Study On Deformation Evolution Characteristics And Early Warning Indicators Of Mine Slope With Gently Inclined Weak Intercalation Layers

The southwest region of China is rich in high-quality limestone mineral resources,which is an important source of building materials for a large number of infrastructure constructions in China.However,in the Permian limestone strata widely distributed in the area,there are multiple layers of slowly dipping weak interlayer,and sliding damage often occurs along the slowly dipping weak interlayer,which poses a serious threat to the stability of slopes,therefore,it is significant to carry out research on the deformation evolution characteristics and early warning indicators of such slopes.This thesis takes a typical slope containing weak inclusions in Huangshan limestone quarry as the research object,uses engineering geological analysis,indoor creep mechanics test,field monitoring,numerical simulation and other means to reveal the creep characteristics of weak inclusions and the long-term deformation evolution characteristics of slopes containing weak inclusions,and establishes early warning indicators and comprehensive early warning methods for such slopes,the specific research results are as follows.(1)The causes of formation and natural properties of the weak interlayer are analyzed.The muddy or mud-bearing tuff in the tuff is damaged by the stress concentration on the contact surface of soft and hard rocks,and physical and chemical reactions occur under the groundwater and various geological effects,forming a soft and weak interlayer that is significantly different from the original rock;the composition of the soft and weak interlayer is dominated by calcite,quartz,gypsum and pyrite and other detrital minerals,i.e.,the interior is mainly calcareous cementation,while containing a small amount of gypsum and pyrite,and the overall mechanical strength is low.(2)The creep evolution law of the Permian weak interlayer was obtained.Through the shear creep test of the weak sandwich,we obtained that the creep of the weak sandwich contains three stages of attenuation creep,steady-state creep and accelerated creep,and has transient deformation characteristics;at low stress level,the weak sandwich only shows attenuation creep and steady-state creep characteristics;at high stress level,the weak sandwich specimen also has an accelerated creep stage,showing the complete three-stage creep characteristics,and finally the viscoplastic damage occurs,and the accelerated creep stage has short time and large deformation.(3)The deformation evolution characteristics of slopes containing soft inclusions are revealed.By analyzing the long-term displacement,stress and plastic zone evolution characteristics of the slope through numerical simulation,we get that the slope first appears deformation at the trailing edge,and with the increase of creep time,the displacement of the slope grows continuously;under the influence of the overlying tuff load,the trailing and leading edge positions of the soft sandwich are subject to compressive stress and enter the plastic state;as the tuff is continuously squeezed downward,the compressive stress concentration is formed at the foot of the slope,and the distance between the soft sandwich at the leading edge and the foot of the slope is shorter,and the tuff at the foot of the slope also enters the plastic state by compressive shear.After creeping for a certain period of time,the weak interlayer will eventually enter the plastic yield state under compressive stress and pass through the plastic-plastic zone with the foot of the slope,and the slope will slide along this plastic zone.(4)A comprehensive warning index for slopes with weak inclusions is established,and a comprehensive warning method for slopes is proposed.According to the displacement-time curve of the slope containing weak inclusions,the horizontal displacement,deformation rate and improved tangent angle are taken as the key warning criteria,and the four warning values of each warning criterion are determined,and the comprehensive warning index table for different key points of the slope is established by combining the macroscopic deformation warning index of the slope;the improved tangent angle and deformation rate are taken as the main deformation warning criteria,and the horizontal displacement and macroscopic deformation are the auxiliary warning criteria,and the comprehensive warning method of the slope containing soft inclusions is proposed,and the feasibility of the comprehensive warning index and method is verified by the example of the Eagle’s Mouth landslide.