Shaft Grouting HATS2A Hong Kong
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In this thesis I have been following 5 grouting rounds at Cyberport shaft and 4 grouting rounds at Sandy Bay shaft. There were some communication problems between the grouting team and the geologists, resulting in missing water inflow measurements. The rock quality was very poor (Q-value 0.1 – 1), with coarse ash tuff as the most common rock mass in Cyberport, and rhyolitic tuff as the most common rock mass in Sandy Bay. The Q-values were below 1, with Cyberport just a bit higher than Sandy Bay. The rock mass was highly fractured, which was indicated by a low RQD value. Sand and silty infill was found in both shafts. Sandy bay hit a fault zone at grouting 3, with a very jointed rock at various orientations, often clay infill on joints. Micro cement with super plasticizer was the primary grouting material. Water to cement ratio 1 was mostly used. The ratio was sometimes dropped down to 0.8 and 0.6 after a certain amount of micro cement w/c 1 had been pumped. Polyurethane was used to block leakages. Pressure at 40 bar was mostly used as stop criteria. 5 out of 5 grouting rounds in Sandy Bay were with 40 bar as stop criteria, and 6 out of 9 in Cyberport. 60 bar pressure as stop criteria was only used twice, in round 3a and 5c at Cyberport. Grouting was normally stopped by overpressure, which means that the pressure exceeded 40 bar. If the stop criteria had been 60 bar, higher amounts of micro cement would most likely have been pumped into the rock mass. The drilling pattern followed a standard description mentioned in the method statement. Every contour hole was placed 1 m from each other, forming the outer circle. Ten holes were placed in the middle of the shaft. 5m overlap between the different grouting screens was set as minimum. The water level sometimes fell to alarm level, measured from the piezometer. When this happened, grouting was immediately started to increase the water level, and it worked. Water level started increasing just hours after grouting was started. Material costs were low for both shafts. This is directly related to the small amount of material that was pumped into the rock mass. Infill of sand and silt might be the reason to this. Labour costs are roughly estimated to around 308 000 NOK per day. Delay and deviation from the planned time usage, when it comes to grouting works, will cost the project around 1 130 000 NOK, for the grouting rounds mentioned in this thesis. Sandy Bay only needed one extra grouting round, this at grouting number 2. Cyberport on the other hand, needed four extra grouting rounds, this at grouting number 3, 4 and 5.