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  Evaluation of Multi-Standpipe Grouting Technique for Mae Ngad - Mae Kuang Water Diversion Tunnel Project

  Tunnel excavation in Mae Ngad - Mae Kuang Water Diversion Tunnel Project has hit several water-bearing zones. Inflow more than 500 liters/minute was frequently recorded but the allowable water inflow level for this project is 60 liters/minute per 100 meters. An insufficient capacity of water pumping of the project results in flooding by as much as 0.5 meters. Multi-standpipe grouting is conducted in those zones to reduce permeability of the surrounding rock mass. The grouting technique is conducted by inserting three standpipes into drilled holes at different depths and injecting individual grouts to each standpipe so that different zones along the boreholes can be treated properly by different materials and operational techniques. Two grout mixes is used in this project site. One is the combination of cement slurry with sodium silicate and silica gels. Another is the mixture of sodium silicate with silica gel. Control of water ingress into the tunnel after grouting is satisfactory. Based on the assessment of the grouting result, actual grout take is around 25-50 percent of as design and jacking is usually observed when grouting pressure reaches 30-50 bar.

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