REINFORCED FLEXIBLE PAVEMENT DESIGN OVER EXPANSIVE CLAY SUBGRADE

Transcription

1 Indian Geotechnical Journal, 41(2), 2011, REINFORCED FLEXIBLE PAVEMENT DESIGN OVER EXPANSIVE CLAY SUBGRADE C.N.V. Satyanarayana Reddy 1 and K. Chinnapa Reddy 2 Key word Geotextile, reinforcement, pavement, expanive oil, anchorage, afe bearing capacity Abtract: Flexible pavement contruction in expanive oil i expenive due to large pavement ection reulting from low CBR value in wet condition. The volume intability of oil affect contructed pavement and demand frequent maintenance. Hence effort are to be made for reducing large pavement ection and alo to uppre welling of ubgrade. Though the ue of granular and CNS cuhion in pavement contruction help in reducing volume change affecting pavement layer, it cannot reduce required large pavement ection. Hence, in the preent paper, a reinforced flexible pavement deign methodology ha been formulated for expanive ubgrade with the objective of pavement thickne reduction and well control of ubgrade. Tet track tudie have been done on unreinforced and reinforced flexible pavement ection laid over elected expanive ubgrade. The urface level have been oberved for well over a period of two year. The propoed deign methodology ha been validated from the Elatic layer theory. Introduction Expanive oil undergo alternate hrinkage and welling due to moiture fluctuation and poe low trength in rainy eaon due to poor drainage condition. A a reult, flexible pavement contructed over uch oil are not only expenive but alo reult in poor performance and premature failure. Variou technique uch a uage of moiture barrier (Steinberg, 1992) to control welling and cuhion (Sand, Moorum, Coheive Non-welling Soil, Lime tabilized oil) to uppre welling and erve a capillary cut-off have been tried by variou reearcher (Katti, 1979; Natarajan and Shanmukha Rao, 1979) and have been oberved to have met with limited ucce. Treatment of expanive oil uing tabilizer ha been tried to improve volume tability of oil. However, uniform mixing of oil i difficult and cannot be relied upon for large-cale uage. So far none of the exiting pavement deign methodologie are aimed at reducing the deign pavement thickne over expanive oil. Hence, in the preent reearch work, it i propoed to ue geotextile for reinforcing flexible pavement. A there i no etablihed deign procedure for reinforced flexible pavement over oft clay, in the preent paper, a deign methodology enuring afety againt rik of hear and ettlement failure in ubgrade ha been formulated. The deign ha proviion for well control of ubgrade alo. The reinforced and conventional unreinforced flexible pavement ection (Tet Track) have been laid for performance appraial againt welling of ubgrade. The detail of tudy are preented in ubequent ection. Material Propertie Expanive Soil: The expanive oil ued in the tudy wa procured from Hanamkonda town, Andhra Pradeh. Moorum: The moorum ued a ubbae material in the tudy wa procured from a Quarry in Hanamkonda. It may be een from Table 1 that the expanive oil i High Compreible Clay with high well potential a free well index value i more than 50%. The moorum ha CBR above 20% and platicity index i le than 6%. So, it i uitable for ue in ub bae coure of unpaved road Geotextile: Woven geotextile i ued in thi tudy. The propertie of geotextile a determined from laboratory tet are preented in Table 2. The load-elongation repone of the geotextile i preented in Figure 1 and 2 baed on wide width tenion tet. Aggregate: Grade II aggregate ha been ued in Wet Bound Macadam (WBM) bae of tet track. The propertie of the aggregate evaluated from laboratory tet are preented in Table 3 and 4. Stone Screening: Type A Stone Screening atifying MORTH pecification were ued in forming WBM bae of Tet track. The gradation characteritic of the material i preented in Table 5. Binding Material: Moorum ued in ub bae coure of tet track with propertie given in Table 1 wa ued to erve a binding material in forming WBM bae. 1 Profeor, Department of Civil Engineering, Andhra Univerity, Viakhapatnam, , cnvnreddy@rediffmail.com 2 Reearch Scholar, Department of Civil Engineering, Andhra Univerity, Viakhapatnam,

