| In our country,the proven coal under three circumstances reached 10 billion tons,and the coal under buildings accounted for more than 60%.In order to liberate more coal under three circumstances,it is increasingly common to intrude protective coal pillars for mining.However,this will lead to the movement and deformation of the foundation soil of the building,and the initial equilibrium state of the base and foundation is damaged,resulting in the decrease of the safety and reliability of the building.Therefore,how to correctly evaluate the influence of mining on building foundation,it is an urgent problem to be solved.The research object of this paper is the existing pile foundation affected by horizontal displacement of soil in mining area.The deformation control equation of existing single pile in mining area is derived by combining theoretical calculation and numerical simulation.Considering the engineering practice,the horizontal response is discussed of pile with cap under the influence of mining,and the influence of different factors is analyzed on the horizontal response of pile body.The main contents and results are as follows:(1)The horizontal displacement of soil free field in the mining tensile zone is calculated by using the probability integral method and the three-dimensional calculation model of surface movement and deformation.Combined with the soil displacement method and the p-y curve theory,the control equation of single pile deformation is derived.A threedimensional model including the lower coal seam and the upper pile foundation was established to analyze the horizontal displacement law of the pile body at different distances between the single pile and the mining face.The results show that the horizontal displacement of soil free field decreases from top to bottom in the mining tensile zone;the closer to the working face,the greater the horizontal displacement and overall inclination of the pile.(2)In order to make the research more suitable for engineering practice,a threedimensional model including lower coal seam and upper cap-pile foundation is established,and the influence of different pile top constraint forms is discussed on the horizontal response of pile body.The results show that the pile top displacement varies with the pile top constraint.The pile top displacement of the fixed single pile is reduced by about 11% compared with that of the non-cap pile,the hinged single pile is reduced by about 14%,the fixed double pile by about 25%,and the hinged double pile by about28%.The depth of the maximum horizontal displacement of the pile is affected by the pile top constraint,and the depth of the fixed single pile is about 10d(d is the pile diameter),the hinged single pile about 7.5d,the fixed double pile about 12 d,and the hinged double pile about 10d;the bending moment of pile is affected by the pile top constraint.When the pile top is fixed to the pile cap,the pile top bending moment of the double piles increases by about 50% compared with that of the single pile.When the pile top is hinged to the pile cap,the maximum bending moment of the hinged double piles increases by 20%–60% compared with that of the single pile.(3)Based on the three-dimensional model including the lower coal seam and the upper cap-pile foundation,the influence of soil properties,pile length and other factors is analyzed on the horizontal displacement of the pile.The results show that when the soil around the cap changes from hard soil to soft soil,the displacement of pile top decreases under different pile top constraints,and the reduction of hinged single pile is the most obvious.When the pile length is different,the displacement of pile top changes little;at the same time,The analysis demonstrated that when the pile diameter is 1 m,the influence range of pile cap on the horizontal displacement of pile body is more than 15 d,which is less affected by factors such as pile length and pile top constraint form. |
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