Depth factors for undrained bearing capacity of circular footing by numerical approach

The undrained vertical bearing capacity of embedded foundation has been extensively studied using analytical and numerical methods.Through comparing the results of a circular embedded foundation in the literature,a significant difference between the bearing capacity factors and depth factors is observed.Based on the previous research findings,numerical computations using FLAC code are carried out in this study to evaluate the undrained bearing capacity of circular foundations with embedment ratios up to five for different base and side foundation roughness conditions.Unlike the foundation base,the roughness of the foundation side has a significant effect on the bearing capacity.The comparison of the present results with numerical studies available in the literature shows that the discrepancy is related to the procedures used to simulate the foundation side interface conditions and to the estimation of the bearing capacity.

Load eccentricity effects on behavior of circular footings reinforced with geogrid sheets

In this paper, an experimental study for an eccentrically loaded circular footing, resting on a geogridreinforced sand bed, is performed. To achieve this aim, the steel model footing of 120 mm in diameterand sand in relative density of 60% are used. Also, the effects of depth of first and second geogrid layersand number of reinforcement layers （1e4） on the settlement-load response and tilt of footing undervarious load eccentricities （0 cm, 0.75 cm, 1.5 cm, 2.25 cm and 3 cm） are investigated. Test results indicatethat ultimate bearing capacity increases in comparison with unreinforced condition. It is observed thatwhen the reinforcements are placed in the optimum embedment depth （u/D ？0.42 and h/D ？0.42）, thebearing capacity ratio （BCR） increases with increasing load eccentricity to the core boundary of footing,and that with further increase of load eccentricity, the BCR decreases. Besides, the tilt of footing increaseslinearly with increasing settlement. Finally, by reinforcing the sand bed, the tilt of footing decreases at 2layers of reinforcement and then increases by increasing the number of reinforcement layers.

Axisymmetric alternating direction explicit scheme for efficient coupled simulation of hydro-mechanical interaction in geotechnical engineering-Application to circular footing and deep tunnel in saturated ground

Explicit solution techniques have been widely used in geotechnical engineering for simulating the coupled hydro-mechanical(H-M) interaction of fluid flow and deformation induced by structures built above and under saturated ground, i.e. circular footing and deep tunnel. However, the technique is only conditionally stable and requires small time steps, portending its inefficiency for simulating large-scale H-M problems. To improve its efficiency, the unconditionally stable alternating direction explicit(ADE)scheme could be used to solve the flow problem. The standard ADE scheme, however, is only moderately accurate and is restricted to uniform grids and plane strain flow conditions. This paper aims to remove these drawbacks by developing a novel high-order ADE scheme capable of solving flow problems in nonuniform grids and under axisymmetric conditions. The new scheme is derived by performing a fourthorder finite difference(FD) approximation to the spatial derivatives of the axisymmetric fluid-diffusion equation in a non-uniform grid configuration. The implicit Crank-Nicolson technique is then applied to the resulting approximation, and the subsequent equation is split into two alternating direction sweeps,giving rise to a new axisymmetric ADE scheme. The pore pressure solutions from the new scheme are then sequentially coupled with an existing geomechanical simulator in the computer code fast Lagrangian analysis of continua(FLAC). This coupling procedure is called the sequentially-explicit coupling technique based on the fourth-order axisymmetric ADE scheme or SEA-4-AXI. Application of SEA-4-AXI for solving axisymmetric consolidation of a circular footing and of advancing tunnel in deep saturated ground shows that SEA-4-AXI reduces computer runtime up to 42%-50% that of FLAC’s basic scheme without numerical instability. In addition, it produces high numerical accuracy of the H-M solutions with average percentage difference of only 0.5%-1.8%.

Influence of Nonassociativity on the Bearing Capacity Factors of a Circular Footing

Numerical computations using the finite difference code FLAC (fast Lagrangian analysis of continua) are presented to evaluate the soil bearing capacity factors Nc,Nq and Nγ for circular smooth and rough footings. The influence of nonassociative flow rule on the ultimate bearing capacity of a circular footing is investigated. The footing rests on the surface of a homogeneous soil mass and a Mohr-Coulomb yield criterion have been assumed for the soil behavior. The values of ultimate bearing capacity factors Nc,Nq and Nγ are obtained for a wide range of values of the friction angle for five different values of the dilation angle. The values from the numerical simulation are found to decrease significantly with the increase of nonassociativity of the soil. The results are compared with those derived from existing classical solutions.