Study On Prediction And Prevention Of Rockburst In Anlu Tunnel

The ANLU tunnel(DK993+173～DK1006+360)is the longest tunnel from ZHUANGZHOU to KUNMING with a total length of 13187 m and maximum depth of 565 m.the geological conditions are more complicated,rockburst of the tunnel is the main engineering geological problems.In this paper,in close connection with practice of the ANLU tunnel project,and on the main line of the rockburst,the problems are elaborated in detail.This study contents and the conclusions are mainly include the following:(1)Making use of some measure methods of field such as draulic fracturing method,the geostress status in the engineering rockmass has been ascertained and the systematic recognition of the geostress field in the area has been attained:the current state of geostress field in the surveyed area is mainly squeezed from the direction of NW and maximum principal geostress directions are generally N46.7°～50.7°W.(2)According to detailed analysis of the two borehole test results,current tectonic geostress is mainly dominated in the engineering area and what's more its intensity is very stronger,the relationship of the three main stress is showed:S_H＞S_h＞S_v(3)According to the test results,the maximum principal stress value in tunnel body of the engineering area is about 17 Mpa～20Mpa,the Minimum principal stress value about 10Mpa～12Mpa.According to survey results analysis,the current tectonic geostress of the engineering area is relatively strong,so in the tunnel excavation process,possibilities of rockburst disaster can not be ruled out.It is proposed that deep-lying tunnels of 350～450 m depth are made design in relative higher geostress,tunnels of more than 450 m depth design in the highest stress.(4)According to detailed analysis of results of uniaxial compression test,rockburst proneness index test and triaxial unloading testing,rockbursts may occur with the mechanical properties of lithology and strength in ANLU tunnel surrounding rock during the tunnel excavation process(5)Based on analysises of field geostress and rock mechanics test results,it's showed middle-intensity or high rockburst will occurred during the tunnel excavation process.