5 3 COST BENEFIT ANALYSIS RESULTS sccscoccscoccecscoscscaccecaccscacscscnscecsscccasescscescscnecs 38 CHAPTER 6 ER 41 111 1V List of Tables Table 1 1 List of Input Parameters Required in ExSPRS pp 5 Table 3 1 Summary of Example Input Data Fort Worth Case 0 12 Tabl
5. C Nonlinear Figure 3 2 Subgrade Shear Failure Check Input Structure Roughness Model In order to estimate IRI and PVR more accurately two environmental related questions are asked 1 What is the percentage of time within a typical year that the pavement is exposed to wet season moisture level approaching saturation 2 What 1s the quality of the pavement drainage system The user needs to make appropriate selections according to his her experience Once all the relevant information for the EVALUATION module is provided the user can proceed to view the Evaluation Outcome by clicking the Perform Evaluation Checks button at the bottom right hand side of the window 3 2 EVALUATION CHECKS OUTCOME The Evaluation Checks Outcome window is divided into four panels to present the results for the four Evaluation Options see Figure 3 3 The top left portion presents the outcome of the fatigue cracking and rutting check the top right section presents the results for the subgrade shear failure check the bottom left section 1s for the roughness check results and finally the bottom right portion shows the results for the longitudinal shrinkage cracking LSC check 15 EXSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 Sele EWALUATION module This se Lion is used En perform both structural and performance evaluation checks on the pavement section Additional E valuation Information Required Ev
6. Update and Return Method Figure 4 7 Moisture Control Method of Using Sloped Sections itsloped se s minimize concentration of ater minimize needed road width avoid the eed for an inside ditch and minimize costs Qutsloped roads with clay rich slippery road surface materials often require rock surface stabilization or limited use during rainy periods to assure traffic safety asloped sections best control the road surface water but concentrate water and thus require a system of ditches cross drains and extra road width for the ditch Crown sections are appropriate for higher standard two lane roads on gentle grades They Inslope with Ditch Section also require a system of inside ditches and cross drains It is difficult to create and maintain a crown on a narrow road so generally insloped or outsloped road drainage is more effective for rural roads Recommended design details shown on right m a ExSPES Expert System for Pavement Remediation Strategies September 2008 Version 1 0 REMEDIATION module This section provides several remediation strategies to consider based on the evalutaron results Remediation Strategies to Consider Stabiization Undercut Backfil Geosunthethics Decreasing Clay Content Deep Dynamic Compaction Moisture Control Moisture Control f Vertical moisture barriers f Drainage improvement Vegetation treatment Drain Improvement f Sloped Sections f Cross
7. is also provided as a choice to double check the cases when the pavement structure fails the Texas triaxial check If triaxial test results are provided in the INPUT module no further information is required and the rightmost question in the EVALUATION module under the Subgrade Shear Failure model is grayed If on the contrary the triaxial test results are not available the subgrade condition is used to estimate these parameters The user also needs to select the analysis option and axle load type in order to execute the MTRX also known as LoadGage check By default the LoadGage program runs a linear analysis to predict the stresses However for the advanced user a nonlinear option is included to permit modeling of the stress dependency The nonlinear analysis option will provide a more realistic prediction of the stresses induced under loading Jooste and Fernando 1995 for thin pavements This analysis in MTRX uses equation with and material constants determined from resilient modulus testing Uzan 1985 14 Y Y Select condition of the subgrade Good subgrade Angle of intemal friction degree 35 Fair subgrade Cohesion of soll Poor subgradel Classification of soit ES Weak subgrade O Men weak subgrade Subgrade shear failure Do you want to perform the MTR check Select axle load type e Ur Jiu Single C No E C Dual Axle Select analysis option Linear C Tandem
8. shaped to pass high clearance vehicles to block traffic 4 1 2 1 2m 4 1 2m gt Recommended design details shown on right Figure 4 9 Moisture Control Method of Using Water Bars ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 REMEDIATION module This section provides several remediation strategies to consider based on the evalutaion results Remediation Strategies to Consider Stabilization Undercut Backfil Geosynthethics Decreasing Clay Content Deep Dynamic Compaction Moisture Control Moisture Control von Dealing with Steep Road Grades Drainage improvement piii suci Try to avoid steep road grades in excess of 12 to 18 It is Drain Improvement very difficult and expensive to properly control drainage on C Sloped Sections steep grades C Cross drain Steep road grades are undesirable and problematic but en occasionally necessary On grades up to 10 Culvert cross drains or rolling dips are easy to use Between 10 Update and 15 frequently spaced culvert cross drains work often in conjunction with armored ditches On grades over 15 it is difficult to slow down the water or remove it from the road surface rapidly On such steep grades it is best to use frequently spaced cross drain culverts with armored ditches Also the road surface will need armoring or surfacing with some for
9. A good design relies on not one single factor but many factors combined ExSPRS program tries to identify a more critical combination of considerations in hoping for a favorable alternative Expertise is invaluable to apply the findings to assist engineers in their decision making process The following paragraph will discuss how to compare cost estimations and benefit results based on the example presented in this manual As prevailing distress problems are different for each district the concentration of the design goal changes which in turn will yield different user preferences In the example case let s assume longitudinal cracking 1s reported to be the main issue and thus decreasing subgrade moisture susceptibility become more critical than other aspects Computational results shown in Figure 5 3 indicates placing a geosynthetic reinforcement layer near base subgrade interface provides the most benefits in keeping longitudinal cracking problem away Also by referring to the cost estimation using geosynthetics seems to be a very cost effective choice Thus original 38 design with geosynthetic reinforcement is very favorable compared to other possibilities Please keep in mind that the values used in this example as benefit input were hypothetical and are for demonstration purpose only After the analysis 15 complete the program provides a Save Results button at the bottom of the Cost Benefit Analysis module which allows the user to sa
10. CD ROM Shell 1978 Shell Pavement Design Manual Asphalt Pavements and Overlays for Road Taffic London England Steward J Williamson R and Mohney J 1977 Guidelines for Use of Fabrics in Construction and Maintenance of Low Volume Roads FHWA TS 78 205 The Asphalt Institute 1982 Research and Development of the Asphalt Institute s Thickness Design Manual MS 1 9 Ed Research Report 82 2 RR 82 2 Maryland 204 p Thompson M R 1966 Lime Reactivity of Illinois Soils Journal of the Soil Mechanics and Foundations Division ASCE Vol 92 No SMS Uzan J 1985 Granular Material Characterization Transportation Research Record 1022 Transportation Research Board Washington D C pp 52 59 Uzan J Livneh M and Shklarsky E 1972 Cracking Mechanism of Flexible Pavements Transportation Engineering Journal Proceedings of the American Society of Civil Engineers February pp 17 36
11. base course towards the asphalt layer If the tensile strength of the asphalt layer 1s also inadequate the crack may propagate through to the surface after which another new cracking cycle begins Uzan et al 1972 Bell and Wright 1991 During a dry weather cycle subgrade shrinkage will cause lateral forces which may exceed its tensile strength The increase in the lateral shrinkage stress of soil 1s the main reason for the development of longitudinal cracks A finite element model is incorporated in ExSPRS to estimate the threshold moisture contents for the initiation and propagation MCp of the longitudinal cracks in the pavement structure This model also estimates the most likely location for such cracking 10 A thorough description of the theory and the model used in ExSPRS 1s provided in TxDOT Research Report TX 0 5430 2 To utilize this model the user needs to either provide laboratory results of the shrinkage strain or use the shrinkage strain vs moisture content relationships later referred to as shrinkage strain model developed under this research project If information regarding the shrinkage strain is available and the user selects any of the first three test options two inputs are required 1 the tensile stress under dry condition and 2 the shrinkage strain value that can be obtained from a shrinkage strain characterization test such as linear shrinkage bar test or the volumetric shrinkage strain test Mean
