Paper No 05-2281

TITLE:

STRUCTURAL CONTRIBUTION OF GEOSYNTHETIC-REINFORCED WORKING PLATFORMS IN FLEXIBLE PAVEMENT

Author(s):

Woon-Hyung Kim

Former Graduate Assistant, Dept. of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA Tel: (608) 265-4491, Fax: (608) 263-245, e-mail: woonhyungkim@yahoo.co.kr

Tuncer B. Edil (Corresponding Author)

Professor, Dept. of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA Tel: (608) 262-3225, Fax: (608) 263-2453, e-mail: edil@engr.wisc.edu

Craig H. Benson

Professor, Dept. of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA. Tel: (608) 262-7242, Fax: (608) 263-2453, e-mail: benson@engr.wisc.ede

Burak F. Tanyu

Engineer, GeoSyntec Consultants, Chicago Branch 55 W Wacker Dr., Suite 1100, Chicago, IL, 60601. Tel: (312) 658-0500, Fax: (312) 658-0576, e-mail: btanyu@geosyntec.com

Paper submitted for presentation and publication at the

Transportation Research Board 84th Annual Meeting January 9-13, 2005 Washington, D.C.

(Total words = 6612)

Kim et al. 1

Abstract: A study was conducted in the field and with a large-scale model experiment (LSME) to evaluate the structural contribution of a 0.30-m-thick geosynthetic-reinforced granular layer used as a working platform for construction over soft subgrade. The study was conducted in the context of the 1993 AASHTO design guideline, where the structural number (SN) of the pavement is based on layer coefficients (each defined using a resilient modulus). Working platforms reinforced with geosynthetics had smaller elastic deflections and larger elastic moduli than unreinforced working platforms having the same thickness. Reinforcement factors ranging from 1.2 to 1.8 were obtained in the field and 1.7 to 2.0 in the laboratory, with greater reinforcement factors for the less extensible geosynthetics (geogrid, woven geotextile) for a 0.3 m-thick granular working platform. Of the four geosynthetics tested, the geogrid resulted in the greatest increases in modulus. Reinforcing the working platforms with geosynthetics resulted in increases in layer coefficients ranging from 50 to 70%. Similarly, increases in structural number for a typical pavement structure were realized ranging from 3 to 11% when all other factors were equal. Key Words: working platform, structural contribution, elastic modulus, geosynthetic reinforcement, flexible pavement, large-scale model experiment. INTRODUCTION Working platforms are commonly constructed on top of soft subgrades to support heavy equipment during construction of highway pavements. Granular materials such as crushed rock or gravel are generally used. Geosynthetics may also be included as reinforcement, to reduce the required thickness of the working platform and to reduce rutting (1, 2). Although the primary function of working platforms is to facilitate construction, they may also be included as a structural component of the pavement (i.e., as a granular subbase) if a layer coefficient is included in the design for the working platform. The objectives of this study were to evaluate the elastic deformation of four different geosynthetic-reinforced granular layers used as working platforms, to define a modulus and layer coefficient for each working platform, and to evaluate the structural contribution of the working platforms in the context of the structural number (SN) used in flexible pavement design. Tests were conducted in the field on several test sections employing a geosynthetic-reinforced working platform and in the laboratory in a prototype-scale test apparatus called the Large-Scale Model Experiment (LSME). LSME tests were conducted on two-layer systems consisting of reinforced granular materials and a soft subgrade using repetitive loadings simulating long-term vehicle traffic.

MATERIALS Three granular materials were used in the LSME and the field: a typical base course (Grade 2 gravel) and two crushed rocks referred to herein as “breaker run stone.” Grade 2 gravel is a broadly graded crushed rock that generally classifies as GW or SW in the Unified Soil Classification System (USCS) and is required to fall within upper and lower gradation boundaries defined by the Wisconsin Department of Transportation (WisDOT)

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(3). Breaker run stone consists of crushed rock that is not screened or processed after initial crushing. Thus, breaker run stone contains a broad range of particle sizes, ranging from fines to cobbles. The breaker run stone and Grade 2 gravel used in this study were retrieved during re-construction of a portion of Wisconsin State Highway (STH) 60 near Lodi, WI. Particle size characteristics and other physical properties of the materials are summarized in Table 1. All of the materials are coarse-grained, contain little fines, and classify as well-graded gravel (GW) or sand (SW) in the Unified Soil Classification System (USCS). The two breaker run stones differ primarily in particle size, with one of these materials having no cobbles and less gravel than the other. Compaction tests conducted on the Grade 2 gravel indicated that it is insensitive to compaction water content. A compaction test was not conducted on the breaker run because of its large particle size. However, given the granular composition of both breaker run stones and their low fines content (≤ 5%), insensitivity to water content was assumed.

