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Roads in Louisiana are often built over weak subgrade soils due to the soft nature of subsurface soils and the presence of high water tables, which create many design and construction challenges. A common practice in Louisiana is to stabilize/treat the upper part of subgrade with cement or lime, depending on the subgrade soil type. This practice can help reduce the risks of excessive permanent deformations (rutting) by spreading the tire pressure into a wider area, thus reducing the vertical pressure on top of the untreated subgrade layer.

20-2GT 1000337, SPR: TT-Fed/TT-Reg, The primary objectives of this research are to monitor the short-term (during the construction) and long-term behavior and performance of geosynthetic Load Transfer Platform (LTP) in the state of Louisiana; evaluate and verify (and maybe modify) important design factors and parameters for geosynthetic LTP: load distribution (between piles, geogrid, and soft soil), settlement, and lateral thrust. A design spreadsheet could be developed which will be easy for the engineers to use; conduct finite element parametric study to evaluate the effect of different variables and parameters on the performance of geosynthetic LTP for embankment; and propose design and construction guidance that are needed to establish the department’s design policies and specification.

80/20 SPR, There are three main objectives of this study. The first is to evaluate the effect of fines content on the value of internal friction angle of sand soils mixed with fines typically encountered in Louisiana. The second objective is to evaluate the effect of fines content on the interface friction angle between sand soils mixed with fines and both concrete and steel surfaces. Lastly, the study will determine the threshold percent of fines content beyond which the sand soils mixed with fines will behave as cohesive soils, rather than cohesion less soils, and the effect on design of driven piles.

Bottom ash is a by-product of the energy industry and the residual of burning coal in a kiln, firing process. Bottom ash is black and the consistency of coarse sand with gravel clinker, traces. The product is used in other states as embankment material, and this project will, evaluate the product for use in Louisiana., Many laboratory tests were conducted to evaluate the properties of the bottom ash material., Those tests included moisture content, standard and modified Proctor, grain size distribution, California Bearing Ratio (CBR), nuclear moisture density, direct shear, pH, and resistivity, tests., A test section was constructed with the bottom ash material. The purpose of the test section, was to evaluate the in-situ properties of the material in the field, the construction techniques, and the potential field quality control methods and devices to monitor field construction., The results of the Dynamic Cone Penetrometer (DCP) and the nuclear moisture density, gauge appeared to be the most effective tools in evaluating the material. The DCP results, were repeatable and closely matched typical values for sand strength/stiffness. The nuclear, gauge proved to be an appropriate tool for construction control., Implementation of the bottom ash material should provide the Louisiana Department of, Transportation and Development (LADOTD) an effective embankment alternative at a low, cost. The material also has relatively low density, which could provide another lightweight, embankment alternative for soft subsurface soils., Recommendations include future test sections with field monitoring due to the limited scope, of the project. A draft specification has been included for review and approval by the chief, engineer.

The primary objectives of this research include: performing static and dynamic load tests on, newly instrumented test piles to better understand the set-up mechanism for individual soil, layers, verifying or recalibrating previously developed empirical set-up models for piles driven, in soft cohesive soils (prior LTRC Project 11-2GT), and developing an analytical methodology to, estimate the duration of pile set-up., Minor objectives include: developing a model to predict spatial distribution of excess pore water, pressure due to pile driving, establishing a relationship between vertical shaft displacement, and associated shear resistance by analyzing strain gage data from instrumented test piles, developing a method to predict the pile tip resistance at different axial tip displacements, and, calculating the total and effective stress parameters (e.g., adhesion factor).

