Hydraulic Characteristics Of Unsaturated Lime-treated Loess At Different Temperatures

Loess is a kind of unsaturated soil widely distributed in Northwest China,which has strong permeability and obvious collapsibility.The "Western Development" and "Belt and Road Initiative" strategies have continued to advance.A large number of engineering projects are being constructed in Northwest China.Lime improvement is widely used to improve engineering properties of loess.The seasonal and day-night temperature differences are large in the area.The temperature difference will cause changes in the hydraulic characteristics of lime-treated loess.Hydraulic characteristic is an important engineering property,which is closely related to problems such as landslides and subsidence.Therefore,thermal-hydraulic characteristics of unsaturated lime-treated loess are worth studying.In this paper,the thermal-hydraulic characteristics of untreated and lime-treated loess were experimentally studied.The effects of temperature and lime treatment on the water retention characteristics,permeability characteristics and pore structure were analyzed.The following conclusions could be drawn.(1)The relationship between the total suction and water content of Whatman No.42 filter paper was measured at different temperatures(0 ?,5 ?,10 ?,20 ? and 40 ?)by the vapour equilibrium technique.The corresponding calibration curves for Whatman No.42 filter paper at various temperatures were determined.The experimental results indicated that the water retention capability of Whatman No.42 filter paper decreased with increasing temperature.The effect of temperature on the water retention capacity gradually reduced with increasing the suction.(2)The water retention curves of untreated and lime-treated samples(28 d,90 d)were measured at different temperatures(0 ?,5 ?,10 ?,20 ? and 40 ?)by the filter paper method.The experimental results indicated that the water retention capacity and volume change of compacted loess were effected by lime treatment over curing time and temperature changes.These effects all decreased with the moisture content dropping.The temperature effect on the water retention capacity also decreased with increasing temperature.(3)Permeability tests on saturated untreated and lime-treated samples(28 d,90 d)were carried out at different temperatures(0 ?,5 ?,10 ?,20 ? and 40 ?).The results showed that the saturated hydraulic conductivity and intrinsic hydraulic conductivity of compacted loess decreases with lime treatment over curing time.The saturated hydraulic conductivity of all samples and intrinsic hydraulic conductivity of lime-treated samples raises with increasing temperature.The intrinsic hydraulic conductivity of untreated samples hardly changes with temperature.(4)The pore structures and freezing characteristics of untreated and lime-treated samples(28 d,90 d)were investigated at different temperatures(0 ?,5 ?,10 ?,20 ? and 40 ?)by the Nuclear Magnetic Resonance(NMR)tests.The results showed that the pore structures were affected by lime treatment over curing time.Temperature has little effect on the pore structures.The freezing characteristics combined with Clapeyron function was transformed.And the transformed curve was compared with the water retention characteristics.The freezing characteristics of unsaturated samples are in good agreements with the water retention characteristics.But the freezing characteristics of saturated samples are not.