| Summary: | 碩士 === 朝陽大學 === 營建工程系碩士班 === 87 === The lateral earth pressure envelopes have established for sands and clays only. There are no available guidelines for lateral earth pressure envelope in gravel formations. Therefore, this research collects twenty six deep excavation cases, all with in situ monitoring data, in gravel deposits in Taichung areas. Monitoring results of horizontal strut forces, inclination and deformation of retention systems, and surface settlements for each case were synthesized and analyzed.
About 57% of the maximum lateral deflections occurred at the top of the retaining wall, and the creep of the wall deformation after completion of excavation is negligible. There is a direct and positive relationship between maximum surface settlement and maximum lateral deflection. The value of apparent earth pressure has the tendency to increase as the depth of excavation increased. Therefore, the apparent cohesion could be present while shearing because of interlocking effects between granulars. The distributions of apparent earth pressure at different excavation depths are normalized and obtained as follows: for excavation depth (H) less than 15 m, the coefficient of apparent earth pressure (TN) is 0.07; for H between 15 and 20m, TN is 0.09; and for H between 20 and 27m, TN is 0.11. Above the envelope curve of apparent earth pressure by gradient distribution is all 0.1H、0.65H and 0.25H. For H less than 27 m, the magnitude of calculated TN is less than half of the suggested value for dense sands by the code. According to the transformation of apparent earth pressure and strut force, we can find the cohesion is about 1.0~2.0 t/m2 ；friction angle is about 45°~55°; it is similar to earth pressure at rest is about 0.1~0.3 in the gravel. It is also found that the types of horizontal struts (H-steel beams) could be suggested for different excavation depths. For depth less than 15m, the strut is suggested to use H300x300x10x15. For depth between 15 and 20m, the strut is suggested to use H350x350x12x19. The horizontal interval between struts could be increased to 7 to 9 m in order to increase the operation space and to decrease the cost of construction.
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