04-2GT, This research study investigates the potential benefits of using reinforced soil foundations to improve the bearing, capacity and reduce the settlement of shallow foundations on soils. To implement this objective, a total of 117, tests, including 38 laboratory model tests on silty clay embankment soil, 51 laboratory model tests on sand, 22, laboratory model tests on Kentucky crushed limestone, and 6 large-scale field tests on silty clay embankment soil, were performed at the Louisiana Transportation Research Center to study the behavior of reinforced soil, foundations. The influences of the different variables and parameters contributing to the improved performance of, reinforced soil foundation were examined in these tests. In addition, an instrumentation program with pressure, cells and strain gauges was designed to investigate the stress distribution in soil mass with and without, reinforcement and the strain distribution along the reinforcement. The test results showed that the inclusion of, reinforcement can significantly improve the soil’s bearing capacity and reduce the footing settlement. The, geogrids with higher tensile modulus performed better than geogrids with lower tensile modulus. The strain, developed along the reinforcement is directly related to the settlement, and, therefore, higher tension would be, developed for geogrid with higher modulus under the same footing settlement. The test results also showed that, the inclusion of reinforcement will redistribute the applied load to a wider area, thus minimizing stress, concentration and achieving a more uniform stress distribution. The redistribution of stresses below the reinforced, zone will result in reducing the consolidation settlement of the underlying weak, clayey, soil which is directly, related to the induced stress. Insignificant strain measured in the geogrid beyond its effective length of 4.0 ~ 6.0B, indicated that the geogrid beyond this length provides a negligible extra reinforcement effect.

LTRC Number: 05-5GT, State Project Number: 736-99-1312, This research study aims at evaluating the performance of base and subgrade soil in flexible pavements under repeated loading test conditions. For this purpose, an indoor cyclic plate load testing equipment was developed and used to conduct a series of large-scale in-box tests and full-scale field tests on several pavement sections., The in-box cyclic plate load tests were conducted to evaluate the performance and benefits of geogrid base reinforcement in flexible pavements. A total of 12 tests were performed on unreinforced and geogrid-reinforced pavement sections. The parameters investigated in this study included the aperture shape (geometry) of the geogrid, location of the geogrid within the base layer, and geogrid tensile modulus. The stress distribution and permanent vertical strain in the subgrade, the development of excess pore water pressure in the subgrade, and the strain distribution along the geogrids were also investigated. The test results showed that the inclusion of geogrids can significantly improve the performance of flexible pavements on weak subgrades [California Boring Ratio (CBR) ≤ 1%], and that the traffic benefit ratio (TBR) can be increased up to 15.3 at a rut depth of 0.75 in. (19 mm). Better performance was observed when the geogrid was placed within the upper one third of the base aggregate layer. The inclusion of geogrid helps redistribute the applied surface load to a wider area on top of the subgrade layer, thus reducing the accumulated permanent deformation within the subgrade., Full-scale field tests were also conducted on several test lane sections built at the Pavement Research Facility (PRF) site using two types of loadings: cyclic plate load test and rolling wheel load test. These sections include blended calcium sulfate (BCS), stabilized BCS, stabilized recycled asphalt pavement (RAP), and stabilized soil as base/subbase materials. The differences in pavement responses of the tested sections to cyclic plate and rolling wheel loads were investigated. The measured rut depth caused by rolling wheel load, in all test sections, were much higher than those measured from the cyclic plate load test. The difference can be as much as 3 to 7 times between these two types of loading. This is mainly due to the effects of principal stress rotation and lateral wander on the permanent deformation of pavements. The field test results also indicate that the cyclic plate load test can be a good performance indicator test for the evaluation and pre-selection of pavement sections for field tests.

LTRC project 07-2GT, State project 736-99-1408, This research project presents the calibration of resistance factors for the Load and Resistance Factor Design (LRFD) method of driven, piles driven into Louisiana soils based on reliability theory. Fifty-three square Precast-Prestressed-Concrete (PPC) piles that were tested to, failure were included in this investigation. The predictions of pile resistances were based on static analysis (-method for clay and, Nordlund method for sand), three direct CPT methods [Schmertmann method, De Ruiter and Beringen method, and Bustamante and, Gianeselli (LCPC) method], and the average of the three CPT methods. Also, dynamic measurements with signal matching analysis of pile, resistances using the Case Pile Wave Analysis Program (CAPWAP), which is based on the measured force and velocity signals obtained, near the pile top during driving, were calibrated. The Davisson and modified Davisson interpretation methods were used to determine, measured ultimate load carrying resistances from pile load tests. The predicted ultimate pile resistances obtained using the different, prediction methods were compared with measured resistances determined from pile load tests. Statistical analyses were carried out to, evaluate the capability of the prediction design methods to estimate measured ultimate pile resistance of driven piles. The results showed, that the static method over-predicts pile resistance, while the dynamic measurement with signal matching analysis [CAPWAP-EOD (end of, drive) and 14 days BOR (beginning of restrike)] under-predicts pile resistance. Among the three direct CPT methods, the De Ruiter and, Beringen method was the most consistent prediction method with the lowest COV. Reliability based analyses using the First Order Second, Moment (FOSM) method, the First Order Reliability Method (FORM), and the Monte Carlo (MC) simulation method were also conducted, to calibrate the resistance factors () for the investigated pile design methods. The resistance factors with the target reliability (Ｔ）of 2.33, for the different design methods were determined and compared with American Association of State Highway and Transportation Officials, (AASHTO) recommendation values. In addition, the evaluation of different design methods was performed.