12. equations based on literature review to quantify required volume of mixing sand see Figure 4 20 The user 15 encouraged to explore all remediation strategies that are of interest After studying the feasible modification methods the user can proceed to the COST BENEFIT module by selecting the button on the bottom right screen to determine which of the strategies are economically feasible As mentioned at the beginning of this chapter this module was to provide the user with the remediation option available to him her based on the evaluation checks For each remediation strategy selected the user needs to provide additional information in order for that strategy to be analyzed and its benefit and cost determined This is covered in the next chapter 30 ExSPRS Expert System for Pavement Remediation Strategies september 2900 Version 1 0 Decrease Clay Content Mowafy ef af 1985 suggested a reduction of swelling potential can be achieved by decreasing the clay content of the problematic soil Hudyma and Burcin Avar 2006 also suggested the use of soil mixing to mitigate expansive soils is a promising yet not very well documented modification technique For a given initial water content and normal pressure there is a critical clay content at which the amount of swell is zero Below the critical value the soil will shrink and above that the soil is susceptible to swelling To accomplish the controlled clay content the swell susceptible
13. from INPUT module and follow the program steps through other modules It is best not to navigate to the next module before completing the information on the current one To select a particular option with check box or radio button move the pointer to it and then click with the left mouse button To select a particular option from a drop down list move the pointer to the downward arrow land click once while scrolling through the choices click with left mouse button when the desired answer 1s highlighted To enter data for a particular variable move the cursor to the field or cell Then type in the required data To position the cursor to an input field move the pointer to the field and click on it Hints are provided for all sections of the program that require interaction with the user as shown in Figure 1 2 Table 1 1 provides a list of all required inputs in order to execute the program A default value is provided in the program for each input A case study will be followed as an example to demonstrate the program eres Ee Thickness in E Select payment layer type and click update after each layer 2 Design Properties ESAL millions Tire Pressure psi 1 00 Analysis Period years Road Length mile Mumber af Lanes Serviceability Indes both directions Reability in decimalz Lane widthfft 1 2 C Dep EE WIESE po Treated 12 Did you run ane of the following shrinkage characterization test u
14. tabulated in Table 5 2 with fr meaning increase 4 meaning decrease 1 meaning either increase or decrease is possible and meaning no change The information can assist the user as a guide to estimate the appropriate input values Additional information can be found in TxDOT Research Reports 0 5430 1 and 2 Table 5 2 Summary of Parameter Changing Trend for Remediation Strategies Remediation Strategies Parameters Geo Moisture P Stabilization Dynamic Clay Compaction Content Mir ksi 3 BEA _ LL 9 3 2 8 51 Triaxial Test Expansive clays are usually chemically stabilized with cement lime or fly ash to reduce their plasticity index liquid limit volume change potential and maximum dry density and to improve optimum water content shrinkage limit and shear and tensile strength properties Croft 1967 Little 1999 Thompson 1966 Bell 1996 Basma and Tuncer 1991 Different results are reported by researchers on how much these parameters changed The use of geosynthetics as reinforcement for subgrade soils in both wet and dry conditions increases tensile strength and initial stiffness of the subsoil decreases long term vertical and horizontal deformation reduces desiccation cracking fatigue cracki
15. that does not require any specialized equipment However unless a suitable backfill material is available near the job site removal and replacement is generally a much more expensive operation than the use of additives For this reason removal and replacement is mostly used in urban areas where dust and environmental impacts make the use of additives less desirable Removal and replacement may also be the best option in areas where deep deposits of peat and muck cannot be treated with the use of additives For lower classification roads economic constrains have to be taken into account If this remediation is selected the program calculates the recommended replacement depth Figure 4 14 provides an example of the calculated undercut and backfill depth in inches provided by the program 28 ExSPRS Expert System for Payement Remediation Strategies September 2008 Version 1 0 EDIATION module This section provides several remediation strategies to consider based on the evalutaion results Remediation Strategies to Consider Mm MEET ERE a ens I ud E ERE te Undercut and Backfill Undercut and backfill is a popular remedial procedure for soft subgrade The procedure is to cover the soft subgrade with a thick layer of granular material or to remove a portion of the soft material to a predetermined depth and replace it with granular material The undercut and backfill method is a simple procedure that does not require any specialized e
16. the COST BENEFIT module shows the input needed for cost estimation of selected remediation strategies The user needs to either select from the drop down list or to enter numerical values for each activated remediation method Unit cost for each strategy will be provided at the right side for quick reference The following sections discuss these cost input for each remediation in detail e Stabilization Recall that in the REMEDIATION module the appropriate stabilizer was selected For this example the stabilizer was lime This information is passed and loaded in this module ExSPRS automatically loads accordingly cost information in a drop down list with different mix percentage As an example the user can select 4 mix The unit cost for 4 lime stabilization of 12 inch lift is retrieved to be 11 3 yd 12 inch lift means the total treatment depth that was entered in INPUT module As a special note for each remediation strategy there maybe more than one possible treatment activities available To continue with the lime stabilization example the user 1s required to identify mix percentage but not the lift thickness In construction however it maybe achieved by stabilizing one single layer of 12 inch two layers of 6 inch each or other lift thickness combinations The rule of thumb used in ExSPRS is always to select the cheapest one among possible pool of activities In this case a single layer of 12 inch treatment is cheaper than 2 runs of 6 i
17. to estimate cost Unit length of 1 mile 15 recommended Number of Lanes for both directions This refers to the total number of lanes in both directions For low volume roads it is usually 2 or 4 Lane Width This input is also used to estimate cost The standard 12 ft lane 15 used as default Depth of Treated Subgrade This is the thickness of the stabilized layer between the base and subgrade in in 3 Subgrade Properties PI Plastic index in percentage Tex 106 E It is a measure of the range of water contents where the soil exhibits plastic properties The PI is the difference between the liquid limit and the plastic limit PI LL PL LL Liquid limit in percentage Tex 104 E The liquid limit LL is the water content where a soil changes from liquid to plastic behavior P200 Percentage of materials passing the 75 um No 200 sieve Tex 110 E e OMC Optimum moisture content is the water content in percentage at which the soil can be compacted to the maximum dry density This value is used as the upper limit of moisture variation e MC under dry condition This constant moisture content value in percentage under dry condition No further weight loss in 24 hr in 104 F oven is used as the lower limit of moisture variation e MDD Maximum dry density is the maximum value obtained by the compaction curve using the specified compactive effort Once the basic inputs are provided the user can select the performance
18. two types of moisture barriers commonly used for pavement Horizontal moisture barriers are designed to stop rainwater from penetrating into the subgrade soils However based on literature the horizontal moisture barriers DO NOT produce a smoother ride than the unprotected pavement nor reduce the moisture variance effectively On the other hand vertical moisture barriers DO work but they are expensive and complicated to construct Sites in wet and semi arid climates with cracked clay soils and shallow root zones will show the greatest benefit from using vertical moisture barriers Jayatilaka ef al 1993 Deep vertical moisture barriers 78 ft usually outperform the shallow ones lt 6 ft in maintaining a more constant moisture regime Gay and Lytton 1988 Figure 4 6 Moisture Control Method of Using Moisture Barriers 24 ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 REMEDIZ JON module This section provides several remediation strategies to consider based on the evalutaron results Remediation Strategies to Consider Stabilization Undercut Backfil Geosynthethics Decreasing Clay Content Deep Dynamic Compaction Moisture Control Outsloped Insloped or Crown Sections Moisture Control f Vertical moisture barriers f Drainage improvement f Vegetation treatment Drain Improvement f Cross drain Water Bars Steep f Control Irdets Qutlets
