Vol 54, No 1 (2017)

The settlement of piles in soft soil can last for several decades because of the creep or viscoelastic behavior of soft soil around the pile. This paper proposes nonlinear viscoelastic pile shaft and pile base load transfer (t − z) models based on the modified Burgers model in which the spring is substituted by a hyperbolic model. Using these models, we developed a nonlinear approach to calculate the time-dependent settlement of a vertically loaded single pile and pile groups in layered soft soil. Parametric studies were conducted to investigate the influence of the calculation parameters on the time-dependent settlement of a single pile. The time-dependent settlement of a well-instrumented pile loading test was calculated. Theoretical results were in close agreement with measured results and demonstrate the effectiveness and accuracy of the proposed approach.

This paper proposes a single exponential model and a double exponential model to simulate the relationship between pile displacement and unit skin friction developed at the pile-soil interface. Based on the proposed two models, two simple analytical approaches were presented for nonlinear analysis of the response of a single tension pile. A highly effective iterative computer program was developed by using the load transfer method. Comparisons of the present computed results, the calculated results derived from other analytical methods, and measured results were made to demonstrate the reliability of the proposed analytical methods.

The result of experimental studies of the operation of CFA piles in weak clay soils arranged for the foundations of renovated buildings are presented. A method using data on the auger impressing force and the physical-mechanical characteristics of the soils around the shaft of the CFA pile is proposed for calculating the carrying capacity of the soils.

A series of electro-osmotic consolidation laboratory tests was conducted to investigate the influence of soluble salt on the electro-osmotic consolidation of soft clay. Remolded soil samples with different salinities of KCl, NaCl, and CaCl₂ were tested in the modified electro-osmosis oedometer experimental system. Final water content, vane shear strength, and pH value of test soil samples were analyzed by monitoring the changes in the electric current, volume of drainage, and vertical settlement during the tests. The results showed that addition of soluble salts can improve the electro-osmotic consolidation of soft clay. However, excessive salinity will reduce the efficiency of electro-osmotic consolidation. The optimal salinity of the soluble salt was determined for each type of salt. Moreover, an improved consolidation efficiency can be achieved by using CaCl₂ rather than KCl or NaCl.

Soil reinforcement by natural fibers is a cost-effective and reliable technique for improving the stiffness and stability of soil. Coir is an eco-friendly, biodegradable organic material that has high tearing strength, stiffness, and durability compared to other natural reinforcement materials. In this study, the potential of coir geotextile as a reinforcement material was studied through a set of laboratory experiments. Remarkable improvement in strength and settlement properties were obtained with the provision of geotextiles. Bearing capacity improvement by a factor of 5 and a reduction of footing settlement by 87% was obtained by the suggested method. The optimum benefit was realized with the provision of three layers of reinforcement for a width of 3B (B is the foundation width), the topmost geotextile layer being positioned at a distance of 0.25B from the base of footing. Bearing capacity enhancement by a factor of 2.57 and settlement reduction of 73% was obtained even with the provision of a single layer of coir geotextile.