COMPREHENSIVE GEOLOGICAL PREDICTION AND ENGINEERING COUNTERMEASURES FOR TUNNELING UNDER LANDFILL

The Jigongshan Mountain tunnel,part of the Banyin Expressway in Shenzhen,is designed to cross underneath the Xiaping Municipal Solid Waste Landfill. Due to the prohibition of preliminary geological surveys in the landfill region,the geological conditions and the distribution of leachate and landfill gas remain unknown in the tunnel section under the landfill. Moreover,considering the risk of environmental disaster,the traditional geological prediction methodology is no longer suitable for the project of tunneling under a landfill. This study develops an innovative strategy of geological prediction for tunneling under a landfill. It is based on multiple geological and geophysical methods. It includes tunnel geological prediction(TGP),transient electromagnetic method(TEM),geological drilling,and chemical analysis. We also performed comprehensive detection and analysis on the quality of surround rock and the distribution of leachate and landfill gas under the landfill. The results show the following findings:(1)The comprehensive prediction method can improve the accuracy of the determination of surround rock quality ahead of the tunnel. (2)Potential leachate pathways connecting the landfill bottom and the tunnel are detected,however,no leachate and landfill gas leakage occur yet. (3)In the tunnel sections with high leakage risk,enhancement of the lining material and waterproof layer is put into practice during tunnel construction. This study offers a valuable reference for similar investigative projects concerning tunnel construction in regions with potential environmental risk.