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Study of Ultimate Bearing Capacity of Rock Masses Based on Critical Slip Field

Author: ShiLin
Tutor: ZhuDaYong
School: Hefei University of Technology
Course: Geotechnical Engineering
Keywords: Ultimate bearing capacity of rock mass Intermittent joints Anisotropy Earthquake loads Critical slip fields Hoek-Brown nonlinear failure criterion Nonlinear unified strength criterion
CLC: TU470
Type: Master's thesis
Year: 2012
Downloads: 34
Quote: 0
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Abstract


Earth pressure, slope stability and bearing capacity of foundation are the threemajor classic problems in geotechnical stability analysis. Conventional calculations ofbearing capacity were formulated in terms of a liner Mohr—Coulomb failurecriterion.In fact, The jointed rock mass is a organic complex including rock andstructure of the face,which has the heterogeneity、discontinuity、anisotropic inherentcharacteristic and nonlinear destruction features;what is more,based onMohr—Coulomb strength theory, the effect of intermediate principal stress is ignoredby the formula of ultimate bearing capacity which limits the full function of rockstrength and the effect on strength of orientation, length and arrangement of joints isnot discussed quantitatively which demonstrats the strength anisotropy of this kind ofrock mass.In order to reflect ultimate bearing capacity of rock mass more truly，Strengthparameters are obtained according to Hoek-Brown nonlinear failure criterion,combining with the critical slip fields,minimum upper bound solutions are obtained.Firstly, Considering the jointed rock mass possesses complex mechanicalbehaviors, the critical slip field method is modified based on the generalizedHoek-Brown failure criterion to calculate the ultimate bearing capacity of joined rockmasses. By transforming the shear strength of each point on the Hoek-Brown strengthenvelope into the Mohr-Coulomb linear relation, the critical slip field method basedon the Mohr-Coulomb criterion is improved and a new iterative procedure is thusestablished. Using the newly developed critical slip field method based on theHoek-Brown failure criterion, the passive earth pressure and ultimate bearing capacityof jointed rock masses is computed. The effects of values of GSI and mi on theultimate bearing capacity are comprehensively analyzed. Then, Based onHoek-Brown strength theory, the effect of intermediate principal stress is ignored bythe formula of ultimate bearing capacity which limits the full function of rockstrength.The characteristics of rock and the effect of intermediate principle stress onrock strength are taken into account, and then the Hoek-Brown nonlinear failurecriterion under unified strength is put forward and the equations that can determine the instantaneous strength parameter are obtained. combining with the critical slidingfield theory to solve the bearing capacity of foundation considering the impacts ofearthquake loads. Finally, The formulas of the parameters m， s in Hoek-Browncriterion can be obtained based on the characteristics of the mechanical effect andcompressive-shear fracture behaviour of rockmass containing intermittent joints, andthen, the formula of ultimate bearing capacity of rock mass containing intermittentjoints is presented combined with the critical sliding field theory. The effect onstrength of orientation, length and arrangement of joints is discussed quantitativelywhich demonstrats the strength anisotropy of this kind of rock mass.The results of comparative studies show that the proposed method can readilyyield the critical slip surfaces and associated values of ultimate bearing capacity ofrock mass with reasonable accuracy.What is more,the bearing capacity will enhancein various degrees when unified theory is applied. The existing methods of the bearingcapacity of the foundation are conservative. The bearing capacity of foundation willreduce with the effects of earthquake loads. And then, the anisotropism of ultimatebearing capacity is shown by the parameters m、 s,it has been proved that theanisotropism of ultimate bearing capacity is not only relevant to the orientation ofjoints,but also a function of confining pressureσ3.

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