Seepage Analysis for Rock Tunnel Construction Based on Analytical Methods
Lanting WU1, Jianping SUN2#+
1China Communications Construction Company Limited (Singapore Branch), Singapore, 2CCCC-SJ PTE LTD, Singapore

Rock tunnel/cavern excavation involves high risk of unforeseen ground conditions. One of the risks is the chance of hitting the water bearing zone. And rock grouting is considered as the most efficient method to reduce the water inflow. To determine whether rock grouting is needed, the probing should be carried out first. If the expected water inflow from probe hole is larger than the allowable maximum water inflow, the grouting will be carried out to achieve the strict requirement on the water inflow. After grouting, check hole(s) will be drilled on the same face and same length as the grouted hole. If water inflow is still higher than threshold value, grouting procedure will be repeated until to achieve the grout target. Although many researchers conducted studies related to water flow into subsea tunnel and rock grouting, the knowledge on the practical execution is still limited. Based on other researchers’ work, the analytical solutions of water flow for each step of subsea tunnel construction (i.e. probe hole, tunnel before grouting, tunnel after grouting and check hole) have been derived. Based on the study on these analytical solutions, the key findings are summarized as below: 1. The variation of water flow in probe hole is within 3% when the probe hole diameter increases from 48mm to 60mm, which means there is little influence of probe hole diameter change on the water flow into the probe hole. 2. The variation of water flow into probe hole can be up to 25% when the water pressure in probe hole increases from 0m water head to 12m water head, which means it is important to measure the water pressure and water flow quantities simultaneously. 3. There is a linear relationship for the water flow between probe hole and tunnel, which tally with the actual practice. 4. Decreasing the permeability of the grouted zone contributes to a decrease of the water inflow. However, when the permeability of the grouted zone decreases to a certain value, the water inflow is no longer decreased significantly, which tally with the practical experience.