兰州大学机构库 >土木工程与力学学院
地基土性质对地下水浮力影响试验研究
Alternative TitleExperimental Study on the Influence of Foundation Soil Properties for Groundwater Buoyancy
刘博怀
Thesis Advisor张豫川
2018-05-03
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword地下水浮力 模型试验 电镜试验 折减系数
Abstract

随着地下空间的发展,基坑的开挖深度也越来越深,地下水引起的工程抗浮问题逐渐成为人们关注的焦点。但是在某些工程中对地下水浮力的监测结果显示,建筑物受到的实际浮力小于按照传统的方法计算得到的地下水浮力,因此仍按照传统方法计算地下水浮力并进行抗浮设计,就可能会造成工程经济和时间的浪费。而在设计过程中对地下水浮力进行折减的方法在工程规范中虽然有规定,但不够明确,如果盲目的对浮力进行折减很可能引起抗浮事故。为向工程提供参考依据,对地基土如何影响地下水浮力进行研究显得尤为重要。

本文对工程中计算地下水浮力的不同工况进行了划分,结合渗流理论和浮力计算方法的分析结果设计了试验内容。试验主要包括宏观模型试验和微观电镜试验,其中模型试验主要研究了地基土在不同渗透性、不同渗流水位和不同渗流路径下对地下水浮力的影响。而微观试验则从地基土渗透前后颗粒结构和孔隙变化方面进行了分析,从机理上解释了模型试验现象。

由模型试验结果得知:在粘土地基中,建筑物基底和地基的接触面四周封闭时,渗流速率、孔隙水压力、渗流能量等均受到较大影响,而开放工况则不然。此外,通过比较渗透数量级分别为10-5cm/s、10-6cm/s、10-8cm/s的粉土地基、灰土地基、粘土地基的渗流和浮力变化规律。发现在三种地基中均表现为实测浮力<孔隙水浮力<理论浮力,其中渗透系数越小的地基对孔隙水浮力和实测浮力的折减也越大。但这种折减效果会随着渗流水位的增加而逐渐减弱,并趋于稳定。将浮力折减系数随地基渗透系数变化规律进行拟合,发现呈线性增长的关系。最终粉土地基的折减系数为0.85~0.94,灰土地基为0.75~0.79,粘土地基为0.63~0.70。由微观试验结果分析可知,地基中的孔隙面积是影响浮力折减的主要原因,其中低渗性地基渗流前后颗粒结构一直较为紧密,孔隙增大情况相对于高渗性地基较弱,所以在渗流水位较高时仍能对浮力造成较为可观的折减。因此建议工程中遇到低渗性地基或一般性渗透地基但渗流水位较低时,应该考虑浮力适当折减,但前提是做好基坑肥槽的回填和防渗。

Other Abstract

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.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226599
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
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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