19. 0 i 2 Undercut and Backfill Depth in 15 Cost LEY 11 54 I 3 Geospntethics Tensile strength Ib Select Cost dy 0 i 4 Decreasing Clay Content Depth 12 Cost LE 0 77 5 Deep Dynamic Compaction Proctor Select Cost 8r wW 5 Moisture Control ll AO Baers Barrier film thickness Select Cost w Erro Jar ean Culvert diameter Select Cost LF 0 Culvet zpaceing ft 500 Sloped section Select Cost EY D Woon Big diameters lin Select No of big trees to be removed per mile 110 of trees less Select Cost Ea E than 12 per acre Hardwoods Select Roadside width for smaller trees 19 Cost acre E Modified Input Original Stabilization Geasyntethics Moisture Content ndercut amp Dynamic Decreasing clay Backfill Compaction content Mr optimum iksi Mr wet iksi MOD pef ipsi Soil Class Perform Cost Benefit Analysis Figure 5 1 Cost and Benefit Analysis Basic Assumptions 34 For a typical lower classification pavement cost analysis only the agency costs are considered due to the fact that the low volume roads typically experience low daily traffic The user costs are considered minimal and are omitted in cost estimates Construction time estimation is also omitted assuming that the agency cost to be the controlling parameter The agency cost is estimated using unit cost approach Unit p
20. 1 Moisture Control Method of Using Inlets and Outlets 27 Figure 4 12 Moisture Control Method of Using Root Barriers 2 Figure 4 13 Moisture Control Method of Removing 28 Figure 4 14 Undercut and terere dian eta eat ta rae na 29 Figure 4 15 Deep Dynamic Compatto anna E EE E 30 Figure 4 16 Decredsing Clay E 31 Figure ostana Bene HEADS io 34 Figure 5 2 Pavement Parameters Modified for Each Remediation Strategy 39 Figure 5 3 Cost Benefit Results for the Remediation Strategies sese 40 vll vill CHAPTER 1 INTRODUCTION Rural low volume farm to market access roads roads connecting communities and roads for logging or mining are commonly referred as low volume roads Low volume roads commonly have an average daily traffic ADT of less than 400 vehicles per day and usually have design speeds less than 50 mph 80 kph AASHTO 2002 This research project was focused on low volume roads over expansive clayey soils in Texas In spite of the over conservative pavement designs recommended and widely used in Texas for roads in high PI clay areas these costly pavements often fail prematurely This failure occurs primarily because of the highly variable properties of the clay throughout the year due to moisture fluctuations A significant amo
21. 24 Number of big trees to be removed per mile 10 Number of trees less then 12 per acre Up to 400 Roadside Width for smaller trees ft side Undercut and Backfill Undercut and backfill depth in ee o Compaction Depth in Percentage of standard proctor density l 5 1 Percentage of hardwoods 0 25 1 2 Deep Dynamic Compaction 5 2 BENEFIT INPUT The benefit input portion of this module is based on comparing structural and performance evaluation results for the original design and that after using a remediation strategy These changes in evaluation results are caused by changes in input parameters The user will be asked to provide new input for those changed parameters by either performing laboratory tests or use their best estimation The benefit input table will originally show the values of the original design for cases being analyzed First column automatically loads the user s input from earlier 36 steps The other columns are designated for remediation strategies as identified with corresponding remediation keyword The values in these columns need to be modified if the corresponding remediation strategy was selected in REMEDIATION module Parameters that are likely to be impacted by the remediation strategy are bolded The following are some general discussions on changes of expansive subgrade soil properties caused by each remediation strategy The changing trend of the parameters under each treatment is
22. RS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 IATION module This section provides several remediation strategies to consider based on the eralutaion results Remediation Strategies to Consider Stabilization Undercut Backfill Geosunthethics Moisture Control Ro Q t B a rri e rs f Vertical moisture barriers Protection of road structure from the effect of tree root damage can be achieved by placing a standard root barrier of 4 foot deep as Vegetation Treatment this will be deep enough to prevent roots getting under the barrier in normal C Vegetation Removal undisturbed soil For situations where the road is built over reactive clays a barrier to the depth of the zone of influence normally 5 10 foot deep Update and Retun should be considered For well constructed roads in good condition it is possible to reduce the depth of the root barrier by utilizing the road base as part of the barrier Using the road base as a horizontal seal root barrier may be placed vertically running from the top of pavement shoulder into the road base where it can be bound o the road base using bentonite to provide a waterproof and root proof seal The benefit of this system is that it allows more soil area for the tree to live in under the road t Drainage improvement Vegetation treatment ROOT BARRIER ROOT BARRIER Lime trench can also be used between the pavement st
23. aluation Checks Outcome shear zrerqu m Tt ee M0 presen fadus ci 4 Slope Fatigue and Subgrade Rutting Check r Subgrade Shear Failure Check Fatique Cracking m Texas triaxial check Fatigue Cracking milions 1 057 Pass DesignD cover im B8 Required D_caver fin hs Subgrade Putting milions 0 021 Fail MTB check Faile d Required 20 year accumulated a 18 kip ESALs fi Failed Design D Base in Required D Base in 1 3 Roughness Check Longitudinal Cracking Check Put onen The cracking in the subgrade induced by the shrinkage strain is initiated at The predicted PYR is 2 60 inches Failed moisture content of 21 60 IRI check The shrinkage induced cracking in the subgrade propagates to surface at moisture content of 15 80 The predicted IRI is 2 11 m m Passed Graph of crack initiation at the top of subgrade across pavement section Figure 3 3 Evaluation Checks Outcome results If an evaluation was not selected in the INPUT module the designated results panel will be blank For the fatigue cracking and rutting check the corresponding allowable load repetitions are reported in million ESALs Fail Pass flags are also shown for each one The design traffic provided by the user in the INPUT module is also reported here for comparison An overall Fail Pass flag is also reported for this evaluation check In the
24. antify benefit and 2 Outcome which compares cost and benefit among alternatives The input portion is shown first when the user first views this module As shown in the top of Figure 5 1 all remediation strategies selected by the user are active and their corresponding treatments and unit are provided Again if a remediation is not selected the corresponding section is grayed out The second portion of the input is associated with the updated parameters of the pavement system that are impacted by the remediation strategies These parameters are listed in a tabular format see Figure 5 1 In the second portion of the COST BENEFIT module the outcome identifies and compares the cost and benefit of all eligible alternatives Once all the inputs such as the detailed modification activities unit cost and modified pavement parameters are provided the cost benefit analysis is computed This outcome is presented in a similar tabular format at the bottom of the screen In this chapter the inputs and outcome of the cost benefit analysis is described 5 1 COST ANALYSIS ASSUMPTIONS Before describing the COST BENEFIT module there are some basic assumptions made to simplify the procedure without compromising the results accuracy These assumptions are presented first 33 ud ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 Sele TS pc iw 1 5tab l zat on Stabilizer Amount Select Cost 5 10
25. bgrade in Yes Coefficient of Linear Extensibility COLE test es Linear Bar B c ERU ORE en 24 Yes Yolumetic Shrinkage Strain T est f Mo Use Built in Model LL 161 Moisture Content in Dry Condition 37 12 o ey eee e MI P200 2 1 00 Maximum Dry Density perl 192 4 Evaluation Options The following the evaluation considerations Please select all that apply Structural Check Performance Check Longitudinal Cracking Subgrade Shear Failure Roughness Load Input File Save Input File Figure 1 2 ExSPRS Start up User Interface Table 1 1 List of Input Parameters Required in ExSPRS Percent of time pavement is exposed to saturation moisture level Design Properties Angle of internal friction from Triaxial tests degrees Design wheel load kips Tire pressure psi Pavement drainage quality Subgrade Modulus during wet season 51 CHAPTER 2 INPUT MODULE In this chapter the following items are discussed as used in the INPUT module Layer properties Design properties Soil properties Preliminary information regarding structural and performance evaluations O O O The ExSPRS INPUT module is developed through an interactive screen which allows the user to rapidly create the input data The default values for a typical low volume road build over high PI clayey subgrade in Texas are displayed in the screen data input fields at the time the
26. ckness over geosyntheticz no modification i needed Evaluation Check Figure 4 4 Use of Geosynthetics the placement of the geosynthetic material If has chosen to select this option as a remediation strategy to consider then the user should answer those questions One option is to use the subgrade resilient modulus which requires no further action since that value was already provided in the IVPUT module Further questions are only required if the user decides to use the other two very approximate methods the use of these two options is discouraged for project level studies Upon selecting one of the two lower radio buttons the appropriate menu will be activated To ensure that the geosynthetic material can be place at the recommended depth middle graph in Figure 4 4 directly without further construction modifications the user needs to provide maximum tolerable depth of rutting during the design life of the roadway in inches Commonly used value of 2 inch was provided as default The Update button needs to be selected The program will show whether thicker layers above subgrade are required for the section with the geosynthetic to be fully functional without losing it s anchorage strength To return to the main remediation tab select the Return button or directly click on the tab 27 Moisture Control Many pavement distress problems are caused by moisture variation and migration The moisture control remediation meth
