IN-SITU TEST FOR SHEAR STRENGTH OF STRUCTURE PLANE IN PLATY ROCK MASS AT XIAOYOUYING,BEIJING

Strength of rock mass is largely determined by the strength of structure planes in the rock mass. This is especially true to platy rock mass.It is significant to get the strength parameters of structure planes in the rock mass directly by in-situ test both for the stability analysis of rock mass and for engineering design.In order to understand the strength property of platy rock mass,in-situ tests for the strength of the structure plane in dolomite platy rock mass at Xiaoyouying in Fangshan District of Beijing are carried out.Traditional in-situ tests will result in a high cost,and bring more difficulties for the shear strength of rock mass.To get rid of the heavy reaction frame,according to the relationship between the attitude of platy planes and the direction of tectonic stress in the rock mass,three test rock blocks,laterally disconnected from their parent rock in different forms,are dug out vertically on the horizontal ground of the test site.Beside two parallel vertical free surfaces,a certain free room is left between test block and its parent rock.This room is just a reaction frame for loading,where a jack and steel pads can be put and horizontal test loads can be applied vertically to the free surface of the test block.This makes the test get rid of cumbersome reaction equipment totally.The state of the tectonic stress in the test block changes with the forms of block disconnection from its parent rock and the varied tectonic stresses in different states,adding upon the stresses caused by horizontal test loads,forms different normal and tangential stresses in the pre-concerted shear plane at last.By means of the test method explained above,and based on the data of the local tectonic stress in Beijing territory,a pretty good result has resulted from the in-situ test for the shear strength(c,)of platy planes in the dolomite platy rock mass at Xiaoyouying in Fangshan district of Beijing.The strength parameter will be a helpful reference for the design of extra high voltage network foundation and for the stability analysis of engineering rock masses in mountain areas with similar platy rock mass.