Piezocone penetration tests (PCPT) have been widely used by geotechnical engineers for subsurface investigation and evaluation of different soil properties such as strength and deformation characteristics of the soil. This report focuses on the verification of the PCPT settlement prediction methods for estimating the magnitude and time-rate of consolidation settlement of embankments over fine-grained soils. The settlement prediction methods involve the interpretation of piezocone penetration soundings and dissipation tests to determine the consolidation parameters, which include constrained modulus (M), overconsolidation ratio (OCR), and the horizontal and vertical coefficients of consolidation (ch ,cv). This Louisiana Transportation Research Center (LTRC) research team selected two case study sites, Juban Road Interchange Bridge at I-12 and Bayou Courtableau Bridge, to verify the PCPT predicted magnitude and time-rate of settlement. The embankments at each site were instrumented with horizontal inclinometers and vertical extensometers to monitor/measure their settlement with time. Both conventional one-dimensional consolidation tests and PCPT tests were performed to determine the consolidation parameters needed to calculate the magnitude and time-rate of consolidation settlements. The predicted magnitude and time-rate of consolidation settlements estimated using the laboratory one-dimensional consolidation tests and the PCPT tests were compared with field measurements. The results of this study showed that the piezocone penetration and dissipation data can reasonably estimate the magnitude and rate of consolidation settlement within the same range of accuracy as of the laboratory calculation. Friendly, visual basic software (Louisiana Embankment Settlement Prediction Program from PCPT, LESPP-PCPT) was also developed to calculate the magnitude and time-rate of consolidation settlements for symmetrical and unsymmetrical embankments utilizing the PCPT and dissipation

The objectives of this research study are to develop a three-dimensional FE, model for simulating the behavior of a battered pile group foundation subjected, to lateral loading, and to verify the model using results from a unique static, lateral load test that was conducted at the M19 eastbound pier of the I-10 Twin, Span Bridge.

The load and resistance factor design (LRFD) has been used increasingly and has become mandatory for the design of all bridge, projects funded by the Federal Highway Association (FHWA). Compared to the allowable stress design (ASD) method, LRFD can, achieve a compatible reliability between the bridge superstructure and substructure. The uncertainties of load and resistance are, quantifi ed separately and reasonably incorporated into the design process. Therefore, this reliability-based design approach will, generally produce a more effi cient and consistent design than the traditional ASD factor of safety approach. To achieve these goals, many researchers have been working to develop a reasonable way to implement the LRFD method in bridge substructure design and, to determine appropriate resistance factors for diff erent regional soil conditions.

