Study On Stability Of Soil-Rock Mixed Slope Along Qinba Mountain Area

The soil-rock slope is between the soil slope and the rocky slope,the structure is mostly loose,the pore ratio is large,the water permeability is strong,the slope stability is weak.Compared with the soil slope and the rocky slope,the current research on the soil-rock slope is not deep enough.The instability of the soil-rock slope in Qinling-Daba Mountains of Shaanxi has many characteristics,such as larger quantities,large frequency and heavy disaster,which seriously influence the safe use of infrastructure.In this paper,on the basis of the investigation of the geological environment conditions of the highway slope,the mechanical performance test of the soil-rock slope is conducted,and the stability of the slope is systematically studied by the traditional limit equilibrium method and the numerical simulation method.By introducing the concept of block stone threshold and the index of stone content,the soil-rock is redefined,and the slope is divided into three categories: soil slope,rocky slope and soil-rock slope.The similarity gradation theory is set up to establish the relation between the engineering field and the laboratory test.The logarithm of the maximum dry density of the soil-rock mixture and the similar gradation ratio is linearly decreasing,and the increasing relation of the two times of the gentle dip parabola is found with the stone content.The shear strength of soil-rock mixture increases with the increase of normal stress and stone content,and the shear displacement increases with the increase of stone content.When the stone content is less than 40%,the internal friction angle,cohesive force and stone content linearly increase or decrease respectively.When the stone content is more than 40%,the internal friction angle and cohesive force increase or decrease with the stone content.Under the low shear stress level,only the instantaneous elastic strain and the initial attenuating creep are found in the soil-rock mixture,and the slow steady creep will occur at the middle shear stress level,but the accelerated creep will not occur,and the accelerated creep failure will occur at the high shear stress level.Two polynomial relations of friction angle,cohesive force and stone content,water content and maximum dry density are established.The fitting of the shear strength parameters is preferable to that of the test shear strength parameters.The sine-cosine displacement wave is set up to establish the three-dimensional limit equilibrium equation under the action of pseudo dynamic action.The active lateral direction of the shear force at the bottom of the soil strip is considered,the size and the direction of action of the force are presumed.The relationship between the three-dimensional slope stability safety factor and time,the ratio of slope width to height,internal friction angle,cohesive force,peak acceleration amplification factor,seismic horizontal direction and vertical acceleration coefficient is analyzed and studied.An automatic search technique and a single variable alternation transformation gradient descent method are used to optimize the global and regional conditions for the calculation of the sliding surface,and create a sliding surface with arbitrary shape and the minimum safety factor.According to the shear creep test curve,a new creep constitutive model with elastic modulus,viscoelastic body,improved viscoelastic body and viscoplastic body is put in place in the series.The difference scheme of three dimensional creep constitutive models is derived,and the constitutive model FLAC3 D program module is compiled and the crawl parameters are fitted.The static stability safety factors of two typical soil-rock slopes are more than 1,but after long-term stability analysis,the creep damage will occur on the two slopes,and Slope 1 will slide along the base covered surface,and Slope 2 is the local sliding of the shallow surface soil-rock mixture,and the displacement of each point on the slope shows a rapid increase,then gradually relatively stable and then accelerated.Field displacement monitoring is in accordance with the numerical simulation results.Slope 1 remains relatively stable about 60 days.At this time,it is a favorable time for the protection and reinforcement construction,and the engineering protection measures in the slope class-2 platforms add two rows of anti slide piles to avoid the slope creep instability.The study shows that,by establishing the relationship between on-site and indoor maximum dry density of the soil-rock mixture,the relationship between the shear strength and the stone content,water content and the maximum dry density can quickly solve the shear strength,and the practical popularization is strong.When the pseudo dynamic three-dimensional limit equilibrium method is adopted,the lateral action of the shear force at the bottom of the soil strip has little influence on the stability safety factor of the slope,and it can be taken into consideration.The impact of time,width to height ratio,internal friction angle,cohesive force,peak acceleration magnification coefficient,horizontal direction and vertical acceleration coefficient is uniform,and the critical sliding surface of the slope can be used to search the safety factor to effectively solve local convergence problem.According to the creep shear test,the creep constitutive model is developed and the numerical simulation of the soil and rock slope can be performed.The stress and strain state inside the slope can be obtained accurately,and its long-term stability and failure mode can be judged.