Cone penetration tests for the examination of plugging effect of open-ended piles

摘要

A series of model tests has been conducted to study on the applicability of cone penetration tests for the examination of the plugging effect of open-ended piles. The results obtained by the tests were as follows. 1. Vertical distributions of the cone resistance of the ground inside piles are wholly different between in case of plugged open-end piles and unplugged piles. 2. If the plugging effect is not mobilized, a peak of the cone resistance of the ground inside the pile appears at the center of the soil column inside the pile. However, in case of the pile plugged enough, the cone resistance of the inside ground keeps on increasing with the depth (see Fig. 10). 3. If the open-ended pile is not plugged, there is no difference in the cone resistance of the ground around piles before and after the pile driving. 4. The vertical distribution of the cone resistance of the ground around the open-ended pile plugged enough is similar to that around the closed end pile. 5. In the shallow area of the ground around the plugged pile, the cone resistance decreases because of the deformation of the ground following the pile installation. 6. In the area beneath the bottom tip of the pile, the cone resistance increases because of the compression of the ground accompanied with the pile driving. Figure 10 shows a summary of the vertical distribution of the cone resistance inside the open-ended pile. Figure 11 is a schematic figure zoning the ground into the areas with the reduction of the cone resistance and with the increment of cone resistance. In Fig. 11, the area in which the reduction of the cone resistance appears is indicated as (1), and the area with increase of the cone resistance is indicated as (2). The range of the areas (1) and (2) depends on the level of the plugging effect. The results of the cone penetration tests are different in the cases of the plugged pile and the unplugged pile. Hence it is possible to examine the development of the plugging effect by use of cone penetration tests. In the present study, no data of in-situ tests were taken into consideration. Further research is required to develop a test method for in-situ investigations of the plugging effect of open-ended piles by use of cone penetration tests.