Abstract: The coefficient of permeability is predominantly determined by the pumping test. There are many analytical methods to interpret the test results for the coefficient of permeability. In general, the test conditions of the in-situ measurement method are more consistent with the actual subsurface condition than that of the laboratory test condition, because laboratory test method cannot simulate the on-site soil layers accurately. It is necessary to determine the site coefficient of permeability by in-situ measurement for a specific soil layer in an actual project in Beijing. Throughout the dewatering wells around the site, a non-pressure complete well point was used for the pumping test, an average coefficient of permeability of the soil layer in the zone by the groundwater variation in the stage of the deep excavation and foundation construction was measured by the in-situ pumping test. The results show that: (1) after a long period of discharge of groundwater, the groundwater level changes significantly; (2) the actual coefficient of permeability k value of the first aquifer layer measured within the dewatering depth ranges from 40 to 50m/d, which is lower than the empirical value recommended in the survey report. (3) The analysis shows that the cobble stratum filled with medium to coarse sand has a significant influence on the coefficient of permeability, and the long-term drainage is the main reason for the decrease of coefficient of permeability. (4) Comparing with the groundwater inflow to the excavated area, the difference of groundwater inflow of different coefficient of permeability is large, which directly affects the construction cost.

Key words: in-situ pumping test, permeability coefficient, dewatering