27. clay soils could be mixed with coarse fractions of granular materials in the field Hudyma and Burcin Avar 2006 reported by mixing two different expansive sols from southern Nevada with different percentage of fine grained silica sands the plasticity index were decreased by up to 75 which changed the expansive soils into low Pl non expansive solls Hudyma and Burcin Avar 2006 used swell index or swell pressure in kN m2 in a generic empirical predictive equation Eq 1 to quantify the swell potential change The Pl of the mixture can be predicted by a simple equation Eq 2 vo Sand 10 Swelllndex MINE Swellindex y exp soil JI s sand Fi sa mixture exp sei sand Figure 4 16 Decreasing Clay Content 31 32 CHAPTER 5 COST BENEFIT MODULE In this chapter the following items are discussed as used in the COST BENEFIT module Determination of unit costs for selected remediation strategies Estimation of updated pavement input parameters for selected remediation strategies Cost comparison of selected alternatives Benefit comparison of selected alternatives O O O The COST BENEFIT module is the last module in the program It provides the user with cost benefit comparison of the original design and selected remediation strategies This module is separated into two parts 1 Input which acquires assumptions to estimate unit costs and updated pavement characteristic parameters to qu
28. consider based on the results of pavement structure and prevent water penetration to subgrade the evalutaion checks In the E next module an analysis is Decreasing Clay Content This strategy is used for problematic soil and is an performed to show the cost and easy to accomplish remediation method to reduce the swelling shnnking potential of the problemetic subgrade soils benefit of each Strategy Deep Dynamic Compactation This strategy be used to maximize unit weight and densisty soils This treatment i considered as of the most economical in situ soil improvement method avaliable Moisture Control These are ways intended to directly control the moisture varition These include using vertical moisture barriers improve surface drainage of the pavement and vegetation removal Please make sure that all questions are answered for each Back remediation strategy considered before proceeding to the Analysis Proceed to the Cost Benefit module of Remediation Strategies with Cost Benefit Comparison section Figure 4 2 Selection of Remediation Strategies 4 2 DETAILS OF REMEDIATION STRATEGIES TO CONSIDER To explore the details of each modification method the user can click on the corresponding highlighted tab All activated remediation strategy tabs are parallel and the user can explore any of the solutions in any order 20 Stabilization Clayey soils are often stabilized with calcium based stabilizers to im
29. drain Water Bars Steep Bars Control Inlets Outlets Update and Return Cross Drain Structures culvert cross drains are used to move ditch water across the road They are the most common type of road surface drainage and are most appropriate for high standard roads where a smooth road surface profile is desired However the pipes are expensive and the relatively small culvert pipes used for cross drains are susceptible to plugging and require cleaning Place Outlet Pipe at Natural Ground Level or Riprap Amor the Fill Material Figure 4 8 Moisture Control Method of Using Cross Drain Structures 23 ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 REMEDIATION module This section provides several remediation strategies to consider based on the evalutaion results Remediation Strategies to Consider MEE IEEE EA BERE Bu LIRE Moisture Control Vertical moisture barriers Water Ba rS Drainage improvement Water b are M Vegetation treatment used to control en rh SE A rm Drain Improvement drainage on iX i C Sloped Sect ss closed or inactive XR C Cross drain roads 4 wheel tot y i drive roads skid x C Steep Bars roads and skid C Control Inlets Outlets trails Water bars 7 frequently 7 N crite Update and Retum spaced for 47 x FE maximum erosion Woe control and can be
30. e 5 1 Summary of Cost Analysis Assumptions Fort Worth Case Study 36 Table 5 2 Summary of Parameter Changing Trend for Remediation Strategies 37 vi List of Figures Heure LE ESPRS PIOS 3 Figure 2 Ex SP RS Start up User Inter lack anne re la 4 Figure 2 1 Selecton or Evaluation Models a a 9 Figure 3 1 gt Eyalual on see rd DE 14 Figure 3 2 Subgrade Shear Failure Check Input Structure pp 15 Figure 3 3 Evaluation Checks Outcome pt 16 Figure 3 4 Longitudinal Cracking Check Graphical Result sess 17 Figure 4 1 Logic Flowchart of Recommended Remediation Strategies 19 Figure 4 2 Selecton or Remediation a an 20 Figure 4 3 Stabilization Window of Remediation Module pp 21 Figure 4A Use OP Ges V MIN CUCS er 22 Figure 4 5 Hierarchy of Moisture Control Methods Re 23 Figure 4 6 Moisture Control Method of Using Moisture 24 Figure 4 7 Moisture Control Method of Using Sloped Sections 25 Figure 4 8 Moisture Control Method of Using Cross Drain Structures esses 25 Figure 4 9 Moisture Control Method of Using Water Bars pp 26 Figure 4 10 Moisture Control Method of Dealing with Steep 26 Figure 4 1
31. each modulus because of the effects these values have on the final solution Layer Description The type of layer being HMA base or subgrade should be identified for each layer The first layer is HMAC by default For surface treatment a thickness of 0 5 in and a modulus of 300 ksi are recommended After the layer type is selected from the drop down list for each layer the user needs to click Update button 2 Design Properties ESAL One direction cumulative 18 kip 80 kN equivalent single axle load ESAL applications in millions at the end of the design period 10 years in this case This value can be obtained from the Transportation Planning amp Programming Division Analysis Period Length of analysis period in years usually 10 years for low volume roads serviceability Index This input pertains to the initial pavement serviceability index which is a function of pavement type and construction quality Typical value ranges between 4 0 and 4 2 Reliability It is a means of incorporating some degree of certainty into the design process The level of reliability to be used for design of low volume roads ranges from 50 to 80 This number should be entered in decimal format Design Wheel Load Load on one single axle or a set of tandem axles in kips Tire Pressure Default value is 100 psi Higher tire pressure is one of the reasons for higher tensile strains and stresses within pavement Road Length This value is used
32. evaluation options 2 2 EVALUATION OPTIONS INPUT Four evaluation options as depicted in the input screen are provided 1 Structural checks that consider fatigue cracking and rutting as well as subgrade shear failure 2 Performance checks that consider longitudinal cracking and roughness The user can deactivate any or all of the options except the fatigue cracking and rutting check Based on the user s selections additional input based on lab testing data and or his her subjective judgments are required The appropriate modules in the right hand side of the INPUT module will be activated depending on the evaluation options selected as shown in Figure 2 1 O A LIE Wodulusiksi No more layers 2 Design Properties ESAL millions 0 Tite Pressjire psi Analysis Period pears T Road Length mile Serviceability Index 40 Euros EE Reability in decimals 8 Design Wheel Load 1 a8 qaid Ln 3 Subgrade Properties FI 29 Optimum Content 3 LL 161 Moisture Content in Dry Condition 27 P200 2 1100 Maximum Dry pef 4 Evaluation Options The following the evaluation considerations Please select all that apply Structural Check Perform ance Check iw Fatigue Cracking and Autting le Cracking W Subgrade Shear Failure iw Roughness Version 1 0 Fatigue Cracking and fe The subgrade exhibits exceptionally low strength during
33. example used in this manual for illustration the section passed the fatigue cracking performance and failed the rutting The overall evaluation check is considered as failed and therefore remediation to prevent rutting 1s required In this example both the Texas triaxial Tex 117 E method and MTRX method were used The Texas triaxial check proposed a required cover depth of 15 in MTRX check required a base thickness of 13 in The original design failed both checks Under the roughness check results the total PVR was estimated to be 2 6 in Since in this example the acceptable PVR limit of 2 in was provided the PVR check also failed The IRI check gave 2 1 m km which passed the criteria for farm to market roads Details of IRI criteria can be found in Research Report TX 0 5430 2 The longitudinal shrinkage cracking check estimated that at a moisture content of 21 6 the shrinkage cracking initiates and at 16 8 the longitudinal crack propagates up to surface At 16 the bottom right of the LSC results panel there is a button Graph of crack initiation at the top of subgrade across pavement section that provides the user with the location and distribution of stresses The user can click to see the distribution of critical points along a 12 ft lane 144 inches in X axis cross section view depth of inches along y axis as shown in Figure 3 4 The critical locations are near the 42 18 in 3 5 1 5 ft range from the pavement edge