Four geosynthetics were used in the study (a geogrid, a woven geotextile, a nonwoven geotextile, and a drainage geocomposite). Properties of geosynthetics used in this study are summarized in Table 2. Drainage geocomposites are used primarily for drainage, but the contribution of the geocomposite as a reinforcing element was the focus of this study.

LARGE-SCALE MODEL EXPERIMENT (LSME) The LSME test is a test apparatus for evaluating deflections during cyclic loading of a prototype-scale pavement structure (or parts of it) in a manner that replicates field conditions as closely as practical. A detailed description of the LSME is beyond the scope of this paper, but can be found in Tanyu et al. (4). A schematic of the LSME is shown in Fig. 1. A circular steel plate having a diameter of 250 mm (i.e., an area of 0.05 m2) and a thickness of 25 mm was used to apply the repetitive load provided by the actuator. Subgrade and Pavement Profile The subgrade and pavement profile tested in the LSME consisted of five layers (Fig. 1): sand, simulated soft subgrade (expanded polystyrene foam, or EPS), a thin (0.025 m) layer of Grade 2 gravel, the geosynthetic reinforcement layer, and the working platform material. EPS was used in lieu of earthen subgrade materials to facilitate replication of experiments. A series of tests was conducted on a variety of different EPS materials to identify an EPS with similar stress-strain behavior as a typical soft subgrade soil in Wisconsin. Details of this testing program are beyond the scope of this paper, but can be found in Tanyu et al. (4). The EPS that was used exhibited a modulus similar of soft-subgrade soils found in Wisconsin (7 MPa or lower) under the loads applies in the LSME. The EPS also underwent plastic deformation, as occurs in a conventional subgrade soil in response to long-term repetitive loading (4). Some embedment of the EPS into the overlying gravel occurred, but to a lesser extent than may occur in the field over the long-term. The thin layer of Grade 2 gravel placed over the EPS was used to facilitate interaction with the geosynthetic (i.e., an interface obtained by placing the geosynthetic directly against the EPS was not considered realistic).

Kim et al. 3

Base course and asphalt concrete layers were not incorporated in the LSME to simplify the setup and to eliminate ambiguities in data interpretation that can arise when the surface layer is much stiffer than the underlying layers. However, the stress reduction provided by these layers was accounted for when selecting the load applied to the working platform (see following section).

Each lift of Grade 2 gravel was compacted until the dry unit weight exceeded 95% of the maximum dry unit weight (Table 1). Breaker run stone was compacted to the same dry unit weight (20.0 kN/m3) used at the field control site (see subsequent discussion). Because of their insensitivity to water content, both materials were placed compacted at their existing water content (< 5%).

Applied Loads and Pavement Deflections Each profile in the LSME was subjected to two stages of repetitive loading: (i) 1,000 cycles of high intensity loading simulating construction traffic directly on the working platform and (ii) 10,000 cycles of lower intensity loading simulating vehicular traffic on the finished pavement. The lower intensity loading, the focus of this study, simulated the stress at the working platform level due to the load on the asphalt surface by a design vehicle. The load applied to the working platform was calculated using the program KENLAYER (5), assuming that a 7 kN wheel load applied a contact pressure of 140 kPa on the surface of the asphalt. A detailed discussion of this calculation is beyond the scope of this paper, but can be found in Tanyu et al. (4). The calculation indicated that the stress on the surface of the working platform in a pavement structure similar to STH 60 would be about 20% of the contact pressure on the road surface (4). This stress was applied with a circular loading plate (diameter = 0.25 m) using a haversine load pulse with an amplitude of 1.4 kN and consisting of a 0.1-s load period followed by a 0.9-s rest period (i.e., the same load pulse specified in a laboratory resilient modulus test (4). The contact area of the plate was smaller than the effective area of stress increase on an actual working platform under the overlying layers (i.e., in an actual working platform, the stress would be distributed over a region having diameter > 0.25 m). The effect of this difference in stressed area is believed to be minimal, because the load-deflection data were analyzed in a manner that explicitly considers the contact stress and contact area. Nevertheless, this limitation should be kept in mind when interpreting the results of the study.

Vertical deflections were measured directly underneath the loading plate and at distances of 300, 450, and 650 mm away from the center of the plate using position transducers anchored to the surface of the working platform (6). Earth pressure cells were installed at various locations within the profile, but the data obtained from the earth pressure cells were deemed unreliable. Additional details regarding instrumentation used to monitor the pavement profile can be found in (6).

