Evolution Mechanism Of Slope With Locking Section Due To Excavation

Lucid waters and lush mountains are invaluable assets.Ensuring harmony between human and nature is becoming the basic strategy for China’s modernization drive in the new era.In the process of engineering construction,artificial excavation of slope contributes to irreversible changes in geological environment,aggravating the occurrence of landslide disaster,and seriously threatening the safety of people’s life and property and the construction of major engineering and ecological environment.The development and evolution of slope with locked segment has strong concealment and abruptness,and the economic losses and casualties caused by it are often more severe.Therefore,it is of great scientific and practical significance to study the deformation evolution mechanism of slope with locking section due to excavation.This paper concentrates on the critical scientific problems of the deformation effect and stability evolution mechanism of locked slope due to excavation.Taking Wan Huayan locked slope as an example,the geomechanical model of locked slope is generalized.Based on in-situ deformation monitoring,methods of mathematical analysis,geomechanical model test and numerical simulation,revealing the deformation evolution mechanism of locked slope due to excavation,evaluating the influence degree of the locking section on slope stability quantitatively,establishing the relationship between the length of the locked segment and the deformation of slope,the stability state and the stress of the locking section in the process of slope failure.According to the evolution process,deformation law and stress distribution characteristics of the slope with locking section,the identification criterion of the evolution state of the locked slope is proposed.The major research results are as follows:(1)By analyzing the engineering geological conditions of Wan Huayan locked slope,the geological model of locked slope is generalized.Based on the disast-prone geological environment of slope,macroscopic evolution process and in-situ deformation monitoring data,the internal relationship between slope structure characteristics and slope deformation law is established.The slip-rotation failure mode of locked slope is proposed according to the difference of failure mode,macroscopic form,deformation direction and sliding surface in different parts of slope deformation evolution process.(2)Based on the generalized geological model of locked-segment slope,five factors and five levels orthogonal tests were carried out to quantitatively evaluate the influence of mechanical and geometric parameters of the locking section on slope stability.The results indicate that the influence degree of each parameter is length L,elastic modulus E,Poisson’s ratio μ,shear strength index(C,φ),among which length L is a significant factor.Based on the large deformation theory,the excavation deformation of slope with five different lengths of locking section is calculated for significant factors.Combined with the failure process of slope,the evolution law of deformation displacement field,stress-strength ratio of locking section and shear strain increment of slope with the length of locking section are analyzed.The slip-control mechanism of locked section is revealed,and the relationship between the length of locking section and the failure process of slope is established.The results show that with the increase of the length of the locking section,the stress concentration of the locking section and deformation of slope decrease,and the slope safety factor increases gradually.When the length of the locking section reaches 40%of the leading edge width of the slope,the factor of safety is in a critical stable state.(3)Through three groups of large-scale physical model tests(Test I is unlocked segment,Test Ⅱ is locked segment length L = 15 cm,Test Ⅲ is L = 30 cm),the influence of different lengths of locking sections on the deformation evolution of slope due to excavation under the same conditions is explored.The evolution stage and characteristics of locked slope are defined,and the corresponding instability mode is established.The experimental results indicate that the unlocked slope produces progressive failure of multistage sliding surface as a whole,locked slope(L = 15 cm)produces multistage sliding surface slump-torsional progressive failure,and locked slope(L = 30 cm)produces shallow displacement progressive failure.(4)The slope cracks,macroscopic failure modes and deep deformation characteristics of the three groups of model tests were compared and analyzed,it indicates that: a.In test I,there are no longitudinal cracks on the side slope,and a number of transverse through-through cracks are developed.There is basically no horizontal inclined deformation,and the deformed body is cut out as a whole along the shear outlet of the leading edge.The shallow and deep multistage sliding surfaces are developed,and the shape,depth and deformation of the sliding surfaces are basically the same.b.The locked slope(L = 15 cm)develops transverse shear cracks and longitudinal tensile cracks(the main longitudinal cracks are along the side of the locked segment),giving rise to large horizontal inclined deformation;Shallow and deep multistage sliding surfaces are developed.The left wing sliding surface of the locking section is the deepest,followed by the top,and the right wing is the shallowest;The deep sliding surface is cut out on the first slope of the left wing of the locking section,and the right wing of the locking section is relatively stable without shear outlet.c.The locked slope(L = 30 cm)has transverse shear fractures and oblique tensile fractures.The oblique fractures are approximately symmetrically distributed along the axis of the locked segment,giving rise to slightly horizontal inclined deformation;The shear outlet of the leading edge of slope is blocked from sliding at the locking section,resulting in obvious expansion phenomenon and fragmentation of slope surface;Only the shallow slip surface is developed,and the shape,depth and deformation of the slip surface in each section are basically the same.The results can be used as deformation criterion for identification and evolution of locked landslide.(5)In the three groups of model tests,the load transfer path is gradually downward and forward from the upper part of the slope.The differences are as follows: a.On the cross section of the no locked slope,the magnitude and variation law of earth pressure at each point are basically the same,and there is no obvious stress concentration section.b.The locked slope(L = 15 cm)forms a high stress concentration along the longitudinal section of the locking section,and the stress ratio of the left wing,back wing and right wing of the upper locking section in the cross section is 1:22.2:4.6;The small side of the back of the locked segment bears tension and the large side bears extrusion pressure.c.The stress concentration degree(stress ratio is 1:20:3)on the cross section of the locked slope(L = 30 cm)is slightly lower than that of the slope(L = 15 cm).The back of the locked segment is under compression,which is different from the stress distribution of the tension zone in the back of the locked segment L=15 cm.The results can be used as the stress criterion for identification and evolution of locked landslide.(6)By establishing a three-dimensional numerical simulation model of the Wan Huayan locked slope,the influence of the locking section on the deformation and failure characteristics and failure mode of the slope during excavation is clarified based on the overall deformation of the slope,the horizontal displacement of typical sections and the displacement curves of characteristic points on the slope.The deformation and instability mechanism of the locked slope is revealed: The upper shallow layer is deformed as a whole.When the deformation is partially blocked by the locked segment,the sliding surface moved down,the middle and lower flanks are torsional deformed,and gradually become sliding rotation failure.