Researches On The Bearing Capacity And The Failure Mechanism Of Foundations Near Slopes Based On The Unified Strength Theory

The foundation near a slope has been widely appeared in the transportation,architecture,water conservancy and other engineering construction fields.The influence of slope on the foundation bearing capacity is complicated,thus it has important guiding significance to optimization designs of footings near slopes to further study the bearing capacity and the failure mode of foundations near slopes.Most of existing theoretical studies on the bearing capacity of foundations near slopes are based on the Mohr-Coulomb strength criterion,in which the positive effect of the intermediate principal stress on the improvement of soils strength is not considered.The Unified Strength Theory reasonably considers the intermediate principal stress effect,that is applicable to different engineering materials.Therefore,this paper deduced theoretical formulations of the bearing capacity of strip foundations near slopes based on the Unified Strength Theory,and the Discontinuity Layout Optimization method was utilized to conduct numerical simulations of the bearing capacity and the failure mechanism of strip foundations near slopes.The main research contents and conclusions are as follows:(1)Based on the Unified Strength Theory and the Meyerhof’s theory,a solution of the bearing capacity for foundations near slopes under the symmetric failure mode was derived.The correctness of obtained results was verified by comparing with model test results in the literature.The results show that the strength effect of lateral soils around the foundation can be reasonably explained by an equivalent free surface.The intermediate principal stress has a marked improvement effect on the bearing capacity of foundations near slopes.The bearing capacity of foundations near slopes is consistent with that of foundations on the level ground when the horizontal distance of footing from the slope shoulder reaches the critical distance,and the critical distance increases with the increase of the intermediate principal stress effect.The reduction effect of slope angle is more obvious with the larger effect of intermediate principal stress.(2)Considering contributions of the soils strength behind the slope,two asymmetric failure modes including the slope face failure and the below-toe failure were established,and new solutions of Meyerhof’s bearing capacity for foundations near slopes were deduced.It is found that the effect of intermediate principal stress on the bearing capacity of foundations near slopes under the asymmetric failure mode is more remarkable than that under the symmetric failure mode,and the critical distance of footing from the slope shoulder under the asymmetric failure mode is smaller.Besides,the bearing capacity of foundations near slopes decreases gradually with the increase of slope height under the below-toe failure mode while it remains unchanged under the slope face failure mode.(3)In view of two modes of reinforced foundation’s general shear failure and composite failure,new calculation equations of the bearing capacity for reinforced foundations near slopes were deduced,and the validity and influence characteristics of parameters were analyzed.It can be concluded that the bearing capacity of the reinforced foundations near slopes increases clearly with the improvement of the intermediate principal stress effect and the tensile strength of reinforcements.As the vertical spacing between reinforcement layers increases,the bearing capacity of reinforced foundations near slopes in the case of general shear failure increase first and then decreases,while it gradually reduces in the case of composite failure.Moreover,the bearing capacity of reinforced foundations near slopes increases first and then remains constant with increasing the number of reinforcement layers.(4)The numerical models of foundations near slopes were established by utilizing the Discontinuity Layout Optimization method,and six failure modes of foundations near slopes and four failure modes of reinforced foundations near slopes were obtained.With changes in the footing position,the geometric dimensions of the slope,and the soil strength,the mode of the slope face failure,the slope toe failure,the below-toe failure,the bilateral failure,the horizontal foundation failure,or the slope failure may occur to the foundation near a slope.When the top layer spacing of reinforcement or the number of reinforced layers is large,the mode of the failure above reinforcements or the failure between the reinforced layers is appeared in reinforced foundations near slopes respectively,and the enhancement effect of reinforcements is small.Additionally,the enhancement effect of reinforcements on the bearing capacity of reinforced foundations near slopes is greater under two modes of general shear failure and composite failure.Based on the Unified Strength Theory,calculation formulas for the bearing capacity of foundations near slopes and reinforced foundations near slopes are established,and a series of calculation diagrams of foundation bearing capacity including failure modes are given by using the Discontinuous Layout Optimization method in this paper.This study can reflect comprehensive effects of various factors in combination with the intermediate principal stress effect,which can provide a certain theoretical reference for optimization designs of footings near slopes and the determination of the foundation bearing capacity.