Piezocone penetration tests (PCPT) have been widely used by geotechnical engineers for subsurface, investigation and evaluation of different soil properties such as strength and deformation characteristics of the, soil. This report focuses on the verification of the PCPT settlement prediction methods for estimating the, magnitude and time-rate of consolidation settlement of embankments over fine-grained soils. The settlement, prediction methods involve the interpretation of piezocone penetration soundings and dissipation tests to, determine the consolidation parameters, which include constrained modulus (M), overconsolidation ratio (OCR), and the horizontal and vertical coefficients of consolidation (ch ,cv). This Louisiana Transportation Research, Center (LTRC) research team selected two case study sites, Juban Road Interchange Bridge at I-12 and Bayou, Courtableau Bridge, to verify the PCPT predicted magnitude and time-rate of settlement. The embankments at, each site were instrumented with horizontal inclinometers and vertical extensometers to monitor/measure their, settlement with time. Both conventional one-dimensional consolidation tests and PCPT tests were performed to, determine the consolidation parameters needed to calculate the magnitude and time-rate of consolidation, settlements. The predicted magnitude and time-rate of consolidation settlements estimated using the laboratory, one-dimensional consolidation tests and the PCPT tests were compared with field measurements. The results of, this study showed that the piezocone penetration and dissipation data can reasonably estimate the magnitude and, rate of consolidation settlement within the same range of accuracy as of the laboratory calculation. Friendly, visual basic software (Louisiana Embankment Settlement Prediction Program from PCPT, LESPP-PCPT) was, also developed to calculate the magnitude and time-rate of consolidation settlements for symmetrical and, unsymmetrical embankments utilizing the PCPT and dissipation tests for use by geotechnical engineers.

04-2GT, This research study investigates the potential benefits of using reinforced soil foundations to improve the bearing capacity and reduce the settlement of shallow foundations on soils. To implement this objective, a total of 117 tests, including 38 laboratory model tests on silty clay embankment soil, 51 laboratory model tests on sand, 22 laboratory model tests on Kentucky crushed limestone, and 6 large-scale field tests on silty clay embankment soil were performed at the Louisiana Transportation Research Center to study the behavior of reinforced soil foundations. The influences of the different variables and parameters contributing to the improved performance of reinforced soil foundation were examined in these tests. In addition, an instrumentation program with pressure cells and strain gauges was designed to investigate the stress distribution in soil mass with and without reinforcement and the strain distribution along the reinforcement. The test results showed that the inclusion of reinforcement can significantly improve the soil’s bearing capacity and reduce the footing settlement. The geogrids with higher tensile modulus performed better than geogrids with lower tensile modulus. The strain developed along the reinforcement is directly related to the settlement, and, therefore, higher tension would be developed for geogrid with higher modulus under the same footing settlement. The test results also showed that the inclusion of reinforcement will redistribute the applied load to a wider area, thus minimizing stress concentration and achieving a more uniform stress distribution. The redistribution of stresses below the reinforced zone will result in reducing the consolidation settlement of the underlying weak, clayey, soil which is directly related to the induced stress. Insignificant strain measured in the geogrid beyond its effective length of 4.0 ~ 6.0B indicated that the geogrid beyond this length provides a negligible extra reinforcement effect.

02-04GT, Accelerated load testing of paved and unpaved roads is the application of a large number of load repetitions in a short period of time. This type of testing is an economic way to determine the behavior of roads and compare different materials, structures, and construction alternatives for the design of highways under a large number of load applications. Currently, numerous accelerated pavement testing (APT) facilities are being used worldwide. Heavy vehicle simulators (HVS) and the cyclic load actuators are the most commonly used facilities. Smaller scale model-testing facilities are also available., This report presents a feasibility and cost-efficiency study for different accelerated load facilities to determine the most useful facility for conducting comparative studies and preliminary investigations on paved/unpaved roads along with the Accelerated Load Facility (ALF) at the Louisiana Transportation Research Center (LTRC). Heavy vehicle simulators (wheel beam assembly), cyclic load actuators, and the Model Mobile Load Simulator (MMLS) were reviewed and compared based on the literature findings, personal communication with researchers, and coordinating site visits to selected facilities. The comparisons included the applications, advantages, limitations, and costs of each of the three alternative facilities., Based on the feasibility study, the MMLS was excluded due to its limited influence depth reasoned by the wheel size and wheel load. The HVS and the cyclic load actuators were found to be more useful for base, subbase, and subgrade related studies. Due to various applications, and based on the inherent advantages of both facilities (speed and cost), the cyclic load actuator facility has been recommended for research purposes at the LTRC. This facility can be used for wide range of research related to asphalt concrete layers, base course layers, subgrade layers, and the reinforcement layers. Its compact size and speed of testing will allow for more preliminary investigations prior to ALF testing.

