Study On Ultimate Bearing Capacity And The Failure Mechanism Of Strip Footings On Sand Overlying Clay

The bearing capacity of rigid footings is a classical problem in geotechnical engineering.Due to some natural or artificial reasons,a sand layer overlying clay with an infinite depth are common in reality,which arouses more concerns in academia.Meanwhile,horizontal loading and nearby footings are usual in practice,which brings more requirements of the bearing capacity theories of the footings under inclined loading and nearby footings on sand overlying clay.In this paper,the limit analysis method is adopted in studying these issues.The corresponding bearing capacity theories and analysis of the failure mechanism are proposed as follows:(1)A brief introduction of the bearing capacity and the failure mechanism of the rigid strip footings on sand overlying clay is reported,and the achievements and existing problems of the current researches is summarized.(2)For vertically loading,a total of 81 data of the bearing capacity are collected from the literature.Based on a limit analysis procedure(discontinuity layout optimization(DLO)),a numerical model is established to compute the bearing capacity.A set of design charts is proposed to illustrate the reduction factor of the bearing capacity.Two simplified approaches are developed based on the data from DLO.With comparisons to the database of the literature,statistical analyses of the uncertainties of the numerical model and the two simplified approaches are carried out,respectively.(3)For inclined loading,a numerical model is established to determine the bearing capacity and the failure mechanism.The solution is illustrated as a set of design charts with the use of dimensionless parameters.A typical one-sided failure mechanism is observed.Parametric studies are performed to show that soil properties,geometric parameters,and load inclinations are all related to the bearing capacity and failure pattern.A simplified model is developed based on artificial data generated through DLO.Validations are carried out to demonstrate the accuracy of the developed model.(4)For two interfering strip footings,the bearing capacity and the failure mechanism is determined by using the DLO procedure.The results are showed as a set of design charts in a form of reduction factor of the bearing capacity.Three typical failure mechanisms are observed.The effects of soil properties,geometric parameters,and the spacing between footings on the shape and sizes of the failure slips are analysed.Considering the three types of failure mechanisms,a simplified model is developed by using the polynomial regression method.Validations of the accuracy of the simplified model for the various mechanisms are carried out,respectively.