| Landslide is the most widespread and serious geological hazard in slope destruction types, and the evolutionary process contains the beginnings, developing and dying from the entire cycle activity of the landslide, therefore, the study for the landslide evolutionary process plays a significant role in understanding the geological transformation function, the development trend forecasting and the control measures design with different times of the landslide. With the economy developing, a large number of the important fundamental constructions about the national economy and people’s livelihood may be seriously harmed and potentially threatened by landslide disasters. Hence, it is urgent to carry out the research of the landslide treatment method systematically and provide scientific basis for the engineering practice.The antislide pile conducted as the main control measures in landslide treatment with the advantages of the good antislide capacity, the widespread application conditions, not easily deteriorating the state of landslide, safety and convenient operation and the further verifying the geological conditions, has being widely used. However, the antislide pile design theories and methods are not mature, and the antislide pile bearing behavior, the pile-soil interaction mechanism, the load transfer mechanism and the slope failure mechanism are not clear and need to be deeply studied. Those disadvantages to a large extent affect the accuracy and the reliability of the design, and can’t meet the need of the growing engineering construction. Therefore, the study for the interaction mechanism of the antislide pile and the slip mass is one of the important application problems which need to be solved urgently in antislide pile engineering.On the basis of the establishment of the landslide geological analysis model, the illuminating of the landslide fundamental evolutionary characters, and the rock stratum structure characteristics of the hard and soft interbedded Jurassic strata in Three Gorges Reservoir Region, the study for pile-soil interaction mechanism based on the thrust load caused landslide-antislide pile system evolutionary process was analyzed in this paper, and the correlation method for the optimization design of antislide pile was extended from the results of the study and applied to the engineering cases. The main achievements are as follows:(1) Based on the mechanical model of the three-phase sliding pattern, the genetic mechanical mechanisms of the thrust load caused landslide and the retrogressive landslide were compared and the differences were discussed. The thrust load caused landslide fundamental formation conditions were analyzed in the aspects of landform conditions, formation lithology conditions, geotectonic conditions and the hydrogeology conditions. The development laws of the deformation failure process and crack complete system of the typical thrust load caused landslide—Xintan landslide in the Three Gorges Reservoir Region were summarized. The thrust load caused landslide generalized geological mechanical model was established from the aspects of landslide shape characteristics, the material composition, the structure composition and the dynamic factors. The driving force control method of simulating the progressive thrust load caused landslide evolutionary process and the displacement control method of the applicable mutational thrust load caused landslide were proposed. The formation lithology characteristics and the distribution laws of the Jurassic strata in Three Gorges Reservoir Region were summarized, the differences of the physical and mechanical properties of the soft and hard rock were compared and analyzed, and the generalization model of the hard and soft interbedded rock strata was proposed.(2) The evolutionary process of thrust load caused landslide was simulated by indoor physical model test method. The cloud data of the landslide model surface in different evolutionary phases were obtained by three-dimensional laser scanner, indicating the deformation evolutionary law of the thrust load caused landslide and the matched properties by stages of the crack system. Based on the displacement time history curve of the typical monitoring points from landslide surface and the generalized correlation dimension method, the multiple fractal dimension change rule in thrust load caused landslide evolutionary process was analyzed, and on this basis, the thrust load caused landslide evolutionary process was divided into the trailing edge compression stage, the uniform deformation stage and the accelerating deformation stage. The displacement multiple fractal dimension corresponding to the trailing edge compression stage has a tendency of dimensionality reduction, the multiple fractal dimension in the uniform deformation stage has a trend of decreasing first and then increasing, the multiple fractal dimension in the accelerating deformation stage has a tendency of increasing dimension. Based on the model tests, the thrust load caused landslide evolutionary process was reappeared by numerical simulation method. The results fit the model tests well, verifying the stages in thrust load caused landslide evolutionary process and indicating the nonlinear decline rule of stability coefficient in landslide evolutionary process.(3) The half-model method considering the landslide characteristics and the pile-soil interaction was proposed, which emphasizes the generation procedure of the slip mass before piles, and the reliability of the generation model was verified. The portable test device of the multi-loading frame type landslide geological mechanical model was invented, which can be used to simulate the landslide deformation failure characteristics in multi-loading conditions before or after the treatment and the interaction process of landslide and the antislide piles. A test equipment is developed to realize the automation of water level fluctuation simulation. In the same time, a multi-field monitoring system is provided to realize the monitoring of displacement, stress, temperature and so on. Considering the effect of disturbance signal on the monitoring data, a platform based on Lab VIEW program is established to realize the filter of monitoring data.(4) The interaction process between cantilever end of the antislide piles and the thrust load caused landslide was studied by the physical model test method.