Research On Deformation, Failure Mechanism And Stability Of Slope Stabilized With Soil-Cement Columns

During the exploitation and construction of channel, it is inevitable to produce large amount of manual excavated high slope. The slope soil texture was mostly found in weak and unstable stratum, like silt clay, clay, filling soil. The slope is not stable enough. Therefore, it is very necessary to carry out treatment on the slope. Since the slope is large in height, long in extension line and extensive in range, there exist the problems of long construction periods and high construction costs when use the traditional reinforced concrete anti-slide pile program. Currently, using the deep mixing method or high-pressure jet grouting to form the soil-cement column to strengthen the soft soil foundation has been widely used in the engineering construction. However, there are no unified standards for the stability analysis to follow when the soil-cement column is used to strengthen pit, slope and embankment. There lack of relevant research materials in deformation and failure characteristic, anti-slide mechanism, reasonable column structure and computational theory design and so on. The theory researches lag far behind the engineering practice.Based on the above mentioned information, laboratory test, model test, numerical simulation and theoretical analysis have been conducted in this paper to make systematic research on the anti-slide characteristic, working mechanism and computational theory when using the soil-cement column to strengthen the slope on the basis of relevant researches from home and abroad. The major research works and results are as follows:(1) In the laboratory, tests containing 178 samples have been completed, including uniaxial compression, radial split and triaxial compression. The strength feature, and deformation and failure characteristic of soil-cement column have been analyzed. The soil-cement dilatancy angle model equation has established according to the influencing factors on the dilatancy process of soil-cement. Meanwhile, in accordance with the purpose of this research, a constitutive model and strength criterion are choosed for modelling the mechanical property of soil-cement.(2) This paper has made a detailed introduction to the application of limit equilibrium method and finite element strength reduction to the principle, methods of slope stability analysis and their feasibilities. This paper conducted analyses on the equivalence of D-P strength criterion and M-C strength criterion and discussed the relevant parameters. Results revealed that the effective range of D-P Criterion Parameter a is 0≤a≤(?)/6. And the computational precision of D-P Criterion on slope stability has been analyzed and the yield criterion range adopted by the strength reduction method has been extended.(3) In this paper, combining the strength reduction technique, Abaqus was applied to make a numerical simulation analysis on the deformation and failure characteristic and anti-slide mechanism of slope strengthened by the soil-cement column. Results indicated that by using the isolated soil-cement column to strengthen the slope, the soil-cement column with larger stiffness and strength would deflect into S-shape, which could lead to the bending failure of soil-cement column when the slope lost its stability. In the traditional limit equilibrium method, only shear failure is occurred in the column, the calculated results would over estimate the stability of strengthening slope. Through the numerical simulation, it is found that the sliding force was adjusted between the shear wall and slide mass due to the effect of interface friction when the soil-cement shear wall was used to stabilize the slope. And then, the general shear failure would occur in the stabilized slope, which means that the shear wall has effectively mobilized its slide-resistant capacity.(4) Use the geometric affinity constant of 20:1 to build soil-cement column composite foundation lateral shear model test. Test results showed that deformation and failure characteristic, anti-slide mechanism of isolated soil-cement column and soil-cement shear wall are similar to that of the numerical simulation. The regularity obtained from the model test has proved the reasonability of numerical simulation results.(5) This paper, based on the numerical simulation and model test research, has put forward a few simplified methods to analyze the overall stability of the isolated soil-cement strengthening slope. Through the analysis on 8 examples, it is proved that the equivalent shear strength method has high precision, which should be given priority to adopt in design. Further, combine Support Vector Machine(SVM), Particle Swarm Optimization(PSO) with Strength Reduction Method(SRM) to establish SRM-SVM-PSO design optimization technique for soil-cement shear wall strengthening slope and use Matlab to write relevant programs. The analysis on computational example showed that, through optimizing the design variable of shear wall, the safety and economy of strengthening slope are satisfied.(6) Take the third line & four line shiplock channel slope strengthening engineering of Changzhou hydraulic project as an example, this paper further illustrated the deformation and failure characteristic and reasonable structure of channel soft soil slope strengthened by the high-pressure grouting column. Saturated-unsaturated soil seepage consolidation theory has been adopted and the effect channel water level changes on saturated-unsaturated seepage field and stability of the slope reinforcement has been analyzed. According to the analysis result, this paper provides relevant suggestion on the design and construction of using high-pressure grouting pile to strengthen the approach channel slope.