34. gland pp 119 135 e Fernando E Liu W and Lee T 2001 User s Guide to the Texas Modified Triaxlial MTRX Design Program e Giroud J P and Noiray L 1981 Geotextile Reinforced Unpaved Road Design Journal of Geotechnical Engineering Division Proceedings of the ASCE Vol 107 No GT9 pp 1233 1254 e Gurung N 2003 A Laboratory Study on the Tensile Response of Unbound Granular base Road Pavement Model Using Geosynthetics Geotextiles and Geomembranes 21 pp 59 68 e Jooste F J and E G Fernando Development of a Procedure for the Structural Evaluation of Superheavy Load Routes Research Report 1335 3F Texas Transportation Institute Texas A amp M University College Station Texas 1995 4 42 Little D N 1999 Evaluation of Structural Properties of Lime Stabilized Soils and Aggregates Vol I Summary of Findings National Lime Association Publication Montanelli F Zhao A G and Rimoldi P 1999 Geosynthetic Reinforced Pavement System Testing amp Design http www tenax net Mowafy Y M Bauer G E and Sakeb F H 1985b Treatment of Expansive Soils A Laboratory Study Transportation Research Record 1032 pp 34 39 Rollings K M and Christie R 2002 Pavement and Subgrade Distress Remedial Strategies for Construction and Maintenance I 15 Mileposts 200 217 Utah DOT research and development report No UT 02 17 R S Means 2007 The 2008 RS Means Heavy Construction Cost Data on
35. he vertical compressive strain on top of the subgrade E is the HMA modulus f to fs are empirical coefficients If the loss of stiffness during wet season is a concern the user is prompted to provide the saturated subgrade modulus in ksi This modulus will be used in the check to account for the worst case scenario Subgrade Shear Failure This option utilizes the Texas Triaxial Design method and LoadGage to check the subgrade shear failure If the user desires to check for the subgrade shear failure the Texas Triaxial Test Tex 117 E results will be required However if the test data is not available default values are assigned by the program based on some general questions The user is strongly encouraged to minimize the use of the default values for this purpose as much as possible Longitudinal Shrinkage Cracking The longitudinal shrinkage cracking is believed to be initiated in the subgrade as a bottom up crack The subgrade cracks under the combined action of shrinkage by drying and the resistance to shrinkage due to base layer on one hand and to the deeper constant moisture layers of the clay on the other hand Resistance to the shrinkage results in shear stresses at the interface of subgrade and base which in turn produce compression stress in the granular courses and tension stress in the clay When the tensile stress equals the tensile strength cracking 15 initiated Upon further drying the crack propagates through the
36. in purpose of decreasing clay content method is to reduce problematic subgrade volumetric change potential by diluting expansive soils with non expansive fills Similar to undercut and backfill every soil characteristic property will change For the purpose of this example changes to the parameters required based on the remediation strategies are made based on educated guess Again laboratory testing would need to be carried out in order to obtain those values The modified values are shown in the highlighted section of Figure 5 2 5 3 COST BENEFIT ANALYSIS RESULTS Figure 5 3 represents the cost analysis results for our example case The original design costs about 347 000 mile followed by the cost of all remediation strategies For example subgrade stabilization using 4 lime costs 160 000 mile and to control moisture variation by using drainage improvement moisture barriers and vegetation removal requires an additional of 110 000 mile However for the remaining four remediation strategies the cost was less than 50 000 mile To justify the benefit of each remediation method before after analysis results should be carefully studied The detailed results for evaluation models are presented in this table with a GREEN color for those that passed the criteria and a RED color for those failed Cost benefit analysis opens the door for more in depth understanding regarding how to reach a reasonable and satisfactory design for low volume road
37. is section is used to perform both structural and performance evaluation checks on the pavement section Additional Evaluation Information Required Evaluation Checks Dutcome Longitudinal cracking Select parameters to include in the shrinkage strain model v Plasticity Index FI Liquid Limit LL le Maximum Dry Density MOD v Dptiamurm Moisture Content Subgrade shear failure Do you want to perform the check Select axle load type Select condition of the subgrade fe Y ues f Single Axle No Select analysis option t Dual Azle Linear Tandem Arl Nonlinear Houghness gt Percent of time the pavement is exposed to moisture levels approaching saturation Quality of pavement drainage Less than 1 Excellent water is drained within 2 hours 1Zt05 feos j Poor water is drained within 1 month Fair water i drained within 1 week f Greater than 25 Very poor water is never drained Perform Evaluation Checks Figure 3 1 Evaluation Options Subgrade Shear Failure Model Figure 3 2 depicts the input structure for subgrade shear failure check By default the Texas Triaxial method is used The required cover depth from this method may be over conservative in districts where the climate is drier or where the soils are not as moisture susceptible Fernando et al 2001 To account for this conservatism the modified triaxial design method MTRX
38. m of pavement to resist erosion For seasonal or low use roads interim drivable water bars could also be constructed Control Inlets Outlets Figure 4 10 Moisture Control Method of Dealing with Steep Grades ExSPRS Expert System for Pavement Remediation Strategies september 2008 Version 1 0 REMEDIATION module This section provides several remediation strategies to consider based on the evalutaion results Remediation Strategies to Consider Stahilization Undercut Backfil Geozynthethics Decreasing Clay Content Deep Dynamic Compaction Moisture Cond Vertical moisture barriers C O n t ro n E ts n d u tl e ts Drainage improvement Water should be controlled directed or have energy dissipated at the inlet and outlet of culverts rolling dips or other cross drainage structures This can ensure that water and debris enters the cross drain efficiently without plugging and that it exits the cross drain without damaging the structure or causing erosion at the outlet f Vegetation treatment Drain Improvement Sloped Sections Cross drain uds dap ubt CONTR VIRI 80 pps amd pee ad rodon of the Use masonry concrete or metal inlet 7 Water Bars structures to control water in the ditch Steep Bars direct the water into the cross drain v Control Inlets Outlets pipe and prevent ditch down cutting Fi ESP
39. map the right is to identity areas with sulfate heave The Counties with Sulfate Concentrations considerations based on 45 E ane incomporated into this program Based onthe determine ifthe pavement is inthe shaded areas This will allow us to select appropriate stabilizers ES Eagle Ford Formation Eagle Ford formation also going by the name Bor uillas Formation YELLOW zone shows sulfate concentration gt 100ppm and GREEN zone shows areas with known sulfate heave potential Based an the Texas County map determine if area is in a sulfate concentration zone Yes overlap with YELLOW zone Yes overlap with GREEN zone f Neither What is the highest sulfate concentration 1000 Organic sails in general pase significant problems due to their low strength high compressibility low permeability and poor compaction Hint If organic content of the soil sample exceeds 1 itis considered organic rich ls organic rich soil a concern es itis a concen Regular mis design and construction practices can be TS i Reference implemented but a minimum 24 hours of mellewing is Scala R dati recommended at this level sa wo 150 300 Q u ecommendations Pe Lime Lime Cement Line Fly Ash FS Fly Cement A E Stabilizers Figure 4 3 Stabilization Window of Remediation Module Geosynthetics For the scope of this research the geosynthetic reinforcement 15 assumed to be targe
40. may click the Next button at the bottom right hand side of the INPUT module to proceed to the EVALUATION module 11 Table 3 1 Summary of Example Input Data Fort Worth Case Study Number of Layers 3 Compacted Description of layers HMAC Flexible Base Subgrade 200 l Analysis period years Initial Serviceability index Reliability in decimal Design wheel load kips Tire pressure psi Road length mile Total number of lanes Lane width ft Depth of treated subgrade in Percent of time pavement is exposed to saturation moisture level Pavement drainage quality Subgrade Modulus during wet season ks1 PI LI P200 OMC 90 Dry MC MDD pcf 92 3 6 PVR Limit in Sulfate Content ppm 1000 un e c Ex ON om un Soil Properties 12 CHAPTER 3 EVALUATION MODULE In this chapter the following items are discussed as used in the EVALUATION module o Information regarding evaluation models o Outcome of possible distresses and failures of the design being evaluated Based on the district survey and literature review conducted under research project TX 0 5430 the most prevailing distresses for low volume flexible pavements are longitudinal cracking rutting shoving and excessive roughness The main causes for these distress problems can be categorized into two areas 1 Inadequate support which is caused by inadequate layer thicknesses poor construc
