| Abstract:The subway which is under large-scale constructions recently in Guangzhou has to go through the karst area.In view of the regional karst geological environment, carrying out analysis of karst foundation stability and bearing capacity, searching new material and new craft for karst filling, have important guiding significance for subway and underground space constructions in Guangzhou,the Pearl River Delta region and even the whole country.In this paper, on the basis of a large number of references at home and abroad, the geological forming conditions,tectonic background and hydrology-weather condition of Guanghua basin are concluded; through model test and numerical simulation, the stability especially during the shield construction on the hidden karst foundation is analyzed; laboratory test for grouting slurry material proportion, the field test experimentation and numerical analysis method are combined to study the effect of the clay cement grout which is used to fill hidden karst caves. This main research content of this article is as follows:(l)Through the data collection, sorting and analysis of the main line of Guangzhou subway, the spatial distribution regularity of karst cave is studied; through the statistical analysis of roof height, thickness of top plate, karst cave size, location,a geological generalized model is proposed; and the forming mechanism, development rules of karst and influence factors and causes of the ground subsidence are studied.(2)According to the similarity theorem, the physical and mechanical indexes of similar material is got.Similiar material and the appropriate ratio of mixture for the experiments are selected to meet the similarity criterion at the most extent; the plane strain model is designed to study the influence of the distribution of the location of karst cave;bearing capacity and the progressive failure characteristics of karst foundation, through the step by step load, is obtained and the change laws of strata stress and displacement are also analyzed.(3)According to the upper bound analysis method based on finite element theory, this paper proposes a self-adapting meshing method was proposed based on indexes of unit energy dissipation density and a programme is designed to implement it,for the the shear zone of karst tunnel foundation may be difficult to be deduced accurately. The programme is applied to calculate the foundation ultimate bearing capacity under different working conditions.And the foundation ultimate bearing capacity and the laws of failure mode, compared with model test results, are in good agreement.(4)Based on typical engineering geological conditions,the influence of karst cave’s size, location, shape and the distance between tunnel and karst caves on the stability of karst foundation is analyzed by the three-dimensional finite element numerical simulation of the construction process going through karst region.(5)According to specific worksite, local soil is collected to carry out the laboratory experiment to test the strength of the clay slurry concretion and afterwards get the propriate mix proportion; the filling process was also carried out to study the grouting construction technology and quality control measures; the stress and deformation of the caves after the filling are calculated and analyzed, campared with the results before the filling process,the effectiveness of the filling processing scheme is demonstrated combined with in-situ test. |
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