Reduction of Interface Friction between Pressed-in Caisson and Soil deposits by Non-Friction Method

• Main Authors: Weng, Chen-Shao, 翁承劭
• Other Authors: Fang, Yung-Show
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/61776273137716842942

碩士 === 國立交通大學 === 土木工程系所 === 103 === This thesis investigated the reduction of interface friction between the pressed-in caisson and the soil by the air-jet direct shear tests. A special air jet direct shear experiment was designed and constructed at the National Chiao Tung University soil mechanics laboratory to simulate no-friction method(NF) method and air jet method for the construction of a pressed-in caisson. Direct shear tests were used to study the interface friction between concrete sample and Ottawa sand, and the reduction of interface friction angle by the thin steal of NF sheet. The relation between the applied air pressure and the interface friction angle was studied by varying the air pressure ratio(APR). The APR is defined as the ratio of applied air pressure (σa) and the interface normal stress (σn), during the air-jet direct shear test. Test results indicated that the residual internal friction of the medium dense Ottawa sand(Dr=55%) was 31.3°. By using the NF sheet, the interface fiction angle between the concrete sample and Ottawa sand was reduced to 22°. By place of the NF sheet between the sand and the concrete sample, the interface angle was reduced to 16.7°. Test results of the air-jet direct shear test indicated that the interface friction angle between NF sheet and the concrete sample was reduced to 12.7°, 9.6°, and 8.8°, corresponding to an APR ratio of 1, 2, and 3 respectively. However, the interface friction angle remain a constant after the ratio exceeded 3. In other words, an increase of APR beyond 3 has no effect on the friction angle between the concrete sample and the NF plate. The ultimate interface angle was 8.8°. Test results of press-in caisson indicated that the air- jet method could effectively reduce the friction between caisson and soil up to 7.9°. However, pumping compressed air into the ground might have adverse effects to the deposits surrounding the caisson.