Geosynthetic Displacements and Strains Displacements in the geosynthetics were measured using linear variable differential transformers (LVDTs) attached to steel tell-tale wires running through polyethylene

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tubes. Tell-tales were attached to the geosynthetics at 0, 130, 255, and 510 mm from the center of the loading platform in the cross-machine direction.

Strains in the geosynthetic were measured with a series of resistance type strain gages attached on the upper and lower surfaces of the geosynthetic. Strains were measured at five distances from the center of the loading plate (0, 130, 255, 380, and 510 mm) in the cross-machine direction of the geosynthetic. Procedures described in (7-9) were followed when mounting the strain gages. Additional details regarding the geosynthetic instrumentation can be found in (6). FIELD EXPERIMENT A field experiment is being conducted on a 312-m long pavement segment of STH 60 that contains twelve test sections with different pavement profiles. Edil et al. (10) provide a detailed description of the test sections. The subgrade at the test site consists of soft lean silt (ML) or lean clay (CL) having comparable deformational characteristics as the EPS used in the LSME (4, 10). Data from five of these test sections at STH 60 were used in this study. Four of these test sections were constructed with a 0.3-m-thick working platform of breaker run stone reinforced with the four aforementioned geosynthetics. A control section was constructed without geosynthetic reinforcement using a 0.84-m-thick working platform of breaker run stone. Test sections were not constructed using a working platform of Grade 2 gravel.

The geosynthetic materials were placed over the subgrade with the machine direction oriented parallel to the traffic lanes. Breaker run stone was placed over the geosynthetics in a single 0.30-m lift, while the unreinforced breaker run in the control section was placed in 0.15-m-thick lifts. Care was taken to avoid installation damage of the geosynthetics when placing the breaker run stone. However, no assessment of installation damage was made.

A 0.25-m-thick base course consisting of 0.11 m of Grade 2 gravel and 0.14 m of salvaged asphalt was placed on top of the working platform in each section. This composite base course was overlain with a 0.13-m-thick AC layer.

ANALYSIS Back-calculation of Elastic Moduli from the LSME KENLAYER was used to back-calculate the elastic modulus of each of the geosynthetic-reinforced layers using surface deflections and applied loads measured in the LSME. A two-layer profile consisting of simulated soft-subgrade and a working platform was used in the analysis. The average elastic deformation over the last 500 load cycles under the applied load in the LSME was used. The elastic modulus of the working platform was assumed to follow the power function:

2kb1r σ kM = (1)

where k1 and k2 are empirical constants and σb is the bulk stress. This model has been shown to be satisfactory for a wide range of granular materials (11) and laboratory tests

Kim et al. 5

conducted by Tanyu et al. (4) have shown that this model adequately describes the resilient modulus of the granular materials used in this study. The elastic modulus of the soft subgrade was assumed to be constant, which is reasonable for the low stresses applied to the subgrade layer. Uniqueness of the KENLAYER solution was assessed by conducting a series of sensitivity analyses where the initial conditions and the constraints for each layer were varied. Essentially the same material properties were obtained in each case, suggesting that the inversion provided nearly unique parameters (4) Back-calculation of Elastic Modulus at STH 60 Elastic moduli for the test sections at STH 60 were obtained by back-analysis of deflections measured using a falling weight deflectometer (FWD) (10). Details of the back-analysis can be found in (6). The back-analysis was conducted with the multi-layer elastic analysis program MODULUS (12). MODULUS was used rather than KENLAYER because MODULUS contains routines that can be used directly for analyzing FWD data.

A four-layer system (asphalt concrete, base course, working platform, and subgrade) was used in the analysis. The geometric mean temperature on the surface of AC layer at the time of FWD testing was used to set constraints on the modulus of the AC layer. Elastic moduli for the other layers were adjusted iteratively until the measured and predicted deflections matched within an accepted tolerance (6). As with the KENLAYER analyses of LSME data, uniqueness of the solution was evaluated using different initial conditions when beginning the inversion. Similar moduli were obtained regardless of the initial condition, indicating that the solution effectively was unique.

Once the elastic modulus of the working platform was back-calculated using MODULUS, an additional analysis was conducted with KENLAYER to determine the range of bulk stresses and vertical strains operative in the subbase layer in the field. The back-calculated elastic moduli obtained from MODULUS were used as input to KENLAYER for this analysis. The bulk stress and vertical strain obtained from KENLAYER at mid-depth of each layer were assumed to represent field conditions. RESULTS AND DISCUSSION LSME Tests Elastic deflections (δe) under the loading plate of the LSME as a function of the number of load cycles are shown in Fig. 2 for working platforms of Grade 2 gravel with and without geosynthetic reinforcement. For all cases, the elastic deflection increases rapidly within the first 100 cycles, and then levels off after approximately 1,000 cycles. In addition, the elastic deflections are smaller for the 0.46-m-thick layer for all loading cycles (i.e., approximately half of the deflections measured in 0.30-m thick).