41. mmended Remediation Strategies 19 4 1 REMEDIATION STRATEGIES FOR CONSIDERATION Figure 4 2 shows the selection of remediation strategies The user has the choice to decide which one s out of the recommended modifications to be considered and analyzed for the original candidate design When a specific strategy is selected the user will notice that a new tab 15 activated Figure 4 2 shows where both Stabilization and Undercut Backfill are selected and thereby their tabs are activated see Figure 4 2 For demonstration purpose and the example provided in this manual all recommended remediation strategies are selected for further illustration This module shows the remediation strategies that resulted from the evaluation check results Once the user determines and selects which of the remediation strategies might be suitable for consideration the user can proceed to the COST BENEFIT module where a cost analysis is performed and the benefits of the selected remediation strategies are provided for comparison Stabilization this 12 one of the most Commonly usec method to reduce the moisture variation induced swellingchrinking problem the base sugrade is stabilized with a calcium based stabilizer zuchlas lime cemendor fly ash Undercut and Backfill This i a popular remedial procedure for soft subgrade This REMEDIATION module provides several strategies to Geosynthetics Use of geosynthetics can increase bearing capacity of the
42. more realistic designs and rehabilitations The results from this study offered a new design procedure that provides the following information e Identify most relevant soil properties and corresponding test procedures to characterize and address highly expansive subgrade problems e Propose quantitative analyzing models to predict flexible pavements failure on expansive subgrade specifically for low volume roads e Create an interactive expert system program to guide the user through design procedures and provide realistic layer thicknesses for low volume roads Rank feasible design alternatives for rehabilitation and maintenance to minimize the cost without compromise performance The design guideline for low classification roads over high PI clays developed to address the issues summarized above 15 referred to as Expert System for Pavement Remediation Strategies ExSPRS This program can be used to evaluate the structural and performance adequacy of low volume flexible pavement designs and to achieve cost effective designs with appropriate modifications The program mimics human expert decision making process for this purpose Finally cost benefit comparisons are made between possible alternative modifications based on modified inputs for each strategy The goal 1s to help pavement engineers to design low volume roads that avoid costly over designed yet underperforming roads over expansive subgrade This document provides a user s guide
43. n Strategies September 2008 Version 1 0 RE DIATION module This section provides several remediation strategies to consider based the evalutaion results i Remediation Strategies to Consider Stabilization Undercut Backfil Geosy Deep Dynamic Compaction Deep dynamic compaction treatment is considered as one of the most economical in situ soil improvement methods available which is approximately 1 to 1 20 sq ft of surface area Rollins and Christie 2002 However almost all compacted soils have a tendency to expand and produce uplift pressures of considerable intensity when given access to water An increase initial moisture content will reduce the magnitude of swell and swell pressure Mowaty ef af 1985 In order to reduce swell and swell pressure compaction should occur at higher moisture content Deep dynamic compaction is used to maximum unit weight and density of soils This solution may be temporary due to water infiltration Figure 4 15 Deep Dynamic Compaction Decreasing Clay Content When undercut and backfill is not economically feasible another method which 1s referred to as decreasing clay content provides an alternative As the name implies this process is to dilute expansive soils with non expansive fill It is less time consuming and cheaper compared to undercut and backfill when quantities of non expansive fills are limited When this method 15 selected the program provides the user with the
44. nch layer and that is the reason the unit cost of 11 3 is reported If the costs need to be modified in the future then the file installed with the program called CostAnalysis v2 xls needs to be updated An example for each tab sheet in the excel file can be followed to update the proper unit cost e Undercut and backfill depth 1s automatically inputted from previous calculation The cost associated with this method includes excavation and backfill No extra input is needed e Geosynthetics The only information needed from the user is to select the tensile strength for the geosynthetic R S Means 2007 reports the tensile strength per fabric sheet in terms of pounds Ib The available options are 120 lb 200 lb and 600 lb Other associated installation costs are not considered due to lack of information e Moisture control methods have three different categories which are identified as a Moisture Barriers b Drainage Improvement and c Vegetation Removal All encountered costs will be added up together for the final cost estimation of moisture control a Moisture Barriers Regular drainage geotextile 1s assumed The user will be asked for the geotextile film thickness 35 b Drainage Improvement There may be several ways to improve drainage Additional costs considered by the program include grading sloped sections and the use of culvert either to build cross drain structures water bars or as inlet and outlet The user needs to
45. ng and rutting and helps in holding the pavement system together better Gurung 2003 1983 Abd El Halim et al 1983 Cicoff and Sprague 1991 Steward et al 1977 Giroud and Noiray 1981 Montanelli et al 1999 However the benefits of using geosynthetics are more noticeable for future performance rather than initial parameter values Measured values of stresses strains deflections and other parameters are highly case specific As many researchers have suggested an average design improvement factor could be used From literature review this improvement factor ranges from 1 5 to 2 37 Moisture control methods do not change soil properties but rather minimize moisture migration and fluctuation Thus prevent or minimize the subgrade from expanding during wet seasons and shrinking during dry periods With moisture control remediation implemented parameters such as subgrade modulus shrinkage strain and triaxial test results will be controlled in a much smaller variation range for worst case scenarios Undercut and backfill method removes poor subgrade and replaces it with high quality fill This procedure changes every aspect of subgrade soil thus new tests are required to identify soil characteristic properties Deep dynamic compaction is a temporary method to densify unstable or weak subgrade With high energy impacts unit weight dry density strength stiffness and swell shrinkage potential of subgrade soils are modified The ma
46. ods are offered in a hierarchical style as shown in Figure 4 5 This remediation strategy focuses on measures that directly deal with minimizing moisture change in the subgrade These remediation strategies are grouped into three main categories 1 use of vertical moisture barriers 2 improve drainage and 3 treat nearby vegetations Figure 4 5 Hierarchy of Moisture Control Methods 23 This portion of the program is illustrative rather than analytical The user can explore useful information design methods and references for different methods by first selecting one of the three moisture control groups then further specifying a method if selection question shows up Figure 4 6 shows an example informational screen of using moisture barriers The user can click Next Picture button to read more As presented in the flowchart in Figure 4 5 there are five methods to improve the drainage They are use sloped sections cross drain structure water bars inlets and outlets and to avoid steep grades Figures 4 7 to 4 11 show example informational screens of these drainage improvement methods Figure 4 12 and 4 13 depicts example informational screens of vegetation treatments ExSPRS Expert System far Pavement Remediation Iretegies september 098 Version 1 0 Moisture Control Vertical moisture barriers t Drainage improvement Vegetation treatment picture Update and Return Moisture Barriers There are mainly
47. program starts These default values can be used as a starting point for the user to edit or use as desired At the bottom of the screen two buttons are provided to recall data from an existing file or save the input in a file for future use The Load Input File button is used to load a previously saved input file The Save Input File allows the user to type in a file name with no spaces and save the current input file under the default program folder The INPUT module has four sections as shown in the left portion of the input screen The right part of the input screen is grayed out That section is related to the evaluation options and is activated when the required information is provided in the right hand portion The following section will discuss the INPUT module in detail 2 1 BASIC INPUT Basic input includes layer properties design properties and subgrade properties A brief description of the basic design inputs are given below 1 Layer Properties e Number of layers This program is restricted to three and four layer pavement systems including subgrade since its specific target 1s the lower classification roads Layer Property Table Layer thickness in in layer modulus in ksi and Poisson s ratio for each layer should be input The representative moduli of materials can be obtained either from the Falling Weight Deflectometer tests or laboratory tests The user 1s advised to make a reasonable input for
