【作者】 陈婷婷；

【导师】 王贵君；

【作者基本信息】 河北工业大学 ， 结构工程， 2009， 硕士

【摘要】 双排桩支护结构作为一种新的支护结构体系在深基坑工程中得到了广泛地应用,但人们对双排桩的作用机理还不是很清楚,所以还有许多问题值得我们的研究。实际工程中就出现了一种降低前排桩,在前后排桩之间加设起加强作用的肋板或斜撑,与前后排的帽梁整体现浇的支护结构形式,本文称其为双排高低桩支护结构。本文针对这种双排高低桩支护结构形式,根据天津某基坑工程实例,使用ANSYS软件,建立三维实体模型,进行有限元分析,通过分析有限元计算结果得出双排高低桩支护结构的工作机理;进一步研究后排桩长度,排距,桩前被动区土体加固,斜撑刚度等因素对双排高低桩支护结构支护效果的影响;主要结论如下:1.双排高低桩支护结构的桩身侧向位移呈现为“两头小,中间大”的变形曲线。2.支护结构上土压力的大小与支护结构的位移大小密切相关。总的来说,桩后土压力大小标高-11.5m以上介于静止土压力与朗肯主动土压力之间,标高-11.5m以下至桩底段要小于朗肯主动土压力;在基坑开挖到一定深度时,桩间土压力就不再变化,说明桩间土体与支护结构共同工作,土压力大小介于静止土压力与朗肯主动土压力之间。随着基坑的开挖,前排桩向坑内位移,必然导致桩前的土压力增大,但是由于开挖面的卸载,竖向应力减小,导致水平应力减小,两种作用相叠加的结果使作用在前排桩桩前的土压力远小于被动土压力。3.后排桩最大弯矩发生在前后排桩间连梁位置,前排桩最大弯矩发生在桩顶至基坑开挖面之间的位置,后排桩弯矩反弯点发生在后排桩的根部,前排桩弯矩反弯点发生在在基坑开挖面以下5-6m左右,反弯点以上右侧受拉。前后排桩的最大应力绝对值相差不大,说明前排桩承受的土压力大小差不多,受力比较合理。4.土体塑性区域主要发生在桩前基坑开挖面以下部位,由于塑性区的发展与土体性质密切相关,所以说对桩前被动区土体加固可以有效控制塑性区的发展。5.双排高低桩支护结构的最大特点是桩顶位移增量很小,主要原因是斜撑起到了很重要的作用。双排高低桩支护结构在斜撑充分发挥作用的情况下起到了自撑的作用,可以有效的控制桩后土体的水平位移,从而确保周围环境的安全。6.双排高低桩支护结构对桩后土体水平位移的控制要强于等高的双排桩支护结构。7.增大后排桩长度对减小坑后土体位移有一定作用,但影响很小,而且还会增加工程造价,除非是为了满足整体抗倾覆要求,一般在实际工程中可以适当减小后排桩长度以减少造价。8.增大前后排桩排距可以减小桩身最大水平位移。同时应注意,斜撑的安置以与水平线成450角为宜。更多还原

【Abstract】 Retaining structure with double-row piles as a new supporting structure system has been widely used in deep excavation, at the same time, many scholars have done a lot of research on it. But the mechanism of the retaining structure with double-row pile is still not clear. Retaining structure with double-row piles whose front pile is lower than the rear pile has been used in deep excavation.In this paper, a three-dimensional finite element model of this new retaining structure form, according to a foundation pit project in Tianjin has been proposed. In this model, the finite element software Ansys is used .Through the analysis of the results of finite element calculation, we can get the working mechanism of the high and low double-row piles. And then some factors which have influences to the working result of the retaining structure are analyzed, such as the length of the rear pile, the array pitch of the front pile and the rear pile, the reinforcement of the passive domain soil and the stiffness of the brace. The main results are as following:1. The maximal horizontal displacement of retaining structure occurs in the middle of the pile.2. The earth pressure on the retaining structure is related with the displacement of the the retaining structure. Above 11.5m, the earth pressure on the back of the rear pile is between the static earth pressure and the active soil pressure of Rankine, and below 11.5 m, the earth pressure on the back of the rear pile is smaller than the active soil pressure of Rankine. When the foundation pit is excavated to a level, the earth pressure between the piles will not change. It indicates that the earth between the piles and the piles work together. The earth pressure between the piles is also between the static earth pressure and the active soil pressure of Rankine. The earth pressure on the front of the front pile is smaller than the passive soil pressure of Rankine.3. The maximum moment of the rear pile occurs under the beam connecting the two piles, and the maximum moment of the front pile occurs between the top of the pile and the excavated bottom. The maximum moment of the two piles is nearly equal, that indicating the retaining structure is reasonable.4. The plastic strain occurs in front of the front pile under the excavated level. The size of the plastic area is related with the property of the earth, so reinforcing the earth in front of the front pile can control the size of the plastic area. 5. As the excavation proceeded, the increment of displacement of pile top is very small, for the oblique brace playing an important role. Retaining structure with double-row piles whose front pile is lower than the rear pile can support itself to control the displacement of soil behind the pile effectively, so as to ensure the safety of the surrounding environment.6. Retaining structure with double-row piles whose front pile is lower than the rear pile can control the horizontal displacement of soil behind the pile better than double-row piles with pile top at the same altitude.7. Increasing the length of the rear pile has a little effect on reducing the displacement of soil behind the pile, but also increase the project cost, unless it is in order to meet the requirements of the overall anti-overturning , we can be appropriate to reduce the rear pile length in order to reduce the cost.8. Increasing the array pitch can reduce the maximal horizontal displacement of retaining structure. When you do it, you should notice that 450 is the appropriate angle for the bevel between the oblique brace and the horizontal.更多还原