Abstract
In this study, the ellipsoidal soil cave with vertical collapses in the covering karst area is studied. Based on certain assumptions, the mechanical model of karst collapse caused by groundwater drop was established. Then, based on the negative pressure calculation formula of soil cave cavity according to Boyle–Mariotte’s law, the expression of the stability coefficient of the soil cave was proposed. Subsequently, the feasibility of the theoretical formula was verified. The calculation example analyzed the relationship of groundwater parameters and overburden thickness. The results show that when the initial groundwater level is higher than the top of cave, the law between the stability coefficient of soil cave and groundwater drawdown shows the jumping horizontal broken line. Thus, soil cave tends to collapse when the falling groundwater level drops over the vault; when the initial groundwater level ranges from the bottom to the top of the cave body, the stability coefficient and groundwater drawdown show a negative correlation law, the curve is steep at the early stage and then becomes gentle at the latter stage, and the higher the initial groundwater level in the cave is, the greater stability coefficient of soil cave reduces; when the initial groundwater level is lower than the bottom of the cave, the effect of drawdown is limited. In addition, for the small drawdown or low initial groundwater level, the stability coefficient of soil cave first decreases and then increases with the increases in thickness of overburden, and the thinner the overburden is, the greater the drawdown rate is; when the drawdown or the initial groundwater level is higher, the stability coefficient of soil cave positively relates to the thickness of the overburden layer.
Highlights
Sinkholes widely spread all over the world, especially in Florida [1,2,3], southwest China [4, 5], Jordan [6], Italy [7], Spain [8, 9], Iran [10], and so on. e sinkhole collapse has caused devastating damage to buildings, roads, railways, and other facilities [11], leading to huge economic losses [2, 12], and threatening the safety of people’s lives and properties. e development of sinkhole consists of two stages: internal collapse and surface collapse. e internal collapse is a slow process of soil failure, while the surface collapse is a sudden process of soil collapse caused by the expansion of soil holes [13]. e collapse is related to many factors such as weather, hydrology, geology, and human activities [14, 15]
When all the factors act together or one or two main factors act, the rapid development of internal collapse leads to the surface collapse
The survey of Tazerbo wellfield in southeast Libya showed that sinkholes and subsidence resulted from groundwater withdrawal [16], and forty-one sinkholes collapsed in the southern suburbs of Liuzhou, Guangxi, China, in May 10, 2012; loss of soil particles due to heavy rainfall was responsible for the above phenomenon [17]. ere are other areas where heavy rainfall and flooding exacerbate the sinkhole collapse disaster [18]
Summary
Sinkholes widely spread all over the world, especially in Florida [1,2,3], southwest China [4, 5], Jordan [6], Italy [7], Spain [8, 9], Iran [10], and so on. e sinkhole collapse has caused devastating damage to buildings, roads, railways, and other facilities [11], leading to huge economic losses [2, 12], and threatening the safety of people’s lives and properties. e development of sinkhole consists of two stages: internal collapse and surface collapse. e internal collapse is a slow process of soil failure, while the surface collapse is a sudden process of soil collapse caused by the expansion of soil holes [13]. e collapse is related to many factors such as weather, hydrology, geology, and human activities [14, 15]. Based on Terzaghi’s assumption and excess pore water pressure theory, Long and Lujuan [4] proposed the groundwater level critical value for the formation, evolution, and roof collapse of the soil cavern, which can be used for the precaution of surface collapse sinkholes. Xiao [27] studied the effects of water-gas mutual drive, negative pressure action, negative pressure suction, and submersible erosion caused by the change of the groundwater level, as well as the influence of these effects on the stability of the sinkhole, and obtained the mathematical expression of the karst collapse factor. To study the spatial effect of soil cavity in the process of groundwater level change and to analyze the influence of hydrodynamic conditions on the stability of soil cavity, the soil cavern model is set as a common ellipsoid. G + F cH + ΔP − (2/3)cc S where c is the natural bulk density of overburden (the multilayer soil is weighted average), z represents the depth of a particle, H is the thickness of overburden soil (the distance from arch foot to ground), C, φ are the cohesion and internal
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