Bearing Mechanism Of Squeezed Branch Disk Pile

As a new type of pile based on multi-level bored piles, the squeezed branch disk pile has been marked economic and social benefits. Specific hydraulic equipment is used with the present pile facility to form the 'branch' and 'disk' in appropriate layers, and squeeze compactly the surrounding soil. Therefore, the potential reserve of foundation soil is exploited in view of partially improvement of the physical properties and mechanical indices of soil. Also, the load-bearing mechanism of base pile has been changed, and its bearing capacity has been greatly improved because the end load-bearing area of base pile is enlarged and the original friction pile with one end load-bearing point has become a friction pile with multiple end load-bearing points.Based on the static loading tests about two pile types, namely 6 piles of Yuzhou Power Station, the settlement behavior of single pile is analyzed, and the stress and compressing deformation of test pile body is computed by using the nonlinear formula of concrete stress-strain under one-way pressure. In addition, the load transfer function models of friction and end-bearing of some subsections are set up, and the condition of any resistance is analyzed by introducing the curves of settlement - subsection resistance(s-SR) and settlement - subsection resistance ratio (s - SRR). Finally, the effect of the sizes and shapes of branch and disk, the obliquity of foundation bottom and the degree of squeeze on the bearing capacity is discussed. And the main achievements, which can be regarded as references in design and construction practice, are made in the following aspects.1. All of load-settlement (Q-s) curves are gradually declining when the load is less than the bearing capacity of pile, while the settlement-time logarithm (s-logt) curves appear as an abrupt or gradually declining change on condition that the final load is close to vertical bearing capacity of pile or not.2. The load transfer function model of skin friction is a linear strain-hardening elastic-plastic and that of the end-bearing a power function, while there exists the phenomenon of soften-unloading for the skin friction and end-bearing after the displacement is greater than the ultimate value.3. The s-SRR curves can vividly illustrate the varying process and distribution of resistance of pile cell on the upper section of pile, and the transferring course of principal and subordinate resistance subsection.4. Through the distribution and transfer of resistance of every subsection of pile, the end-bearing of disk will be adequately utilized, and then the bearing capacity of pile will be improved in a large scale.5. The resistance of branch consists of end-bearing and friction of skin, and the ultimate end-bearing of disk is difficult to be obtained unless the settlement of pile is much great. In addition, the obliquity of foundation base under the branch and disk don't have influence on their end-bearing.