黄明, 付俊杰, 陈福全, 江松. 桩端岩溶顶板的破坏特征试验与理论计算模型研究[J]. 工程力学, 2018, 35(10): 172-182. DOI: 10.6052/j.issn.1000-4750.2017.06.0435
引用本文: 黄明, 付俊杰, 陈福全, 江松. 桩端岩溶顶板的破坏特征试验与理论计算模型研究[J]. 工程力学, 2018, 35(10): 172-182. DOI: 10.6052/j.issn.1000-4750.2017.06.0435
HUANG Ming, FU Jun-jie, CHEN Fu-quan, JIANG Song. THEORETICAL CALCULATION MODEL AND MODEL TEST ON THE FAILURE CHARACTERISTIC OF KARST ROOF UNDER ROCK-SOCKETED PILE[J]. Engineering Mechanics, 2018, 35(10): 172-182. DOI: 10.6052/j.issn.1000-4750.2017.06.0435
Citation: HUANG Ming, FU Jun-jie, CHEN Fu-quan, JIANG Song. THEORETICAL CALCULATION MODEL AND MODEL TEST ON THE FAILURE CHARACTERISTIC OF KARST ROOF UNDER ROCK-SOCKETED PILE[J]. Engineering Mechanics, 2018, 35(10): 172-182. DOI: 10.6052/j.issn.1000-4750.2017.06.0435

桩端岩溶顶板的破坏特征试验与理论计算模型研究

THEORETICAL CALCULATION MODEL AND MODEL TEST ON THE FAILURE CHARACTERISTIC OF KARST ROOF UNDER ROCK-SOCKETED PILE

  • 摘要: 基于分离相似设计方法,开展了顶板厚度和溶洞直径变化下桩端顶板的破坏特征模型试验,并构建了相应的安全厚度理论计算模型。1)溶洞顶板厚度的大小影响了桩基嵌岩端荷载的传递路径,厚度越大传递范围越广,形成的剪切带体积越大。顶板厚度t≤1.0d时(d为桩径)顶板临空面处易发生冲切破坏,此时溶洞顶板的自身稳定性起控制作用,顶板厚度越小,溶洞临空面处脱落体积越小;顶板厚度1.0d< t ≤2.0d时,表现为锥形冲切失稳驱动上部剪切错动的破坏;顶板厚度t >2.0d时,表现为上部剪切错动驱动临空面的锥形冲切失稳,且溶洞直径小于剪切错动体的横向宽度时,剪切破坏最终发生在桩-岩界面的竖向投影范围以内。顶板厚度较小,对应的Q-S曲线为典型的陡降型曲线,而厚度较大时Q-S曲线为典型的缓变型。2)顶板具有一定厚度情况下(t≥2.0d),洞径较小(l≤3.0d)时,桩端剪切变形较为显著,上部剪切错动达到一定程度后,顶板临空面才发生冲切破坏,此时Q-S曲线呈现缓变型趋势;洞径较大时(l >3.0d),顶板临空面处冲切现象较显著,且洞径越大锥形冲切块的体积越大,此时Q-S曲线呈陡降型变化特征。3)以锥形冲切破坏计算模型进行工程设计风险较大,而冲-剪破坏理论模型与顶板岩体强度、完整性、桩径、嵌岩深度、施工方法及工艺等相关,故现场条件下即可计算出顶板的最小安全厚度值。

     

    Abstract: Based on the isolated similar design method, the model test research on the failure characteristic of karst roof under a rock-socketed pile was carried out with the change of roof thickness and cave diameter, and a formula was also presented. It shows that:1) The thickness of karst roof impacts the load transfer path of the rock-socketed pile, the thicker the roof, the wider the transfer range, and the larger the volume of a shear zone. When the thickness of the roof is no more than the diameter of the pile, punching failure will happen around the free face of the roof, and the stability of the roof around the free face play a vital role. The thinner the roof, the smaller the volume of the tapered block. When the thickness of roof is greater than the diameter of the pile, but littler than two times of the diameter, the upper shear failure happens firstly, and then induces the punching failure around the free face. When the thickness of the roof is greater than two times of the diameter of the pile, the punching failure around the free face happens firstly, and induces the upper shear failure latterly, which will happens within the projection of the pile in the condition that the diameter of the cave is less than the transverse width of the shear zone. The load-settlement curve is of a rapid-falling style with a thinner roof, while the load-settlement curve is of a slow-change style with a thicker roof. 2) The shear deformation of the roof is significant when the diameter of the cave is less than three times of the pile diameter (the thickness of the roof is greater than two times of the pile diameter), the punching failure happens after the upper shear failure of the roof, and the load-settlement curve is of a slow-change style. The greater the diameter of a cave, the larger the volume of the tapered punching block, and the load-settlement curve is of a rapid-falling style when the diameter of the cave is greater than three times of the pile. 3) It is of great risk to calculate the safe thickness of the karst roof under the pile tip using the punching failure formula. However, the punching-shear failure model is providential, and related to the strength of the karst roof, the integrity of rock, the diameter of the pile, rock-socketed depth, the construction method and technologies. This approach can be used to calculate the safe thickness of the cave roof quickly in site.

     

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