736-99-1003, The objective of this study was to develop resilient modulus prediction models for possible application in the quality control/quality assurance (QC/QA) procedures during and after the construction of pavement layers. Field and laboratory testing programs were conducted to achieve this objective. The field testing program included conducting GeoGauge, light falling weight deflectometer, and dynamic cone penetrometer in situ tests. The laboratory program included performing repeated load triaxial resilient modulus tests and physical properties and compaction tests on soil tested in the field. A total of four cohesive soil types and three types of granular materials at different moisture-dry unit weight levels were considered., Comprehensive statistical analyses were conducted on the field and laboratory test results. Regression models that correlate the resilient modulus to the results of different in situ test devices and soil physical properties were developed. A good agreement was observed between the predicted and measured values of the resilient modulus. The results of this research study demonstrated a promising role of the different in situ tests considered in the QC/QA procedures of the construction of pavement layers.

LTRC Number: 07-2GT, State Project Number: 736-99-1408, The first report on Load and Resistance Factor Design (LRFD) calibration of driven piles in Louisiana (LTRC Final Report 449) was, completed in May 2009. As a continuing effort to implement the LRFD design methodology for deep foundations in Louisiana, this, report will present the reliability based analyses for the calibration of the resistance factor for LRFD design of axially loaded drilled, shafts. A total of 16 cases of drilled shaft load tests were available to authors from Louisiana Department of Transportation and, Development (LADOTD) archives. Out of those, only 11 met the Federal Highway Administration (FHWA) “5%B” settlement, criterion. Due to the limited number of available drilled shaft cases in Louisiana, additional drilled shaft cases were collected from, state of Mississippi that has subsurface soil conditions similar to Louisiana soils. A total of 15 drilled shafts from Mississippi were, finally selected from 50 available cases, based on selection criteria of subsurface soil conditions and final settlement. As a result, a, database of 26 drilled shaft tests representing the typical design practice in Louisiana was created for statistical reliability analyses., The predictions of total, side, and tip resistance versus settlement behavior of drilled shafts were established from soil borings using, the FHWA O’Neill and Reese design method via the SHAFT computer program. The measured drilled shaft axial nominal resistance, was determined from either the Osterberg cell (O-cell) test or the conventional top-down static load test. For the 22 drilled shafts that, were tested using O-cells, the tip and side resistances were deduced separately from test results. Statistical analyses were performed, to compare the predicted total, tip, and side drilled shaft nominal axial resistance with the corresponding measured nominal, resistance. Results of this showed that the selected FHWA design method significantly underestimates measured drilled shaft, resistance. The Monte Carlo simulation method was selected to perform the LRFD calibration of resistance factors of drilled shaft, under strength I limit state. The total resistance factors obtained at different reliability index () were determined and compared with, those available in literature. Results of reliability analysis, corresponding to a target reliability index () of 3.0, reveals resistance, factors for side (side), tip (tip), and total resistance factor (total) are 0.20, 0.75, and 0.5, respectively.

LTRC Number: 11-4GT, SIO Number: 30000280, The Load and Resistance Factor Design (LRFD) calibration of deep foundation in Louisiana was first completed for driven piles (LTRC Final Report 449) in May 2009 and then for drilled shafts using 1999 FHWA design method (O’Neill and Reese method) (LTRC Final Report 470) in September 2010. As a continuing effort to implement the LRFD design methodology for deep foundations in Louisiana, this report will present the reliability-based analyses for the calibration of the resistance factor for LRFD design of axially loaded drilled shafts using Brown et al. method (2010 FHWA design method). Twenty-six drilled shaft tests collected from previous research (LTRC Final Report 449) and eight new drilled shaft tests were selected for statistical reliability analysis; the predictions of total, side, and tip resistance versus settlement behavior of drilled shafts were established from soil borings using both 1999 FHWA design method (Brown et al. method) and 2010 FHWA design method (O’Neill and Reese method). The measured drilled shaft axial nominal resistance was determined from either the Osterberg cell (O-cell) test or the conventional top-down static load test. For the 30 drilled shafts that were tested using O-cells, the tip and side resistances were deduced separately from test results. Statistical analyses were performed to compare the predicted total, tip, and side drilled shaft nominal axial resistance with the corresponding measured nominal resistance. Results of this showed that the 2010 FHWA design method overestimates the total drilled shaft resistance by an average of two percent, while the 1999 FHWA design method underestimates the total drilled shaft resistance by an average of 21 percent. The Monte Carlo simulation method was selected to perform the LRFD calibration of resistance factors of drilled shaft under strength I limit state. The total resistance factors obtained at different reliability index () were determined and compared with those available in litera

