Model Test Study On The Influence Of Dewatering On Surrounding Subsidence Of Loessfoundation Pit

In view of the existing problems of loess foundation pi under the condition of high groundwater level,In order to study the influence of the foundation pit dewatering on the environmental settlement.A comparative test method was used in the similar model test,and the effects of different precipitation regimes on land subsidence are studied.Then on the basis of experiment,waterproof curtain was set and the recharge system was enabled.The effect of the most reasonable curtain depth and recharge pressure to settlement control are studied.The following conclusions are obtained:1)The soil samples made of silicate cement showed similar properties to the original structural loess samples.The experiments were carried out under the condition of undisturbed loess,remolded loess and two kinds of manual configuration soil samples.Under certain moisture content,the curves of the properties ot two kinds of soil samples were obtained are consistent with the original loess.In the experiment,cement selected to the preparation of artificial soil samples,Structural strength,collapsibility coefficient,consolidation coefficient,permeability coefficient,etc.can reach more than 90%of the original loess,Moreover,the method is more simple and easy to operate to prepare a large number of soil samples for model test,The final selection of 1%of the amount of cement mixed with the soil moisture content of the test required for the preparation of 10%;2)In the process of dewatering in phreatic layer of loess foundation pit,after the water yield of the precipitation well was basically stable,there was a great difference in the rate of sedimentation.As the example of the maximum value of A3 in the test 1a.the final settlement value was-7.41mm.Within 1-4 days of precipitation,the settlement value increased at a large rate,an average of-1.82mm per day.The growth rate decreased in 4-9 days,the average daily-0.39mm.The ground subsidence caused by precipitation was basically stable at about 1 to 2 days after the cessation of precipitation.After precipitation stopped,the settlement value will produce a slight rebound.The maximum and minimum rebound amplitude were 5%and 1%.The average is about 3%.During the precipitation process,the water level change of each measuring point presents funnel shape.Within one day after the rain stops,The water level rises rapidly.3)In the process of foundation pit dewateringwith the increase of single precipitation depth,the ground subsidence was also increasing.The final settlement value of A3 point in a single drop depth of-4cm was-7.41mm when depth of-5cm was-7.54mm and drop depth of-6cm was-7.61mm.In engineering practice,greater the depth of single precipitation produced greater impact on the surrounding.In the process of dewatering,the settlement of the surrounding soil was in a funnel shape,with the distance from the foundation pit settlement value increases first and then decreases.The maximum settlement value of A23 at 30cm was-7.24mm,when point D3 in the pit edge wast-6.55mm,and the point A33 in edge of the model box was only.-4.12mmTherefore,the dewatering of foundation pit has a great influence on the buildings with a certain distance,resulting in the precipitation along the direction of the larger span of the building to produce uneven settlement;4)Waterproof curtain can reduce the influence of precipitation on ground settlement of deep foundation pit.The final settlement value of the building was reduced:when the depth of water curtain,was increased.The settlement value of D4 is-6.76mm when the curtain depth was 45cm.The 1.46mm is reduced by-8.22mm when the curtain was not set.The settlement value of D4 was-6.56mm when the curtain depth was 55cm.After the curtain depth to more than 50cm,the effect to increase depth of curtain to control settlement is not obvious;5)Reasonable recharge pressure can reduce the influence of precipitation on the settlement around the foundation pit.Increase recharge pressure would lead to the final settlement value of the building and the inclination rate decreases.Before recharging,the maximum settlement value of point D4 in building A is-6.65mm and,the inclination rate was 0.178%.When the pressure was 0.15MPa,the maximum settlement value was-5.24mm and the slope rate was reduced to 0.101%.After the recharge pressure exceeds 0.15MPa,the maximum settlement value decreased.However,the tilt rate increased rapidly to 0.131%,The reason was that the pressure is too large to cause sudden surge around the well,while soil stability was destroyed;In this paper,though the similarity model test,the effect of engineering dewatering on the loess foundation pit and surrounding land subsidence was studied.lt was pointed out that reasonable dewatering depth,curtain depth and recharge pressure should be adopted in the foundation pit dewatering.Finally,based on the experiment,the next research direction was discussed.