INVESTIGATION OF ENGINEERING GEOLOGY IN SATURATED LOESS FOR SELECTION OF TUNNEL CONSTRUCTION METHODS IN YINTAO WATER SUPPLY PROJECT,GANSU PROVINCE

The 13th,14th and 15th tunnels on general main canal of the First-phase Engineering of Gansu Yintao Water Supply Project go through saturated loess stratum in al-lQ2.Underground water level is about 4 to 37 meters higher than the tunnel crest.The saturated degree of loess is generally 98～100℅.The saturated loess stability is poor.Choosing the method of the construction in the tunnel is very important.its the engineering characteristics are examined using engineering geology methods.The Drucker-Prager elastic-plastic model and associated flow rule are adopted.The stability of the traditional drilling and blasting method is assessed for the tunnel.It is found that the drilling and blasting method,can cause the large lower stress area in the tunnel surroundings.The displacement of the tunnel is quickly developed and very large.Consequently,the tunnel crest can fall and collapse.It can results in sinking in the ground.The paper further analyzes the adaptability of the shield tunneling method.This construction method has lower risk.It quickly closes to round the rock using the shield in the construction process.Therefore, it is suggested that this tunnel choose the shield tunneling method.