Earth Pressures Due to Vibratory Compaction
Dr. Yung-Show Fang
|關鍵字:||土壓力;振動夯實;邊界摩擦;擋土牆;承載力;潤滑層;砂;Earth Pressures;Vibratory Compaction;sliding block testing device;boundary friction;plastic sheet method;retaining wall;bearing capacity;lubrication|
Earth Pressures Due to Vibratory Compaction Student : Tsang-Jiang Chen Advisor : Dr. Yung-Show Fang Institute of Civil Engineering National Chiao Tung University Abstract To model plane strain conditions in the laboratory, the frictional resistance between the soil and side walls of the soil box should be reduced as much as possible. In this dissertation, a new sliding block testing device for measuring the friction at the interface between soil and different materials at low stress conditions is described. Interface friction angles for eight different methods for reducing boundary friction were investigated using the proposed testing method. Test results indicated that the friction angle obtained with the plastic sheet method is nearly independent of the normal stress. On the other hand, the interface friction angle of the grease method was quite high under low normal stress conditions. Thus, the plastic sheet method appears to be a more appropriate technique under low normal stress conditions to reduce the boundary friction for laboratory scale model tests. As compared with the grease method, advantages of the plastic sheet method include constant friction angles, less time for preparation and clean-up, and lower cost. To investigate their applicability, both lubrication systems were used in some large-scale laboratory retaining wall experiments. Earth pressure measurements obtained near the side walls indicated that, under a low normal stress, the plastic sheet method was more effective in reducing side wall friction. In the second part of this dissertation, with the plastic-sheet technique developed in the first part of this study, experiments were conducted to investigate the earth pressures due to vibratory compaction. To study the compaction-induced stresses experimentally, a unique non-yielding retaining wall was designed and constructed at National Chiao Tung University. Air-dry Ottawa sand was used as backfill material. Vertical and horizontal stresses in the soil mass were measured in loose and compacted sand. Based on the test results, the following conclusions can be drawn. (1) For a loose backfill, the vertical and horizontal earth pressure in the soil mass can be properly estimated with the equation □v = □z and Jaky’s equation, respectively; (2) The compaction process does not result in any residual stress in the vertical direction. The effects of vibratory compaction on the vertical overburden pressure are insignificantly; (3) After compaction, the lateral stress measured near the top of backfill is almost identical to the passive earth pressure estimated with Rankine theory. The compaction-influenced zone rises with rising compaction surface. Below the compaction-influenced zone, the horizontal stresses converge to the earth pressure at-rest; (4) When total (static + dynamic) loading due to the vibratory compacting equipment exceeds the bearing capacity of foundation soils, the mechanism of vibratory compaction on soil can be described with the bearing capacity failure of foundation soils; (5) The vibratory compaction on top of the backfill transmits elastic waves through soil elements continuously. For soils below the compaction-influenced zone, soil particles are vibrated. The passive state of stress among particles is disturbed. The horizontal stresses among soil particles readjust under the application of a uniform overburden pressure and constrained lateral deformation, and eventually converge to the at-rest state of stress.
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