For the thinner (0.30 m) working platforms, the long-term (> 1000 cycles) elastic deflections are 8% to 12% smaller when geosynthetic reinforcement is included. However, geosynthetic type has no significant effect. For the thicker (0.46 m) working platform, the average elastic deflection is 24-27% smaller when the geogrid or woven geotextile is used as reinforcement, whereas the elastic deflections for the working platforms reinforced with the nonwoven geotextile or the drainage geocomposite are

Kim et al. 6

similar to those for un-reinforced working platforms. Smaller elastic deflections have been observed by others (13, 14) in reinforced granular materials.

Elastic deflection basins at 10,000 cycles are shown in Fig. 3a and gauge strains and displacements in the geosynthetic under loading plate are shown in Fig. 3b. Both graphs correspond to 0.30-m thick working platforms. The deflection basins for the geosynthetic-reinforced working platforms are shallower relative to the basin for the un-reinforced working platform, but the basins for all four geosynthetics are similar (Fig. 3a). Flatter defection basins were obtained for the thicker (0.46 m) working platforms, and the thicker (0.46 m) working platforms reinforced with the geogrid or the woven geotextile were flatter than all others (6). Similar observations for geogrid-reinforced granular materials have been reported (15, 16).

Tensile strains and displacements in the geosynthetics varied by type. Tensile strains of ≈ 2% and tensile displacements of 0.02-0.04 mm occurred in the less extensible geosynthetics (geogrid and woven geotextile), whereas tensile strains and displacements in the more extensive geosynthetics (nonwoven geotextile and drainage geocomposite) were near zero. Moreover, small compressive strains occurred in the less extensible geosynthetics at a radial distances between 130 and 380 mm from the center of the loading plate (6). Perkins (2) observed similar strain distributions in crushed stone base courses reinforced with a woven geotextile and a geogrid.

The smaller elastic deflections and shallower deflection basins obtained with geosynthetic reinforcement indicate that the geosynthetic-reinforced working platforms are stiffer than the unreinforced working platforms. However, the reinforcement effect diminishes with increasing thickness of the working platform, at least for the more extensible geosynthetics. A likely reason for this phenomena is that more stress distribution occurs in a thicker working platform, resulting in smaller strains at the base of the working platform where the geosynthetic is located. In fact, strain in the less extensible geosynthetics generally decreased as the thickness of the working platform increased (6), which has also been observed by others (2, 17).

The reinforcing effect is also evident in the results of the KENLAYER analysis, which are reported in Table 3 for the working platforms 0.30-m thick. Also reported in Table 3 is a “reinforcement factor,” which is defined as the modulus of a reinforced working platform normalized by the modulus of an unreinforced working platform having the same thickness. In all cases, the reinforced working platforms have higher modulus than the unreinforced working platforms, with reinforcement factors ranging from 1.7-2.0. The largest increase in modulus was obtained for the geogrid (reinforcement factor = 2.0), and the lowest for the drainage composite (reinforcement factor = 1.7). Similar increases in modulus were obtained using the woven geotextile (reinforcement factor = 1.9) and nonwoven geotextile (reinforcement factor = 1.8). The relative magnitudes of these moduli are also consistent with the elastic deflections under the center of the loading plate. That is, the largest moduli correspond to the lowest deflections (geogrid), and vice versa (drainage geocomposite) Field Tests Data from FWD tests conducted at STH 60 were inverted using MODULUS to determine the elastic modulus of each of the five different working platforms evaluated in the field

Kim et al. 7

study. Data were collected five different times over a two-year period, with approximately 10 replicate tests being conducted each time along the centerline of each test section. The average of all moduli back-calculated for each test section is reported in Table 3 along with the range of these moduli for each test section. The moduli reported in Table 3 are from the 40-kN FWD load because the stress on the working platform from this load was closest to that applied in the LSME. Results for other loads are in (6) along with a compilation of all the data. The moduli for the un-reinforced working platform (the control section) have also been adjusted to correspond to a working platform 0.30-m thick using the method described in Tanyu et al. (4). This adjustment was made so that differences between the moduli would not be confounded by the effects of stress and strain distribution due to differences in thickness between the working platforms. Reinforcement factors for each of working platforms are also reported in Table 3. As was obtained from the LSME tests, all of the working platforms with geosynthetic reinforcement have greater elastic modulus than an unreinforced working platform of the same thickness (Table 3). The largest modulus was obtained with the geogrid (reinforcement factor = 1.8) and the lowest with the drainage geocomposite (reinforcement factor = 1.2). Similar moduli and reinforcement factors (1.5) were obtained for both geotextiles (woven and nonwoven). A direct comparison between the moduli at the STH 60 site and those from the LSME cannot be made because different granular materials were used in the field (breaker run stone) and the LSME (Grade 2 gravel). In addition, different programs were used for analysis (MODULUS and KENLAYER) and different loading methods were employed (single impact pulse from FWD vs. repetitive periodic pulse in the LSME). Nevertheless, the hierarchy of the reinforcement effect is the same (geogrid providing greatest reinforcement and drainage composite least reinforcement), and the reinforcement factors are very similar. Implications for Pavement Design

