Study On In-situ Stress Measurement Method Considering Non-linear Elasticity Of Rock Mass In Deep

In-situ stress is the basic load condition and an important factor that must be considered in the design,construction and stability safety analysis of underground rock mass engineering.Based on the assumption of rock mass elasticity assumption the traditional In-situ stress measurement theory wills produce large deviations in deep rock mass.Therefore,this paper analyzes the non-linear elastic properties of deep rock mass,develops the calibration technique suitable for deep release method,and proposes a superposition algorithm of original rock stress component considering stress relief path.Meanwhile,the existing hollow inclusion strain gauges are improved to greatly improve the accuracy,convenience,stability and performance of the measurement in the probe structure,cementing material,acquisition method.The main contents are as follows:Uniaxial and triaxial static mechanical loading tests were carried out on deep granites in the Sanshandao Gold Mine Shandong Province and the Jinchuan No.2 Mine with a depth of 800m.Aiming at the characteristics of deep granite,such as large crystalline particles,developed joints and cracks,and outstanding anisotropy,a multi-confining pressure step load test was designed to obtain the stress-strain curve of the elastic deformation section of the specimen under the confining pressure of 10MPa,30MPa and 50MPa.A hyperbolic nonlinear model between mean stress and deformation modulus is proposed.The model has three main physical parameters a,b,K0 and discusses its physical meaning.The maximum pressure of the confining pressure rate test device cannot satisfy the in-situ stress in deep rock mass and the multi-size core universal high confining pressure calibrating device and high pressure long-acting loading calibrating system are developed,which is made up by manual loading system,high pressure hull,multi-caliber adaptive cover plate,high strength self-sealing leather case.The radial pressure is up to 100MPa and keeps 2 months in 60 MPa;Using high pressure technology,High pressure calibration test is carried out and a non-linear elastic model of rock is established considering the whole loading process.The non-linear model is introduced into the in-situ stress calculation formulas of parameters,derives the lift the core of the relationship between average stress and the strain formula,puts forward a method of the non-linear rock mass in-situ stress measurement of confining pressure correction;Because the errors introduced by temperature to the measurement results can not be neglected,indoor temperature calibration tests were carried out in the thermostat for the core of-795 level in Sanshandao Gold Mine.In order to minimize the measurement error of strain gauge and acquisition circuit caused by temperature change,temperature compensation is carried out for the measurement strain gauge and acquisition circuit respectively.Temperature compensation algorithm was used to calculate the thermal channel(T1)data from 424?? to 359??,with a correction of 15%.After adopting the double temperature compensation algorithm,the compensation correction values of each measurement channel are between 10 and 23 ??.In the process of releasing,the temperature change of the measuring point is about 3°,and the whole rule accords with the characteristics of the releasing curve of the hollow inclusion,and the temperature change value is stable.The k coefficients are introduced to eliminate the influence of epoxy resin adhesive about 1.5mm thickness between hollow inclusion strain gauge and rock mass on in-situ stress results.The variation values of k1,k2,k3 and k4 coefficients are discussed when the average stress of core is from 0 to 30 MPa,which respectively are 1.021 to 1.163,0.967 to 1.140,0.738 to 0.788,1.944 and 1.132 in this paper.The maximum error is 8.14%,10.27%,4.06%and 11.84%,when the value is fixed by subsections.The maximum error is 11.34%,13.01%,5.48%and 18.1%,when each stage is calculated by the same value.The piecewise method is helpful to improve the calculation accuracy;Based on the non-linear characteristics of deep rock mass,an algorithm of piecewise superposition of in-situ stress is proposed considering stress relief path in this paper,and the error caused by linear fitting parameters in traditional calculation method is eliminated.The calculated strain value of each stage in the algorithm is the relieved strain value collected by the strain gauge with the minimum time interval.The calculated values of the stress in the previous stage are used to obtain the K and G parameters in the next stage,the initial calculation parameter is K0 and G0 with unstressed state completely.The piecewise superposition algorithm and the traditional algorithm are used for comparison calculation in the in-situ stress at-795 level respectively.The results show that considering the non-linear characteristics of deep rock,the double temperature supplementary correction to remove strain and the coefficient of k piecewise value to improve calculation accuracy,the proposed algorithm is average 19%larger than the traditional algorithm,and the three principal stress directions and dip angles of the two algorithms are the same basically.