An Elastoplastic Constitutive Model Considering The Influence Of Temperature For Clayey Soil On K₀ Coefficient

Temperature variation is one of the important factors affecting the geotechnical properties of soil,the research on the effect of temperature on the stress-strain characteristics of soil has become an important topic in the field of geotechnical engineering in recent years.K₀ coefficient is one of the most commonly used parameters in engineering,Investigating its influencing factors and change law is vital for determining the stress states of foundation.However,there are few researches on the influence of temperature on K₀ coefficient at present.This paper investigates the influence of temperature on K₀ coefficient of saturated clayey soil through experimental and theoretical methods.Temperature-controlled confined compression tests were conducted on standard sand-bentonite mixtures to obtain the change law of K₀coefficient with temperature.A quantitative relationship between the K₀ coefficient and the inclination of the elastoplastic yield surface was derived,which was then combined with the results of the temperature-controlled confined compression test results.Thus,the variation of the inclination of yield surface with temperature was obtained.By introducing the relationship between the inclination of yield surface and temperature into the theoretical framework of the Unified Hardening constitutive model,a new elastoplastic constitutive model for saturated clayey soils considering the temperature effect on the K₀ coefficient was established.The model is then verified by predicting various types of temperature-controlled mechanical tests.The details of the research are as follows:（1）Experimental investigation on the influence law of K0 coefficient with temperature:Firstly,constant temperature and variable load confined compression tests were conducted for saturated standard sand-bentonite mixed samples with different sand mixing ratios（70%,85%）at different temperatures（5℃,25℃,55℃）,then the confined compression curves and K₀ coefficient-stress relationship curves at different temperature was obtained respectively.It was found that when the samples was in overconsolidated state,the effect of temperature on the confined compression curve and K₀ coefficient was not significant.When the samples was in normal consolidation state,the sample underwent volume contraction deformation as the temperature increased,causing the confined compression curve shifted downward and K₀ coefficient decreased.Secondly,constant load and variable temperature confined compression tests at different stress levels were then conducted to obtain the change law ofΔK₀ with temperature at each stress level.It was found that K₀ coefficient of soil increaseas rapidly as temperature increased,which was caused by the pores in soil decreased,the relative motion between the soil particles decreased,and the internal structure of the soil gradually became denser.After reaching a peak value and then the K₀ coefficient gradually decrease as the temperature did not change significantly,which was caused by the underwent volume contraction,the pore reduction,the strength increase of normal consolidation.The cooling process followed opposite law to heating process.（2）Theoretical investigation on change law of the inclination of yield surface with temperature:The variation of K₀ coefficient can be reflected by the inclination of yield surface in constitutive model.Based on the inclined ellipse yield function,a mathematical relationship between K₀ coefficient and the inclination of yield surface was derived.According to the experimental results of K₀ coefficient at different temperatures,a relationship formula between the inclination of yield surface with temperature was established.The formula can reflect the influence of temperature and overconsolidation ratio on the inclination of yield surface simultaneously.That is,under normal consolidation or slight overconsolidation state,the inclination of yield surface increases with temperature increased,and decreases with temperature increased under heavy overconsolidation state.（3）Modeling investigation on elastoplastic constitutive model considering the temperature effect on the K0 coefficient:Based on the non-isothermal UH model,the relationship formula between the inclination of yield surface with temperature yield surface was introduced,a novel elastoplastic constitutive model considering the temperature effect on the K₀ coefficient of clayey soil is established.The proposed model is used to predict temperature-contralled confined compression test,isotropic temperature change test,and temperature-controlled triaxial tests under both drained and undrained conditions.The results showed that the proposed model can reasonably reflect the mechanical behavior of clayey soils under coupled stress and temperature effects,with a good agreement between the calculated data and measured data.Especially for the triaxial undrained stress path,the model can clearly show the applicability of undrained stress path prediction when inclination occurs on yield surface.The above research results are of great significance for understanding the effect of temperature on mechanical behavior of calyey soil and improving geotechnical engineering design.