①The adding of the antislide piles changed the landslide evolutionary process, leading to the results that the proportion of the main deformation stage of the landslide in the whole evolutionary process became larger, the proportion of the initial stage became smaller, the increasing amount and the decreasing amount was the same, and the proportion of the failure deformation stage is about the same. In main deformation stage, antislide piles played a role in reinforcement. The driving force loads was absorbed by the deformation of the antislide piles and the slip mass, and absorbed by producing large range of slip mass deforming when there was no antislide piles. After changing into the failure deformation stage, the slip mass behind the piles reached the ultimate bearing capacity, became shear failure from the nearby of the pile top, was unable to absorb more driving force load through the antislide pile retaining wall, and the landslide without embedding the antislide piles became shear failure along the bulge deformation leading edge contour.②The displacement field from the slope surface and the soil arch effect in landslide evolutionary process were obtained by the3d laser scanning and the computer aided testing technology.③The evolutionary law of the stress soil arch was achieved by the soil stress testing data from the area behind or between the piles in different depth:with the increasing backside driving force of the landslide, the influencing range of the stress soil arch became large, and the landslide presented the changing trend of the increasing soil arch height in horizontal direction and the increasing soil arch depth in vertical direction. When the landslide changed from the initial deformation stage to the main deformation stage, the form of the stress soil arch space changed a lot. When the landslide changed from the main deformation stage to the failure deformation stage, the change of the stress soil arch was not obvious. When the slip mass reached the ultimate bearing capacity, the landslide model was damaged, the soil stress decreased quickly, and the stress soil arch disappeared.④In the process of thrust load caused landslide, the landslide trust point position coefficients behind the piles were changeable. The changing law of the landslide trust point position was in correspondence with the landslide evolutionary process. When the thrust load caused landslide-antislide piles system in initial deformation stage, the landslide trust increased slowly, the point position raised gradually, and the horizontal stress of the antislide piles in the same depth was close. When the thrust load caused landslide-antislide piles system in main deformation stage, the driving force point position behind the piles declined step by step, and the trust presented a linear growth trend. When the thrust load caused landslide-antislide piles system in failure deformation stage, the resultant force point behind the piles dropped slowly and tended to be constant, and the driving force had the tendency of increasing but the increasing rate was smaller than main deformation stage.(5) The interaction process between the fixed end of the antislide piles and the thrust load caused landslide was studied through the physical model test method.①On the condition that the displacement was the loading control term, the pile lateral soil stress and the fixed end bending moment increased first, then decreased gradually until constant. The response sensitivity of fixed end bending moment and the pile lateral stress to loading decreased with the increasing depth of the slip band.②The soil stress of the fixed end before the piles presented the inverted triangle distribution law. The soil stress of the fixed end behind the piles was small on the whole, and the soil stress near the pile footing was large. The distribution law of the cantilever end of the antislide piles was an approximation parabolic shape with the properties that large in the middle, and small in the ends. In the same loading condition, the changing range of the soil stress of the fixed end in different depth was related to the slide bed lithology, the maximum soil stress of hard rock composing the slide bed was larger than the soft rock, and the center of the bent deformation position for the fixed end was higher.③The bending moment of the fixed end on the whole met with the distribution law of decreasing with the depth from the sliding surface increasing, and the maximum bending moment of the fixed end was increasing with the increasing of the dip angle of the rock stratum on the condition of same lithology. On the condition of different lithology, the fixed end bending moment of the hard rock containing the slide bed closer to the sliding surface was larger than the soft rock.(6) The results from numerical simulation show that the distribution rules of landslide driving force at the back of the piles is related not only to the materials in sliding body, but also to the sliding stage, the geological structure, the shape of the landslide, the soil and rock mass characteristics, the strain and stress of the antislide structures and so on. The overall distribution of landslide driving force form meets the parabolic distribution. With the increase of shear strength parameters of sliding body, the landslide driving force would decrease as well as the gradually rising of acting point of force. The distribution of landslide driving force at the back of antislide piles is more easily effected by the friction angle rather than cohesive force in sliding body. The part of the antislide piles outside the sliding body forms a cantilever. At the top central segment of the cantilever, the horizontal stress is negatively related with the thickness of the sliding band and positively related to the angle of the slope. At the lower central segment, the horizontal stress is positively related with the thickness of the sliding band and negatively related to the angle of the slope. The landslide driving force is slightly effected by the length of the piles that in the soil. Meantime, the structure of the sliding bed rock mass has a great effect on the stress and deformation of the embedded antislide pile segment. In detail, when the sliding bed is formed with bedding rock, the angle of the bedding rock has a great effect on the