大比尺钢管桩桩周土开挖条件下稳定性试验研究

发布时间：2018-07-08 19:42

本文选题：大比尺 + 钢管桩　；参考：《山东建筑大学》2017年硕士论文

【摘要】：随着我国城镇化进程不断推进,许多既有建筑物因缺少地下停车场等设施,其使用功能上的缺陷日益凸显出来,既有建筑地下空间的开发和利用越来越引起人们的重视。既有建筑地下增层时,需要先利用原有的桩基或者设置新的桩基承担既有建筑物的荷载,然后开挖土方,增设地下室。在开挖桩周土过程中,桩基稳定性会明显降低。钢管桩基础是最常用的桩基形式之一,通过大比尺模型试验的方法研究钢管桩的稳定性具有十分重要的意义。为了能够顺利开展模型试验,设计并制作了2.5m×2.5m×3.0m土工模型箱。它由四周围起的竖向钢板和外围通过螺栓相连的水平箍组成。模型箱四个大角上的角钢与相邻的竖立钢板通过螺栓固定后,可形成模型箱的“临时骨架”,同时防止箱内装满的土体沿两钢板接缝处泄漏。提出了模型箱的竖向钢板、水平箍和连接螺栓的设计方法,并通过一个实例介绍了模型箱的设计过程。本文针对土体为中砂的情况,对大比尺钢管桩桩周土开挖条件下的桩身稳定性问题进行了试验研究。通过模型实验,(1)研究了桩周土在不同开挖比条件下桩身以及支撑的荷载-应变变化规律;(2)通过改变钢管桩的回转半径、偏心距、支撑位置、支撑数目、支撑刚度、开挖比等因素,得到桩身屈曲极限荷载,分析不同因素对桩身稳定性的影响;(3)验证课题组提出的虚拟嵌固点法理论在大比尺钢管桩工况下的可靠性;(4)验证本文提出的桩身受压极限荷载计算方法。通过对试验数据进行分析可以看出,(1)轴心受压时,靠近桩端处应变最大,偏心受压时,靠近桩顶处应变最大;荷载处于一定范围内时,桩身应变与支撑应变呈线性关系,支撑应变是桩身应变的1/4~1/5倍,在破坏时倍值发生突变;(2)对于大比尺钢管桩,试验所得稳定性数值与课题组提出的虚拟嵌固点法较吻合,验证了虚拟嵌固点法的可靠性;(3)当开挖比较小时,屈曲破坏点出现在桩土接触面附近,随着开挖比的增大,破坏位置逐渐接近桩身中上部;(4)偏心受压对桩身的承载力影响较大,偏心距为40mm以及80mm时,极限荷载与轴心受压对比,分别降低50%和65%;(5)施加水平支撑可以明显提高桩身极限荷载,支撑设置在桩身中部时对极限荷载的提高作用更显著;(6)开挖比较小时,随着回转半径的增大,钢管桩的极限荷载增大;(7)对于轴心受压桩和偏心受压桩,提出了桩身极限荷载计算方法,通过与试验对比验证了本文提出的计算方法的可靠性。
[Abstract]:With the development of urbanization in our country, many existing buildings, because of the lack of underground parking facilities and other facilities, the defects in their use function are increasingly prominent, and the development and utilization of underground space of existing buildings has attracted more and more attention. When the existing building is added to the ground, it is necessary to first use the original pile foundation or set up a new pile foundation to bear the load of the existing building, then excavate the earth and add the basement. The stability of pile foundation will be reduced obviously during excavation of soil around pile. Steel tube pile foundation is one of the most commonly used pile foundations. It is of great significance to study the stability of steel tube pile by the method of large scale model test. In order to carry out the model test successfully, a 2.5m 脳 2.5m 脳 3.0m geotechnical model box was designed and manufactured. It consists of four sides of the vertical steel plate and the periphery through bolts connected to the horizontal hoop. After the angle steel on the four large angles of the model box and the adjacent vertical steel plate are fixed by bolts, the "temporary skeleton" of the model box can be formed, and the leakage of the soil filled in the box along the joint of the two plates can be prevented at the same time. The design method of vertical steel plate, horizontal hoop and connecting bolt of model box is put forward, and the design process of model box is introduced by an example. According to the condition that the soil is medium sand, the stability of the pile body under the condition of soil excavation around the pile with large scale steel pipe pile is studied experimentally in this paper. Through model experiments, (1) the load-strain variation of pile body and bracing under different excavation ratios is studied, (2) by changing the radius of rotation, eccentricity, support position, number of braces, stiffness of bracing, and so on, The ultimate buckling load of pile body is obtained by excavation ratio and other factors. The influence of different factors on pile stability is analyzed; (3) the reliability of virtual fixed point method proposed by the research group is verified under the condition of large scale steel pipe pile; (4) the method proposed in this paper is verified to calculate the ultimate load of pile under compression. Through the analysis of the test data, it can be seen that (1) the strain near the end of the pile is the largest when the axial center is under compression, and the strain near the top of the pile is the greatest when the load is in a certain range, the strain of the pile is linearly related to the strain of the support. The supporting strain is 1 / 4 / 1 / 5 times of the strain of pile body, and it has a sudden change during the failure. (2) for the large scale steel pipe pile, the stability obtained from the test is in good agreement with the fictitious fixed point method proposed by the research group. (3) when the excavation is small, the buckling failure point appears near the pile-soil contact surface, and with the increase of excavation ratio, the failure position is gradually close to the upper part of the pile body. (4) eccentric compression has a great effect on the bearing capacity of pile body. When the eccentricity is 40mm and 80mm, the ultimate load and axial compression are reduced by 50% and 65%, respectively. (6) the ultimate load of steel pipe pile increases with the increase of the radius of rotation when the support is set in the middle of the pile body. (7) for the axial compression pile and eccentric compression pile, the ultimate load of steel pipe pile increases with the increase of the radius of rotation. The calculation method of ultimate load of pile body is put forward, and the reliability of the proposed method is verified by comparing with the test.
【学位授予单位】：山东建筑大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU753.3

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