Kiyotaka ANNAKA
Performance tests for lubricants to reduce skin friction during immersion of caisson foundation
Supervisor: Hirofumi TOYOTA
There is a caisson foundation used for large structure. The method of construction is that a precast concrete box is immersed by excavation of bottom soil of the box. There is some possibility that the skin friction between the box and soil interferes that the precast concrete box sinks to enough depth. Therefore, introduction of friction reduction method is necessary for the caisson foundation.
The method, where a lubricant is injected between the box and soil, is usually applied to the foundation. Bentonite slurry is commonly used for the lubricant. Bentonite, which exhibits highly expansive behavior, is suitable as lubricant because bentonite slurry is pasty liquid.
In the box shear test, concrete mortar plate was placed in the lower box, and lubricant was put on the concrete mortar, and soil sample was set in the upper box. The performance of K-lubricant was evaluated using the box shear tests comparing with that of the bentonite-lubricant.
The main results are summarized as follows:
1. The K-lubricant is more difficult to penetrate into soils than the bentonite-lubricant.
2. Friction reduction of K-lubricant is initially superior to that of the bentonite-lubricant.
3. In the case of sand, persistence of K-lubricant is superior to that of the bentonite-lubricant under low confining stress. However, this effect doesn¡Çt appear under high confining stress.
4. In the case of clay, persistence of K-lubricant is inferior to that of the bentonite-lubricant.
5. When K-lubricant and the bentonite-lubricant are mixed with cement grout, each of shear strengths between soil and cement mortar becomes bigger than the case without lubricant is obtained.
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