Study On The Influence Of Dry Wet Cycle On The Mechanical Properties Of Sandstone With Non Uniform Structural Planes With Strike

Rock masses with non-uniform structural planes in strike are widely present in the southwest region,and geological problems such as rapid weathering and rock mass collapse often occur in geotechnical engineering such as foundation pit excavation and slope treatment.The southwest area is hot and rainy in summer.Under the condition of dry wet cycle,the weathering of rock mass intensifies,the mechanical strength decreases,and finally its stability decreases.This article takes sandstone with non consistent structural planes as the research object,and sets different strike difference angles,rock bridge lengths,and structural plane inclination angles for structural plane parameters.The mechanical characteristics of rock samples with non consistent structural planes in natural conditions and after dry wet cycles are studied using indoor uniaxial compression tests;Through high-definition cameras and combined with the failure morphology of rock samples,further research was conducted on their failure modes and characteristics,and the following results were achieved:(1)Through uniaxial compression tests on sandstone with non consistent structural planes under natural conditions,it was found that the influence of structural plane parameters on the mechanical strength of sandstone with non consistent structural planes is as follows: inclination angle of structural planes>difference angle of strike>length of rock bridge.The difference angle of strike is directly proportional to the peak strength of the rock mass containing structural planes,and the peak strain,elastic modulus,and deformation modulus also increase to varying degrees with the increase of the difference angle of strike;The peak strength and peak strain of the rock also show a significant increase with the increase of the dip angle of the structural plane.(2)When the strike difference angle(0°-20°)is small,the structural planes of sandstone containing structural planes are easy to penetrate,resulting in overall shear failure of the "Z" shaped failure surface;As the difference angle of strike(40°-140°)increases,its failure characteristics gradually transition to shear failure dominated by one structural plane;Finally,as the difference angle of strike(160°-180°)gradually reverses,it shows local compression shear failure caused by the interconnection of two structural planes.When the inclination angle of the structural plane is small(15°-30°),the rock mass undergoes relative displacement due to the compression closure of the structural plane;As the inclination angle of the structural plane increases(45°-60°),the closure phenomenon of the structural plane decreases,and the main failure surface develops from weaker structural planes,and the shear failure characteristics of the rock mass are enhanced;As the structural plane is relatively vertical(75°-90°),the lateral expansion phenomenon of the rock intensifies,and the characteristics of tensile failure become prominent.From the energy evolution of rock specimens,brittle failure is prone to occur when the strike difference angle is small(0°-20°)and reverse tilt(180°);As the inclination angle of the structural plane increases,the energy storage capacity of the rock increases significantly,and the deterioration of the rock strength and mechanical properties of the structural plane decreases.The brittle characteristics of the rock during the failure process are enhanced.(3)When the strike difference angle(0°-20°)is small,the structural planes of the rock mass containing structural planes are easy to penetrate,resulting in overall shear failure of the "Z" shaped failure surface;As the difference angle of strike(40°-140°)increases,its failure characteristics gradually transition to shear failure dominated by one structural plane;Finally,as the difference angle of strike(160°-180°)gradually reverses,it shows local compression shear failure caused by the interconnection of two structural planes.When the inclination angle of the structural plane is small(15°-30°),the rock mass undergoes relative displacement due to the compression closure of the structural plane;As the inclination angle of the structural plane increases(45°-60°),the closure phenomenon of the structural plane decreases,and the main failure surface develops from weaker structural planes,and the shear failure characteristics of the rock mass are enhanced;As the structural plane is relatively vertical(75°-90°),the lateral expansion phenomenon of the rock intensifies,and the characteristics of tensile failure become prominent.From the energy evolution of rock specimens,brittle failure is prone to occur when the strike difference angle is small(0°-20°)and reverse tilt(180°);As the inclination angle of the structural plane increases,the energy storage capacity of the rock increases significantly,and the deterioration of the rock strength and mechanical properties of the structural plane decreases.The brittle characteristics of the rock during the failure process are enhanced.(4)The sandstone containing structural planes after wet and dry cycles exhibits more tensile failure characteristics in the failure mode,slightly reducing the control of the structural planes over the failure mode.The development direction of the rock fracture surface deviates slightly along the direction of the rock fracture angle.The dry wet cycle effect reduces the brittleness and enhances the ductility of rock masses with smaller dip angles of structural planes,and the failure characteristics of rock masses with more vertical structural planes are characterized by increased tensile failure and increased fragmentation.In practical engineering,for rock masses containing structural planes with small differences in strike angles,more attention should be paid to preventing their overall sliding;For rock masses with structural planes with large differences in strike angles,it is necessary to prevent local instability and coherent failure.