Study On Frost Heave Deformation And Protection Technology Of Pile And Anchor Retaining Structure Of Foundation Pit In Seasonal Frozen Area

Deep foundation pit engineering in seasonal frozen soil area usually goes through winter period and freeze-thaw cycle period.There are serious frost heave disease and freeze-thaw cycle in deep clay foundation pit in seasonal frozen soil area.Due to the complexity of geological and hydrological conditions,the difference of foundation pit support,as well as temperature,rock and soil material discontinuity and other factors,at present,there are few studies on the factors that reflect the frost heave force of overwintered foundation pit,and the frost heave deformation of pile anchor supp.ort of foundation pit and the countermeasures to prevent deformation.The existing research is mainly from the perspective of design safety.One scheme is to propose the physical and mechanical parameters of rock and soil materials in frozen soil and freeze-thaw cycle by considering frost heave force and freeze-thaw cycle,and increase the external load of the supporting system or reduce the strength parameters of the soil supported in the foundation pit during the design.Another design idea is that because the freezing temperature is generally low and the freezing time is relatively short,the effect of frost heave is ignored and only anti-freezing measures are considered.None of the above proposed solutions from the mechanism of soil frost heave in foundation pit.Therefore,It is significant to study the stress and strain mechanism of pile-anchor support system in cohesive soil under frost heave and put forward the corresponding technical measures to reduce the frost heave.This paper takes the foundation pit engineering in Shenbei New District,Shengshen City,Liaoning Province as the research object,proposes the monitoring scheme according to the actual situation of the site,and analyzes the obtained data.According to characteristics of rock and soil medium freezing process,based on the knowledge of heat transfer,the finite element simulation software for numerical simulation of the heat preservation measures and put forward two kinds of foundation pit,the results show that foundation pit base of wintering a cycle of internal force will decrease as the winter temperature and pressure of soil,soil water ice phase transformation in the internal of frost heaving force makes the soil pressure increased.When the temperature rises in spring,the phenomenon of thaw settlement occurs and the soil pressure decreases.When the temperature drops in winter,the horizontal displacement of pile top continues to increase,and then becomes stable under the constraint of the increase of anchor cable stress.When the temperature rises in spring,the horizontal displacement of pile top has a slight increase trend due to thaw settlement,and then presents a stable trend.The vertical displacement of the pile top varies stably with a small value,not exceeding 8.5mm,which belongs to a deformation value under normal working conditions.Therefore,it shows that the frost heave of foundation pit soil has little effect on the vertical displacement of pile top and can be ignored.During the freezing period,with the increase of freezing time,the range of temperature change in soil body increases,and with the increase of freezing time,the freezing depth of soil body increases.The water content decreases and the ice content increases in the region with low soil temperature.Aiming at the key problem of overwintering protection of foundation pit,this paper puts forward two different thermal insulation measures,namely laying a thermal insulation layer on the surface of foundation pit and adding a water stop curtain,and finds that both measures can effectively prevent frost-heaving of foundation pit during overwintering.