The reinforcement factors reported in Table 3 can be used to estimate the elastic modulus and structural contribution of geosynthetic-reinforced working platforms if the resilient modulus of the granular material used for the working platform is known. In a mechanistic-empirical design method, the estimated modulus of the working platform can be used directly in the analysis. There is an effort to incorporate geosynthetic reinforced layers in mechanistic-empirical pavement design (18). In the conventional AASHTO design method (19), the estimated modulus would be used to determine a layer coefficient for the working platform, and the working platform would be treated as a subbase. That is, the layer coefficient a3 in conventional AASHTO design procedure (19) would be used to define a layer structural number for the working platform.

The structural number, SN of the pavement is the summation of structural numbers for each of the pavement layers: 33221 mSN mSN SN SN ++= (2)

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where SNi is the structural number of the layer i and mi is the drainage modification factor for layer i. The structural number of each layer is a function of the layer coefficient (ai) and the thickness of the layer (Di): (3) iii Da SN = Usually Di is in units of inches. The layer coefficient is a measure of the effectiveness of a given material to function as a structural component of the pavement. In the 1993 AASHTO guideline (19), the layer coefficient is related to the resilient modulus (Mr) of the layer material using empirical equations developed by Rada and Witczak (20). For example, the equation for granular subbase material is: a3 = 0.227 log Mr3 – 0.839 (4) where a3 is the layer coefficient and Mr3 is the resilient modulus of the granular subbase material (in units of lbs/in2). This approach was used to estimate a3 for 0.30 m-thick working platforms of Grade 2 gravel reinforced with each of the geosynthetics. Elastic moduli obtained from the LSME tests on a 0.30 m-thick layer of Grade 2 gravel (Table 3) were used in the computations to demonstrate the effect of reinforcement on a3. Reinforcement with geosynthetics increased a3 by 50-70%, with largest increase with the geogrid (Table 4). The a3 in Table 4 were used to compute structural numbers (SN) for pavements having a similar profile as used at the STH 60 site. Properties of the asphalt concrete (a1 = 0.4, thickness = 125 mm) and base course (a2 = 0.14, thickness = 254 mm) were assumed to be the same when computing the SNs. For simplicity, the drainage modification factors were assumed to equal 1.0. The layer coefficients and SNs are summarized in Table 4, along with the percentage increase in SN using each geosynthetic. SNs computed for the pavements with working platforms reinforced with less extensible geosynthetics (geogrid, woven geotextile) are greater than those for working platforms reinforced with more extensible geosynthetics (nonwoven geotextile and drainage geocomposite). However, the percentage increase in SN obtained with the geogrid is much larger (> 2 times) than those obtained with the other geosynthetics, suggesting that the geogrid is the most effective geosynthetic in this study, at least in terms of improving the SN.

SUMMARY The objective of this study was to quantify and evaluate the structural contribution of granular working platforms reinforced with geosynthetics that are used for constructing highway pavements over soft subgrade. Four geosynthetics (geogrid, woven geotextile, nonwoven geotextile, and drainage geocomposite) were considered. Moduli of the reinforced working platforms were obtained from prototype-scale tests conducted in the laboratory on simulated pavement systems and field tests on test sections incorporated into a secondary highway in Wisconsin. The effect of geosynthetics was expressed in terms of the “reinforcement factor,” which is defined as the elastic modulus of the geosynthetic-reinforced working platform divided by the elastic modulus of an

Kim et al. 9

unreinforced working platform having the same thickness and constructed with the same granular material.

Working platforms reinforced with geosynthetics had smaller elastic deflections and larger elastic moduli than unreinforced working platforms having the same thickness. Reinforcement factors ranging from 1.2 to 1.8 were obtained in the field and 1.7 to 2.0 in the laboratory, with greater reinforcement factors for the less extensible geosynthetics (geogrid, woven geotextile) for a 0.3 m-thick granular working platform. Of the four geosynthetics tested, the geogrid resulted in the greatest increases in modulus.

