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含水地层(指一般的飽和含水地层)中的結构物,由于受水压力和水浮力的作用,外力的計算比較复杂些。从国外的一些地下結构物的計算实例看来,外力計算都曾作过一些不同的假定和簡化,因此計算的方法也不尽相同。下面准备略談一下有关这方面的問題。处于水中的物体,不論是土壤或結构物,均会减輕重量。根据阿基米德原理,其减輕的重量,应等于所排开的水的重量。因此位于地下結构物顶部的地层,当为干燥土壤(或具有天然湿度的土壤)时,土壤的重量为土壤顆粒(或土壤顆粒加上所含的水份)和空气重量的总和;空气重量可忽略不計,一般以其体积与土壤总体积之比, n=V_1/V即隙率来表示其容量(图一)。当結构頂版以上的地层处于地下水中时,作用于頂版的荷重将有所改变。原土壤部份受浮力作用,重量将减輕,空隙部份被水填滿,重量增加。土壤的单位重将改变为:
Structures in aquifers, which are generally saturated aquifers, are computationally complex due to water pressure and buoyancy forces. From the calculation example of some underground structures abroad, there are some assumptions and simplifications made in the calculation of external forces, so the calculation methods are not the same. Here is a brief look at the issues in this area. Objects in water, whether soil or structures, will lose weight. According to Archimedes’ principle, the weight lost should be equal to the weight of the water being drained. Therefore, the formation located on the top of the subsurface structure, when it is dry soil (or soil with natural humidity), the weight of the soil is the sum of the soil particles (or soil particles plus the moisture contained) and the weight of the air; Neglected, generally its volume and total volume of the soil ratio, n = V_1 / V that is, the capacity of the void (Figure 1). When the formation above the top plate in the groundwater, the load acting on the top plate will change. The original soil by the buoyancy effect, weight will be reduced, the void part of the water filled, weight. The unit weight of soil will change to: