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87-1GT, The considerable increase in using geosynthetics in soil reinforcement made it necessary to develop methods of measuring the interaction properties and modeling load transfer in reinforced-soil structures. The large number of factors that influence the interaction mechanism makes it difficult to standardize the equipment design, testing methodology and data interpretation procedure. The factors are mainly related to the equipment boundary effects, testing conditions, and soil and geosynthetics properties., In order to develop a methodology for evaluating the interface properties of geogrids, a pull-out box and a direct shear box are constructed and instrumented. A testing program is conducted to evaluate the performance of the facility and the effect of different testing parameters (a.g. specimen dimensions, soil thickness, box boundary effects, pull-out rate, soil compaction and relative density, and confining pressure) on the pull-out interaction mechanism of geogrids. Standard equipment design and testing procedure are recommended to overcome most of the limitation in the current practice., A data analysis procedure is established to determine the interface properties and the confined reinforcement characteristics from pull-out test results. The data analysis incorporates the effect of reinforcement extensibility on the soil-geogrid interface mechanism. The interface parameters are evaluated through comparison with the results from tests performed in the large direct shear box.

92-10GT, The report presents a procedure for predicting creep strains of geosynthetics using creep tests at elevated temperatures. Creep testing equipment was constructed and tests were performed on two types of geosynthetics: High Density Polyethylene (HDPE) geogrid, and Polyester (PET) geogrid) typically used in soil reinforcement applications., The procedure for extrapolating creep strains from elevated temperature tests using the Arrhenius Equation was evaluated. The results showed limitations associated with the estimation of the equation parameters and the corresponding predictions of creep strains., The testing program and analysis demonstrated the applicability of applying the shift factors to the HDPE geogrid to predict the response at longer time intervals. The analysis was applicable to creep loads lower than 40 percent Tmax for the PET geogrid, the increase of creep strains at elevated temperatures was not sufficient to successfully establish the master curves in a form consistent with the WLF equation. This is mainly due to fact that creep tests were perofrmed at temperatures close to the glass-transition temperature of the PET geogrid (75C). Tests at higher temperatures would be required to obtain more measurable response of creep strains and to evaluate the applicability of temperature-shift factors in predicting creep strains for the PET geogrid.

LTRC No. 95-1GT, S.P. No. 736-99-0760, This study evaluates two methods for repairing slope surface failures of clayey soil embankments. One method involves reinforcing the cohesive soils with randomly oriented synthetic fibers; the other method incorporates non-woven geotextiles. The performance of soils reinforced using these two methods was studied in the laboratory and in the field. In the laboratory, a parametric study was conducted to compare the performances of soil and fiber-soil in terms of their shear strengths. Both a large direct shear and a standard triaxial apparatus were used to experimentally evaluate the shear strengths of the reinforced materials. The interface friction between the geotextile fabric and the soil was also evaluated using the large direct shear apparatus. The specimens of soil, fiber-soil, and fabricsoil materials were tested at various moisture contents and confining stresses. Various fiber contents were also used to evaluate their effect on shear strength. The laboratory results indicated that, in the short term, the fiber reinforcement will compensate the loss of soil shear strength caused by the increase in soil moisture content. The best results were achieved with a fiber content of 0.1% by weight., Field evaluation included experimental repairs of failed slopes and monitoring their performance. Site investigations indicated that slope surface failures occurred when surface water trapped in fissures or cracks saturated the adjacent soils. To investigate the long-term stability, seven experimental slope sections with fiber and geotextile reinforcements were constructed at various compaction efforts and moisture contents. The performance of these slopes was monitored and the results indicated that repairing failed slopes with the non-woven geotextile was a good option to battle repetitive surface failures in slopes of high plastic soils. Accordingly, a simple procedure of repairing the slope with the low-cost material was recommended for use by maintenance crews in daily rehabilitation activities.

State Project No. 736-99-0658, This report presents the construction and performance evaluation of the LTRC reinforced-soil test wall. The 20 ft. high, 160 ft. long wall was constructed using low quality backfill. Its vertical front facing was constructed with modular blocks. It consisted of three sections reinforced with various geogrid reinforcement types and spacing. The backside of the wall was a one-to-one slope reinforced with woven and non-woven geotextiles., The test wall was constructed to evaluate the design procedure and performance of geosynthetic-reinforced structures constructed with marginal silty-clay backfill over soft clay foundation. The instrumentation program consisted of monitoring wall deformation, foundation settlement, strains in the reinforcement, vertical and horizontal stresses in the soil, and pore water pressure under the wall. Results of the monitoring program from construction through four months after completion of the wall are detailed in this report., The results of the instrumentation program showed relatively high deformations due to both the design of the wall with low factors of safety and to the high settlement of the foundation soil. These deformations, however, occurred mostly during construction. The results of strain measurements in the reinforcement were used to evaluate the effect of reinforcement stiffness and spacing on the shape of the failure surface and on the distribution and magnitude of stresses in reinforcement layers., The results show promising performance of silty-clay soils as a backfill material in reinforced-soil walls providing proper design and control of soil compaction and moisture. However, long-term performance of the wall needs to be monitored for a complete evaluation of these types of walls.

97-6GT, A tremendous amount of scour data already exists for the highway bridges monitored by the Louisiana Department of Transportation and Development (DOTD). More than one hundred and twenty bridges are being monitored at a frequency of one to several times per year and at various locations from the bridges' centerlines., The scour data collected is still in the format of traditional paper files and there existed a need to develop ready-to-use computer software using modern database technology to perform scour data management. Such software was needed to speed plotting historical cross sections and to identify scour critical bridges., This report presents the manual of the software program developed for database management of scour data of the Louisiana highway bridges. The program has the capabilities of data retrieval of a specific bridge using a variety of data search routines. The program retrieves bridge information, survey plans, and soil boring data. It plots the cross-sections and longitudinal sections at any survey location and date. The program also displays contour plots at any selected date and historic plots of scour at any selected location., The database software can be installed on any DOTD computer having Microsoft Windows 95, 98, and NT systems. The database can be installed in any directory in the user's computer or can be accessed remotely from the DOTD server.

State Project No. 736-99-0658, The considerable increase of using geosynthetics in mechanically stabilized earth (MSE) walls has raised the need to evaluate their interface shear strength and pullout properties in various types of backfills. This report investigates the use of a marginal silty-clay soil of medium plasticity as a suitable backfill in MSE walls. The interface parameters between the geosynthetics and the soil were evaluated in pullout tests. The testing program included performing laboratory and field pullout tests on four types of geogrids and three types of geotextiles. Laboratory pullout tests were carried out using the large pullout testing equipment at the Louisiana Transportation Research Center (LTRC). Field pullout tests were performed in a test section of the LTRC full-scale reinforced test wall. The pullout test section contained geogrid and geotextile specimens at various wall elevations., The testing program evaluated the effect of reinforcement type, length, and confining pressure on the pullout resistance. Laboratory and field tests were performed using the same type of soil at a similar density and moisture content. Laboratory and field results compared well for the extensible reinforcements of medium to low stiffness modulus. However, field pullout results were significantly higher than laboratory results for the rigid geogrids., The pullout resistance factor (F* ) and the scale effect correction factor (a) were established for the geogrid and geotextile specimens. These values can be used to determine the pullout resistance of these types of geosynthetics at various confining pressures and specimen lengths.