Study On The Structure And Stability Of The Embankment Above The Mined-out Area

This paper is based on the design of the embankment of a proposed highway in the mined-out section,the theoretical analysis method is used to comprehensively analyze and evaluate the surface stability of the goaf,and the numerical simulation method is used to study the structure and stability of the embankment above the goaf.The related research work and the results obtained are as follows:(1)Comprehensive analysis and evaluation of the surface stability of the mined-out section of the proposed highway.According to the basic information of the mined-out area underneath a proposed highway,using probability integral method,stop mining time evaluation method and mining depth mining thickness ratio evaluation method,comprehensive analysis and evaluation of the surface stability of the proposed highway underneath the mined-out area is carried out by section.The results show that the surface stability level of the mined-out area under the proposed highway ranges from basically stable to unstable.(2)The mechanical parameters of the deep rock mass in the mined-out area are solved.Based on Hoke-Brown strength criterion and its correlation with Mohr-Coulomb strength criterion,comprehensive consideration of various factors such as the structure,stress state,and strength of the deep rock mass in the mined-out area,in the absence of original mechanical parameters,the elastic modulus,bulk modulus,shear modulus,cohesion and internal friction angle of each deep rock mass in the goaf are obtained.(3)The overlying rock failure law and subsidence law of the mined-out area under the proposed highway are studied.Under the special geological conditions of the minedout section of the proposed highway,six kinds of grid models of mined-out areas with different mining depths were established using Rhino6.0 and Gridle,and the models were calculated and analyzed by FLAC3 D.The results show that between the maximum surface settlement and the mining depth,there is an exponential decreasing function with e as the base,and with the increase of mining depth,the maximum surface settlement in the goaf tends to be relatively constant,the yield volume of the overlying rock near the surface decreases,and the settlement form of the deep rock mass gradually appears from "columnar" to "funnel".(4)The critical mining depth in response to the mined-out area under the soil embankment of different heights is studied.Numerical simulation is carried out by filling the earth embankment of the same size and the same material on the surface of the goaf with different mining depths,and the critical mining depth and its prediction formula for the response of the mined-out area under the soil embankment with a height of 4～8m are obtained,based on this,the critical working condition and the most unfavorable working condition of the goaf section of the proposed highway are defined.(5)The scheme to improve the structural stability of the embankment in the minedout section was studied.Based on the defined critical conditions and the most unfavourable conditions,combined with the idea of transformation,the problem of embankment stability in the mined-out section of the highway to be constructed is transformed into the problem of the most extreme value of the function.The results show that the combined structure scheme of plain clay embankment and plain fly ash embankment respectively with three-layer reinforced 9% lime-improved soil foundation is the best scheme under critical conditions and the most unfavorable conditions;Under the same foundation conditions,compared with filling the embankment,the foundation settlement after filling the fly ash embankment is reduced by about 20%,and the maximum settlement on the top of the embankment is reduced by about 60%,therefore,the use of fly ash to fill the embankment is beneficial to reduce the settlement of the foundation and embankment of the mined-out section of the highway.Reinforcement treatment cannot effectively reduce the foundation settlement of the mined-out section of the highway,but it can effectively restrain the slope slippage of the embankment.The effect of reinforcement is not positively related to the number of reinforced layers.