| The construction method of "upstream sediment heightening fill" is generally adopted in reservoir reinforcement engineering of loess hilly region in southern Ningxia and its surrounding provinces.There have few complete theoretical analysis and summary data of the technical feasibility analysis as well as construction techniques of "upstream sediment heightening fill" for a long time in the project.At present,the design and construction of "upstream sediment heightening fill" project mostly depend on engineering experience.Although it basically meets the needs of the project,some problems and deficiencies are still exposed in the long-term application.In view of the large strain consolidation problems from "upstream sediment heightening fill",this thesis studies the consolidation calculation method of upstream sediment heightening fill under the loading method of layered roller compaction by referring to the idea of piecewise linear finite difference method.Take the eliminating danger and reinforcing engineering of Yashigou reservoir as the research object,where located at Guyuan city Pengyang county of Ningxia,a piecewise linear model for large strain consolidation(CS2)was introduced and the one-dimensional large strain consolidation model of silt in front of dam with piecewise linear difference was established combining with the stack preloading measure in practice.The graded loading process was simulated during the earth dam constructions and difference between large strain consolidation and small strain consolidation in the one-dimensional consolidation process of upstream sediment heightening fill was explored.On this basis,the piecewise linear drainage plate-surcharge preloading coupling consolidation model was established,and by using the radial consolidation model,the degree of consolidation,the dissipation of excess pore water pressure and the change of pore ratio of the silt soil were simulated and calculated under the loading condition after the plastic drainage plate inserting into the silt soil in front of the dam.The main research contents and conclusions are as follows:(1)Consolidation and Permeability instruments were used to carry out experiments on consolidation and permeability characteristics of upstream sediment heightening fill at different depths under progressive loading conditions.The results show that:?Under the same load,with the increase of depth,the strain of silt soil sample decreases gradually;?The void ratio of silt soil at different depths gradually decreases with the increase of load.The e-lgp curves all show a linear state,and there is an obvious logarithmic relationship between the void ratio and consolidation pressure;?The silt soil at different depth of the permeability coefficient are decreased with the increase of consolidation pressure,the decrease is slowly in later stage,presents the obvious nonlinear,and the void ratio is closely related to the permeability coefficient,the permeability coefficient decreases with the decrease of the void ratio,the relationship between permeability coefficient and consolidation pressure?void ratio and permeability coefficient can be well expressed by single exponential decay equation.(2)The piecewise linear difference one-dimensional large strain consolidation model of upstream sediment heightening fill is established,and write Fortran calculation program.The calculation analysis shows that:?In initial stage of consolidation,there is a small difference between the degree of consolidation of large strain and small strain based on the settlement strain of upstream sediment heightening fill.With the increase of time,the degree of consolidation of large strain develops slowly;?At the same time and same depth the calculated value of excess pore water pressure large strain is greater than small strain.Under the condition of certain geotechnical parameters of silt soil,when the strain of silt soil is large,the excess pore water pressure obtained by consolidation of small strain has obvious dissipation;?After the completion of the fourth grade dam adding,the value of the excess pore water pressure reaches the maximum,and the effective stress of the soil is the minimum at this time.(3)The piecewise linear drainage plate-surcharge preloading coupled consolidation model was established and write Fortran calculation program.The conclusions as follows:?The consolidation rate of silt was significantly accelerated when vertical drainage board was added to the calculation model.Compared with the calculated degree of silt consolidation when vertical drainage board was not added,the same degree of consolidation was achieved 43 days in advance;?Due to the arrangement of vertical drainage board,the overpressure of static hole in silt gradually dissipates with the increase of time.The construction period of 163 days can be saved when the plastic drainage plate is arranged in the sludge soil and the plastic drainage plate is not arranged. |
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