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Due to rising price of land in Kaohsiung, apartment buildings outnumber townhouses. During the deep excavation of new apartment construction projects, the settlement of adjacent land often happens due to the displacement of retaining walls, which endangers adjacent buildings and results in the protests of residents. This problem usually happens when diaphragm walls are displaced (lateral displacement) during excavation. In order to ameliorate such problems, current engineering projects usually adopt inner buttresses for diaphragm walls to reduce displacement. However, the geology of most regions in Kaohsiung is composed of alternating sand and clay stratums; therefore, at the joining section of the inner buttress and diaphragm wall, the effect of the buttress is not good because the clay contains mud inside. Therefore, CCP improvement piles are used to replace the inner buttress of the diaphragm walls by arraying them as is done for buttresses. The purpose of this study was to explore the improvement on the displacement of diaphragm walls during deep excavation using the improved pile buttresses. The study adopted RIDO numerical value to carry out data analysis for the arrangement of the improved buttresses and to verify its feasibility. Two kinds of cases, with or without the buttresses, were used for the numeric analysis. The buttress model proposed by Hsieh and the model for the ultimate resistance of soil to the pile proposed by Reese are used for the feedback analysis of the diaphragm with the improved buttresses. The results showed that the displacement of the diaphragm wall is close to that of the monitoring values, if the spring constant of the soil is increased to 3 times that of Hsieh’s model. The displacement of the diaphragm wall at the final excavation is well agreed to that of the monitoring values, if the Reese model is used. The depth of excavation in this case is only 9 m in total, the Reese model is require the further study through the number of case studies to proof its feasibility.
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