An evaluation of rocky desertification comprehensive control is very important to optimize and improve strategy for rocky desertification control modes. This paper aims to (Ⅰ) analyze the relationship among agricultural structure, industrial resources situation, economy benefit and ecology benefit; (Ⅱ) evaluate the comprehensive benefit of karst rocky desertification control by orchard-herbage intercropping, and further find its own advantages and disadvantages; (Ⅲ) provide ecological economic and sustainable development reference for rocky desertification control in the southwest karst area of China.A comprehensive prevention and control of rocky desertification area has been implemented in combination with tropical fruit tree intercropped by legume herb in Tianfang village, Nanpanjiang town, Xingyi City of Guizhou Province,where the rocky desertification is serious. To evaluate the comprehensive benefit of the demonstration area, we investigated the agricultural structure, industrial resources situation, and the benefits of economy and ecology before (2014) and after (2017 and 2020) karst rocky desertification control, and then adopted correlation analysis, Redundancy Analysis (RDA) and Structure Equation Modeling (SEM).By converting cultivated land to orchard (mango and Macadamia intercropped with herbage or green manure) the agricultural industrial structure ,industrial resources development,economic benefit and ecological benefit of the demonstration area showed a good trend after 6 years of rocky desertification comprehensive control. Correlation analysis showed that the agricultural industrial structure and industrial resources development situation were significantly correlated with economic benefit and ecological benefit, except for farming/forest-grass area ratio and commodity output value of agricultural products. RDA analysis showed that there are five variables which are the important contributing factors to the changes of economic benefit and ecological benefit such as, proportion of orchard land, migrant worker population, economic contribution rate of migrant workers, commodity output value of agricultural products farming/forest-grass area ratio SEM further showed that the rocky desertification control are able to couple the coordinated development of ecological environment and industrial resources, and at the same time achieve ecological restoration and economic benefit.Conclusions are drawn as follows, (Ⅰ) The rocky desertification control in orchards intercropped by fruit tree has increased the number of labor force and migrant workers,and improved the economic benefits by increasing commodity output value of agricultural products and migrant workers income. (Ⅱ) The ecological environment has been improved by increasing forest and grass coverage,soil erosion and water loss and surface runoff loss in the comprehensive control area of rocky desertification has been reduced. (Ⅲ) The rocky desertification control by orchard covered with fruit tree and intercropped by crops controlling rocky desertification will improve both economic benefit and ecological benefit. Overall, rocky desertification control by fruit tree intercropping orchard is an effective way to achieve sustainable development in the southwest karst area of China The study results provide a basis for the comprehensive control of karst rocky desertification.

Karst collapse columns (KCCs) are formed in the process of geological evolution in North China coalfield. Their roots are developed in the Ordovician or Cambrian carbonate rocks, and pass upward through Carboniferous, Permian, Triassic strata, and even enter the Jurassic, Cretaceous and Quaternary loose rock strata. Over the past 80 years, more than 10,000 mines have been exposed in 39 mining areas in the coalfields of North China, resulting in more than 20 major water inrush accidents. Therefore, the study on KCCs is of important theoretical and practical significance for the systematic understanding of karst hydrogeological conditions of mines in North China and of prevention and control of karst water disaster as well.This study systematically summarized the spatial distribution characteristics of KCCs in the coalfields of North China, mainly focusing the areas along the Fenhe river, the western foothills of Taihang mountain, the foothills of eastern and southeastern Taihang mountain, the foothills of southern Yanshan mountain, and the west side of the Tanlu fault zone. The plane shapes of KCCs are mostly circular and elliptical, and their cross-sections are mainly cone-shaped. KCCs are usually filled and cemented by broken debris of wall rock and secondary minerals, so most of the collapsed columns in the coalfields do not conduct (contain) water, and only few cases of water inrush occur there. KCCs usually form in such basic conditions as soluble rocks and special stratigraphic structures, multi-stage and multi-source fluid erosiveness, geological tectonic evolution, and paleokarst groundwater flow. Five theories on the genesis mechanism have been put forward, namely “karst gravity collapse”, “gypsum dissolution collapse”, “vacuum absorption collapse”, “hydrothermal origin” and “groundwater internal circulation”.According to the current research on the formation and evolution of KCCs in the Huainan coalfield in the southern margin of North China, this study shows that consisting of Ordovician or Cambrian carbonate rocks, KCCs move through fluid migration channels of faults and fractures generated by multi-stage tectonic movements in this area, and are accommodated with the paleokarst formed by dissolution in the carbonate rocks. After a long-term process of dissolution, transportation, and collapse, KCCs are finally formed with the joint effect of the self-gravity of the rock mass, the in-situ stress, and the vacuum negative pressure in the cave. The formation of KCCs is related to the multi-stage tectonic movements in Mesozoic, and the Yanshan movement might be the key stage of its formation and development.In this study, the water inrush mechanism of KCCs in the mining process is reviewed from the aspects of mining-induced water inrush mechanism, seepage transformation mechanism, and water inrush model. Four modes of water inrush of KCCs in working face or roadway, as well as the mechanical mechanism and seepage transformation mechanism of water inrush are analyzed, and the reasons for the sudden and hysteresis of water inrush are also explained. The technical route for KCC detection and prevention are determined by geophysical prospecting, geochemical prospecting, roadway