Study On Shear Mechanical Properties And Influence Of Interface Between Rock Foundation And Independent Footing

The footing is an important part to ensure the safe and normal use of the building within the design service life.At the same time,cost of the footing occupies a very large proportion in the whole building.Independent footing is widely used in footing design because of its advantages in structure form and cost performance.The early research on independent footing mainly focused on soil foundation,and the research work related to the independent footing on the rock foundation starts late,and the relevant results are not enough to satisfy the needs of engineering construction.Compared with the soil foundation,the rock foundation has the typical characteristics of large modulus of elasticity,small deformation,high bearing capacity and strong binding effect on the contact surface with the footing,which leads to the great difference between the stress characteristics of the independent footing on the rock foundation and the soil foundation,and the corresponding analysis and design methods will also be different.At present,the research on the restraint effect of rock foundation on independent footing pays more attention to the reaction of foundation and ignores the distribution and effect of the shear stress on contact surface.The research on the contact surface of rock and concrete mainly focuses on the shear stress and the stability analysis of dam.In order to further study the specific behavior of the constraint of rock on the footing,optimize the design method of the independent footing on the rock foundation.This paper mainly analyzes the shear stress of the contact surface between the footing and the foundation,explores the influence of the shear stress of the contact surface on the stress characteristics of the independent footing on the rock foundation,and analyzes and verifies it with the method of in-situ test and numerical simulation.The main research contents and conclusions of this article are as follows:(1)Collecting and summarizing the domestic and foreign research results on independent stress characteristics,failure modes,and design methods of footings,it is found that the research objects are mainly independent footings on soil foundations.Summarizing the research status of the shear mechanical properties of the interface between the foundation and the footing at home and abroad,it is found that little attention has been paid to the influence of the shearing effect on the stress and bearing capacity of footings.(2)Investigating the shear mechanical properties and influencing factors of the interface between the foundation and the footing,it is found that the constitutive relation of the rock-concrete interface can adopt rigid plastic or elastoplastic model.The influencing factors mainly include rock types,rock mass properties,test methods,physical mechanics of the interface Characteristics,etc.,these factors cause the shear stress distribution at the interface of the substrate to be significantly non-linear.The influence of the shearing effect of interface on the bearing characteristics and the design value of the bearing capacity of the independent footing on the rock foundation was studied.The analysis found that the shearing effect of interface had a significant influence on the bending effect of the footing,but little effect on the load bearing of the punching,local compression and splitting of the footing.After considering the shearing effect of the interface,the formula for calculating the reduction of the bending moment of independent footing under the action of the central load is given.(3)Combined with the independent footing field test,the influence of the shear stress of the base interface on the development of crack of footing and the distribution of the base reaction force was analyzed.The analysis found that the influence of the base shear stress on the base reaction force was consistent with the influence of the footing height,and the influence effect gradually decreases with the height of footing increase;the influence of the shear stress of interface on the development of cracks of footing is limited.When height of the footings are relatively small,the effect is obvious,and when the height of the footings are relatively large,there is basically no effect.(4)With the aid of finite element analysis software,the magnitude,distribution,influencing factors of shear stress at the interface between rock foundation and base of footing and the influence of shear stress on the mechanical characteristics of foundation are analyzed.The results show that width-height ratio of footing is large,the shear stress increases first and then decreases along the axis.With the width-height ratio of footing decreasing and friction coefficient of interface increasing,the shear stress gradually tends to be uniform and then concentrates to the edge.The influencing factors include widthheight ratio of footing,load and friction coefficient of interface.