Study On The Mechanism Of Ground Fissure Movement During Pumping And The Safety Avoidance Distance Of Xi'an Ground Fissure

Ground fissure is a kind of regional urban geological disaster,which is widely distributed all over the world.Nowadays,14 ground fissures have appeared in Xi'an area because of groundwater extraction,which has brought serious threat and impact to line engineering,constructions and land resource planning.In the past,the research on ground fissures often focused on the damage mechanism and prevention measures,but the mechanism of ground fissures under the action of extracting underground water is not clear.At the same time,in recent years,the exploitation of underground confined water has been restricted,and the activity of ground fissures has decreased.However,the buildings in ground fissure site are still avoiding according to the safety distance stipulated by the peak period of pumping activities,which brings a lot of challenges to land resources and engineering design.Therefore,it is necessary to study the mechanism of ground fissure movement under the action of pumping and the safe distance of ground fissure site under the background of decreasing ground fissure activity,which has great practical significance for the rational use of land resources.Based on the existing engineering data and field geotechnical investigation,this paper sums up the geological background of Xi'an and the development characteristics of Xi'an ground fissures.Based on the Terzaghi consolidation theory and the seepage theory of confined aquifer in groundwater dynamics,taking the ground fissure under the action of pumping confined groundwater in Xi'an area as the research object,the deformation mechanism of aquifer and the stress deformation mode of ground fissure under the action of pumping are theoretically analyzed.Using FLAC^3D numerical simulation software based on fast Lagrange method to simulate and analyze the activity mechanism of ground fissures with different permeability,the main activity law of ground fissures in Xi'an under the action of extracting confined water is obtained;at the same time,taking the newly-built primary school project of a ground fissure site in Xi'an high tech Zone as the research object,selecting the differential settlement on both sides of the building base as the research index,the ground fissures are analyzed Based on the numerical simulation analysis of the deformation of the building foundation affected by the ground fissure,the deformation law of the natural foundation affected by the ground fissure under different avoidance distances is studied.The main research results are as follows:(1)The main effects of extracting confined water on stratum are horizontal deformation and vertical consolidation settlement deformation;in addition,the deformation modes of the two sides of ground fissure are different,which makes the hanging wall more prone to deformation.The aquifer deformation caused by pumping activities aggravates the deformation difference between the upper and lower sides of the ground fissure,which is the main cause of ground fissure activities.(2)The location of pumping wells influences the ground fissure activities.The calculation results show that the ground fissure activity caused by pumping from the hanging wall is greater than that from the footwall,which is consistent with the actual survey results.The settlement funnel caused by hanging wall pumping is blocked by ground fissures,and there is a large difference of shear strain near the ground fissures,which leads to the shear relative displacement of the two plates.While when pumping in the footwall,the settlement funnel is evenly distributed across the ground fissures,and the upper and lower plates do not produce large shear relative displacement,which is the main reason for the different pumping of the two plates.(3)The permeable of ground fissures has a certain influence on the activity of ground fissures.The impermeability ground fissure blocks the seepage recharge from the ground fissure to the pumping pan,limits the development of the groundwater depression funnel,and causes stronger tension and shear action at the ground fissure.The overall differential settlement of the impermeable ground fissure is larger.(4)On the premise that the ground fissure is inactive,the influence of the ground fissure on the building decreases with the increase of the avoidance distance,and increases with the increase of the base load;in addition,the soil strength and the base area also have a certain influence on it.