2 87 Indian Geotechnical Journal, 41(2), 2011 Table 1 Engineering Propertie of Expanive oil and Moorum Engineering Property Expanive Soil Moorum Specific Gravity Grain Size Analyi a) Gravel (%) b) Sand (%) c) Fine (%) Atterberg Limit a) Liquid Limit (%) b) Platic Limit (%) c) Shrinkage Limit (%) IS Claification Symbol CH SM-SC Compaction Characteritic a) Optimum Moiture Content (%) b) Maximum Dry Denity (g/cc) Soaked CBR Value (%) Shear Parameter (Undrained) a) Coheion b) Angle of Internal Friction Percent Swell (%) Swell Preure Fig. 1 Tenile tet reult for a woven geotextile in warp direction Fig. 2 Tenile tet reult for a woven geotextile in weft direction

3 88 Reinforced Flexible Pavement Deign over Expanive Clay Subgrade C.N.V. Satyanarayana Reddy and K. Chinnapa Reddy Table 2 Propertie of Woven Geotextile Property Bae Polymer Ma per Unit Area (g/m 2 ) Value/Decription High Tenacity Polymer 295 Thickne (mm) 0.5 Table 5 Gradation of Stone Screening IS Sieve Deignation (mm) Percent by Weight Paing Tenile Strength Elongation at Break (%) Apparent opening ize 100kN/m in Warp and 50 kn/m in Weft 9.8 & 8.7 in warp and weft 130 micron Flexible Pavement Deign Methodology Unreinforced Cae The deign methodology baed on Safe Bearing Capacity (SBC) of ubgrade developed by Satyanarayana Reddy and Ramamoorthy (2005) with the following conideration ha been ued in thi tudy. Table 3 Gradation of Grade II Aggregate IS Sieve Deignation (mm) Percent by Weight Paing Table 4 Engineering Propertie of Aggregate Property Specific Gravity Value 2.80 Cruhing Value (%) 22.3 Impact Value (%) 20.7 Abraion Value (%) 23.5 SBC Method of deign Conideration 1. The afe bearing capacity of ubgrade oil i reduced by 20% to account for action of repetitive wheel load. 2. Pavement thickne deign baed on conideration of 80% afe bearing capacity of ubgrade oil i critical over the cae of increaing tatic wheel load by 15%. 3. The loading due to moving vehicle in aturated clayey ubgrade i taken a equivalent to trip load ince in aturated condition the exce pore water preure do not get diipated quickly. 4. The load bearing mechanim of pavement component layer i due to paive reitance offered by material of the layer under applied wheel load and o 2:1 load diperion (tan α =0.5, where α i diperion angle with vertical )i valid for diperion of wheel load through the flexible pavement layer. 5. The hape of contact area of tyre with pavement i conidered a rectangular with two emi circular area at the end (Figure 3). 6. The pavement width equivalent to dipered width of wheel at ubgrade level act a a urface trip footing over weak ubgrade oil, particularly aturated clay. 7. Veic bearing capacity theory i valid for clayey ubgrade.

4 89 Indian Geotechnical Journal, 41(2), 2011 Where, h i the deign pavement thickne in cm C i anticipated number of vehicle pae in term of tandard axle. P i Equivalent Single Wheel Load in kg. Fig. 3 Shape of tyre contact area The pavement thickne (h) required for tranmiion of wheel load without any rik of hear failure in ubgrade ha been worked out by equating vertical tre due to wheel load and overburden to afe bearing capacity of oil uing the expreion given below. P av. h q ( B 2h tan )( L 2h tan ) e where, P i equivalent ingle wheel load in kn. B i width of load contact area = b+s b i width of contact area of ingle tyre and S i center to center pacing of tyre. Le i length of contact area of equivalent rectangular ection. q i afe bearing capacity of ubgrade By conidering a tandard axle load of 10.2 t with tyre contact preure of 5.62 kg/cm 2, the value of B and Le have been worked out to be 47.7 cm and cm repectively. The center to center pacing of tyre i taken a 0.3 m. To account for moving vehicle on road, the afe bearing capacity ha been reduced by 20% (Prakah, 1981). Keeping wheel load unchanged, for the expanive oil under tudy the required pavement thickne ha been worked out to be 110 cm. Leonard et al. (1974) reported increae of wheel load up to 15% in high peed vehicle. So, deign pavement thickne required ha been alo worked out by increaing wheel load by 15% and maintaining afe bearing capacity of oil in tatic condition. The required deign thickne ha been found to be 91 cm. Hence, to evaluate rik of hear failure in ubgrade, it i preferable to conider reduction in afe bearing capacity of oil rather than conidering increae in wheel load. CBR method of deign The