临江地下结构抗浮计算方法研究

Study of anti-buoyancy calculation method for underground structures near riverside

临江地下结构进行浮力计算时,其抗浮设计水位直接采用地面高程或江河水位是不合理的,需要对场地进行渗流分析才能确定。在沿用本奈特假定的前提下,推导出一种简化算法用于临江二元地层的渗流分析,可得到强透水层中的水头分布。在此基础上,提出地下结构物底板水压力的实用计算方法为抗浮设计提供依据。其方法适用于堤前、堤后覆盖层有不同的厚度和渗透系数,以及宽度为有限或无限的边界情况。该法计算简便,结果足够精确。经过算例验证和比较,堤后小型结构物对强透水层中的水头分布影响不大,但大型结构物和堤后宽度收窄将会显著抬高水头。位于覆盖层中的地下室底板浮力呈中部大、四周小的分布形态,但位于强透水层中时则呈线性分布。

It is unreasonable to calculate the buoyancy force value of underground structures near riverside directly using ground elevation or river level as anti-buoyancy water level. Seepage analysis of the field is necessary for anti-buoyancy design. Based on Bennett hypothesis, a simplified algorithm for seepage analysis of double strata near riverside is presented to calculate the hydraulic head distribution in high-permeable layer. A practical method is followed to calculate the buoyancy force on the bottom slab of underground structures for anti-buoyancy design. This method can be applied for different boundary conditions, e.g., the blankets with different thicknesses and permeability on the upstream and downstream of levee, or the blanket with finite or infinite width. This algorithm only requires simple calculation parameters, but the results are accurate enough for using. After verification and comparison, a conclusion can be drawn that downstream small-scale structures in high-permeable layer have little influence on hydraulic head distribution, but the large-scale structures or the narrow-width blanket downstream will rise the head dramatically. The buoyancy in the middle of bottom slab is greater than the surrounding area when the bottom slab of basement locates in the blanket. But it changes to linear distribution when the bottom slab of basement intrudes into high-permeable layer.