Structural contributions of the working platforms were estimated by treating them as a subbase in the conventional AASHTO design method for flexible pavements with a layer coefficient and computing a structural number for the pavement system. Reinforcing the working platforms with geosynthetics resulted in increases in layer coefficients ranging from 50 to 70%. Similarly, increases in structural number for a typical pavement structure were realized ranging from 3 to 11% when all other factors were equal, with the largest increase in structural number obtained the geogrid was used a reinforcement. ACKNOWLEDGEMENTS Financial support for this study was provided by the Wisconsin Department of Transportation (WisDOT) through the Wisconsin Highway Research Program (WHRP). The authors appreciate Amoco Fabrics and Fibers Co., Tenax Corporation, and Yahara Materials for supplying the geosynthetics and Grade 2 gravel. The conclusions and recommendations in this report are solely those of the authors, and do not necessarily reflect the opinions or policies of WisDOT, WHRP, or the material suppliers. REFERENCES 1. Montanelli, F., A., Zhao, and P. Rimoldi. Geosynthetic-Reinforced Pavement System:

Testing and Design. Proceedings of Geosynthetics ’97, IFAI, Vol. 2, Long Beach, California, 1997, pp. 619-632.

2. Perkins, S. W. Mechanical Response of Geosynthetic-Reinforced Flexible Pavements.

Geosynthetics International, Vol. 6, No. 5, 1999, pp. 347-382. 3. Wisconsin. Standard Specification for Highway and Structure Construction,

Wisconsin Department of Transportation, Madison, Wisconsin, 1996. 4. Tanyu, B., W. H. Kim, T. B. Edil, and C. H. Benson. Comparison of Laboratory

Resilient Modulus with Back-Calculated Elastic Moduli from Large-Scale Model Experiments and FWD Tests on Granular Materials. Resilient Modulus Testing for Pavement Components, ASTM STP 1437, G. Durham, A. Marr, and W. De Groff, eds., ASTM, West Conshohocken, PA, 2003, pp. 191-208.

5. Huang, Y. H. (1993) Pavement Analysis and Design, Prentice Hall, Inc., Englewood

Cliffs, New Jersey.

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6. Kim, W. H. Behavior of Geosynthetic-reinforced Aggregate Platforms Over Soft

Subgrades. Ph.D Dissertation, University of Wisconsin-Madison, Madison, Wisconsin, 2003.

7. Farrag K. (1999) “Strain Gage Installation on Geosynthetics,” Louisiana

Transportation Research Center, Louisiana State University, Baton Rouge, LA. 8. Chew, S. H., W. K. Wong, C. C. Ng, S. A. Tan, and G. P. Karunaratne. Strain

Gauging Geotextiles Using External Gauge Attachment Method. Grips, Clamps, Clamping Techniques, and Strain Measurement for Testing of Geosynthetics, ASTM STP 1379, P.E. Stevenson, Eds., ASTM, West Conshohocken, PA, 2000, pp. 97-110.

9. Hayden, S. A., D. N. Humphrey, B. R. Christopher, K. S. Henry, and C. P. Fetten.

Effectiveness of Geosynthetics for Roadway Construction in Cold Regions: Results of a Multi-Use Test Section. Proceedings of Geosynthetics ’99, Vol. 2, Boston, MA, 1999, pp. 847-862.

10. Edil, T. B., C. H. Benson, M. Bin-Shafique, B. Tanyu, W. H. Kim, and A. Senol.

Field Evaluation of Construction Alternatives for Roadway Over Soft Subgrade. In Transportation Research Record: Journal of the Transportation Research Board, No. 1786, TRB, National Research Council, Washington, DC., 2002, pp. 36-48.

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Properties of Granular Materials”, Transportation Research Record, 345, Transportation Research Board, National Research Council, Washington, DC, 15-31.

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1987-1, Texas Transportation Institute, The Texas A&M University System, College Station, Texas, 1991.

13. Fannin, R. J., and O. Sigurdsson. Field Observations on Stabilization of Unpaved

Roads with Geosynthetics. Journal of Geotechnical Engineering, ASCE, Vo. 122, No. 7, 1996, pp. 544-553.

14. Leng, J., M. A. Gabr. Characteristics of Geogrid-Reinforced Aggregate Under Cyclic

Load. In Transportation Research Record: Journal of the Transportation Research Board, No. 1786, TRB, National Research Council, Washington, DC., 2002, pp. 29-35.