required pavement thickne over the expanive oil under tudy ha been calculated uing US ARMY Corp of Engineer formula (1961) given below: (1) A i Contact area in cm 2 For calculation of deign pavement thickne value, 30 million tandard axle were conidered a vehicular traffic and a tandard axle load of 10,200 kg with dual wheel configuration and a tyre contact preure of 5.62 kg/cm 2 ha been taken. The value of deign pavement thickne ha been worked to be 91.5 cm. (The value i le in comparion to the value obtained from SBC concept, which mean that the pavement will have rik for undergoing hear failure if deigned baed on CBR method) Reinforced Flexible Pavement The deign formulation for reinforced flexible pavement ha been done after thorough tudy of Giroud and Noiray method of deign a it i the only rational method of deign available, other (Bender & Barenberg, 1978; Koerner, 1986) being empirical. Both hear and ettlement failure criteria have been conidered in deign. The exiting method (Bender & Barenberg, 1978; Giroud & Noiray, 1981) do not cover the apect of fabric placement condition at ubgrade on performance of reinforced pavement. Apart from treing the need for holding the fabric in poition at ubgrade, the deign of fabric ha been alo done for well control purpoe. The conideration involved in deign are given below. Deign conideration 1. The oil ubgrade i ubjected to vertical preure equal to 80 percent of it afe bearing capacity due to membrane effect of geotextile fabric placed at ubgrade level. 2. Initially due to wheel load tranmiion, the overlying pavement material get punched into underlying oft ubgrade and a a reult geotextile get trained and derive required tenile trength to upport wheel load. 3. The deformed hape of fabric will have right angle kink along the boundarie of load diperion followed by elliptical deformed hape on either ide (Figure 4). 4. Geotextile fabric are held in poition by anchorage in longitudinal trenche made in houlder region of pavement. h = (0.447log10C ){ P/ ( CBR ) - A/ (6.45) } 0.5 (2)

5 90 Reinforced Flexible Pavement Deign over Expanive Clay Subgrade C.N.V. Satyanarayana Reddy and K. Chinnapa Reddy Deign for wheel load The fabric-deformed hape at ubgrade level conidered in the propoed deign methodology ha been given in Figure 4. The deformed hape i more likely a geotextile get punched into oft ubgrade initially until reinforcing action of fabric tart and thereafter top. Such a deformed hape with right angled kink at boundarie of load diperion ha been propoed by Binquet and Lee (1975) in the theory of deign of reinforced oil bed over oft oil. The diplaced oil below load diperion width reult in heaving on either ide which may be treated a elliptical. The other form conidered by reearcher are parabolic, triangular and arc of circle (Giroud & Noiray, 1981; Natarajan, Mathur, Murthy, 1989) are appropriate in ubgrade of moderate trength where local or punching hear doe not occur. But in oft ubgrade, the deformation will be due to punching of overlying material into it, reulting in uniform ettlement at ubgrade. The elliptical hape for heave i compatible with uniform deformation at ubgrade under wheel load. Fig. 4 Deformed fabric hape at ub grade adopted in deign From free body diagram (Figure 5) of deformed fabric below the load diperion width, the tenion developed in the fabric ha been worked out by conidering equilibrium of force in vertical direction uing the equation given below. T B+2h R Tan L-(B+2h R Tan) ( q 0.8 q)( B 2hR tan ) 2 Elliptical Deformed Shape B+2h R Tan (3) The train induced in fabric ha been worked out uing the equation 4 given below B 2hR tan The deign thickne of reinforced flexible pavement ha been conidered in exce of the value required to initiate hear movement in ubgrade uing the relation P av. h 0.8q ( B 2h tan )( L 2h tan ) e The minimum value of h for reinforced flexible pavement ha been worked out to be 45.5 cm By adopting pavement thickne in reinforced cae (hr) above 45.5 cm. the deign requirement of fabric ha been worked out for different permiible value of ettlement at ubgrade and data generated ha been preented in Table 6. hr (cm.) Table 6 Deign Requirement of Fabric q T (kn/m) 10mm (%) 15mm u 20mm (4) (5) 25mm The value of rut againt ettlement have been obtained by equating half volume of rectangular portion to half the volume of elliptical portion. The axle length (L) ha been taken a 2.44m. The value of rut o calculated have been given Table 7. Table 7 Value of rut againt ubgrade ettlement Settlement (mm) Rut (mm) Fig. 5 Free body diagram of deformed fabric at ub grade below load diperion width

