Study And Application On The Treatment Of Heat Drainage Consolidation Method For Shaft Foundation

In recent years,the construction of large-scale infrastructure such as roads,railways,airports and subways has brought new challenges to the soft soil foundation treatment of the coastal cities in the southeast.The heat drainage consolidation method is a new and promising method for soft foundation treatment.It has the some advantages such as simple construction,economic and so on.At present,there are a lot of research results about the influence of temperature effect on soil.But the mechanism of action is complex when the temperature is taken as a means of foundation treatment to shorten the duration of the three issues related to Thermal-Hydro-Mechanical coupling.Therefore,it studies the consolidation of shaft foundation under the influence of temperature from the three aspects of theory,model test and numerical simulation in this paper.(1)Thermo-elastic nonlinear consolidation equation of fully coupled porous media is deduced by considering the effect of heat infiltration and based on the classical consolidation theory and heat transfer theory.The problem of consolidation of point heat source is reduced by Fourier transform,Laplace transform and its inverse transformation.The expression of temperature and pore pressure is given.On this basis,the problem of heat consolidation of finite length cylindrical heat source is solved,which provides a theoretical basis for the experiment.(2)The influence of temperature on the permeability coefficient is studied based on the existing theory of shaft consolidation,and the consolidation solution of single-side drainage of shaft foundation under the influence of temperature effect is given.And there is an example of the analysis aiming at the numerical parameters of Ningbo soft clay.The results show that the temperature has a significant effect on the consolidation behavior of the shaft foundation.At the same time,the temperature is higher,the consolidation degree of the foundation is greater.But The effect of temperature on soil consolidation will decrease with the increase of temperature.Under the same temperature condition,the smaller the ratio of borehole is,the faster soil consolidation will be.(3)The variation law of temperature,super-pore water pressure and soil subsidence in the shaft foundation is discussed by the large-scale model text of the mud and silty clay in Ningbo which is on normal temperature and heat drainageconsolidation.The results show that the temperature outside the shaft is gradually increased and spread to the distance,and then gradually stabilized with the increase of time.the excess pore water pressure is generated due to the difference of the thermal expansion coefficient between soil particles and pore water with the increase of temperature.and the greater the pore pressure generated from the shaft.With the increase of temperature,the permeability coefficient of soil will be improved,and the progress of drainage consolidation is accelerated,and the pore pressure dissipation rate of the heat drainage consolidation test will be improved compared with that of the consolidation test.The time of the heat drainage consolidation test is less 39.87%than the time of the consolidation degree reaching 90% in the case of water cycle temperature of 50 ?.The change of the initial consolidation pressure of the soil by changing temperature will change the settlement of the soil.The final settlement of the soil in heat drainage consolidation test is increased by 12.02% ? The heat drainage consolidation method can not only accelerate the consolidation process of the foundation obviously,but also increase the settlement of the foundation and ensure the foundation treatment effect.(4)Based on the large commercial finite element software Abaqus,the finite element model of the heat drainage consolidation is established by using the model as the prototype and modified Cambridge model as constitutive model.is verified by comparing with the model test results.And the reliable rows of the model are verified by comparing with the model test results.Finally,the influence of different heat drainage consolidation method on foundation treatment is calculated and analyzed under the actual working conditions of different cycle temperature and different shaft spacing.The results show that temperature change will affect the settlement of the soil.In a certain temperature range,the surface subsidence will gradually increase with the increase of heating temperature.The higher the temperature is,the faster the consolidation speed of the soil will be when the applied load is constant.But with the increase of the temperature,the consolidation effect of the same temperature difference will be weakened gradually.When the temperature load and the top load are constant,the consolidation degree of the soil will increase with the decrease of the drainage distance.And when the drainage spacing is small,the effect of lifting the drainage spacing is not significant.The test results are consistent with the theoretical results.When the heating temperature of the soil reaches 60 ? and the variation ofdrainage diameter ratio on consolidation curve is 8,the heat drainage consolidation method can achieve an ideal foundation treatment effect.