| With the development of society and rapid growth of national economy,China's urbanization process has become more and more fast,a lot of skyscrapers and the underground traffic system and underground shopping mall and some very large construction projects have sprung up along with urbanization.Especially in the rapid economic development of the eastern coastal area,the region with a wide range of soft clay stratum,restricted by geographical conditions have to large buildings construction on the basis of this kind of soft soil.Since the natural soft soil has unique structure(high moisture content,large porosity and large compression deformation),so it lead to the drainage consolidation of foundation settlement is slow,poor stability and engineering problems,soft clay under the load show the sudden destruction often can do great harm to the engineering at the same time.How to characterize the structural physical and mechanical properties of soft soil,and on this basis to effective calculation and forecast of soft soil engineering construction and post-construction settlement is still the construction problems.The established can reflect the structural characteristics of structural soft soil and time dependency based on the up and down the load of the elastic-viscoplasticity constitutive model is considered to be an effective way to solve this problem.Based on this,the main works are as follows:Seize the two characteristics of macro-pore and cementation,used silty clay,kaolin,cement and salt to make structural soil indoor.The samples were modeled by one-dimensional consolidation and SEM test.The results showed that the samples had certain structural characteristics and the corresponding compression index,rebound index and structural yield stress were obtained,it provide the foundation to establish the elasto-viscoplasticity constitutive model.To change ratio of raw materials,different porosity and cementation of artificial structural soil specimen was obtained by controlling the content of salt and cement ratio.Compaction undisturbed triaxial shear compression test with loading rate of 0.07 mm/min under three confining pressures(50 kPa,100 kPa and 200 kPa).The effects of structural characteristics(pore ratio and cementation)on the strength deformation,pore water pressure and stress path of structural soils were investigated,and the corresponding shear strength indexes were obtained.Three different loading rates(0.007mm/min,0.07mm/min and 1mm/min)of consolidation undrained triaxial shear compression test were used for the structural soil samples with three different structural characteristics in different pressure(50kPa,100 kPa and200kPa),the effect of structural characteristics on the strain rate effect was explored.In the new model,the Asaoka's superloading and Hashiguchi's subloading yield surface is used as a reference yield surface at a specified strain rate.A relative overstress relation is used and two material parameters0 c and m? about the rate sensitivity are added into the new model,which can be determined by triaxial compression tests with different strain rates.An elasto-viscoplasticity constitutive model which can consider the stress-strain characteristics and rate sensitivity of structural soils was established.The verification of shear creep test of structural soils shows that the proposed model can characterize the structural characteristics,strain softening and rate sensitivity of structural soils,which lays the foundation for the numerical calculation of soft soil engineering.Based on the modified Cambridge model and the structural elasto-viscoplasticity constitutive model,the coastal road embankment project in Japan Huga City was numerically analysised with the aid of ABAQUS.Combined with the results of field observation,the long-term settlement of embankment is predict more effectively by the structural elasto-viscoplasticity constitutive model,which provides guidance for post-construction settlement control and verifies the correctness of constitutive model. |
PDF Full Text Request