48. prove their engineering properties including strength volumetric change potential and permeability Figure 4 3 depicts the screenshot of stabilization window Three questions are asked in this module First the user is asked to locate their project using the map provided see Figure 4 3 to decide whether the location is susceptible to sulfate heave problem which is one of the main factors that affects the final stabilization method and stabilizer recommended Second the user is asked to provide the laboratory tested sulfate concentration in ppm Tex 145 E The default value for this question will be set to no sulfate concentration if the user answer for the first question is Neither or Tex 145 E is not carried out Finally the user should indicate whether the subgrade is an organic rich subgrade To facilitate the responses to these questions the user can take advantage of the specially treatment recommendations references and the recommended stabilizers provided at the bottom left part see Figure 4 3 ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 REMEDIATION module This section provides several remediation strategies to consider based on the evalutaton results Remediation Strategies ta Consider 1217570 Undercut Geospnthethics Decreasing Clay Content Deep Dynamic Compaction Moisture Control Stabili Z ation Potential areas with known sulfate heave potential Hint The
49. provide culvert diameter spacing and slope description gentle or steep c Vegetation Removal The user needs to select from drop down lists of the following information diameter of big trees meaning diameter bigger than 12 inch to be removed per road length entered in INPUT module number of small trees diameter less than 12 inch per acre percentage of hardwoods and roadside width for small trees ft side e Due to the lack of cost data for deep dynamic compaction airport subgrade compaction 1s used as a substitute The user needs to select the percentage of standard proctor density from R S Means available pool of 80 85 90 and 95 e The agency cost for decreasing clay content method includes three parts excavation backfill and mixing Due to lack of information it is estimated the same way as undercut and backfill with half the depth entered by the user meaning a partial mix and replacement Table 5 1 gives an example of summarized cost analysis input that the user can follow to practice with the program Table 5 1 Summary of Cost Analysis Assumptions Fort Worth Case Study n Stabilizer Lime Stabilization percent mix Geosynthetics tensile strength psi 600 Culvert Diameter in Culvert Spacing ft 500 I t E Sloped Section 2 00 Barrier film thickness in 0 3 4 Drainage Moisture Control Vegetation Removal Big Tree Diameters for trees bigger than 12 12
50. quipment it can be used for large scale treatments and when the backfill material is readily available this method is relatively inexpensive Thompson 1982 Following equation by Corps of Engineers can be used to approximate the required depth of granular backfill material 1 1 7 where t Thickness of material layer required in inches S ICBR pr Single or equivalent single wheel load in pounds BR CBR of underlying subgrade soil Tire contact pressure psi 0 23logC 0 15 Number of load repetitions Required depth of granular backfill material in Figure 4 14 Undercut and Backfill Deep Dynamic Compaction Deep dynamic compaction DDC is an economical ground modification method Figure 4 15 This technique involves repeatedly raising and dropping a large weight in a prescribed pattern to densify the potentially unstable or weak underlying materials with high energy impacts The weight may range from 6 to 25 tons and the drop height typically varies from 30 to 60 ft The degree of densification achieved is a function of the energy input 1 e weight and drop height as well as the saturation level fines content and permeability of the material As mentioned by several researchers Mowafy et al 1985 Rollins and Christie 2002 this method is not appropriate for saturated clayey soils and the solution may be temporary due to water infiltration 29 ExSPRS Expert System for Pavement Remediatio
51. r Center for Transportation Infrastructure Systems Expert System for Pavement Remediation Strategies ExSPRS User s Manual Product Number 0 5430 P3 TxDOT Project Number 0 5430 Conducted for Texas Department of Transportation August 2008 Center for Transportation Infrastructure Systems The University of Texas at El Paso El Paso TX 79968 915 747 6925 http ctis utep edu Expert System for Pavement Remediation Strategies ExSPRS User s Manual by Yaqi Wanyan MSCE Enrique Portillo Imad Abdallah MSCE and Soheil Nazarian PhD PE Research Project Number TX 0 5430 Conducted for Texas Department of Transportation Product Number 0 5430 P3 The Center for Transportation Infrastructure Systems The University of Texas at El Paso El Paso TX 79968 0516 Disclaimers The contents of this report reflect the view of the authors who are responsible for the facts and the accuracy of the data presented herein The contents do not necessarily reflect the official views or policies of the Texas Department of Transportation This report does not constitute a standard a specification or a regulation The material contained in this report is experimental in nature and is published for informational purposes only Any discrepancies with official views or policies of the Texas Department of Transportation should be discussed with the appropriate Austin Division prior to implementation of the procedures or results
52. resses using its evaluation models If the input section experience premature distress ExSPRS will use the expert system approach to recommend feasible remediation strategies Based on the remediation selected the modified pavement structure 1s re evaluated The cost benefit analysis module will provide the agency cost estimation of the original pavement section along with the additional agency costs 2 Evaluation Models Input Low volumc Road Design Loop Buck in Remediation Strategies Original Design EEE AE NE SE Figure 1 1 ExSPRS Flowchart for each of the recommended remediation strategies so that the user can judge the cost benefit of each modification selected The user can then decide which of the remediation strategies to use that fits his her requirements and constrains In order to use ExSPRS the user just needs to follow the program and answer different questions to their best of knowledge Some evaluation models require laboratory characteristic test results such as gradation Tex 110 E Atterberg limits Tex 104 E and Tex 105 E moisture density tests Tex 114 E unconfined compressive strength UCS Tex 117 E tests to quantify the properties of the clayey subgrade material Upon execution ExSPRS brings up the INPUT module as shown in Figure 1 2 Before going any further four basic guidelines should be kept in mind when navigating through the program The user should always start
53. rice information was obtained from the RS Means CostWorks Data for Heavy Construction R S Means 2007 These unit cost data can be easily updated with the most current information as they become available RS Means differentiates unit costs for same construction activity with different lift thickness User defined layer thicknesses are interpolated extrapolated based on available lift thickness information Cost analysis is only considered for road lanes and shoulders are excluded By default the roadway section being analyzed is a one mile two lane low volume road with 12 ft wide lanes New pavement is assumed for planning construction activities Only main construction activities are considered which include but not limited to excavation backfill compaction and preparation of subbase base and AC layers Minor activities such as underground utility removal drainage and manhole installation bridge or culvert construction surface detailing and finishing are eliminated e One crew with one shift is used for all activities since expediting with more crew members or shifts results higher unit cost For each activity normal or ideal set of working conditions are considered No variability 1s considered to account for changes in weather or other factors during the construction e For each remediation strategy the cost is considered separately since they are independent of one another Cost Input In Figure 5 1 the top portion of
54. ructure and the tree to create a moisture transfer barrier Figure 4 12 Moisture Control Method of Using Root Barriers ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 REMEDIATION module This section provides several remediation strategies to consider based on the evalutalon results Remediation Tuptegies to Consider Stabilization idercut B ackfil Geasynthethics Decreasing Clay Content Deep Dynamic Compaction Moisture Control Moisture Control E C Vertical moisture barriers E d re Gh Re m ova Drainage improvement Large vegetations often WS 1 exacerbate shrinkage Wade recen Treatment movements by withdrawing moisture from supporting soils Dissimilar soil moisture withdrawal from tree root zones in volumetrically sensitive clays frequently results in differential Update end Retum settlements due to shrinkage Ravina 1984 safe planting distance of trees to avoid soil shrinkage settlement and damage to pavements can be controlled by D H ratio distance to height of trees as following D H 10 Single trees Vegetation treatment D H 1 0 1 5 Groups of trees Figure 4 13 Moisture Control Method of Removing Vegetations Undercut and Backfill Poor subgrade soil can simply be removed and replaced with high quality fill This method which is also called undercut and backfill is a simple procedure
