Study On The Stability Of Road Slope With Red Bedded Rock Mass And Its Reinforcement Technique

In recent years, the rapid development have made in the high standard road in central and west province of China, whose roads more or less pass the red bedded rock mass area. Due to the special geological mechanical characteristic, with low strength, weak wind weather resistance capacity, easy soften and collapsed water. The slope with red bedded rock mass has bad self-stable capacity, which makes the high cutting slope in red bedded area easy to slip, collapse, weathering et al during and after construction, whose slope stability has already become a hot subject in engineering field. So it is important to study the characteristic of red bedded rock mass, stability characteristic of red bedded slope and its reinforcement technique.The project named "The geological monitoring and its predicting system for the road foundation slope in mountain area" from National "863 Plan" is taken as the engineering background, the studies are done by five methods:insitu-investigation, laboratory test, analytical analysis, numerical simulation and insitu-monitoring. The main contents and result are as following,(1) According to the laboratory test, the strength characteristic of mudded intercalation with different water content is studied, showing that the water content has great effect to the shear strength of mudded intercalation of red bedded rock mass. If the water content is larger than the critical water content, the internal friction angle decreases with the increase of water content. The interaction of water and rock mass leads to the strength decrease of mudded intercalation.(2) The three dimensional model for rock sample with structure plane is founded by the numerical analysis software FLAC3D. The surface of structure plane, boundary condition and reinforcement with pile are changed during calculation, to study the variation of strength and deformation characteristic of structure plane. The effect of the undulating angle to the internal friction angle and cohesion of structure plane are analyzed, showing that, when the undulating angle of joint plane is small, the effect of the undulating angle to cohesion is in larger magnitude than that of undulating angle to friction angle; with the increase of undulating angle, the failure mode of joint changes from slipping along joint plane to the compound failure model consists of slipping along joint plane and crushing through saw tooth.(3) The compound effect of structure plane and pile element shows that, after being reinforced by pile, the shear strength and cohesion of structure plane are highly increased. The relationship curve of shear stress and shear displacement for structure plane with and without bolt reinforcement shows the obvious characteristic of elastic before it reaches its peak value; but after it reaches its peak value, the curve for the structure plane without bolt reinforcement shows the characteristic of strain softening, while the curve for the structure plane with bolt reinforcement shows the characteristic of strain hardening.(4) Numerical simulations for bedded rock mass under compressive load are done to study the strength and deformation of bedded rock mass with load of axial compression, normal triaxial compression, and real triaxial compression. The deformation characteristic, stress-strain relationship, and effect of inclination of structure plane to the strength of the bedded rock mass under axial compression are obtained. The normal triaxial compression simulations are done to study the effect of surrounding stress to the strength, surrounding stress to the stress-deformation characteristic, surrounding stress to the shear strength parameters, as well as the inclination of structure plane to the failure modes of rock mass. The real triaxial compression simulations are done to study the relationship between compressive strengths and media principle stress for different minor principle stress.(5) The fitting description model is founded for the corresponding strength characteristic, showing that, the compressive strength of the rock mass can be described by the special model. The compressive strength of rock mass increases with increase of loading velocity, whose behavior is in the linear form. In the simulation tests, it is recommended to choose corresponding velocity according to the real situation.(6) The anisotropic characteristics of stratified rock mass are described by ubiquitous-joint model; the calculation method of safety factor based on ubiquitous-joint model is proposed; then the relationships between stratification dip angle a, inclination and slope stability are analyzed by FLAC3D. According to the value of a, the stratified rock slope can be divided into two types:a≤45°for strict bedding rock slope; 45°<α<90°for oblique stratified slope.One slope in reservoir area is chosen as the background engineering. The dynamic response of pore water pressure in the slope by the fluctuation of water level is studied when considering the infiltration characteristic and fluctuation velocity of water level, the analysis results show that, when the water level fluctuates, the saturated permeability coefficient has great impact on the initial water level under the same infiltration condition; with the increasing of the saturated permeability coefficient, the water level becomes lower with more smooth shape, which has smaller impact on the dynamic and static pore water pressure, and good to the stability of slope; with the increasing of fluctuation velocity of water level, the response of water level lag behind, while the shape of water level becomes steeper, which cause greater dynamic pore water pressure to the slope, and worse to the stability of slope.(7) The reinforcement effect of the pile in red bedded slope is studied by the numerical analysis software FLAC3D. The effects of the pile location, pile length to the deformation and stress of slope are analyzed. The analysis results show that, the location of pile has great influence to the horizontal displacement of slope. If the pile is driven at the mid-bottom place of slope surface, the effect of controlling deformation of rock mass is the best. With increase of the length of pile, the maximum displacement of slope is decreased gradually. There exists a limit pile length Lcr, if pile length is larger than Lcr, the effect of pile length to deformation control will reduce.Numerical calculation model is founded for stratified rock slope by FLAC3D, the stress and deformation response of the rock mass before and after grouting reinforcement have been analyzed. The analysis results show that, after grouting, the displacement and stress contour are more smooth, and there does not exist the stress and displacement mutation, which is good for the slope stability. But due to the limitation area of grouting, the whole displacement of the slope is still very large. After grouting, the tensile and shear plastic zones of the slope are reduced greatly, showing that, grouting can improve the mechanical characteristic of the rock mass, and it capacity to resist the tensile and shear stress.(8) According to the insitu-investigation to the red bedded slope, the failure of the slope has occured many times, showing that the shear strength of the rock mass has surpass its peak strength. The present deformation is the slip deformation due to the shear stress larger than the residual shear strength. The slope stability analysis is done to the unstable slope, the reinforcement of pile to the bedded slope is proposed. The insitu monitoring analysis shows that, each monitoring point is stable after pile reinforcement, there does not happen large displacement on the ground surface, the slope is in stable state.Meanwhile, the disciplines from the present paper are compared with the results of others'test, which validates the correctness of the results from the present paper. The numerical simulation techniques can partly replace laboratory tests, and give guidance for the slope estimation and reinforcement. The results from the slope with pile reinforcement are applied in the Changji highway slope reinforcement, the optimum designs are done to revise the initial design scheme, which reduce the construction cost, construction time, lead to great economical and social effect.