Effect of fibre reinforcement on CBR behaviour of lime-blended expansive soils: reliability approach

The use of synthetic fibres as reinforcement to stabilise expansive soils is gaining momentum. As a contribution towards this growing field of research two different types of synthetic fibres, Fiber Mesh® and Fiber Cast®, were evaluated as a stabilisation 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 fibres as well as curing period were studied. Both deterministic and probabilistic (or reliability) analyses 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 fibre contents and longer lengths and the effect was prominent when lime was used as a stabiliser. There were some exceptions to this behaviour, which were noted in the paper. The probabilistic analysis showed that the amount and lengths of fibres were important factors in CBR strength. It was also determined that the variation in the target CBR value had a considerable effect on optimising the length and amount of the fibres

Effect of polypropylene fibre reinforcement on the consolidation, swell and shrinkage behaviour of lime-blended expansive soil

In this article, synthetic fibres in the presence of lime stabilisation are proposed as an alternative to overcome the issues related to shrink-swell distress in expansive soils. Two types of synthetic fibres, Fiber Cast® (FC) and Fiber Mesh® (FM), were studied by conducting one-dimensional fixed ring Oedometer swell-consolidation and bar linear shrinkage tests. Three dosages (0.2, 0.4 and 0.6% by weight of soil) and two lengths of the fibres (6 and 12 mm) were evaluated with and without lime treatments. The results indicated that FC fibres had better swell restricting performance in the absence of lime treatment, while in the presence of lime both fibres had similar performance in reducing swelling. Shrinkage tests results showed that irrespective of dosage levels, both the fibres had pronounced effect in reducing the linear shrinkage strains up on lime treatment. Non-linear best fit equations have been proposed to relate compression index (Cc) and recompression index (Cr) of expansive clay deposits with and without lime treatment to amount and dosage of FC and FM reinforcements. The proposed non-linear fit provides a mean for recognising, more efficiently, the patterns in the experimental data and predicting the compression indices, Cc and Cr reliably

Target Reliability Approach to Study the Effect of Fiber Reinforcement on UCS Behavior of Lime Treated Semiarid Soil

This paper evaluates the effectiveness of stabilizing expansive soil with two different types of fibers, fiber mesh (FM) and fiber cast (FC), in conjunction with chemical stabilization. The intention of this study is to evaluate the effect of these fibers and lime in stabilizing expansive soil by improving its unconfined compressive strength (UCS) behavior. The effect of varying lengths (6 and 12 mm) and amounts (0.2, 0.4, and 0.6% dosage by weight of soil) of FC and FM fibers and varying curing periods (0, 7, 28, 60, 120, 180, and 360 days) on the UCS and on secant modulus of a semiarid expansive soil, in the presence of lime, was investigated. The main focus of this paper is on the determination of optimum fiber reinforcement parameters (in terms of fiber type, length, and dosage) for the stabilization of expansive soil in terms of UCS, which is of a prime importance in soil stabilization projects for practicing engineers. In deterministic optimization, the uncertainties associated with pavement system subgrade soil are not explicitly taken into account. Hence, resulting optimal solutions may lead to reduced pavement reliability levels. Therefore, this paper also focuses on determining the optimum amounts of reinforcement for desired UCS performance of lime-blended expansive soil using the target reliability approach (TRA). Experimental data were used to develop a parabolic model including factors such as length and dosage of fiber types to predict UCS as a response variable. In addition, it was concluded that TRA can be successfully employed in expansive soil stabilization applications to determine the optimum length and dosage of fiber reinforcemen

Long-Term Performance of a Highway Embankment Built with Lightweight Aggregates

This paper presents the results from a field and numerical studies performed to understand the long-term performance of a bridge approach embankment designed with lightweight, expanded clay and shale (ECS) aggregates to mitigate the settlements on a soft soil foundation. The ECS aggregates and traditional select fill were used to build southern and northern approach embankments, respectively, for a bridge on State Highway 360 in Arlington, Texas. An extensive series of laboratory tests were conducted to obtain the engineering behavior of ECS and the select fill materials before the construction. These properties were then used in the finite element modeling to simulate the embankment sections to verify the long-term performance. The embankment sections were instrumented with vertical inclinometers to monitor the lateral movements for more than four years. This data was used to validate the numerical models with an acceptable amount of accuracy. Then a parametric study was conducted for varied heights of embankments, thicknesses of foundation soil and also compression/recompression indices of foundation soil to develop design charts. The numerical, as well as field data, indicate that there is a two-thirds reduction in settlement of the foundation soil with the use of the lightweight material. The pre-consolidation pressure and the overconsolidation ratios govern the settlement behavior of the foundation soil due to lightweight embankments. The design charts can be useful in either predicting the embankment settlements for a given ECS embankment configuration or determine the allowable height of the ECS embankment for a specified settlement value when constructing in similar foundation soil encountered in this study