| With the rapid economic development in the central and western regions of our country,a lot of bedded rock slopes continue to emerge,resulting in projects such as road cuttings,municipal slopes and building foundation pits,which often suffer from instability and damage of layered slopes.The stability of rock slopes is mainly controlled by fissures,joints,weak interlayers and even karst caves.The abovementioned adverse geological factors are difficult to be fully and accurately understood in advance,which cause really complicated analysis of rock slope stability.Stratiform slopes tend to have a higher risk of slip instability.Although a lot of practical experience is accumulated in the design and construction of foundation pit engineering,the existing support design theories,standards and specifications are still lacking in pertinence,which reducing the value of rock foundation pit engineering.This dissertation mainly adopts theoretical analysis,numerical calculation and field measurement to study the deformation and failure law.It supports the design with the combination of structural planes and karst caves.First of all,the research proposes the description method of karst body structure plane and karst cave shape.The characteristics of the holes are described by Fourier signal processing,and the characteristic parameters of the holes are extracted.After approximate regular PFC numerical simulation,the distribution simulation characteristics of force breaking cave cracks and basic caves and cave structures are similar rule form complex cave structures and form cave models,we analyze the transformation method of cave models,and study the theory of rock slope deformation.Secondly,the numerical simulation study on the deformation and failure law of the slope rock is carried out which is under the development conditions of different combinations of karst caves and structural planes.According to the spatial positional relationship between karst caves and structural planes of different shapes and sizes,the influence law on the stability of rock slopes and the failure characteristics of the slopes are analyzed.Three failure modes and deformation failure mechanisms of rock slopes containing karst caves are summarized.At the same time,the influence law of some factors on sliping failure mode of rock foundation pit are mastered,which are location and shape of karst cave,occurrence of structural plane,etc.Furthermore,a reference table for replacing a cave group with a single cave is proposed,as well as the development law of the crack penetration path between cave groups,which provides a method for simplified analysis of cave groups.In addition,the theoretical calculation formula of the slope stability of the foundation pit and the prediction method of the rock mass sliding surface based on the upper bound limit analysis principle are proposed based on the sliding failure characteristics of the rock mass with the sloping structural plane containing the karst cave.The calculation of the residual sliding force of the rock and soil mass is deduced.The formula is suitable for three failure modes of the slope with karst cave,and can be applied to the calculation of rock and soil pressure under the condition of no karst cave.The influence rules of rock mass strength parameters,structural plane occurrence,karst cave location and other factors on safety factor and residual sliding force are obtained through theoretical analysis and comparison with numerical simulation results.A threedimensional local rock stability analysis method is proposed,that is,the calculation formula of the spatial polyhedron stability coefficient and residual sliding force under the influence of karst caves is considered,which provides a theory for the local sliding instability analysis of rock slopes containing karst caves.The above-mentioned plane and three-dimensional spatial stability theoretical analysis formulas can respectively conduct stability analysis for the potential long,large-scale slippage and local breaking slippage of rock slopes,and provide a theoretical basis for rock slope support design.Furthermore,it is difficult to comprehensively detect and accurately control the direction of the slope along the karst caves and structural plane slope.Therefore,the slope support has to be considered according to the plane strain problem,which easily leads to the problem that the support load is too large and the support is conservative.The concept of sub-section support control considering space effect and the corresponding basic form of support structure are proposed.The numerical analysis method is used to compare and study the difference of the control effects of different subsection support methods and traditional support methods on the deformation of the retaining piles,so as to grasp the structural stress and deformation law of different support schemes.Through the comparison of the calculation results of the displacement of the retaining pile and the force of the structure,the feasibility of the design method of sub-section support is confirmed.The concept of sectionalized support control and the corresponding support structure forms and support design methods provide an important reference for the support design of deep foundation pits and large rock slopes.Then,it is necessary to assume the "pile-rock" interaction mode and the shortage of the horizontal reaction force coefficient according to the elastic fulcrum method to carry out the mechanical analysis of the foundation pit retaining piles.Calculation of the force and deformation of the envelope structure.It can avoid artificial assumptions on the distribution of geotechnical pressure and the horizontal reaction force coefficient in the buried section of the pile body,so that the "pile-rock" interaction process during the construction of the foundation pit is not affected by artificial assumptions.Based on the measured data of the foundation pit project of Xuzhou Metro Sanhuan South Road,the inversion analysis of the geotechnical pressure was carried out.The simplified numerical model,the elastic fulcrum method model and the measured deformation analysis results were compared.The calculation results of the simplified numerical analysis method were confirmed.It can reflect the force and deformation law of the retaining piles in each stage of construction,and consider the influence of the rock stratum along the slope and the reverse side on the deformation of the retaining piles.The calculation result of the residual sliding force of the sliding body calculated by the upper bound limit method in this dissertation is used as the external force load parameter for the simplified numerical analysis.The last but not the least,the comprehensive application and inspection of the research results of this dissertation are carried out based on the rock slope survey data of the deep foundation pit transfer section.The karst cave simplification and modeling were carried out.Through the rock mass stability analysis,the simplified numerical analysis of the retaining piles,and the analysis of the support design by sections,the research results show that: the deformation law of the rock mass is similar to the measured deformation law;compared with the original slope support design scheme,the sectionalized support control method based on space effect can obtain better deformation control effect,and can significantly reduce the support maintenance costs.In this dissertation,there are 199 figures,75 tables and 246 references. |
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