Research On Setback Distance Of Independent-foundation Under Surface Rupture In Strong Earthquake

Under suitable conditions,fault dislocation through the overburden surface will cause surface rupture and damage to the foundation and superstructure of the building.At present,this problem has been one of the hot scientific and te chnological issues in engineering geology,civil engineering research and design ers.Therefore,it is necessary to deeply study its influence on the building and the measures of setback distance and resisting fracture of the buildingIn this paper,the deformation characteristics of the overlying clay and sand layers under normal fault action and the expansion of the rupture zone are studied through the normal gravity model test under large size and strong base rock dislocation and combined with the large deformation numerical simulation technology;Analyzed its response and avoidance to the independent foundation.The main research contents include:(I)In this paper,a set of large-scale fault dislocation model test device capable of simulating normal and reverse fault tests under large size,multi-dislocation momentum and multi-fault dip angle is independently developed.(II)In the free field site,six groups of normal fault free field fault displacement simulation tests were systematically carried out,and the effects of fault dip angle and different types of soil quality on surface rupture were discussed.The main conclusions are:(1)The surface uplift or uneven settlement will gradually increase with the increase of the amount of bedrock dislocation.The V-shaped shear fracture zone will eventually form inside the soil body,and the damage will be concentrated in the upper wall area.Among them,the impact of the clay shear fracture zone the range as a whole is larger than sand.(2)Generally speaking,the changes in surface settlement and earth pressure in and around the V-shaped shear fracture zone are more obvious than in other parts.(3)In the clay site,the fault dip angle increases,the surface uplift height and the influence range of the rupture zone increase,and there is a tendency to spread upward;In different soil conditions,clay is more inclined to the upper wall than the rupture zone where sand ruptures to the surface.Under the same fault displacement,clay may be superior to sand's ability to resist surface settlement;and suggestions for setback are given.(III)In the independent foundation site,six groups of normal faults under the independent foundation site fault simulation test were carried out systematically,The influence of fault dip angle and the thickness of overlying soil layer on the independent foundation on the ground is discussed,and a reasonable independent foundation setback distance is given.The main conclusions are:(1)The surface uplift or uneven settlement will gradually increase with the increase of the amount of bedrock dislocation,and under proper loading dislocations,a V-shaped shear fracture zone is still formed on the soil cross section,Among them,the shear fracture zone of clay mainly shows uplift,and the shear fracture zone of sand mainly shows downward collapse.Generally speaking,the foundation in the upper wall and V-shaped shear fracture zone is not safe.(2)In the independent foundation of clay and sand,as the fault dip angle increases,the influence range of the rupture zone is wider and spreads further upward.(3)In the clay independent foundation site,as the thickness of the overlying soil layer increases,the influence range of the rupture zone increases,and the foundation near the fracture zone is more sensitive to the increase of the soil layer thickness.(4)The base cover thickness and fault dip angle give independent foundation setback suggestion.The maximum reasonable setback distance is 42 m for the upper plate and 18 m for the lower plate.(IV)In the numerical simulation of ground rupture and large deformation,the simulation verified the model test of typical free field and independent foundation site.The thickness of the overburden layer under the free clay site and the amount of bedrock dislocation;the buried depth and size of the foundation under the independent foundation site were analyzed by multiple working conditions: The change of overburden thickness and bedrock dislocation has great influence on the settlement and settlement difference of the upper disk and near the rupture zone,has little effect on the lower disk area.(2)The size of foundation under clay and sand increases and changes,which can effectively reduce the strong earthquake damage in the area near the rupture zone,In the upper and lower disk range except this area,the increase of foundation size has no obvious improvement on reducing strong earthquake damage.(3)Whether clay or sand,the increase of foundation depth can effectively reduce the impact of surface rupture to a certain extent.