6 91 Indian Geotechnical Journal, 41(2), 2011 Deign for well Conideration 1. Geotextile held in poition due to anchorage in longitudinal trenche retrain underlying expanive oil and thu control well to ome extent. 2. The lateral well preure generated in expanive ubgrade due to well controlled by Moorum ub bae and geotextile mobilize neceary frictional reitance in anchorage trenche counteracting tenion induced in fabric a a reult of well control. Conidering a deign pavement thickne of 70cm with 25cm thick WBM bae layer, the thickne of Moorum ub bae will be 45cm. From laboratory tudy, for a cuhion to expanive oil ratio of 0.45, the percentage of well controlled ha been oberved to be A geotextile i flexible and mobilize it trength only upon training, it i not poible to control welling of ubgrade completely. Hence, the requirement of tenile trength of fabric for permiible well of 10mm, 15mm and 20mm ha been worked out baed on free body diagram of geotextile fabric in between anchorage trenche. To cut down the requirement on tiffne of fabric, in the preent tudy it i propoed to anchor geotextile a hown in Figure 6 for a ingle lane pavement. The requirement of geotextile fabric for well control againt different permiible well value ha been given in Table 8. Table 8 Fabric requirement for well control Permiible Swell (mm) Swell controlled by Geotextile (%) Upward preure exerted by ubgrade on fabric (p) T (%) (kn/m) Deign of anchorage trench Unle geotextile fabric are held in poition by proper anchorage, the required tenile trength to upport wheel load or control welling i not mobilied. Hence, it i propoed to anchor geotextile fabric in longitudinal trenche a hown in Figure 6. Normal preure applied on geotextile urface are hown in Figure 7. d 0.4m 1.7m 0.4m P / d P 2 P 1 P 1 P 2 P 3 P 3 Fig. 7 Normal preure applied on Geotextile urface Fig. 6 Propoed reinforced flexible pavement over expanive oil with woven geotextile The tenion (T) developed in the fabric a a reult of well control ha been worked out uing the equation 6 a T = 0.5p x B (6) Where p i preure exerted by expanive oil on geotextile due to well controlled by it. B i clear pacing of anchorage trenche. The train () induced in the fabric againt different allowable well (Sa) value ha been calculated uing the equation = (2Sa / B ) x 10 (7) The hearing reitance on geotextile urface at anchorage trench ha been calculated uing normal preure a indicated in Figure 7 a C a p e 1 tane Ca p C p m 1 tanm am 2 tanm C p tan F d ae 2 e b Ca p tan Ca p Where, 3 3tan e e m m p1 = percentage well controlled in central portion x well preure (p) (8) p2 = percentage well controlled in edge region x p p3 = effective overburden preure at geotextile fabric in anchored trench

7 92 Reinforced Flexible Pavement Deign over Expanive Clay Subgrade C.N.V. Satyanarayana Reddy and K. Chinnapa Reddy b, d are the width and depth of trench for anchoring geotextile fabric C, a e e are the adheion and interfacial friction angle of expanive oil with geotextile fabric C, a m m are the adheion and interfacial friction angle of moorum with Geotextile The frictional characteritic of expanive oil and Moorum with the geotextile have been determined by conducting pull out tet. The reult of tet have been given in Table 9. Table 9 Frictional Characteritic of Soil with Geotextile Soil Expanive Soil Adheion Angle of internal friction Moorum P1= x 70 = kn/m 2 ; P2 = 0.6 x 70 = 42 kn/m 2 ; P3 = 17.5 kn/m 2 By taking depth of anchorage trench a 0.4m, the width of trench required ha been calculated by equating mobilized frictional reitance on anchored portion of geotextile to tenion induced in fabric due to well control. The mobilized frictional reitance ha been calculated by dividing the hearing reitance by a factor of afety of 3. The required width of trench ha been worked out to be 0.4m. Detail of Tet Track Studie Unreinforced and reinforced flexible pavement tet track have laid for tudying their well control