| In southwest mountainous area, the transmission line towers were located in steep terrain which with complex geological structure and gravel soil or broken rock(or extremely broken) foundation. In addition to the vertical load, transmission line tower pile foundation also would be affected by horizontal force, such as earth pressure, wind load, earthquake action, the wire break and so on. So in the design of transmission tower pile foundation, horizontal interaction between pile and soil problem must be studied. In the process of studying horizontal interaction between pile and soil, analytical method based on m method of elastic foundation beam method, it is widely used in foundation design because it had advantages of clear calculation model and simple calculation process. However, the selection of the proportional coefficient m of foundation horizontal resistance coefficient is a big problem in the engineering, in general, specification recommended value was been referenced and adjusted according to the experience. For most gravel soil foundation of transmission line tower, specification provided only range of m value for reference, which had great randomness. What's more, the accumulated experience value were come from horizontal static load test of single pile at horizontal site, if the data is directly used for horizontal force calculation of transmission tower pile foundation, its safety, suitability and efficiency cannot be guaranteed. Therefor, the paper take the proportional coefficient m of foundation horizontal resistance coefficient on slope site with gravel soil foundation in southwest mountainous area as the research object, according to horizontal static load test of single pile, m method theoretical calculation and equivalent conversion method, indoor physical simulation test analysis, numerical simulation method, mainly got the following conclusions and cognition:(1)In the direction along the slope surface, under the same horizontal loading at the pile top, the greater the terrain slope where the single pile's location is, the bigger the pile's horizontal displacement. The position of pile's zero displacement is mainly in 0.6~0.8 times the pile depth, and it will move down as the slope increased gradually. Under the same loading, the greater the terrain slope, the bigger the bending moment. The position of pile's maximum bending moment is mainly in 0.24~0.32 times the pile depth, and it will move down as the slope increased gradually. Under the same loading, the greater the terrain slope, the bigger the soil pressure in front of pile. The position of maximum soil pressure in front of pile is mainly in 0.24~0.4 times the pile depth, and the position of zero soil pressure in front or back of pile are both in 0.6~0.7 times the pile depth.(2)Near the pile top and pile bottom, pile's displacement and bending moment calculated by m method are close to the measured values based on the single pile load test on slope site. But calculated values are much smaller than the measured values in the central of the pile, and the position of pile's zero displacement which calculated by m method is higher than the measured values based on the test. Thus m method which based on the elastic semi-infinite space namely horizontal site can't be applied in slope site directly.(3)Under the same horizontal loading at the pile top, m appears a non-linear decreased with the increase of load and displacement of pile top. Its decreasing process can be divided into three stages correspondingly according to the pile- soil state system namely elastic, plastic and damage state. According to the empirical formula provided by specification, the m value of test site was calculated preliminarily. The m value reduced by an average of 42%~49% as the slope increases every 15° from 15° to 45°. Taking the ground horizontal displacement which corresponding to the measured critical state under different slope as the target, weakening of soil's character on the horizontal ground equivalent instead of increase of slope. The real m value on slope field can be obtained by above equivalent adjustment. The real m value reduced by an average of 18%~36% as the slope increases every 15°.(4)According to the indoor physical simulation of single pile horizontal load test, horizontal diffusion angle of the soil in front of pile decreases about 25.71% on average, and the pile calculated width decreases about 12.97% as the slope increases every 15° from 15° to 45°. The essential reason why the increscent slope will cause the decrease of m value is as follows: As the increasing slope, the range of soil which play a resistance role to pile's horizontal compressive decreased, then the horizontal diffusion angle of the soil in front of pile decreased, thus the pile calculated width decreased. Through the numerical simulation of the single pile horizontal load test, the conclusion can be obtained as follows: The distribution and development of shear and tensile plastic zone agreement with the soil cracks aroud pile based on the process of the field tests and indoor physical simulation experiment. The range of soil plastic zone in front of the pile narrows down obviously with the increasing slope. It confirmed the rule again that horizontal diffusion angle of the soil in front of pile decreases with the increasing slope.(5)Aiming at the pile whose length is 10.5 m, diameter is 1 m in this test site, according to the different between the preliminary calculation based on the specification's formula and m method equivalent adjustment calculation, the linear decrease rule of the pile calculated width b0 with the increase of slope ? summarized as follow:b0'=b0-0.78545·tan?(0°???66.43°)Using this formula instead of b0 in the standard empirical formula, it supplement and perfect the accessor methods of m value by the horizontal single pile load test on slope site.(6)For the pile whose length is 10.5 m, diameter is 1 m in this test site, the paper put forward the m value simple estimate formula on solp site with average slope ? with gravel soil foundation as follow:m=112-61.25·tan?(0°???61.33°)(7)The m value based on the defined formula py=ky·xy is far less than the one based on the standard method . The definied formula only reflect the distribution of soil resistance model, without considering the soil's applying pressure structure and the external load. The m value based on this way is only connected with the soil's density, deformation modulus, poisson ratio, shear strength and other physical and mechanical properties. But m values in regulate empirical formula is a parameters which reflect resistance performance of the pilesoil interaction system. |
PDF Full Text Request