| Cemented material dam(CMD),including cemented soil dam(CSD),cemented sand,gravel,and rock dam(CSGR),and cemented rockfill dam(CRD),is a new damming concept originally proposed by scholars of China Institute of Water Resources and Hydropower Research in 2009,which emphasizes the new concept of optimizing dam structure to make better use of local materials,or optimizing damming materials according to dam structure,and aims to construct a new type of dam having the advantages of both embankment dam and concrete dam.Additionally,it exhibits the advantages of low cost,high security,environment friendliness,and high tolerance of overtopping flood.Substantial progress has been demonstrated and this damming concept has been used in cofferdam construction and part of the permanent projects in China.Currently,key technologies that restrict the development of CSGR dams primarily emphasize the following aspects:(1)technology of efficient construction,equipment and whole-process quality control system,(2)safety assessment of the whole life cycle and the dam construction technology system,and(3)proportion technology with wider ranges of materials and macroscopic and microscomic material properties.Cemented sand,gravel,and rock(CSGR)is a type of CMD.Innovative research has been carried out focusing on the whole life cycle safety assessment of CSGR and quality control of the entire process.Simulation of CSGR dam for the entire construction and operation period and transient seepage field analysis were carried out in this study.Subsequently,evaluation of shear resistance of CSGR dam using probabilistic theory was made based on stress and seepage calculation results.Related achievements have been published in authorized periodicals both locally and abroad.The primary contents and innovations are listed as follows:(1)Quality control of the whole construction process of CSGR damBased on the constraint conditions of every construction process in the Technical Guidelines for CMD(SL 678-2014),the objective function sets of the whole process quality control system are established and the logical diagram and connection diagram of the software and hardware systems are determined.Therefore,the seamless monitoring of the local material testing of CSGR,mixing process,rolling process,and testing of finished products can be realized.The vibration threshold problem of different roller machines is solved mathematically.A rolling quality monitoring system is developed that can realize the real-time monitoring of rolling passes,rolling speeds,rolling times,interval time between adjacent layers,and the finishing elevation of the storehouse.The large construction data of CSGR were deeply excavated to obtain the distribution law of the roller compaction vehicle speed,the fitting relationship between compaction degrees and pass numbers,etc.(2)Whole process simulation of CSGR damBased on the theory of elastic incremental finite element method,the entire process simulation of the Shoukoubao CSGR dam is carried out for the first time.This considers the actual construction schedule and changing of boundary conditions such as air temperature of dam site,water temperature of reservoir,and variation in material properties such as elasticity modulus,degree of creep,self-volumetric deformation,and adiabatic temperature increase.The simulation results prove that the CSGR dam is a structure with low heat generation,uniform deformation,and high safety reliability.According to the displacement distribution of a typical section,the displacement curve is changed gradually at the interface of the upstream(or downstream)slab and CSGR damming zone,without any uncoordinated deformation.Because of the large differences in strength and elastic modulus between an impervious slab and CSGR,considering the unfavorable factors of construction,a transition zone such as a rich CSGR layer or a concrete extrusion wall is suggested to set between them to harmonize the deformation and prevent cracking.(3)Transient seepage field analysis of CSGR damThe seepage theory of unsaturated soil is adopted to describe the porosity of CSGR material,which can reflect the change in permeability coefficient with water content.The transient seepage simulation analysis of the Shoukoubao CSGR dam under a long-time seepage pressure is performed for the first time in this study.According to the calculations,the seepage field of the CSGR dam changes continually with time until a steady seepage state is reached.The saturation line is relatively low in a considerably long time,even though the impervious layer is not used;therefore,the rationality for dam structure design is validated.The calculation results indicate that the seepage free-surface of the CSGR dam is located near the upstream impervious layer and the concrete cushion;therefore,to control the elevation of the seepage line effectively to maintain the CSGR zone in a dry state,a drainage system is suggested to set behind the impervious layer.Furthermore,the drainage of the cushion should be improved such that unfavorable seepage water can be discharged from the drainage system and from the concrete cushion.(4)Shear reliability analysis of CSGRIn view of the low shear strength and high dispersion of CSGR,a strength failure method is proposed to calculate the shear reliability of CSGR.Limit-state equations in terms of uniaxial tensile strength and compressive strength are established based on the Mohr-Coulomb theory and Yu Maohong's double-shear theory.They can be solved by the first-order second-moment method to obtain the reliability index of every point.The results indicate that the CSGR dam exhibits high shear-resistant reliability;the reliability index using the double shear method is lower than that of the Mohr-Coulomb method.Therefore,it is more conservative.Strength reduction analysis indicates that the sections investigated exhibits high safety reserve.Failure zones with reliability indexes lower than the value specified by the standards of China are much small and are primarily located in the lower part of the dam dispersedly,without forming a coherent area,which can be replaced or reinforced to improve the reliability.Shear-resistant reliability analysis of CSGR layers was carried out using three different methods and demonstrated that the CSGR layers possessed high safety and reliability. |
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