| Based on the tunnel construction project of China’s energy channel “Mengx i-Huazhong” railway,this project encountered the construction of large area loes s tunnel in Shaanxi region,and collapsibility is the most important characteristic of loess.On the one hand,when underground water is encountered during the e xcavation and construction of loess tunnel,and when the slope at the tunnel ent rance is subjected to heavy rainfall,the loess with high strength will suffer fro m collapsible deformation,and its strength will be continuously reduced,which will seriously affect the construction safety of loess tunnel.On the other hand,t he project is located in northwest loess region,the temperature changes of they ear,the summer could be up to more than 50 ℃,the highest surface temperatu re and will drop to below freezing in winter,even in one day,the highest temp erature difference between day and night can also be around 20 ℃,the change of the temperature on the deformation characteristics of loess have a significanti mpact.Therefore,it has become an unavoidable problem for engineers and tech nicians to explore the humidifying deformation characteristics of sandy Q3 loess and consider the influence of temperature changes on its deformation characteris tics.At the same time,it is also the focus of the academic circles all over the world.In order to study this problem,this paper conducted a series of experim ental studies on the sandy Q3 loess taken from the site of Menghua railway.T he specific contents are as follows:(1)The humidifying deformation characteristics of sandy Q3 loess were inv estigated by laboratory test.Based on the scanning electron microscope techniqu e,the influence of water content on the microstructure characteristics of remold ed and undisturbed samples of sandy Q3 loess and the differences between undi sturbed and undisturbed soils were analyzed.The soil-water characteristic curve test of sandy Q3 loess was carried out to analyze the effect of net stress on so il-water characteristic curve(SWCC).The compression curves of undisturbed an d remolded soil samples were obtained by the compression test of sandy Q3 lo ess,and the influence of water content on the compression characteristics of undisturbed and remolded soil samples was revealed.The collapsibility test of san dy Q3 loess was carried out to obtain the collapsibility coefficients of undisturb ed and remolded soil samples under different water content.(2)The development of triaxial apparatus for unsaturated soil with triple te mperature control was carried out.Based on the literature research,the advantag es and disadvantages of the existing temperature controlled geotechnical triaxial instrument are summarized and analyzed.A triaxial apparatus for temperature co ntrol of unsaturated soil was developed which can improve the efficiency of sci entific research,accurately control the temperature and measure the volume vari ation.The basic development idea is to expand one pressure chamber into three parallel pressure chambers.The air pressure,confining pressure and backpressure in the pressure chamber are respectively controlled by different controllers.The temperature in the entire instrument is controlled by setting up a water bath.Th e water bath box is connected to the pressure chamber through a nylon pipe.Th e pressure chamber wall is designed with double spiral orifice to ensure the uni formity of temperature throughout the pressure chamber.The maximum controlla ble temperature of the developed device is 60 ℃ and the minimum temperature is-10 ℃.(3)The temperature effect of deformation characteristics of sandy Q3 loess was investigated based on the developed test equipment.The isotropic compressi on tests of sandy Q3 loess under different net stresses(50,100 and 200 k Pa),suction(50,150 and 250 k Pa)and temperature(25,40 and 60 ℃)were carrie d out.The compression curves of sandy Q3 loess with net stress,suction and t emperature change are obtained,and the effects of temperature and suction on t he previous consolidation stress and the parameters λ、κ are revealed.The sucti on cycle test was carried out under different net stress and temperature conditio ns,and the corresponding soil-water characteristic curve and volume variation c urve were obtained,revealing the change rule of SWCC inlet value and volume variation with temperature.The temperature cycle test under different net stress and suction conditions was carried out,and the corresponding volume change c urve with temperature was obtained,revealing the relationship between volume change caused by temperature cycle and the over-consolidation ratio.It is also c oncluded that the coefficient of thermal expansion is independent of suction andnet stress. |
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