大厚度自重湿陷性黄土场地桩基负摩阻力试验研究

发布时间：2018-01-11 01:08

本文关键词：大厚度自重湿陷性黄土场地桩基负摩阻力试验研究　出处：《兰州理工大学》2013年硕士论文　论文类型：学位论文

【摘要】：在我国西北地区,存在着大面积的自重湿陷性黄土,如何避免由于黄土湿陷性产生的负摩阻力给桩基工程带来的巨大危害,已经成为人们关注的重点问题。然而现有的许多理论研究,尤其是桩—土相互作用理论研究的不完整性己不能完全满足日益发展的工程建设的需要。因此对桩基进行现场原位试验依然是研究其属性的行之有效的根本方法,对完善其设计理论,指导工程实践都有着十分重要的意义。本文结合中国移动集团甘肃定西分公司综合楼项目,在大厚度自重湿陷性黄土场地上进行了长时间的桩基浸水载荷试验,设置试验桩三根,试验桩直径800mm,桩长分别为26m、29m、31.5m,注水试坑深度2m。其中试桩-1和试桩-2进行承载力和负摩阻力测试,试桩-3只进行承载力测试,并在试桩-1和试桩-2桩身埋设了大量的钢筋应变计和混凝土应变计,并在桩周45度对角线埋设了两组分层沉降计用以观测土体沉降情况。试验对不同深度下、不同范围内的桩侧负摩阻力的变化特征以及土体的沉降过程进行了分析。现将实验结果及分析总结如下： (1)在本文所指出的特殊浸水条件下,桩侧正、负摩阻力的变化以及土体沉降变化均呈现出多峰值状态,即沿桩身长度向下,正、负摩阻力的分布出现交错分布状态,即不再是由一个中性点将正负摩阻力分开,而是出现了多个中性点；桩周土体沉降量亦沿桩身出现多个峰值,并且其变化趋势直接影响桩侧正、负摩阻力沿桩身交替变化的走势；黄土的实际湿陷情况是分段发生湿陷的,而不是如传统观点所述在单一中性点以上突然出现整段湿陷。 (2)当考虑预浸水作用时,即两桩在相互影响作用下得出了以下结论：单桩竖向承载力试验得出的试桩-2承载力较试桩-1有明显的降低,降低幅度大约为20%左右；试桩-2在预浸水后再加载,其正摩阻力呈现出随荷载增大而增大的现象,而负摩阻力则是随桩顶荷载的增大而增大。桩端阻力由于预浸水的作用,使得试桩-2相较试桩-1基本未发挥,维持在10kN左右,可忽略不计；对于预浸水之后加载,再进行大面积浸水试验后,试桩-2相较于试桩-1,桩侧阻力沿桩身的正负分布区段呈相反的状态；试桩-2在6.5m和约9.7m两个位置处呈现出随时间增长,中性点位置反而上升的规律。
[Abstract]:In Northwest China, there is a large area of self weight collapsible loess, how to avoid because of the huge damage of negative friction resistance of loess collapsibility has brought to pile foundation engineering, has become the focus of attention. However, many of the existing theories, especially the theory of the interaction of soil pile is not complete has not fully meet the growing needs of engineering construction. Therefore on the pile in-situ test is still fundamentally effective method to investigate its properties, to improve the design theory, there are ten important guiding significance in engineering practice.
According to China Mobile group Gansu Dingxi branch building, the pile foundation water load test for long time in thick loess soil, set the test pile three, pile diameter 800mm, pile length were 26m, 29m, 31.5m, 2M. and flooding test pit depth pile test -1 and test -2 pile bearing capacity and negative friction test, only -3 pile bearing capacity test, and the test of pile and -1 pile -2 pile buried large reinforced concrete strain gauge and strain gauge, and in a pile of 45 degree diagonal buried two groups of layered settlement meter for settlement observation. Test of different depth, the settlement process variation of pile side friction in different areas and soil are analyzed. The experimental results and analysis are summarized as follows:
(1) special submergerence pointed out in this paper, the pile side is changed, the negative friction and soil settlement variation showed multi peak state, namely downward along the pile length is, the distribution of negative friction resistance of staggered distribution, that is no longer separated by a neutral point and negative friction resistance but, there is more than one neutral point; pile of soil along the pile settlement also had many peaks, and their trends directly affect the pile side friction along the trend of positive and negative pile alternating loess collapsibility; actual situation is segmented has collapsibility, but not as the traditional view of the in a single neutral point above the whole collapse suddenly appeared.
(2) when the effect of pre immersion is considered, the following conclusions are drawn under the interaction of two piles.
Test the test result of pile -2 pile bearing capacity is -1 significantly reduced the single pile vertical bearing, reduce the amplitude is about 20%; pile -2 in pre immersion after loading, the positive friction presents with the load increases with the increase of the phenomenon, while the negative friction is increased with the top of the pile the load increases. The pile tip resistance due to pre soaking effect, the test pile -2 pile -1 compared to did not play, maintained at about 10kN is negligible; for pre immersion after loading, then a large area of water immersion test, test pile -2 compared with -1 pile, pile side resistance along the pile of positive and negative the distribution section showed the opposite state; pile -2 in 6.5m and 9.7M at two locations showed increased over time, but the rise of the neutral point position.

【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU473.1

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