Mechanism Of Consolidation And Release Of Water In Weak Permeable Water Layer Of Viscous Soil

With the development of society and the advancement of science and technology,the demand for the development and utilization of groundwater in Tianjin has continuously increased,and the proportion of groundwater in the city's water supply has continuously increased.The resulting series of environmental geological problems related to groundwater mining has become a hot issue for human health,ecological environment,urban and rural construction planning and economic development.The purpose of this paper is to study the variation of permeability of saturated soft clay under different load conditions through laboratory tests,and to establish an empirical relationship that can describe the permeability and deformation characteristics of clay soil under load,through the analysis of experimental results and the seepage theory.Under the conditions of groundwater exploitation,whether the over-flow of upper-layer salty water will affect the water quality of the lower aquifer,determine the interrelationship between the cohesive soil aquitard water layer and the underground salt water flow in the coastal area,and the main conclusions are:(1)Cohesive soil compression is mainly divided into two stages:plastic deformation and viscous compression deformation(creep).Viscous compressive deformation has been carried out at all times.The amount of compression at this stage reaches 10%to 25%of the total deformation.(2)With the increase of depth,the compressive deformation of the clay soil gradually decreases,and the deeper the soil deformation becomes,the more stable it is.As the depth increases,the soil samples gradually become denser and their compressive deformation gradually decreases.The cohesive soil samples under the same stress,the strain is relatively stable,which also characterizes the characteristics of ground settlement caused by compaction of clay soil.(3)After a stable pressure is applied to the undisturbed soil,deformation occurs first,and water is released afterwards.The two are not synchronized and there is a certain time difference.The compressive deformation and water release of clay soils decrease with the increase of saturation.In the initial stage of deformation,no water release occurs.With the extension of the observation sequence,some unbound water is released.In the second stage of compression deformation,the pore water pressure gradually dissipates,the effective stress increases accordingly,the pores are instantaneously compressed,and the combined water is released.However,the release of bound water is very difficult,so the change of the later stage deformation is also small.In the stage of rapid deformation,unbound water is released,but the content is small;in the stage of viscous compression and deformation,the combined water is released.(4)The permeability coefficient has little effect on the osmotic pressure,and the difference in the measured permeability coefficients under different osmotic pressures is not significant.In the natural state,with the increase of burial depth in deep cohesive soils,natural loads increase,and the degree of consolidation increases accordingly.In the same period of time,the greater the degree of subsurface viscous consolidation,the lower the flow of water in the underground aquifer.(5)In the natural state,the degree of consolidation of the viscous weak permeable layer is too high,the soil particles of the cohesive soil are densely packed and squeezed,and the gravitational water and weakly bound water in the pores of a small part of the clay soil dissolve with the effluent.In the liquid,the bound water wrapped around the soil particles is difficult to be precipitated.When overflow occurs at this time,the concentration of precipitated ions is low.(6)Since the cations on the surface of the clay particles are hydrated cations,the water molecules adsorbed by the cations hinder the aggregation of cations.Similarly,water molecules adsorbed by anions in weakly bound water also hinder aggregation of anions.Experiments show that the cohesive soil in Tianjin Binhai region is mainly adsorbed by cations,and the retention effect of cohesive soils on the ions of two valences is greater than that of ions of one valence,so the retention effect is Ca2+>Mg2+>Na+>Cl-.