|Alternative Title||Experimental Study on the Influence of Foundation Soil Properties for Groundwater Buoyancy|
|Place of Conferral||兰州|
|Keyword||地下水浮力 模型试验 电镜试验 折减系数|
With the development of underground space，the excavation depth of the foundation ditch is getting deeper and deeper, and the problem of anti floatability caused by groundwater has gradually become the focus of attention. However,according to monitoring of groundwater buoyancy results in some projects, the actual buoyancy is less than the of groundwater buoyancy which is calculated according to the traditional method, so it is still in accordance with the traditional calculation method of groundwater buoyancy and anti floating design, which could cause economic engineering and waste of time. In the design process, the method of reducing the buoyancy of groundwater is stipulated in engineering specifications, but it is not clear enough. If we blindly reduce buoyancy, it is likely to cause an anti floating accident. Therefore, in order to provide reference for engineering, it is very important to study the influence of ground soil on ground water buoyancy.
In this paper, the different conditions of calculating the buoyancy of underground water in engineering are divided. Combined with the analysis results of seepage theory and buoyancy calculation method, the test contents are designed. The experiment mainly includes macroscopic model test and microscopic electron microscope test. The model test mainly studies the influence of different permeability coefficient foundation, different seepage water level and different seepage paths on the buoyancy of groundwater. The microstructure and pore changes of the soil before and after the soil infiltration are analyzed in the microscopic test, and the phenomenon of the model test is explained from the mechanism.According to the model test results, in the clay foundation, the seepage rate, pore water pressure and seepage energy are all influenced by the close contact surface of bottom of the building and foundation, while the open condition is not the same. In addition, the seepage and buoyancy variations of silt foundation, lime soil foundation and clay foundation with 10-5cm/s, 10-6cm/s and 10-8cm/s penetration are compared. It is found that the measured buoyancy force < the buoyancy force of the pore water < theoretical buoyancy in the three foundations, and the smaller the permeability coefficient is, the greater the reduction of the buoyancy force and the measured buoyancy of the pore water is. However, this reduction effect will gradually weaken with the increase of seepage water level. The buoyancy reduction coefficient was fitted with the law of foundation permeability coefficient and found a linear growth relationship. Finally, the reduction coefficient of the silt foundation is 0.85~0.94, the lime soil foundation is 0.75~0.79, and the clay foundation is 0.63~0.70. From the analysis of the microscopic test results, the pore area of the foundation is the main factor influencing the buoyancy reduction, the low permeability foundation before and after the seepage,the particle structure always closely, the pore increase is less than hypertonic foundation, it can still cause considerable reduction of buoyancy when the seepage water level is higher. Therefore, it is suggested that low permeability foundation or general seepage foundation are encountered in engineering, buoyancy should be considered as a proper reduction when the seepage water level is low, but the premise is to guarantee the backfilling and seepage prevention of the foundation pit well.
|刘博怀. 地基土性质对地下水浮力影响试验研究[D]. 兰州. 兰州大学,2018.|
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