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A semi-probabilistic approach to the design of jet grouted umbrellas in tunnelling

机译：隧道中喷灌雨伞设计的半概率方法

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摘要

A possible approach is shown for the design of jet grouted umbrellas, which are often used as temporary supports in tunnelling practice. In the current paper it is argued that such an approach should be probabilistic or semi-probabilistic. Based on published experimental data and statistical analyses of diameter and centroid position along the axis of jet grouted columns, a series of Monte Carlo simulations were carried out to find the influence of possible defects within the column in the umbrella static performance, with reference to two extreme subsoil conditions: clay and sand. Geometrical considerations on the minimum overlapping among columns necessary for continuity on the whole span of the umbrella are drawn. It is shown that, owing to defects, the real shape of jet grouted umbrellas is not that of a regular frustum of cone. It is also shown that overlapping decreases along the span. There is a critical length after which structural continuity is difficult to obtain, depending on the statistical characteristics of the jet grouted columns. Defects in axis orientation have a significant effect on this critical length. Static conditions are also analysed, assuming a simplified two-dimensional arch scheme, with reference to the part of the umbrella in which continuity is guaranteed with the assumed level of confidence (95%). The minimum average thickness of the jet grouted umbrella necessary for equilibrium is found, which generally increases as the umbrella opens up along its axis.
机译：显示了一种可能的方法来设计喷灌雨伞，通常在隧道施工中将其用作临时支撑。在当前的论文中，有人认为这种方法应该是概率的或半概率的。基于已发布的实验数据和沿喷射灌浆柱轴线的直径和质心位置的统计分析，进行了一系列的蒙特卡洛模拟，以找出可能存在的缺陷对伞形静态性能的影响，并参考了两个极端的土壤条件：粘土和沙子。绘制了在伞的整个跨度上连续性所需的列之间最小重叠的几何考虑。结果表明，由于缺陷，喷射注浆伞的真实形状不是圆锥形的平截头圆锥体。还显示出重叠沿跨度减小。取决于喷射灌浆柱的统计特性，存在一个关键长度，在此之后很难获得结构连续性。轴方向上的缺陷对此临界长度有重大影响。假设采用简化的二维拱形方案，还参照伞的一部分以假定的置信度（95％）保证连续性，从而分析静态条件。找到了平衡所需的喷射灌浆伞的最小平均厚度，该厚度通常随着伞沿着其轴线的打开而增加。

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