04-2GT, This research study aims at investigating the potential benefits of using reinforced soil foundations to improve the bearing capacity and reduce the settlement of shallow foundations on soils. To implement this objective, a total of 117 tests, including 38 laboratory model tests on silty clay embankment soil, 51 laboratory model tests on sand, 22 laboratory model tests on Kentucky crushed limestone, and 6 large scale field tests on silty clay embankment soil, were performed at the Louisiana Transportation Research Center to study the behavior of reinforced soil foundations. The influences of different variables and parameters contributing to the improved performance of reinforced soil foundation were examined in these tests. In addition, an instrumentation program with pressure cells and strain gauges was designed to investigate the stress distribution in soil mass with and without reinforcement and the strain distribution along the reinforcement. The test results showed that the inclusion of reinforcement can significantly improve the soil’s bearing capacity and reduce the footing settlement. The geogrids with higher tensile modulus performed better than geogrids with lower tensile modulus. The strain developed along the reinforcement is directly related to the settlement, and therefore higher tension would be developed for geogrid with higher modulus under the same footing settlement. The test results also showed that the inclusion of reinforcement will redistribute the applied load to a wider area, thus minimizing stress concentration and achieving a more uniform stress distribution. The redistribution of stresses below the reinforced zone will result in reducing the consolidation settlement of the underlying weak clayey soil, which is directly related to the induced stress. Insignificant strain measured in the geogrid beyond its effective length of 4.0~6.0B indicated that the geogrid beyond this length provides a negligible extra reinforcement effect., Additionally, finite element analyses were conducted to assess the benefits of reinforcing embankment soil of low to medium plasticity and crushed limestone with geogrids beneath a strip footing from the perspective of the ultimate bearing capacity and footing settlement. Based on the numerical study, several geogrid-reinforcement design parameters were investigated.

LTRC Number: 07-2GT, State Project Number: 736-99-1408, The first report on Load and Resistance Factor Design (LRFD) calibration of driven piles in Louisiana (LTRC Final Report 449) was, completed in May 2009. As a continuing effort to implement the LRFD design methodology for deep foundations in Louisiana, this, report will present the reliability based analyses for the calibration of the resistance factor for LRFD design of axially loaded drilled, shafts. A total of 16 cases of drilled shaft load tests were available to authors from Louisiana Department of Transportation and, Development (LADOTD) archives. Out of those, only 11 met the Federal Highway Administration (FHWA) “5%B” settlement, criterion. Due to the limited number of available drilled shaft cases in Louisiana, additional drilled shaft cases were collected from, state of Mississippi that has subsurface soil conditions similar to Louisiana soils. A total of 15 drilled shafts from Mississippi were, finally selected from 50 available cases, based on selection criteria of subsurface soil conditions and final settlement. As a result, a, database of 26 drilled shaft tests representing the typical design practice in Louisiana was created for statistical reliability analyses., The predictions of total, side, and tip resistance versus settlement behavior of drilled shafts were established from soil borings using, the FHWA O’Neill and Reese design method via the SHAFT computer program. The measured drilled shaft axial nominal resistance, was determined from either the Osterberg cell (O-cell) test or the conventional top-down static load test. For the 22 drilled shafts that, were tested using O-cells, the tip and side resistances were deduced separately from test results. Statistical analyses were performed, to compare the predicted total, tip, and side drilled shaft nominal axial resistance with the corresponding measured nominal, resistance. Results of this showed that the selected FHWA design method significantly underestimates measured drilled shaft, resistance. The Monte Carlo simulation method was selected to perform the LRFD calibration of resistance factors of drilled shaft, under strength I limit state. The total resistance factors obtained at different reliability index () were determined and compared with, those available in literature. Results of reliability analysis, corresponding to a target reliability index () of 3.0, reveals resistance, factors for side (side), tip (tip), and total resistance factor (total) are 0.20, 0.75, and 0.5, respectively.