ability on ubgrade. The tet track have been laid adjacent to Sri Kodanda Ramalayam at Balaamudram, Hanamkonda. For tet track tudie, the deign pavement thickne ha been determined by conidering an average daily traffic of 50 cvd with a growth factor of 7.5% and adopting a tandard axle load of 10.2 ton with dual wheel configuration with a contact preure of 5.62 kg / cm 2 for a deign period of 10 year. It i propoed to have a houlder of 1 m on either ide of tet track. Unreinforced tet track ection ha been deigned in line with IRC and reinforced ection ha been deigned baed on propoed method of deign in the tudy. The detail of unreinforced and reinforced tet track ection follow. A. Unreinforced Flexible Pavement (For a traffic of 1 ma) Total Thickne : 75.1 cm Moorum Sub bae : 52.6 cm WBM bae : 22.5 cm B. Reinforced Flexible Pavement ection with tiff geotextile held in poition at ubgrade (by anchoring into longitudinal Trenche) Total Thickne : 70 cm Moorum Sub bae : 47.5 cm WBM bae : 22.5 cm Fabric Requirement: Should have a tenile trength of 11.2 train of 2.6% for wheel load upporting Should have a tenile trength of 12 train of 1.8% for control of well (i.e. againt a permiible well of 15mm) Stiffne of Woven Geotextile with propertie preented in Table 2 ha been found to meet the above requirement baed on wide width tenion tet and hence it i ued a reinforcement in tet track tudy. C. Reinforced Flexible Pavement ection with tiff geotextile imply placed at ubgrade Total Thickne Moorum Sub bae WBM bae : 60 cm : 47.5 cm : 22.5 cm Fabric requirement i ame a previou cae except that the fabric i imply placed at ubgrade. Tractor dozer ha been ued to remove all debri and vegetation and to level off the exiting ground urface. The ubgrade i then compacted uing 10t roller. Moorum ub bae ha been compacted uing the roller. The compacted material at repective OMC and MDD wa teted for Field CBR to ae the quality. At random, degree of compaction ha been determined and compaction wa continued until degree of compaction achieved wa above 97 percent. WBM layer ha been formed uing Grade II aggregate; Type A tone creening conforming to MORTH 2001 and Moorum a binding material. The ub bae moorum wa ued a binding material alo. After compaction of bae layer, Field CBR tet wa performed to enure CBR above 85%.

8 93 Indian Geotechnical Journal, 41(2), 2011 For tet track, open graded Premix Carpet (PC) of 20 mm thick ha been laid acro each tet track at centre in the form of a 0.3m trip to erve a wearing coure to enable recording of level in different eaon. The reduced level of urface at left (L), centre (C) and right (R) location of tet track ection have been determined in different eaon uing dumpy level and average value of Reduced Level have been preented in Table 10. The reduced level have been determined by taking R.L of Floor level of Ramalayam a m. Reinforced pavement ection with imple placement of fabric exhibited a well of 45mm wherea reinforced ection with anchored geotextile fabric exhibited a well of 16mm only. The tet track tudie confirmed the need for holding geotextile fabric at ubgrade by anchorage in longitudinal trenche. In Table 10, the anchored geotextile fabric reinforced pavement ection indicated control of well a per deign (oberved average well wa 16mm againt deign permiible well of 15mm) and confirmed the propoed concept. Verification from Three Layer Elatic Theory Reinforced Flexible pavement will be table only if ub bae material doe not lip over reinforcing material and ubgrade i not overtreed. Three layer elatic theory (Peattie, 1962) ha been ued to evaluate the tability of propoed reinforced pavement deign option with different thickne and deign thickne i finalized. The vertical and hear tree induced at the level of ubgrade under varying thicknee have been evaluated uing tre-train factor of Peattie (1962) for three layer ytem uing the modulu of elaticity (E) value of WBM bae, Sub bae and ubgrade material (calculated baed on meaured Field CBR value from tet track laid uing Relation uggeted by IRC a given below. E =10xCBR if CBR < 10% (9) E=17.6 (CBR) For CBR > 10% (10) The value of Field CBR value and elatic modulu of the pavement component are tabulated in Table 11. The vertical and hear tree at ubgrade level (where geotextile i being