15. Haas, R., J. Wals, and R. G. Carroll. Geogrid Reinforcement of Granular Bases in

Flexible Pavements. In Transportation Research Record: Journal of the Transportation Research Board, No. 1188, TRB, National Research Council, Washington, DC., 1988, pp. 19-27.

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16. Kinney, T. C., J. Abbott, and J. Schuler. Benefits of Using Geogrids for Base Reinforcement with Regard to Rutting. In Transportation Research Record: Journal of the Transportation Research Board, No. 1611, TRB, National Research Council, Washington, DC, 1998a, pp. 86-96.

17. Collin, J. G., T. C. Kinney, and X. Fu. Full Scale Highway Load Test of Flexible

Pavement Systems with Geogrid Reinforced Base Courses. Geosynthetics International, Vol. 3, No. 4, 1996, pp. 537-549.

18. Perkins, S. W. Mechanistic-Empirical Modeling and Design Model Development of

Geosynthetic Reinforced Flexible Pavements. Report No. FHWA/MN-01002/99160-1A, U.S. Department of Transportation, Federal Highway Administration, Washington, DC., 2001.

19. AASHTO Guide for the Design of Pavement Structures, American Association of

State Highway and Transportation Officials Publication, Washington, DC, 1993. 20. Rada, G, and M. Witcazk. Comprehensive Evaluation of Laboratory Resilient

Modulus Results for Granular material. In Transportation Research Record: Journal of the Transportation Research Board, No. 810, TRB, National Research Council, Washington, DC., 1981, pp. 23-33.

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LIST OF TABLES Table 1. Properties of Grade 2 gravel and breaker run stone used in LSME and field

tests. Table 2. Properties of geosynthetics used in LSME and field tests. Table 3. Moduli of 0.30-m-thick unreinforced and geosynthetic-reinforced working

platforms in the field and LSME (ranges at STH 60 shown in parentheses). Table 4. Layer coefficients and structural numbers for pavements with and without

geosynthetic reinforced working platforms. LIST OF FIGURES Figure 1. Schematic cross section of large-scale model experiment (LSME). Figure 2. Comparison of elastic deflection of working platforms of Grade 2 gravel

under the loading plate of the LSME as a function of number of load cycles. Figure 3. Elastic deflection basins for geosynthetic-reinforced working platforms after

10,000 load cycles in the LSME (a) and gauge strain and displacement in the geosynthetic under loading plate as a function of number of loading cycles (b).

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Table 1. Properties of Grade 2 gravel and breaker run stone used in LSME and field tests.

Soil Fractiona (%) Material Specific

Gravity Cobble Gravel Sand Fines

USCS Symbol

Maximum Dry Unit Weightb

(kN/m3) CBR

Grade 2 Gravel

2.65 0 45 47 8 SW 22.6 33

Breaker Run

(LSME)

NMc 23 49 25 3 GW NMc 80d

Breaker Run

(Field)

NMc 0 30 65 5 GW NMc 80d

a Soil faction refers to the fraction of breaker run smaller than 75 mm (both breaker runs contained cobbles larger than 75 mm).

b Compaction per ASTM D 698. c NM = not measured. d Assumed CBR.

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Table 2. Properties of geosynthetics used in LSME and field tests.

Geosynthetic Type Property Test Method Valuesg (XMD)

Geogrid a

Thickness Mass per Unit Area Aperture Sizee Peak Tensile Strength Yield Point Elongation Offset Tangent Modulus

ASTM D 5199 ASTM D 5261

NAf

GRI-GG1 GRI-GG1

ASTM D 4595

NMh

253.1 g/m2

32 (45) mm 17.2 (16.0) kN/m

20 (11) % 88.3 (115.0) kN/m

Woven Geotextile b

Thickness Mass per Unit Area Wide Width Tensile Wide Width Elongation Offset Tangent Modulus

ASTM D 5199 ASTM D 5261 ASTM D 4595 ASTM D 4595 ASTM D 4595

0.7 mm 268.2 g/m2

35.3 (42.3) kN/m 26 (19) %

147.9 (292.2) kN/m

Nonwoven Geotextile c

Thickness Mass per Unit Area Wide Width Tensile Wide Width Elongation Offset Tangent Modulus

ASTM D 5199 ASTM D 5261 ASTM D 4595 ASTM D 4595 ASTM D 4595

2.7 mm 315.6 g/m2

14.5 (21.8) kN/m 72 (57) %

34.0 (36.8) kN/m

Drainage Geocomposited

Thickness Mass per Unit Area Tensile Strength Tensile Elongation Offset Tangent Modulus

ASTM D 5199 ASTM D 5261 ASTM D 4595 ASTM D 4595 ASTM D 4595

12.7 mm 1700.6 g/m2

50.9 (54.4) kN/m 57 (34) %

675.0 (200.0) kN/m

a Biaxial oriented polypropylene. b Polypropylene slit-film. c Polypropylene needle punched. d Tri-planar polyethylene geonet with nonwoven polypropylene geotextiles. e As reported by the manufacturer. f NA=no standard method available. g Machine direction (XMD=cross-machine direction). h NM = not measured.

