| With the gradual implementation of national strategies such as ’The Belt and Road’and ’Western Development’,economic construction has ushered in unprecedented development opportunities.The development and utilization of mineral resources plays a vital role in promoting social and economic development.There are a large number of Permian limestone strata with weak interlayers in southwest China.The strata are rich in high-quality limestone mineral resources and are an important source of building materials for a large number of infrastructure construction in China.However,the weak interlayer is generally a thin layer of shale containing carbonaceous,silty,calcareous and other mineral components,with low mechanical strength,poor water physical properties and obvious creep effect,which poses a serious threat to the stability of such slopes.At the same time,the oxalic acid formed by the decay of trees,flowers and plants in the mining area gradually infiltrates into the weak interlayer in the form of rainwater or groundwater.The chemical reaction will change the mineral composition and pore structure of the weak interlayer,making the creep characteristics significant.Therefore,in order to reasonably analyze the stability of this kind of mine slope under the influence of acid corrosion,it is urgent to study the mechanical damage effect of weak interlayer under acid corrosion.The research of this paper is supported by the National Natural Science Foundation of China(Yunnan Joint Fund)key project " Research on the disaster mechanism and prevention and control of high slopes in mines with gently inclined weak interlayers in Yunnan area(U1802243).Taking the high slope with gently inclined weak interlayers in Huangshan limestone mine as the research object,considering the objective conditions of the chemical environment faced by the mine,the conventional direct shear test,shear creep test and electron microscope scanning test of acid corrosion were carried out.The influence of acid corrosion on the attenuation law of mechanical parameters and creep characteristics of weak interlayers was analyzed.Based on this,a nonlinear viscoelastic-plastic shear creep model considering acid corrosion damage is proposed.After parameter identification,the model is redeveloped and verified by Microsoft Visual Studio 2010 and finite difference numerical software.Finally,the long-term stability of Huangshan limestone mine slope considering the effect of acid corrosion is analyzed,and its disaster mechanism is revealed.The specific research results are as follows :(1)The damage degradation law and acid etching mechanism of weak interlayer were analyzed.By conducting direct shear tests of weak interlayers with different pH values and soaking times under four normal stresses,it is shown that acid etching has a significant weakening effect on the deformation characteristics and strength parameters of weak interlayers.The shear strength parameters decrease exponentially with the increase of acid strength and acid etching time,and the damage rate increases exponentially.At the same time,the acid etching process will change the mineral composition of the weak interlayer,increase the internal pores,and cause damage to the sample,mainly including the deterioration of the macroscopic mechanical properties and the fragmentation of the microstructure.(2)The statistical damage constitutive model of weak interlayer under acid etching is established.On the basis of considering the influence of chemical acid etching,using the statistical damage theory,assuming that the micro-unit strength of rock under chemical action obeys Weibull distribution,and introducing parameters such as compaction index,post-peak correction coefficient,threshold stress and threshold strain,a statistical damage model of rock under chemical-load action is established.Compared with the results of indoor direct shear test,the correctness and rationality of the model are verified.(3)The nonlinear damage evolution law of weak interlayer is revealed.In order to study the shear creep characteristics of weak interlayer under acid etching,the THMC-B multi-field coupling shear rheometer was developed to carry out the test.With the increase of acid etching and dry-wet cycle,the shear creep deformation characteristics are gradually obvious,and the effect of acid etching on the shear creep of the sample is greater than that of dry-wet cycle.Through the analysis of macro and micro structure,the weak interlayer is subjected to repeated acid etching and acid etching · · · ·long-term.The acid etching effect and the dry-wet cycle affect each other,changing the material composition and pore structure.The creep mechanical properties are sharply weakened,making the weak interlayer more ’fragile’,which together leads to the final failure.(4)The DNVEP element model of weak interlayer considering the influence of acid etching is established.Using the unified rheological mechanics theory,it is determined that the Burgers creep model can describe the shear creep characteristics of the weak interlayer.Then,for the linear Burgers creep model can not describe the nonlinear and accelerated creep characteristics,a six-element nonlinear viscoelastic-plastic NVEP creep model is improved.Finally,the influence of repeated acid etching on the weak interlayer is introduced into the model in the form of damage variable,and the nonlinear viscoelastic-plastic DNVEP creep damage model of weak interlayer considering the influence of repeated acid etching is established.The finite difference form of the model is derived,and the secondary development is realized.The correctness of the constitutive model and development is verified by numerical experiments.(5)The disaster-causing mechanism of mine slope with gently inclined weak interlayer considering the influence of acid corrosion is revealed.Taking the typical gently inclined weak interlayer slope of the dangerous rock mass in the east mining area and the Laoyingzui landslide as the engineering background,the influence of creep time and acid etching environment on the deformation failure and long-term stability of the slope is analyzed.Under the action of long-term repeated acid corrosion,the weak interlayer softens,damages and creeps obviously,and gradually enters the plastic state,which increases the displacement and rate of the overlying limestone in the middle and upper parts.After the creep is long enough,all the weak interlayers enter the plastic state.Due to the continuous downward extrusion of limestone and the short distance between the weak interlayer at the leading edge and the toe of the slope,the limestone at the toe of the slope finally enters the plastic state,and the plastic zone is formed at the limestone at the toe of the slope,which eventually leads to the ’push’ landslide disaster.Through the calculation and analysis of different acid etching environments,the adverse effects of acid etching on the long-term stability of the slope are verified. |
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