| AbstractIn recent years,with the development and utilization of the underground space,the underground chamber is developing towards the direction of large space and complex structure.The traditional underground engineering technology theory based on regular structure is difficult to meet the needs of the construction and development of underground engineering.The stability evaluation method of large underground engineering has become the key technical field of underground engineering research.To this end,the Zhejiang city of Wenling province Changyudongtian mined underground cavern complex carried out in-depth research and analysis.It is intended to summarize the experience of the ancient engineering technology and analyze the scientific mechanism of the long-term stability of the ancient underground caverns with modern technical means,to providing reference for further enriching and perfecting the theory of modern underground engineering technology.The irregular section of cavern stability evaluation method is estimated,and the stability evaluation of Zhejiang city of Wenling province Changyudongtian mined underground caverns was carried,to providing technical support for tourism development and utilization of Changyudongtian mined underground caverns.Changyudongtian in Wenling County of Zhejiang province as a stone mining area,mining stone has more than 1500 years of mining history.There are about 1.55 km2 in goaf,and lots of empty cavern,which are different in size,structure and spatial distribution,and record the development history of stone technology and technology in China.The caverns studied have a span of 8-91 m and a height of 10-53 m.The size of the caverns is a rare large cavern in the modern underground works.All the caverns did not take any supporting measures;only rely on the self,to achieve long-term stability of the cave groups.Therefore,it has positive significance to understanding the structure characteristics of Changyudongtian cavern and the long-term stability of the scientific mechanism,and to further improve the modern underground engineering theory.It is a positive reference to the development and utilization of large underground engineering.In view of the ancient underground caverns without illumination,the actual situation is difficult to obtain the excavation process,structure design and data structure with detailed parameters of underground cavern.So the main structure parameters have obtained through detailed field investigation and measurement.The mechanical parameters of rock mass are obtained through indoor test,and the mechanical parameters of rock mass are revised according to the classification standard of engineering rock mass.The mechanical parameters of rock mass are obtained through indoor test,and the mechanical parameters of rock mass are revised according to the classification standard of engineering rock mass.By comparing various methods of rock mass classification analysis,the surrounding rock classification methods and standards which is applicable to underground caves was determined.The simulation in 2D and 3D numerical analyses through the FLAC software,and the large irregular underground cave complex modeling problem is solved with a variety of software and FLAC3 D.By analyzing the structure characteristics of irregular cavern transverse section and longitudinal section,and analyzing the influence of the side wall of cavern angle,span,height,depth and terrain slope on the stability of surrounding rock,and the stability of large underground caverns,it explains the reasonable structure of the bell-shape cavern.On the basis of the above research,using the analytic hierarchy process,three levels stability assessment model of cavern(Group)was established,and scores by inviting industry experts,and then the weight coefficient of each index was got.Then,stability evaluation index score standard of the irregular cavern(Group)established.The conclusions are as follows:(1)The study area is mainly distributed three type caverns: in open and straight hole type,semi open cover,large cover type,and all of the caverns are bell-shape cavern.The cavern size is large,the span of the cavern is 8-91 m,and the height is 10-53 m.Most of the caverns span between 10~40 m,and the height is concentrated between 10-30 m.(2)The study area is dominated by tuff and intercalated with andesite dyke.The rock mass is intact,and it is massive or thick bedded.In addition,the structural surface is mainly composed of closed drying joints.According to the analysis of this paper,the surrounding rock of the cavern is mainly II type,and the surrounding rock of tunnel connected to the cavern is mainly III type.(3)The surrounding rock area of bell type cavern is the smallest.Especially,the special structure of foundation pit with curved wall and bottom excavation is adopted.Then,a horseshoe shaped cross-section structure formed.Therefore,it can give full play to the stability of surrounding rock,avoid the formation of dangerous rock at the top of the cavern,and ensure the safety of the quarry construction and long-term stability of the cavern.(4)In Changyudongtian geological conditions,rockwall dip of cavern at 70 degrees ~80 degrees,so the surrounding the tension zone of area is smaller,and the stress state of surrounding rock is more reasonable,and more conducive to the stability of the cavern structure,While 60% of the 24 caverns in the study are in line with the law.(5)The span and the height ratio of the cavern,the depth and the height ratio of the cavern are important parameters of the structural characteristics of the cavern.By computation and analysis,this are found that the span height ratio should be less than 1.44,and the buried depth and the tunnel height ratio should be less than 1.8 at the gentle slope.While,the span height ratio should be less than 1.28,and the buried depth and the tunnel height ratio should be less than 1.8 at the steep slope.Through field investigation,it is found that there are 16 caverns,which can satisfy the law of steep slope and satisfy the direction of gentle slope,accounting for 66.7% of the total cavern.(6)The elliptical transverse section cavern is better than the circular one,and the circle is better than the quadrilateral(polygon).The ellipse along the gentle slope and the short axis along the steep slope is the best cross section form for stability.Through field investigation,it was found that 13 of the 24 caves were elliptic cross section caves,3 were circular cross section caves,and 8 were quadrilateral(approximate quadrilateral)cross section caves..(7)Through three-dimensional numerical calculation of surrounding rock under gravity loads,the surrounding rock displacement,stress and the plastic area are smaller,cavern structure is in a stable state,but the stress state of bottom rock cavern and the middle partition wall is not conducive to the stable.For this reason,during the excavation of the cavern,the ancients took 3 measures to excavate the surrounding rock of the cave bottom: to store water in the rock pit,and to excavate some rock masses in the middle wall,so as to enhance the stability of the cave structure.(8)According to the stability evaluation method established in this paper,there are 9 caverns of stable I in the 24 caves,37% of the total caves.There are 15 caverns of II stable cavern,accounting for 63% of the total caves.Through the specific analysis of the related cavern,it shows that the evaluation results of the stability classification method based on the analytic hierarchy process are consistent with the actual situation,and it can objectively evaluate the stability of the cavern.Through this analysis,in Changyudongtian scenic geological conditions better circumstances,with bell type cavern structure to reduce surrounding rock tension area has the superiority of improving cavern stability,especially for the supporting structure of the mined out cavern adaptive.At the same time,the quarrying process,by increasing the cavern wall and bottom radian during excavation and excavated cave span large room top rock and other measures,forming a class of horseshoe cross section structure,improve the surrounding rock overlying bell type cavern structure stress,the formation of a stable number of hundreds of years of underground goaf room.With the bell-shape cavern structure although the surrounding conditions for more stringent,but its unique structure,scientific basis and stable Millennium Project for its existence,is the treasure of engineering technology,modern engineering technology personnel should deeply analyze the overlying bell type cavern structure,mechanism,in order to better use in modern engineering construction.It is positive significance for modern large-scale underground engineering construction. |
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