Kim et al. 15 Table 3. Moduli of 0.30-m-thick unreinforced and geosynthetic-reinforced working platforms in the field and LSME (ranges at STH

60 shown in parentheses). Elastic Modulus, M (MPa)

Geosynthetic-Reinforced

Reinforcement Factor Mreinforced / Munreinforced Unreinforced

Geogrid Woven Geotextile

Nonwoven Geotextile

Drainage Geocomposite Geogrid Woven

Geotextile Nonwoven Geotextile

Drainage Geocomposite

LSME 40 78 76 70 67 2.0 1.9 1.8 1.7

STH 60 93a

(88-106)a163

(135-186) 133

(115-160) 135

(114-155) 110

(98-120) 1.8 (1.5-2.0)

1.5 (1.2-1.8)

1.5 (1.1-1.8)

1.2 (1.1-1.3)

Note: aExtrapolated from 0.84 m to 0.30 m thickness at the mean field bulk stress of 43 kPa taking into account effect of thickness on stress distribution and strain amplitude adjusted to a layer 0.30-m thick using method described in Tanyu et al. (4).

Kim et al. 16

Table 4. Layer coefficients and structural numbers for pavements with and without geosynthetic reinforced working platforms.

Design Element Unreinforced Geogrid Woven Geotextile

Nonwoven Geotextile

Drainage Geocomposite

Working Platform Layer Coefficient, a3

0.10 0.17 0.16 0.16 0.15

Structural Number, SNa 4.58 5.06 4.80 4.69 4.69

Increase in Structural Number

(%) - 11 5 3 3

a SN = a1D1 + a2D2m2+ a3D3 m2 where ai is the layer coefficient of layer i, Di is the thickness of layer i (inches), and mi is the drainage modification factor.

Kim et al. 17

Ground Surface

Sand

Simulated Soft Subgrade(Expanded Polystyrene Foam)

Test Material

Cyclic Load

0.30 to 0.91 m

0.45 m

2.50 m

GeosyntheticsWisDOT Grade 2 Gravel 0.025 m

(Not to Scale)

Reinforced ConcretePit Walls

WoodenWalls

Circular SteelPlate

(d = 0.25 m)Test Pit

(3 m x 3 m x 3 m)

Fig. 1. Schematic cross section of large-scale model experiment (LSME).

Kim et al. 18

0

1

2

3

4

5

6

0 2,000 4,000 6,000 8,000 10,000

GeogridWoven Geotextile Nonwoven Geotextile Drainage Geocomposite

Ela

stic

Def

lect

ion,

δe (m

m)

Number of Loading Cycles, Nc

h = 0.30 m

h = 0.46 mUnreinforced

Grade 2 gravel

Fig. 2. Comparison of elastic deflection of working platforms of Grade 2 gravel under the loading plate of the LSME as a function of number of load cycles.

Kim et al. 19

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

0200400600800 200 400 600 800

Geogrid (h = 0.30 m)Woven Geotextile (h = 0.30 m)Non-woven Geotextile (h = 0.30 m)Drainage Geocomposite (h = 0.30 m)E

last

ic D

efle

ctio

n A

fter 1

0,00

0 Lo

ad C

ycle

s, δ

e (mm

) Elastic Deflection A

fter 10,000 Load Cycles, δ

e (mm

)

Distance From Center of Loading Plate (mm)

Loading Plate(d = 250 mm)

Unreinforced Grade 2 gravel

(h = 0.30 m)

Reinforced

(a)

-4.0

-2.0

0.0

2.0

4.0

6.0-0.1

0.0

0.1

0 2,000 4,000 6,000 8,000 10,000

Geogrid (h = 0.30 m)Woven Geotextile (h = 0.30 m)Non-woven Geotextile (h = 0.30 m)Drainage Geocomposite (h = 0.30 m)

Cum

ulat

ive

Gau

ge S

train

(%)

Cum

ulative Displacem

ent in Geosynthetics (m

m)

Number of Loading Cycles, Nc

Gauge Strain

Displacement

(b)

Fig. 3. Elastic deflection basins for geosynthetic-reinforced working platforms after 10,000 load

cycles in the LSME (a) and gauge strain and displacement in the geosynthetic under loading plate as a function of number of loading cycles (b).