Study Of Hollow Inclusion Strain Cell For In-Situ Stress Measurement And Its Application

The in-situ stress refers to the undisturbed stress in the rock mass,which is the basic data to determine the mechanical state of the crust,and also the important reason for the deformation and failure of the rock mass.The in-situ stress measurement is widely launched in mining,water conservancy construction,engineering construction,transportation industry and many other fields.Through the in-situ stress measurement,engineers can understand the stress state of the engineering area and judge the potential failure form of the surrounding rock,which is helpful for the rational excavation design of geotechnical engineering.Therefore,it is necessary to carry out the study of in-situ stress measurement.The method of in-situ stress measurement with hollow inclusion strain cell was studied by means of finite element numerical simulation in this paper.The process of in-situ stress measurement and the influencing factors of measurement accuracy were analyzed.Some key problems of in-situ stress measurement were discussed in detail from the aspects of measurement point selection,strain gauge installation,analysis of measured data and so on.Firstly,the drilling depth in the process of in-situ stress measurement was studied to make sure the measuring point be located in the original rock stress area.And the range of stress disturbance area formed by roadway excavation was analyzed by means of theoretical analysis and numerical simulation.The results show that the radius of the stress disturbance area is related to the stress form of the roadway.The drilling depth of the test hole should be greater than the radius of the stress disturbance area to ensure that the test point is outside the stress disturbance area.The stress disturbance at the bottom of the test hole was analyzed then,and as a result,the best installation position of the hollow inclusion strain gauge in the test hole was obtained.Based on these,the stress release law of the relieved core in the process of stress relief was further studied to obtain the minimum relief depth.In addition,this paper discussed the formation mechanism of core pancake and revealed the relationship between core pancake and in-situ stress.The error analysis of in-situ stress measurement with hollow inclusion strain cell was carried out,mainly considering the influence of the non-ideal lithologic conditions,the improper value of the correction coefficientsK_iand the characteristics of colloidal materials on the calculation accuracy.Suggestions for improving the measurement performance of the hollow inclusion strain gauge were put forward after studying the influence of the material properties on the observed values.Based on the analysis of the strain gauge observations in all directions,the optimal arrangement of strain gauge in the hollow inclusion strain gauge was proposed.Finally,the measured data of the Sang Zhuling tunnel in Lasa-Linzhi railway were analyzed.to compare the influence of the correction coefficients K_i on the calculation results,two different methods were used to calculate in-situ stress of the measuring points.The distribution law of the ground stress in the engineering area where the measuring point is located was revealed,which provides a certain reference for the engineering practice.