prospecting, drilling, and hydrogeological conditions.At present, the prevention and control of KCC water disaster is mainly carried out from two aspects,exploration and treatment. In terms of exploration, several methods can be used. The technology of three-dimensional seismic exploration can be adopted to preliminarily determine the impacted area of collapse columns. The comprehensive geophysical method can be used to detect the water-bearing area of KCCs. The exact location, shape and hydrogeological characteristics of KCCs can be determined by methods of drilling, the test of pumping (draining) water, geochemical exploration and others. In terms of treatment, two methods can be mainly adopted,water-proof coal (rock) pillar retention and grouting reinforcement/water blocking to cut off the hydraulic connection between the KCCs water channel and the water inrush source. This technology has been successfully applied in the treatment of KCCs in the mining areas subject to karst water disaster such as Hebei and Anhui.As to the research gap and deficiency in the prevention of water disaster caused by KCCs, the following suggestions are put forward,(1) Under the guidance of earth system science, the study on evolution of KCCs can be conducted combined with the formation mechanism of KCCs. Meanwhile, a multidisciplinary method involving petrology, structural geology, hydrology, geomorphology, karst hydrogeology, GIS, RS, and others can also be applied based on the time axis of evolution of regional geological structure.(2) For the precise detection, data and interpretation of small hidden collapse columns, efforts should be made to perfect the basic theory of full-space physics, to develop new equipment, new technologies and new methods, to further improve the precision, resolution, anti-interference competence of geophysical exploration, and to increase the detection depth.(3) Research on the KCCs model of “dynamic monitoring-prediction model-water inrush mechanism” should be conducted. Firstly, a dynamic monitoring system to obtain parameters such as stress, deformation, acoustic emission, rupture (wave velocity), water pressure (position), water chemistry, and water temperature during the water inrush process of KCCs can be established, and an indicator monitoring instrument of stable multi-parameter can be developed. Secondly, with the help of big data and data processing technology of cloud platform, a multi-parameter integrated water inrush prediction model of KCCs can be established based on the dynamic monitoring system characterized by information transmission and the existing water-rock coupling numerical model.(4) The prevention and control technology system of KCCs water disaster should be established and improved. This system will mainly include the technical subsystem such as basic theoretical research on KCCs formation, exploration of KCC basic characteristics, prevention, management and emergency planing of KCC water disaster. In short, the establishment of the system is of important theoretical and practical significance for the research of KCCs and water disaster control.

The spatial distribution of karst underground river pipelines is complex and changeable; therefore, it is of great significance for us to carry out the earth science work in karst areas to develop an effective detection technology for the identification of pipelines. Based on the characteristics that karst underground river pipelines change greatly with seasons and time, the spatial distribution identification of underground river pipelines is studied by the inversion technology of time-lapse 3D resistivity. The results of pilot physical model experiments in limestone medium show that, the spatial distribution of simulated three-dimensional underground river pipeline is well highlighted according to the time-delay inversion imaging of resistivity data respectively collected from water-filled pipelines in rainy season and air-filled pipelines in dry season, The area with large resistivity change is in good agreement with the actual spatial position of pipeline in transverse and longitudinal directions. The closer the resistivity is to the center of the pipeline, the more significant the resistivity change is. In terms of the electrical sounding curve, the resistivity presents a low-high-low feature, and the resistivity contrast between pipeline space and other depth intervals is significant. In terms of the electrical sounding gradient curve, both the gradient value of pipeline space near the overlying clay layer and the value underlying limestone layer are large. The gradient value is positive near the upper contact surface and negative near the lower contact surface. The inversion effect with water-filled pipeline is inferior to that of time-lapse inversion. When the simulated pipeline is filled with water, the pipeline space presents relatively low resistivity. The resistivity value at the bottom of the pipeline is greater than that of the upper part, and the actual spatial position of the pipeline can be effectively reflected. The resistivity presents a high-low-high curve on the electrical sounding curve. However, on the electrical sounding gradient curve, the gradient value of the pipeline space near the overlying clay layer is negative, and it is positive near the underlying limestone layer. It is difficult to effectively identify the karst pipeline through the inversion images only generated by air-filled data. The resistivity rises monotonously and the resistivity value in the pipeline space changes more quickly than that in other depth intervals on the electrical sounding curve, while on the electrical sounding gradient curve, the resistivity gradient value in the pipeline space is slightly larger than that in other depth intervals, but the anomaly in the pipeline space is very weak compared with the time-lapse inversion results and water filling inversion results. It is suggested that when the spatial distribution of underground river pipelines in the field is studied, the 3D resistivity data should be collected in wet season and dry season, respectively, and the time-lapse 3D resistivity inversion image, electric sounding curve and electric sounding gradient curve can be comprehensively analyzed for the research. The subordinate choice is to carry out 3D detection of karst pipeline in wet season and analyze the data comprehensively, so as to obtain a practical detection technology that can effectively locate the underground river pipeline whether it is filled with water or free of water, which can be popularized and applied in practice.