55. s of estimating the tensile strength 1s provided in Research Report 0 5430 2 If the user decides to use the built in shrinkage strain model no extra inputs are required as they were already provided under the soil properties section Roughness Environmental changes cause subgrade volume change induced by swelling and or shrinking The roughness of pavement is the result of the cumulative deformation and differential volumetric change of the problematic subgrade soils The roughness model checks the potential vertical rise PVR of subgrade and evaluates the international roughness index IRI of low volume roads surface If the user reports the subgrade as highly expansive Roughness portion on the bottom right panel PVR check will be evoked The limit of tolerable PVR is also required This value typically varies between 1 to 2 inches Also if excessive roughness is known to be a concern in the area IRI check will be activated to estimate the expected IRI at the end of the design period 2 3 EXAMPLE To understand the steps and modules in ExSPRS an example is provided for the user to follow This also serves as a training exercise Table 3 1 gives an example of summarized input information to input into the program This example will be used in the description of the remaining modules so the user can use this manual to follow along for the remaining chapters Once the required data for all the evaluation checks are completed the user
56. ted for subgrade improvements The reinforcement 15 placed at the interface between base subbase and the subgrade Figure 4 4 illustrates the usage of the geosynthetic reinforcement with some additional references At the bottom half of the window there are three questions regarding the subgrade quality These questions are used to decide the required depth of the pavement above 2 ExSPHS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 REMEDIATION module cl on provide everal remediation Remediation Strategies to Consider NETA camem dis Geosynthetics To lessen or prevent rutting of the pavement layer during construction or cracking due to base deflection under traffic geosynthetics may be placed at or near the bottom of the granular base or on top of the finished subgrade Hopkins ef af 2005 Base Stab Base Required total layer thickness in inches over geosynthetics HW ign Methodol ltz et al 199 A Geosynthetic Please select the method you prefer to estimate quality of subgrade Estimation visually Estimation by hand Based on subgrade resilient modulus hall n G C Estimate by feel of the soil sample G C C Estimate by subgrade response visually C e Maximum tolerable depth of rutting during the design life of the roadway is in Update Return Original trial design met the requirement of aggregate thi
57. tions and improper stabilization 2 Problematic soils susceptible to moisture variation which include subgrade volume change shoulder problems poor drainage or other combined effects The EVALUATION module is used to determine whether the user defined pavement structure meets these criteria The outcome from EVALUATION module provides the user with the option to either modify the original design use different cross sections or materials and restart the analysis over or proceed to the REMEDIATION module to determine suitable remediation alternatives 3 1 EVALUATION OPTIONS In addition to the preliminary inputs required in the IVPUT module several specific questions are also asked in the EVALUATION module window as shown in Figure 3 1 The details for each type of evaluation are presented next Longitudinal Shrinkage Cracking Model If the user selects to provide the shrinkage strain in the INPUT module no additional information is required If the user decides to use the built in shrinkage strain model he she needs to select the index parameters to be used to estimate the shrinkage strain with the built in model Figure 3 1 depicts the selection of soil parameters for inclusion under the top panel The development and validation of the shrinkage strain model used in ExSPRS 1s provided in TxDOT Research Report TX 0 5430 1 13 ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 EVALUATION module Th
58. to Version 1 0 of ExSPRS Although the focus of this research 1s for Texas the new design guidelines will be helpful to other states with similar problems It 1s highly recommended to review research report 0 5430 1 and 2 before going any further and using this program The report provides a solid foundation regarding the theory models and processes used to develop this program 1 1 SYSTEM REQUIREMENT AND INSTALLATION The program will work on a typical computer with Windows 9x 2000 XP Vista or NT operating system To install the program execute the setup file ExSPRS EXE and follow the onscreen instructions After installation double click on the program icon on your desktop to execute the program 1 2 DESCRIPTION OF PROGRAM The Expert System for Pavement Remediation Strategies ExSPRS program has four main modules Input Evaluation Remediation and Cost Benefit Figure 1 1 shows the flowchart of the program ExSPRS uses an expert system approach which manages and incorporates concepts derived from our study and uses structured knowledge to provide analysis to the user as an expert would do This program is specially developed for low volume roads build over expansive clayey subgrade The user needs to provide an initial pavement structure as an input This pavement structure can be obtained using common design software such as FPSI9W ExSPRS will check the candidate pavement structure for several potential structural or functional dist
59. unt of work is required to maintain and rehabilitate these roads The expansive nature of high PI clays despite the fact that they are considered in the design is also of concern since they contribute to the roughness of the road and as such the loss of the functional serviceability of the roads Therefore it is imperative to improve the design and laboratory procedures to address expansive subsoil conditions and then design pavements accordingly to extend the life expectancy of these roads The intent of this research project was to cultivate the vital features of strategies for improving low volume flexible pavement design and thus improving the overall low volume road performance These include 1 Identify the shortcomings of current design and construction practices associated with the less than desirable performance of pavements in low volume roads constructed on high PI clays 2 Identify the most significant soil parameters directly related to the performance of these types of roads 3 Propose practical and dependable laboratory test methods and analyzing models to address the problem of premature failure of low volume roads on high PI expansive subgrade 4 Qualify and quantify current remediation procedures climatic effects and road condition assessment both successful and unsuccessful used to mitigate the shrink swell problems 5 Develop a user friendly expert system design tool to guide the designers through the process for
60. ve the results in an Excel format Gal ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 vw 1 Stabilization Stabilizer Amount 142 Cost Y 11 30 2 Undercut and Backfill Depth in 15 Cost LCY 11 54 3 Geosyntethics Tensile strength Ib 600 Cost 51 2 34 4 Decreasing Clay Content Depth in 12 Cost LEY 10 77 5 Deep Dynamic Compaction Practd 85z Cost 51 0 36 5 Moisture Control Mysore Fane Barrier film thickness 0 44 Cost SY 474 drame Anserement Culvert diameter 12 Cost LF 2 0 50 Culvet spaceing f 500 Sloped section gentle Cost 5 0 15 e vegetation Aemerat Big tee diameters to I No of big trees to be removed per mile 10 Ma of trees less up to 400 Cost Ea 1 0 35 than 12 per acre Modified Input Original Stabilization Geasyntethics Moisture Content Undercut amp Dynamic Decreasing clay Backfill Compaction content Mr optimum ksi 30 X 14 Mr wet ksi 45 o8 e 9 LL GMC MOD IDT psi Sail Class Perform Cost Benefit Analysis Figure 5 2 Pavement Parameters Modified for Each Remediation Strategy 39 ud ExSPRS Expert System for Pavement Remediation Strategies September 2008 Version 1 0 e 1 Stabilization Stabilizer lime Amount faz Cost 5 11 30 2 Undercut and Backfill Depth im Cost LEY 1154
61. wet seasson expands that is not a concern Resilient Modulus Mr of subgrade under wet conditions kai Subgrade Shear Failure RR Are 117 Results Available Angle af internal friction degree Cohesion of soil psi le es Classification of soil Longitudinal Cracking Pavement tends to crack during long drought seasons No that is not a concern Did you run one of the following shrinkage characterization test Yes Coefficient of Linear Extensibility COLE test es Linear Shrinkage Bar Test Yes Volumetric Shrinkage Strain Test f Ma Use Built in Model Roughness The subgrade is highly expansive No that is not a concern limit in 2 Mn that is niat a concern Load Input File Save Input File Figure 2 1 Selection of Evaluation Models Fatigue Cracking and Rutting A layered linear elastic model that computes pavement responses under static loads 15 incorporated in the software to check for the pavement fatigue cracking and subgrade rutting The Asphalt Institute 1982 and Shell 1978 design methods which relate the strains to the allowable number of load repetitions as shown in the following equations are used N fi EJ 2 1 N 2 2 where and N is the allowable number of load repetitions for fatigue cracking and rutting respectively amp is the horizontal tensile strain at the bottom of the HMA g is t

RR-0-5430-P3 - CTIS - University of Texas at El Paso

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