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The tangent modulus method of undisturbed soil is a new method in settlement calculation, which is mainly applied to hard soil with a strong structure, such as silty clay, completely weathered rock, and granite residual soil with an SPT blow count greater than 8. The tangent modulus is mainly obtained from a field plate load test, which can consider the influence of the soil stress level and reflect the nonlinear characteristics of the foundation settlement. In a multi-layer soil foundation, since the deep plate loading test is difficult, a method was proposed to determine the tangent modulus of deep soil. It is assumed that the ratio of the initial tangent modulus to the deformation modulus is equal to the ratio of the unloading–reloading modulus E ur ref to the secant modulus E 50 ref obtained by triaxial unloading–reloading test. Since there are corresponding empirical formulae for SPT counts and the deformation modulus of different types of soils in many regions, the initial tangent modulus can be derived by the above method. In two cases of a composite foundation, the compression modulus and tangent modulus were used to calculate the settlement of the foundation, which is then compared with the measured results. The results show that the proposed method for determining the tangent modulus of deep soil is feasible in theory, and the calculating accuracy of the tangent modulus is significantly higher than that of the traditional compression modulus. [ABSTRACT FROM AUTHOR]

A semianalytical approach has been developed to investigate the nonlinear load–settlement behavior of bored single piles and pile groups embedded in sands. A more rigorous load-transfer function for the pile shaft, adopted to describe the pile–soil interface behavior, is derived from a damage constitutive model of the soil–structure interface. The interface model employed is capable of capturing the strain-hardening/softening and bulk dilatancy properties of the pile–soil interface and reflecting the degradation of the pile shaft skin friction. Meanwhile, an existing analytical solution has been applied to approximately describe the elastic stress–displacement relationship of soils outside the pile–soil interface during shearing. Moreover, the nonlinear stress–displacement relationship of soils at the pile base is simulated by a hyperbolic model considering the particle-crushing behavior of soils. Model parameters can easily be calibrated from laboratory interface shear tests and the physical properties of soils. Based on the matrix displacement method, the governing equation of the load–settlement response for bored piles is computed via an efficient iterative algorithm developed in terms of the midpoint incremental method. The pile-to-pile elastic interaction and the reinforcement effect of neighboring piles are incorporated into the investigation of pile groups. The present approach is verified by comparison with the existing theoretical approach, centrifuge tests, and model pile tests. Extensive parameter investigations are performed to systematically explore the load–settlement response of the single pile and pile groups. [ABSTRACT FROM AUTHOR]

Soil settlement is an essential criterion in the design and performance assessment of geotechnical structures, often evaluated using results from one-dimensional compression test. However, assessment of the results from this test involves graphical methods, which produces inconsistent interpretations on the parameters to be used in design. The nonlinear compressibility curve is also subjected to bilinear idealization with divergence from the actual behavior at high stresses. In order to overcome these problems, a nonlinear mathematical formulation is developed to represent the soil compressibility with high precision over a wide range of stresses. The adequacy of the formulation is validated against a large and diverse dataset comprised of different geological materials, including undisturbed and reconstituted soils as well as stabilized soils. The proposed formulation is dependent on two fitting coefficients, which are defined in terms of commonly used compressibility parameters compression index, recompression index and preconsolidation pressure. A single expression is also derived to calculate soil settlement without numerical discontinuity. Finally, a method for evaluation of swelling pressure of soils is also developed using the parameters of the same mathematical formulation. [ABSTRACT FROM AUTHOR]

The tangent modulus method of undisturbed soil is a new method in settlement calculation, which is mainly applied to hard soil with a strong structure, such as silty clay, completely weathered rock, and granite residual soil with an SPT blow count greater than 8. The tangent modulus is mainly obtained from a field plate load test, which can consider the influence of the soil stress level and reflect the nonlinear characteristics of the foundation settlement. In a multi-layer soil foundation, since the deep plate loading test is difficult, a method was proposed to determine the tangent modulus of deep soil. It is assumed that the ratio of the initial tangent modulus to the deformation modulus is equal to the ratio of the unloading–reloading modulus Eurref to the secant modulus E50ref obtained by triaxial unloading–reloading test. Since there are corresponding empirical formulae for SPT counts and the deformation modulus of different types of soils in many regions, the initial tangent modulus can be derived by the above method. In two cases of a composite foundation, the compression modulus and tangent modulus were used to calculate the settlement of the foundation, which is then compared with the measured results. The results show that the proposed method for determining the tangent modulus of deep soil is feasible in theory, and the calculating accuracy of the tangent modulus is significantly higher than that of the traditional compression modulus.