Effect of Fiber Reinforcement on CBR Behavior of Lime Blended Expansive Soils: Reliability Approach

Use of synthetic fibers as reinforcement to stabilize expansive soils is gaining momentum. As a contribution towards this growing field of research two different types of synthetic fibers, Fiber Mesh® and Fiber Cast®, were evaluated as a stabilization alternative for expansive soils in the presence of lime. California Bearing Ratio (CBR) is chosen as a performance indicator as it is a good pointer towards pavement effectiveness. Variables such as length and amount of the fibers as well as curing period were studied. Both deterministic and probabilistic (or reliability) analysis is presented in this paper. While the deterministic analysis helps in understanding the measured experimental data, the probabilistic approach accounts for the stochastic nature of the experimental data and provides a better rationale for the design methods. The deterministic approach showed that the improvement in CBR increased with higher fiber contents and longer lengths and the effect was prominent when lime was used as a stabilizer. There were some exceptions to this behavior, which were noted in the paper. The probabilistic analysis showed that the amount and lengths of fibers were important factors in CBR strength. It was also determined that the variation in the target CBR value had considerable effect on optimizing the length and amount of the fibers

Soluciones de forma cerrada para la capacidad de carga de zapatas en suelos anisotrópicos cohesivos

Las soluciones de forma cerrada simples para la capacidad de carga no drenada de zapatas escalonadas en suelos isotrópicos cohesivos se derivan al emplear el enfoque cinemático del análisis de límites. Se intentan utilizar tanto el mecanismo traslacional de fallas como el mecanismo modificado tipo Hill, con ángulos de incidencia variables. Se ha determinado, de forma analítica, la mejor cota superior para cada mecanismo, lo cual nos lleva a una expresión analítica para el factor de capacidad de carga. También se ha evaluado la influencia del grado de anisotropía del suelo en el valor correspondiente para el factor de capacidad de carga. Para un amplio rango de grados de anisotropía, la mejora en los valores predichos de la cota superior no garantiza el uso del mecanismo modificado del tipo Hill. En vez de eso, el mecanismo convencional de falla del tipo Hill, con un ángulo de incidencia fijo de n/4, nos entrega una expresión simple y concisa para el factor de capacidad de carga que es analíticamente equivalente al factor convencional de capacidad de carga de Prandtl-Reissner, para el caso de suelos isotrópicos multiplicado por el promedio de la suma del grado de anisotropía más la unidad

Effect of Confining Conditions on the Hydraulic Conductivity Behavior of Fiber-Reinforced Lime Blended Semiarid Soil

The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic conductivity tests have been conducted on expansive clay using two different types of fibers (fiber cast (FC) and fiber mesh (FM)) exhibiting different surface morphological properties. The fiber parameters include their dosage (added at 0.2% to 0.6% by dry weight of soil) and length (6 and 12 mm). Commercially available lime is added to ensure proper bonding between clay particles and fiber materials, and its dosage was fixed at 6% (by dry weight of the soil). Saturated hydraulic conductivity tests were conducted relying on a flexible wall permeameter on lime-treated fiber-blended soil specimens cured for 7 and 28 days. The confining pressures were varied from 50 to 400 kPa, and the saturated hydraulic conductivity values (ksat) were determined. For FC fibers, an increase in fiber dosage caused ksat values to increase by 9.5% and 94.3% for the 6 and 12 mm lengths, respectively, at all confining pressures and curing periods. For FM fibers, ksat values for samples mixed with 6 mm fiber increased by 12 and 99.2% for 6 and 12 mm lengths, respectively for all confining pressures at the end of the 28-day curing period. The results obtained from a flexible wall permeameter (FWP) were compared with those of a rigid wall permeameter (RWP) available in the literature, and the fundamental mechanism responsible for such variations is explained

Evaluation of Diffusion Rate Constants from Soil Column Studies in Lime-Treated Semi Arid Soils—Pb\u3csup\u3e2+\u3c/sup\u3eand Zn\u3csup\u3e2+\u3c/sup\u3eScenarios

Proper estimation of contaminant transport rate through compacted fine-grained soils assumes great importance in the context of remediation of contaminated sites. Integrated use of equilibrium and mass transfer rate tests in conjunction with appropriate mass transfer models provide a useful framework for evaluating leaching of contaminants such as lead (Pb2+) and zinc (Zn2+), which have relatively low pH-dependent solubility. In this article, column experiments were set up to study the diffusion coefficients and break through times using method of slices for two semi-arid soils (Al-Ghat and Al-Qatif) for selected heavy metals (Pb2+ and Zn2+). The studies were carried out on soil samples before and after amending with lime. Breakthrough curves were obtained under different hydraulic gradients for the compacted mixtures and the diffusion coefficients for Pb2+ and Zn2+ were evaluated using POLLUTEv7 relying on advection-dispersion equation, for a liner thickness of 1m. The current study allowed us to observe the movement of contaminants in the clay liners to be predicted in real time. Break through curves showed relatively higher retention levels for the targeted metal ions. The retention strength of these soils was observed to be constant up to five pore volumes, corresponding to the pH of the effluent and pore water of soil slices. Soils amended with lime showed an improvement to the order of 10 times in retention capacity. Under pure diffusion controlled migration both soil lime mixtures performed very well and gave breakthrough times of more than 400 years whereas advective-diffusion gave break through times of 200 years for both metal ions considered in the study