04-2GT, The presence of a weak soil supporting structural foundations results in low load bearing capacity and, excessive settlements, which can cause structural damage, reduction in durability, and/or deterioration in, performance level. Conventional treatment methods replace part of the weak cohesive soil with an, adequately thick layer of stronger granular fill, increase the dimensions of the footing, or combine both, methods. However, an alternative and more economical solution uses geosynthetics to reinforce soils, which, can be done by either reinforcing cohesive soil directly or replacing poor soils with stronger granular fill in, combination with the inclusion of geosynthetics. The resulting composite zone (reinforced soil mass) will, improve the load carrying capacity of the footing and provide better pressure distribution on top of, underlying weak soils, reducing associated settlements., Benefits of including reinforcements within soil mass to increase the bearing capacity and reduce the, settlement of soil foundation have been widely recognized. Many hypotheses have been postulated about the, failure mode of reinforced soil foundation (RSF). However, the failure mechanism of reinforcement is still, not fully understood in RSF as compared to other reinforced soil applications. Therefore, it is important to, investigate the reinforcement mechanism of reinforcing soils for foundation applications.

The main objective of this research is to assess the use of three nondestructive testing devices, the GeoGauge, the LFWD, and the DCP, in order to evaluate the in situ elastic modulus of highway materials for application in the quality assurance/quality control procedures during the construction of pavement layers (base, subbase, and subgrade) and embankments.

02-1GT, With the coming move from an empirical to mechanistic-empirical pavement design, it is essential to improve the quality control/quality assurance (QC/QA) procedures of compacted materials from a density-based criterion to a stiffness/strength-based criterion. The nondestructive in-situ tests such as the Geogauge, Dynamic Cone Penetrometer (DCP), and Light Falling Weight Deflectometer (LFWD) can be effective tools for assessing of subsurface conditions and evaluating the stiffness of pavement materials and embankments. This report evaluates the potential of these three devices to reliably measure the stiffness characteristics of highway materials for possible application in the QC/QA procedures during and after the construction of pavement layers and embankments. To achieve this, field and laboratory testing programs were conducted. The laboratory program included construction of different sections inside two boxes (5 x 3 x 2.5 ft) located at the Geosynthetic Engineering Research Laboratory (GERL) at the Louisiana Transportation Research Center (LTRC). The field tests were conducted on highway sections selected from various projects in Louisiana. In addition, six test sections and three trench sections were constructed and tested at the LTRC Pavement Research Facility (PRF) site. The field and laboratory tests included Geogauge, LFWD, and DCP tests in conjunction with two standard tests such as the Plate Load Test (PLT) and Falling Weight Deflectometer (FWD) test. The California Bearing Ratio (CBR) laboratory tests were also conducted on similar samples collected during the field and laboratory tests. A statistical analysis revealed good correlations between the measurements obtained from the three investigated devices and those obtained from the standard tests, thus demonstrating that the investigated devices can reliably measure the in-situ stiffness of highway materials, subgrades and embankments.

LTRC Number: 05-5GT, State Project Number: 736-99-1312, The inadequacy of many existing roads due to rapid growth in traffic volume provides a motivation for exploring alternatives to, existing methods of constructing and rehabilitating roads. The use of geosynthetics to stabilize and reinforce paved and unpaved, roadways offers one such alternative. Many studies were conducted to evaluate the improvements associated with geogrid, reinforcement of pavements. It is widely believed that geogrid reinforcement of roadways can extend a pavement’s service life and/or, reduce the pavement’s structural thickness., Several design methods were proposed for flexible pavements with geogrid reinforced base layers. These methods were either based, on empirical or analytical approaches. Empirical design methods are usually based on obtaining a performance level from a laboratory, model test, which is then extrapolated to the field conditions for design application. The geogrid reinforced design methods based on, analytical solution do not address all the variables that affect the performance of these pavements. This report is part of a research, study on evaluating the benefits of geogrid reinforcement of base layers in flexible pavements., It presents the findings from large-scale cyclic plate load tests on Accelerated Load Facility (ALF), sections and sections built inside a test box. Another report presented the findings from laboratory, triaxial tests and finite element analyses.

