Study On Engineering Characteristics And Correction Rules Of Bearing Capacity Of Soft Rock

With the buildings become higher,larger and heavier,to meet load design requirements,the foundations of high-rise buildings,bridges,tunnels,subway and other engineering take the deep soft rock layer as the bearing stratum.The engineering properties of soft rock are complex and changeable,and methods of determining bearing capacity in the current code have a history of more than 40 years,the bearing capacity of soft rock foundation determined by field load test in practice are often larger than code value.At the same time,there is a debate whether needing depth and width correction.It is necessary to further analyze the engineering characteristics and the determination of bearing capacity of soft rock,to determine and excavate the bearing capacity of soft rock foundation more reasonable,optimize the basic design and save the project cost.This paper summarizes common failure criterions and modes,bearing capacity determination methods and influencing factors of soft rock foundation combined with knowledge of rock mechanics.Based on the actual project,the paper analyzes the engineering properties and bearing characteristics of soft rock by indoor test and field load test,and draws the following conclusions.There are two main kinds of failure modes,shearing and punching,which are common occurring in high compressive brittle rock and low compressive plastic rock respectively;The factors that affect bearing capacity of soft rock foundation are deformation of foundation,overload and size of foundation and so on;The strength reduction method in code is too conservative when used in most areas;Red sandstone in Lanzhou has weak cementing force,low compression,water softening and disintegration and other characteristics;The strength of sandstone increases with the increase of confining pressure in triaxial test,and the bearing capacity of rock foundation increases obviously after adding overload,they both show that the bearing capacity of the rock foundation can be corrected in depth and can be excavated.Based on the field test results,using numerical simulation software to simulate the load test under different working conditions and carry out the quantitative analysis of correction rules of the bearing capacity of soft rock foundation.The results show that: The bearing capacity of soft rock foundation increases with the increase of the depth and width of the load plate,it is reasonable to correct the depth and width.When considering the influence of depth,the characteristic value of bearing capacity is mainly affected by strength,while considering the effect of width,the characteristic value of bearing capacity is both affected by strength and settlement;In the two engineering examples,the depth correction coefficient ?d is the power function of the depth d,and the width correction coefficient ?b is constant,the results can provide a reference for the reasonable determination of the bearing capacity of soft rock foundation.