Study On Water-Heat Migration And Strength Of Remolded Loess Under Humidification

In recent years,with the gradual advancement of the national “the Belt and Road Initiatives” strategy,the development of western loess regions and the construction of basic equipment will certainly reach a new height,especially in collapsible loess regions.The roads,railways,municipalities,water conservancy and other engineering facilities in the loess area are built in shallow unsaturated loess.Once water immersion occurs,it will inevitably cause a large sudden drop in the strength of the loess and a sudden increase in deformation,which will endanger Engineering construction safety.In order to prevent or reduce the damage to the upper buildings due to collapsible loess immersion,the actual project often uses the immersion pre-wetting method to deal with the collapsibility of loess.Although it can roughly eliminate the collapsible hazard,there are still many problems that need to be solved urgently.A new type of loess humidifying method-high temperature and pressure steam humidification method-has been puts forward in this paper,which is to solve the problems in the pretreatment method of humidification of loess foundation.This study focuses on heat transport and soil strength change in the soil under the wetting effect.The humidification experiment of high temperature and pressure steam under different steam pressure was carried out for remolded loess in Lanzhou,and to discuss the variation law of temperature and moisture field in soil and the distribution of the final state.Simultaneously,direct shear tests were carried out on soils with different moisture content at different locations after humidification treatment to analyze the variation law of remolding loess strength under different steam pressure humidification.Thus,the main conclusions of this paper are as follows:When columnar diffusion mode with high temperature and pressure steam is used to humidify soil,the diffusion range of steam and temperature is similar to that of a round estrade in space.At the same depth level,the steam migration rate gradually decreases under the increase of water and steam migration distance along the radial direction,but the soil moisture content and temperature migration rate gradually decrease.Moreover,because the vapor pressure of the lower vent is larger than that of the upper part,the range of the effect of humidification becomes larger and larger in the depth direction.At the same time,as the pressure of the steam injected into the diffusion column increases,it is affected by humidification at the same depth The range is increasing,and the center optimal moisture content range is gradually increasing.During the humidification process of 0.05 MPa(or 0.1 MPa)steam,each moment corresponds to a humidification range.Although extending the aeration time can increase the range and degree of humidification in the soil,its unit time is affected by The range of the effect of steam humidification increases first and then decreases.It is recommended to control the humidification time within 9h.After being humidified by high-temperature and high-pressure steam,the temperature and water content of the soil at different locations all changed,but the reduction of the shear strength of the soil was less affected by the temperature,which was mainly caused by the increase of water content.The closer the distance to the aeration point is,the higher the moisture content is after humidification,and the lower the shear strength of the corresponding soil is.Meanwhile,when the steam pressure in the injected diffusion column increases,the shear strength of soil closer to the aeration point decreases more than that at a distance.Secondly,by using the coulomb formula to fit the data of shear strength,it is found that the cohesion of the soil is mainly reduced,and the angle of internal friction has almost no effect.Above all,steam humidifying method as a new technology and new methods of soil,compared with the traditional soil humidifying method,has lots of advantages such as controllable range,good uniformity and humidifying localized at same soil,which combine with high energy dynamic compaction method.Consequently,this method certainly has broad application prospects in the big thickness in collapsible loess foundation treatment.