This study is aimed at finding out the disaster mechanism of karst ground collapse in the Zhifang-Miaoshan paleo-clay area of Wuhan and selecting appropriate methods for the monitoring and early warning, so as to effectively reduce the harm caused by karst ground collapse. Through a special karst survey, we have identified the distribution and geological structure of soluble rocks, analyzed the formation and evolution process of karst ground collapse and selected monitoring methods for different collapse stages in the study area. The survey results show that the study area is mostly distributed by paleo-clay with single-layered structure. According to the upper and lower stacking relationship of overburden cohesive soil, soft soil and non-soluble rock (red layer), the geological structure distribution of soluble rock can be divided into three categories (①, ② and ③). In the structure of class ①, the upper part is composed of cohesive soil; the lower part is soluble rock. The cohesive soil is mostly composed of paleo-clay with the value of cohesion C mainly from 42 kPa to 70 kPa, and the φ value mostly from 10.3° to 19.1°. The free movement of the soil particles is limited, and soil holes are usually formed at the bottom of the soil layer in the soil body. In the structure of class ②, the upper part is composed of cohesive soil; the middle part is soft soil (residual red clay in the shape of soft plastic-flow plastic); the lower part is composed of soluble rock, in which the red clay—weathering residues of the limestone surface—is prone to soften in the shape of soft-fluid plastic in water. Mainly distributed in solution grooves with uneven thicknesses, the red clay usually loses with the action of gravity or suction force, and hence is developed into soil holes. In the structure of class ③, the upper part is composed of cohesive soil; the middle part is the red layer (K2E1g red sandstone); the lower part is soluble rock. In this structure, soil holes are difficult to form due to the barrier of red layer; therefore, karst ground collapse is not likely to occur under the natural condition.

According to the different physical and mechanical characteristics of soil bodies, the process mechanism of karst ground collapse is various in different geological structures. Soil-hole collapse mainly occurs in the structure of class ①.The disaster evolution process can be summarized as follows: (A) In the undisturbed stage, the karst water level drops little, and the small value of the suction negative pressure leads to the failure of soil denudation caused by insufficient suction force. Therefore, there is no significant change in the soil body. (B) Affected by the repeated fluctuations of karst groundwater level or human engineering activities, the soil hole is developed initially along the surface of the open karst cave, when the corrosion absorption force is greater than the collapse resistance force of the soil itself. Then the soil of the cave roof collapsed, and the continuous collapse upward contributes to the expanding of the soil hole and the thinning of its roof. (C) The hole continues to expand upwards, and the roof of the soil hole keeps balanced under the friction force generated by the lateral pressure of soil around it. In the early stage of imminent collapse, the ground surface often presents a small amount of subsidence deformation. (D) Induced by natural or man-made factors, the surrounding friction can not balance the gravity of the roof of soil hole. Consequently, the roof may collapse quickly. In the structure of class ②, there mainly occurs compound collapse of mud flow+soil hole. The process of disaster formation and evolution can be summarized as follows: (A) Thick layers of soft soil and cohesive soil are developed on the upper soluble rock. The karst opening is in the stable stage due to the blockage of the cohesive soil. (B) Affected by fluctuations of karst groundwater level or human engineering activities, the soft soil flows and loses to the cave fissure, which forms the mudflow hole, and the hole quickly expands to the top of the soft soil. (C) The soil hole continues to expand upward in the layer of cohesive soil, and the roof of the soil hole keeps balanced under the friction force generated by the lateral pressure of soil around it. In the early stage of imminent collapse, the ground surface often presents a small amount of subsidence deformation. (D) Induced by natural or man-made factors, the surrounding friction can not balance the roof of soil hole (dead weight+loading); consequently, the roof collapsed quickly. Besides, the quick loss of red clay in shapes of soft plastic-fluid plastic accelerates karst ground collapse. In the structure of class ③, it is unlikely to occur collapse because the barrier of red layer makes it difficult to form the cohesive soil.

Combined with the formation mechanism of collapse, the formation and evolution of soil hole can be monitored by optical fiber, and induced factors such as groundwater levels and water pressures should also be monitored. During the deformation and collapse stage, precise leveling or GPS monitoring can be used to monitor surface deformation because the ground surface often presents a small amount of subsidence deformation before the imminent collapse.