04-2GT, This research study aims at investigating the potential benefits of using reinforced soil foundations to improve the bearing capacity and reduce the settlement of shallow foundations on soils. To implement this objective, a total of 117 tests, including 38 laboratory model tests on silty clay embankment soil, 51 laboratory model tests on sand, 22 laboratory model tests on Kentucky crushed limestone, and 6 large scale field tests on silty clay embankment soil, were performed at the Louisiana Transportation Research Center to study the behavior of reinforced soil foundations. The influences of different variables and parameters contributing to the improved performance of reinforced soil foundation were examined in these tests. In addition, an instrumentation program with pressure cells and strain gauges was designed to investigate the stress distribution in soil mass with and without reinforcement and the strain distribution along the reinforcement. The test results showed that the inclusion of reinforcement can significantly improve the soil’s bearing capacity and reduce the footing settlement. The geogrids with higher tensile modulus performed better than geogrids with lower tensile modulus. The strain developed along the reinforcement is directly related to the settlement, and therefore higher tension would be developed for geogrid with higher modulus under the same footing settlement. The test results also showed that the inclusion of reinforcement will redistribute the applied load to a wider area, thus minimizing stress concentration and achieving a more uniform stress distribution. The redistribution of stresses below the reinforced zone will result in reducing the consolidation settlement of the underlying weak clayey soil, which is directly related to the induced stress. Insignificant strain measured in the geogrid beyond its effective length of 4.0~6.0B indicated that the geogrid beyond this length provides a negligible extra reinforcement effect. Additional

The load and resistance factor design (LRFD) has been used increasingly and has become mandatory for the design of all bridge projects funded by the Federal Highway Association (FHWA). Compared to the allowable stress design (ASD) method, LRFD can achieve a compatible reliability between the bridge superstructure and substructure. The uncertainties of load and resistance are quantifi ed separately and reasonably incorporated into the design process. Therefore, this reliability-based design approach will generally produce a more effi cient and consistent design than the traditional ASD factor of safety approach. To achieve these goals, many researchers have been working to develop a reasonable way to implement the LRFD method in bridge substructure design and to determine appropriate resistance factors for diff erent regional soil conditions.

00-3GT, The piezocone penetration test (PCPT) has gained wide popularity and acknowledgement as a preferred in-situ device for subsurface investigation and soil characterization. The PCPT measurements can be utilized for soil identification and the evaluation of different soil parameters. Different interpretation methods have been proposed to evaluate the strength and consolidation parameters of cohesive soils utilizing the piezocone penetration and dissipation test data. This report presents the evaluation of the capability of the current PCPT interpretation methods to reasonably predict the consolidation parameters needed to predict the total and time rate of settlement of cohesive soils. Seven sites in Louisiana were selected for this study. In each site, in-situ PCPT tests were performed and soundings of cone tip resistance (qc), sleeve friction (fs) and pore pressures (u1 and u2) were recorded. Dissipation tests were also conducted at different penetration depths. High quality shelby tube samples were collected close to the PCPT tests and used to carry out a comprehensive laboratory testing program including unconfined compression test, triaxial test and one-dimensional oedometer consolidation test. The tangent constrained modulus (M), overconsolidation ratio (OCR) and the vertical coefficient of consolidation (cv), predicted using the different interpretation methods, were compared with the reference values determined from the laboratory consolidation tests. Results of this study showed that the consolidation parameters of soils can be reasonably predicted from the piezocone penetration and dissipation test data, and hence provide a continuous profile of these parameters with depth. The results of this study were verified by comparing the predicted settlements from PCPT methods with the laboratory calculated and field measured settlements in three selected sites.