International Journal of Geomechanics

A cavity expansion-based theory for calculation of cone penetration resistance $q_c$ in sand is presented. The theory includes a completely new analysis to obtain cone resistance from cavity limit pressure. In order to more clearly link the proposed theory with the classical cavity expansion theories, which were based on linear elastic, perfectly plastic soil response, linear equivalent values of Young's modulus, Poisson’s ratio and friction and dilatancy angles are given in charts as a function of relative density, stress state, and critical-state friction angle. These linear-equivalent values may be used in the classical theories to obtain very good estimates of cavity pressure. A much simpler way to estimate $q_c$ —based on direct reading from charts in terms of relative density, stress state, and critical-state friction angle—is also proposed. Finally, a single equation obtained by regression of $q_c$ on relative density and stress state for a range of values of critical-state friction angle is also proposed. Examples illustrate the different ways of calculating cone resistance and interpreting cone penetration test results.

This paper pertains to the development of a mechanical model to predict the behavior of a geosynthetic-reinforced granular fill over soft soil improved with stone columns. The saturated soft soil has been idealized by Kelvin–Voight model to represent its consolidation behavior. The stone columns are idealized by stiffer springs. Pasternak shear layer and rough elastic membrane represent the granular fill and geosynthetic reinforcement layer, respectively. The nonlinear behavior of the granular fill and the soft soil is considered. Effect of consolidation of the soft soil due to inclusion of the stone columns has also been included in the model. Plane strain conditions are considered for the loading and reinforced foundation soil system. An iterative finite difference scheme is applied for obtaining the solution, and results are presented in nondimensional form. Comparison between the results from the present study and the analytical solution using theory of elasticity shows reasonable agreement. The advantage of using geosynthetic reinforcement is highlighted. Results indicate that inclusion of the geosynthetic layer effectively reduces the settlement. Nonlinearity in the behavior of the soft soil and the granular fill is reduced due to the use of geosynthetic reinforcement layer.

The response of piles subjected to lateral loading (along a single line of action) has been substantially investigated in the past. However, little attention has been devoted to studying how a change in the lateral load direction (say, from east–west to north–south) may affect the overall response. This paper describes a Winkler type of soil–pile interaction model that allows coupling between the two perpendicular directions in a systematic way, by adopting local yield surfaces along the pile. A parametric study is presented for a range of pile lengths and cross sections, applied loads, and changes in direction from previous loadings. An analogy is shown to exist between the response of the pile to changes in the direction of lateral loads and the well-known elementary constitutive phenomenon of the recent stress history. As is commonly assumed in practice the model shows that the direction of the resultant pile response does not have a large impact on the load carrying capacity of the system. However, changes in the lateral load directions alter the global stiffness response, and this could potentially play a significant role in the serviceability design.

This paper addresses numerical simulation of deep penetration of full-flow penetrometers in strain-softening, rate-dependent, cohesive soil, and the observed phenomenon of periodic shear bands. The analysis was conducted using a large deformation finite element approach, modifying the simple elastic–perfectly plastic Tresca soil model to allow strain-softening, with strain-rate dependency being incorporated in order to avoid spurious mesh dependency. Parametric analyses were carried out varying the strain-softening parameters (hence the relative brittleness of the soil), the rigidity index of the soil, and the strain-rate parameter. Increased brittleness of the soil led to reduction in the penetration resistance, but also to increasingly significant oscillations in the resistance–penetration responses. The oscillation was found to result from periodic shear bands evolving cyclically ahead of the advancing cylindrical and spherical penetrometers. Analyses with different values of rigidity index confirmed further that the periodic shear bands were a real material phenomenon, rather than due to errors in numerical simulation. Similar phenomena have been observed for continuous flow problems in granular materials. However, rising strain-rate dependency tended to suppress the oscillations.

A viscoelastic analysis using the hyperbolic and power creep laws is developed for prediction of time-dependent closure of circular tunnels. Effect of support types and installation location in accordance with the convergence confinement method are incorporated in the analysis. The hyperbolic creep law is found to be more practical for simulation of closure response of squeezing ground than the power creep law because it is capable of modeling ground yielding around the tunnel when value of $R_f$ close to 1.0 is used. A parametric study is performed using the hyperbolic law and the results are discussed. Predicted tunnel closure was compared with the monitoring data from a number of tunnels and they were found in good agreement. It is found that the closure and support yielding time are most sensitive to the hyperbolic parameter $E_u∕{({\sigma }_1-{\sigma }_3)}_f$ and creep parameter $\lambda$ . The values of $E_u∕{({\sigma }_1-{\sigma }_3)}_f$ of 200–250 and $\lambda$ of 0.03–0.15 are found to be reasonable for most ground that exhibit squeezing. The analysis is useful in predicting time-dependent closure and support load for tunnels in both rocks and soils.

Argentinean loess has mechanical properties highly dependent on moisture content. Sand and silt particles jointed by clay bridges and precipitated salts form macropores which undergo high volume decrease when loaded or wetted. The constrained deformation modulus is an important parameter for the assessment of settlement and to characterize loessical formations. This work analyzes experimental results obtained in double-oedometer test and standard penetration tests (SPT) performed in silty loess. Typical behaviors observed in double-oedometer test are related to the decrease of soil modulus, collapsibility, cementation, and presence of disseminated cementing nodules. Correlations between the constrained modulus, collapsibility, and the blow count from SPT are presented. The influence of disseminated nodules, moisture content, and collapsed soil structure on the constrained modulus and collapsibility of loess is highlighted.

Immiscible flow governs the macroscopic behavior of aqueous and non-aqueous phase liquids inside the porous media. Ganglia generation and movement of the advancing front during fluid displacement can only be described by means of microscopic models. In this study, a pore network cellular automata is used to simulate the displacement of a nonaqueous phase liquid by water inside a porous media. Pore sizes are generated using random and stochastic fields. The numerical model captures the evolution of interfaces and fluid movement for each pressure applied to the displacing fluid. Observed trends suggest that ganglia size and shape, and fingering are directly related to anisotropy, pore size spatial variability and correlation length. The results show that micro- and mesoscale porous media properties control the nonaqueous phase residual saturation and observed macoscopic behavior.

The effect of nonlinearity of the failure criterion on the passive thrust on smooth and rough vertical retaining walls is studied theoretically. Limit analysis upper bound estimates based on block-type failure mechanisms are constructed. An alternative, a priori linearization, approach is discussed. It is shown that for smooth walls both approaches, as well as the Rankine-type slip line solution, yield similar results. For rough walls, however, the ambiguity in the a priori linearization makes it difficult to compare the results. This deficiency is absent in the limit analysis nonlinear solutions.