| In recent years,there are frequent accidents due to frost heave of foundation pit in seasonal frozen soil area,but the research results of horizontal Frost Heave Mechanism in the freezing process of foundation pit in winter are few.Based on the field monitoring test of the foundation pit in Changping District of Beijing,this paper analyzes the water level transfer law and frost heave characteristics of the soil during the freezing process of the foundation pit,and the change law of the foundation pit deformation combined with the internal force monitoring results of the support structure.At the same time,use the COMSOL software to establish the water thermal coupling model of the foundation pit in winter,put forward measures to eliminate the horizontal frost heave force,and analyze the effect of different measures to eliminate the horizontal frost heave force through the numerical model.The conclusions of the study are as follows:(1)During the overwintering period,when the soil of the foundation pit frost heaves,the internal water migration due to the change of the soil water potential caused by the temperature gradient.The water in the soil has been migrated from the frozen area to the frozen area and away from the wall The moisture in the soil moves towards the wall of the foundation pit,so the freezing of the soil in the foundation pit is caused by the combined action of vertical and lateral moisture migration.(2)Horizontal frost heave caused by lateral water movement in the soil will change the horizontal displacement of the pile top and the horizontal displacement of the slope protection pile,resulting in the formation of cracks on the top of the foundation pit beam.During the freezing period,the maximum horizontal displacement of the pile top increased by 14.6 times,15.6 times,and 10.7 times respectively,and the maximum horizontal displacement of the pile increased by 7.2times,8.6 times,and 6 times respectively.(3)Due to the frost heaving of the soil,the tensile force of the anchor rod increased significantly.The tensile force of the anchor rods in the three monitoring areas increased by 1.4 times,0.786 times and 0.259 times,respectively.Therefore,when designing overwintering foundation pits,it is necessary to consider the influence of soil frost heave on the stability of the supporting structure.(4)Water supplement condition The horizontal deformation of the foundation pit(5)of the pile-anchor supporting section is greater than that of the water supplement condition.Considering the design of reasonable drainage measures to reduce the horizontal frost heave effect of the soil;at the same time,the stiffness condition is the winter winter foundation pit pile top An important influencing factor of horizontal displacement,the greater the rigidity of the pile-anchor supporting structure,the greater the restraint effect on the foundation pit,which can effectively reduce the horizontal frost heave deformation of the foundation pit.(6)The tensile force of the anchor rod in the pile-anchor support section is much greater than that of the soil-nailed wall support section,that is,the restraint effect of the soil nails in the soil-nailed wall support section on the foundation pit soil is less than that of the pile-anchor support section.The constraint effect of soil nails on the foundation pit soil needs to be compensated by the deformation of the foundation pit soil.It can be considered that the horizontal deformation of the foundation pit in the soil nail wall supporting section is smaller than the horizontal deformation of the foundation pit in the pile anchor supporting section.(7)When laying 4cm thick grass curtain,polystyrene insulation board and XPS insulation board on the top of the overwintering foundation pit,the calculated maximum horizontal frost heave force is 93 k Pa,65.6k Pa and 61 k Pa respectively;comparative analysis found that laying insulation The layer can effectively weaken the effect of the horizontal frost heave force on the supporting structure of the foundation pit,where the thermal insulation effect of the grass curtain is weak;The horizontal displacement and horizontal frost heave force of the pile body will decrease with the increase of the thickness of the insulation layer material;when laying polystyrene insulation boards with thickness of 2cm,4cm and 6cm,the maximum horizontal frost heave force is less than that of the insulation layer The time decreased by 55.6%,76.4% and 85.3% respectively.(8)When the overwintering foundation pit is filled with sand with a depth of0.5m and 1.0m and gravel with a depth of 0.5m and 1.0m,the calculated maximum horizontal frost heave forces are 226 k Pa,127 k Pa,186 k Pa,and 108 k Pa respectively;the maximum horizontal frost heave force is reduced by about 17.8%,53.8%,and32.4 respectively when no frost heave measures are provided.%,60.7%;the best effect is when replacing gravel soil with a depth of 1.0m.(9)Compared with the two measures of heat preservation layer and surface layer replacement,the anti-frost heaving effect of the heat preservation layer measure is more obvious and effective,and it is more economical and practical in actual engineering and easy to operate,so it is recommended to use it in actual engineering. |
PDF Full Text Request