Method Of Viaduct Expressway Construction Suitability Evaluation In Short Wall Goaf Collapse Area And Its Application

The large-scale goaf-collapse site,as a typical harmful foundation condition leftover by long-term high strength extraction of coal resources,not only restricts the construction and utilization of the post-mining area but causes significant movement and deformation under the synergistic action of various internal and external loading factors,which leads to deformation and destruction of the buildings(structures)above.Accurate prediction and evaluation of goaf-collapse site stability and foundation deformation is the premise of post-mining area construction and utilization and is also an urgent problem for regional sustainable development.This dissertation reveals the mechanism of fractured rock mass in the short-wall working panel and the regularity of residual displacement and deformation on the surface by using a combination of theoretical analysis,numerical simulation,mathematical modeling,and field investigation.And based on the disturbance depth of additional stress of pile group foundation in goaf-collapse area,a dynamic comprehensive evaluation system of viaduct construction suitability was established,it aims at providing a suitable evaluation approach for the construction and utilization of goaf collapse sites.The innovative results have been achieved as follows:(1)Based on the analysis of stability influence describers and the viaduct structure characteristics above the goaf,correlation analysis of 16 describers affecting the suitability of viaduct construction in goaf-collapse site was conducted based on Decision Making Trial and Evaluation Laboratory(DEMATEL).It is revealed that the main disaster-causing describers of goaf-collapse are the degree of mining,overlying rock lithology,mining thickness,and the relative location between the proposed construction project and post-mining area.The suitability function F=S×C of pile group foundation construction in goaf collapse site is constructed by taking the site stability of goaf S and the quantitative grade of pile group foundation structure stability C as independent variables.(2)Based on the spatial structure characteristics of fractured overlying rock of short-wall working panel,a natural equilibrium stress arch mechanical model was established.The stress arch deflection equation and bending moment equation of the short wall working panel are derived.The temporal and spatial evolution characteristics of overburden movement,the development law,and control mechanism of natural equilibrium stress arch of the short-wall working panel are revealed.It provides a theoretical basis for accurate prediction and identification of residual deformation of short-wall goaf-collapse sites.(3)A probability integration method(PIM)for predicting the residual deformation of a short wall working panel with solid coal on both sides is established.The residual deformation of the goaf-collapse site is equivalent to the difference between the yield stripping of the coal wall in the short-wall working panel and the displacement and deformation of the current mining state,i.e.the displacement and deformation difference of the site at the initial and current state of the mining space are used as the calculation approach for the residual deformation.FLAC3D numerical simulation software is used to simulate strata movement and surface deformation in goaf,and the comparison analysis with the predicted results of the probability integration method shows that the equivalent estimation method is consistent with the simulation results,which proves the feasibility and effectiveness of the proposed method.(4)On the basis of theoretical analysis of horizontal load and subsidence deformation of pile group foundation based on m method of foundation reaction coefficient,Midas GTS NX finite element software is used to establish the finite element model of pile group foundation structure.The surface horizontal displacement was applied at three different positions,namely the outer boundary of the goaf,the center of the goaf,and the inner boundary of the goaf.The internal force,shear moment,and displacement of the pile group foundation were analyzed under the condition of horizontal displacement and vertical stress loading,and the pile-soil synergy mechanism under the influence of the goaf was revealed.The influence depth of pile group foundation load is calculated according to 5P of critical safety depth H_Dz-5P,and the stability of pile foundation is expressed quantitatively by the logistic function model.(5)Based on the process of principal component hierarchical clustering dimension reduction for influencing describers of the stability of goaf-collapse,the time weight vector of stability evaluation is determined based on the coupling of optimization degree and temporal degree,the quadratic weight of time-ordered weighted average operator(TOWA)coupled with fuzzy entropy,a three-stage dynamic comprehensive evaluation model of short wall goaf-collapse site stability is established.Taking suitability as a quantitative index to represent the construction suitability of the goaf-collapse site,the grade division interval of construction suitability of the goaf-collapse site is proposed based on suitability function.(6)Based on the results of the theoretical analysis above,the approach and process of a dynamic comprehensive evaluation of the suitability of viaduct pile group foundation construction in short-wall working goaf in a colliery of Jining city,Shandong Province,were proposed under the engineering background of urban expressway construction in short wall working face.It is predicted that the maximum height of the natural balance stress arch of the short-wall mining panel is 13.5m,the maximum residual subsidence value after yield stripping of both sides of coal wall calculated by PIM is 62mm,the maximum residual tilting value is 0.39mm/m,and the maximum residual curvature is 0.002mm/m².The results of suitability analysis show that the suitability degree interval of viaduct foundation construction is(0.65,0.85),combined with suitability grading quantitative standard and it is feasible to construct a viaduct expressway on the goaf collapse site.The dissertation has 82 figures,26 tables and 194 references.