stress and deformation of the antislide piles. But this affect turns to be small when the sliding bed in formed with inverse rock. In bedding rock, with the increase of bedding rock angle, the stress on the cantilever segment and bedded in soil segment of the antislide piles will increase as well. The displacement at the top of the piles increases as well as the enlargement of the deformation band of the antislide piles; when the layer is thick, the stress and deformation of the antislide piles is controlled by hard rock and the soft rock plays a support role. This condition will turn opposite when the layer is not that thick. With the increase of the thickness of the rock layer, the bedded in soil segment suffers an increasing trend in the absolute value of maximum shear strength and maximum bending moment while the displacement at the top and the deformation part of the antislide pile show a decrease trend; the smaller the ratio of similitude of the thickness of the rock layer is, the more the soft layer is through by the embedded in the soil part of the antislide piles in a unit length. When the ratio of the similitude of the rock layer thickness reached a certain value, the stress and deformation on the piles are controlled by the hard rock; the length of the redundancy of the embedded in soil piles will decrease with the increase of the angle of bedding rock whole the length will not change that much in inverse rock. The length will increase with the increase of the thickness ratio w and the increase of the similitude ratio of the rock layer thickness v. In the meantime, the effective soil bed depth will decrease with them. When w and v reach a certain value, the redundant length of the soil-bed depth is similar to that in the soft had rock sliding bed and the effective soil-bed depth tends to be constant.(7) Based on the method of elasticity mechanics, the stress analysis model of the sliding body at the back of the antislide piles is built and the stress distribution function can be obtained in different evolution stage, in different space position and in the condition with any number of piles. From this, the soil arching effect at the back of the antislide piles is studied under the condition that the piles is of different number, space and sectional dimension. Based on the function of the landslide driving force and the application point position of it, a solution is proposed to find the application point position of the landslide driving force based on physical model test. A more real moment value can be obtained with the position. Based on the limit equilibrium theory, a method that is more suitable for evaluating the stability of the composite layered rock slope of Jurassic in Three Gorges reservoir region and a technique road map is given based on the real steps. The method takes the geometrical characteristics of the rock layer, the strength parameter into consideration and is able to find the factor of safety and the most dangerous sliding surface location of the composite layered rock mass. A new method is put forward on reverse of the traditional "K" method.(8) Majiagou landslide in Zigui county in Three Gorges reservoir region is taken as the research object. Based on the engineering condition of the landslide, the stability and the factors that affect its stability is analyzed. The position region of the application point of landslide driving force can be confirmed with the results of the physical model test of the landslide. The sliding bed is divided into serveral layers according to the intersection relation of the antislide piles and the landslide bed rock with the parameters of thickness ratio, rock bed angle and so on. With the compare of rectangular distribution hypothesis and the normal design that not consider the sliding bed structure characteristics, it is considered that the optimum design method considered the application point of the landslide driving force and the rock layer of the sliding bed is more close to the real condition. For Majiagou landslide prevention and control engineering, it is more dangerous to use the normal design method than the optimum design method.The principle innovation points in this thesis are:(1) On the basis of the landslide’s formation mechanism of mechanics, the generalized geo-mechanical model is established. The evolutionary process of the thrust load caused landslide is simulated by the indoor physical model test, which discovers the evolution law of thrust load caused landslide’s deformation and the suiting characteristics of generated cracks in different evolution stages. Based on the changing law of multi-fractal dimension in the evolutionary process of thrust load caused landslide, the process is partitioned as the rear edge compressing stage, uniform speed deformation stage and accelerated deformation stage.(2) The interaction process between the antislide piles and the thrust load caused landslide is studied by doing the physical model test, and the impact on the evolutionary process from the piles is contrastively analyzed based on the multi-field test information. Through investigating the force and deformation of antislide piles in different evolution stages, the change law of the landslide driving force on the piles’ back surfaces is revealed, and the correspondence between the action point of the landslide driving force and different evolution stages is also analyzed. For the condition of different evolution stages, different spatial position and arbitrary pile quantity, the stress distribution function for the soil mass is theoretically derived in detail.(3) Combined with the hard and soft white characteristics for the Jurassic strata in the Three Gorges Reservoir Region, the stability evaluation method for the composite bedded rock slope is proposed. In the points of the stratum dip, the thickness ratio of soft and hard layers and the similitude ratio of stratum thickness, the impact on the force, deformation and the effective embedded depth of antislide piles from the structural characteristics of the slide bed is systematically studied. The proposed optimum design method, based on the action points of the landslide driving forces and the hard and soft white structural characteristics for the slide bed, provides a reference frame for the antislide pile design. |
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