Research On The Failure Mechanism Of Different Types Of Ground Under Rigid Or Flexible Loads

The bearing capacity of rigid footings and slope stability are considered as the two classical problems in geotechnical engineering.The scarce of land resources,the complexity of soil foundation,the diversity of ground improvement methodoly,and the larger scale and buried depth of foundations require special attention in evaluating the bearing capacity of rigid footings for both both theoretical and practical aspects.Meanwhile,the rapid development of highway and railway brings new challenge in the practical designs of embankment slopes and composite foundations with rigid piles.In this study,limit analysis and finite difference method were adopted to investigate the failure mechanisms of different types of ground and embankment slopes.In addition,the corresponding design and control theoretical methodologies were proposed for different issues,as follows:(1)The investigations of bearing capacity of rigid footings and the stability of pile-supported embankment are reported,and the existing problems in current researches are summarized.(2)A numerical modelling is established by using limit analysis method(Discontinuity Layout Optimization(DLO))to investigate the bearing capacity and failure mechanism of a rigid footing placed on the top of a c-φ soil slope.There are two geotechnical issues simultaneously exist in the model.A set of design charts,which includes six different critical failure mechanisms,is presented.Besides,the design methods in both Chinese and American codes are discussed.(3)The DLO is used to study the bearing capacity of rigid footings on c-φ soils with square void.The issues of bearing capcity and staility are discussed.The effect of different positions of single and double square voids on the bearing capacity and failure mechanism is investigated.Besides,a set of design charts is presented.The most adverse voids position for clay is located directly under the footings,while the most adverse voids position for c-φ soils is placed under the footings with an offset of 0.5-2 times of footing width.(4)A numerical model on the basis of a finite difference method is developed for studying the influences of the footing roughness,dilation angle and surcharge on the failure mechanism and ultimate bearing capacity of the soil foundation with sand overlying clay.Based on the numerical results,the existing practical methods are evaluated,including the weighted average method,the load spreading method and the punching shear method.In addition,a revised method based on the local shear failure is proposed.(5)A finite difference method is adopted to analyze the performance of reinforced ground of a group of stone columns under rigid footings subjected to a vertical load.The investigation on bearing capacity factors is carried out by varying the surface surcharge.The variation of bearing capacity factor and failure mechanism is analyzed.The current design method substantially underestimate the bearing capacity factor.An upper-bound limit formula based on the general shear failure mode is deduced,while a limit equilibrium calculating method subjected to the block failure mode is presented.Finally,a theoretical method based on the comparison of the analytical equations for different failure modes is developed for evaluating the critical failure mechanism and bearing capacity factors.(6)A finite difference method is adopted to analyze the stability of pile-supported embankment by considering different simulation method in the post-failure behavior of piles.The failure orders of piles is determined,and the concept of progressive failure of pile-supported embankment is proposed.The process from local failure to global failure is investigated carefully.Base on the methodology of progressive failure control,the concept of key piles and non-uniform design method is developed.