placed) for different pavement obtained from Peattie theory are given in Table 12. The Table alo preent ultimate bearing capacity of ubgrade (under dynamic action of vehicle) and frictional reitance available at geotextile fabric urface. The pavement ection i conidered to have bae layer of 225mm and the ret ub bae layer. Table 10 Reduced level of urface of unreinforced and reinforced tet track Period Location Unreinforced Tet track Reinforced tet track with anchored geotextile Reinforced tet track with woven geotextile imply placed May 06 L C R Nov 06 L C R May 07 L C R Nov 07 L C R * The Reduced level reported in the table are in meter Table 11 Parameter of Pavement Component layer Pavement Component Field CBR (%) Elatic Modulu (MPa) Subgrade Sub Bae WBM Bae

9 94 Reinforced Flexible Pavement Deign over Expanive Clay Subgrade C.N.V. Satyanarayana Reddy and K. Chinnapa Reddy The data preented in Table 12 infer that for a pavement thickne of 70cm, the induced vertical tre i below dynamic bearing capacity of oil and alo the hear tre induced i le than frictional reitance available at the geotextile fabric. Hence, a thickne of 70 cm i eential to avoid large hear diplacement in ubgrade and alo to prevent lateral lipping of ub bae material on geotextile under the load. Table 12 Vertical and hear tree at ubgrade level from three layer elatic theory Pavement Thickne Vertical tre Shear Stre 0.8q u Frictional reitance at geotextile urface Concluion Flexible pavement thickne hould be taken a greater of the two value obtained from CBR and SBC method to avoid hear and ettlement failure in clay ubgrade. Propoed Method of deign for reinforced flexible pavement with uniform deformation of fabric at ubgrade level with elliptical heaving on either ide yield reaonable tiffne for reinforcing fabric over oft clay ubgrade. The deign thickne finalized from the preent reearch enure afety againt overtreing of ubgrade a it i validated from Peattie three layer Elatic theory. Ue of geotextile a reinforcement at expanive ubgrade under tudy reduced deign pavement thickne by about 40 percent. The geotextile held in poition by anchorage in longitudinal trenche reult in control of additional well (20 percent in the preent tudy) provided ubbae moorum control ome well (65% in the tudy) initially due to it cuhion action. Reference Bender, D.A. and Barenberg, E.J. (1978): Deign and Behavior of Soil Fabric Aggregate Sytem, Tranportation Reearch Record No.671, pp Binquet, J. and Lee, K.L. (1975): Bearing Capacity Analyi of Reinforced Earth Slab, Journal of Geotechnical Engineering, ASCE, 101(12), pp Giroud, J.P. and Noiray, L. (1981): Deign of Geotextile Reinforced Unpaved Road, Journal of Geotechnical Engineering Diviion, ASCE, 107(9), pp IRC 37 (2001): Guideline for Deign of Flexible Pavement. Katti, R.K. (1979): Search for Solution to Problem in Black Cotton Soil, Firt IGS Annual Lecture, Indian Geotechnical Journal, 9, pp Koerner,R.M.(1986): Deigning With Geoynthetic, Prentice Hall, Eaglewood Cliff, New Jerey. Leonard, D.R.et al (1974): Load and Vibration caued by 8 commercial vehicle with Gro Weight Exceeding 32 ton, TRRl Report No.582. M.O.R.T.H. (2001): Specification for Road and Bridge work, Minitry of Road Tranportation and Highway. Natarajan, T.K., Mathur, S. and Murthy, A.V.S.R.. (1989): Geotextile in road pavement-an analytical report, Journal of Indian Road Congre, 47(2), pp Natarajan, T.K. and Shanmukha Rao, E. (1979): Practical Leon on Road Contruction in Black Cotton Soil Area, Journal of Indian road congre, 40(1), pp Peattie (1962): Stre-Strain Factor for Three Layer Sytem, Highway Reearch Board Bulletin 342. Prakah, S. (1981): Soil Dynamic, Mc Graw Hill Book Co. New York. Satyanarayana Reddy, C.N.V and Rama Moorthy, N.V. (2005), Significance of bearing capacity of clayey ubgrade in flexible pavement deign, International Journal of pavement Engineering, 6(3), Steinberg, M.L (1992), Vertical Moiture Barrier Update, Tranportation Reearch Record No. 1362, HRB, Wahington, pp US Army Corp of Engineer (1961): Revied Method of Thickne Deign of Flexible Highway Pavement at Military Intallation, Technical Report No , waterway Experimental Station. Simple placement of geotextile fabric at ubgrade doe not control the well of the ubgrade a it doe not retrain the ubgrade.