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The phyllite-weathered soil is a regional speciality. It is essential to study the changes in shear strength of phyllite-weathered soil under dry-wet cycles to understand the changes in mechanical properties of phyllite-weathered soil in the process of dry-wet climate and to manage the slope of phyllite-weathered soil. This paper simulated 12 dry-wet cycles on the specimens of remodelled phyllite-weathered soil. Direct shear and SEM tests were conducted on the specimens in the 0th, 3rd, 6th, 9th, and 12th drying paths. The effects of moisture content and the number of dry-wet cycles on the shear strength of phyllite-weathered soil were analysed macroscopically and microscopically. The following conclusions were obtained: (1) The cohesion of the weathered soil of phyllite will be reduced by increasing the number of cycles, and the more the number of dry-wet cycles, the more pronounced the reduction; the internal friction angle of the weathered soil of phyllite will be reduced by increasing the number of cycles, but the pattern of the decrease in the internal friction angle is not obvious. (2) The increase in the number of dry-wet cycles will increase the stiffness and brittleness of the phyllite-weathered soil specimen, and it will change from the weak hardening type of plastic damage to the solid softening type of brittle damage after a certain number of cycles. (3) The SEM test found that phyllite-weathered soil particles in Longsheng, Guilin are large, and most of the particles are in face-to-face and angle-to-face contact, which is easy to form a hollow structure, and the dry density value of the soil in the natural state is small. At the same time, the soil is reddish-brown in colour because of the leaching of Fe2 O3. The shear strength index of the cemented phyllite-weathered soil with Fe2 O3 is more significant than that of phyllite-weathered soil in other areas. The soil has a good shear strength index and a small dry density.

The frequent vibration loads during the operation of trains can cause vibration deformation of the tunnel structure and surrounding weak strata, thereby endangering the safe operation of trains. The purpose of this paper is to study the dynamic response of surrounding soil layers caused by train vibrations through the finite difference method with FLAC3D. Based on existing research, we studied the artificially deterministic exciting force function. Then, we simulated the tunnel working conditions of a train with a 3D model, and applied the artificially deterministic exciting force function to the tunnel model. To study the vibration caused by trains in silty soil, we divided the trains into two cases, one-way and two-way. We compared the displacement–time curves of one-way and two-way trains. When the horizontal distance between the monitoring point and the vibration source increases, the peak value of the displacement–time curve decreases. As the speed of the train increases, the peak value of the displacement–time curve increases. The vertical displacement of the ground under the dynamic load of the two-way train is greater than that of the one-way train. In the acceleration–time curve, there is a lag in the ground acceleration response. The faster the speed of the subway train, the greater the peak value of the acceleration–time curve. This study can provide a guide for the evaluation and prevention of ground vibration subsidence and uneven subsidence of strata in the silt area of the Yellow River Region.

Taking dolomite and limestone in Guilin and Liuzhou regions in the north of Guangxi Province as research objects, this paper analyzed their mineral composition and chemical composition and proposed a digital assessment method for multi-source factors on corrosion characteristics in the Karst areas. Specifically, the chemical corrosion test, the corrosion test under the chemical-temperature actions, and the corrosion test under the action of vibration load are carried out from the digital view, respectively. Four aspects can be found in digital assessment results. Firstly, the dolomite in northern Guangxi mainly has a fine crystalline texture and a massive structure with low content of acid-insoluble matters, while limestone mainly has a powder crystalline texture and a massive structure with high content of acid-insoluble matters, and the purity of both dolomite and limestone are very high. Secondly, the difference of corrosion between dolomite and limestone mainly depends on the ratio of CaO/MgO in their chemical composition and the content of silica and acid insoluble matters. Thirdly, the corrosion rates of pure dolomite and pure limestone are basically the same under the same external conditions. Finally, temperature and vibration load have a relatively large influence on the corrosion rates of dolomite and limestone, and the corrosion rates of dolomite and limestone increase with the increase of temperature, but the influence of vibration load on the corrosion rate is more significant than temperature. This research can provide theoretical basis and technical support for large-scale engineering construction and prevention of karst geologic disasters in karst stone mountainous areas in northern Guangxi.

Taking dolomite and limestone in Guilin and Liuzhou regions in the north of Guangxi Province as research objects, this paper analyzed their mineral composition and chemical composition, and then carried out the chemical corrosion test, the corrosion test under the chemical-temperature actions, and the corrosion test under the action of vibration load, respectively. The results showed that: (i) the dolomite in northern Guangxi mainly has fine crystalline texture and massive structure with low content of acid insoluble matters, while limestone mainly has powder crystalline texture and massive structure with high content of acid insoluble matters, and the purity of both dolomite and limestone are very high; (ii) the difference of corrosion between dolomite and limestone mainly depends on the ratio of CaO/MgO in their chemical composition, and the content of silica and acid insoluble matters; (iii) the corrosion rates of the pure dolomite and the pure limestone are basically the same under the same external conditions; (iv) temperature and vibration load have relatively large influence on the corrosion rates of dolomite and limestone, and the corrosion rates of dolomite and limestone increase with the increase of temperature, but the influence of vibration load on the corrosion rate is more significant than temperature. This research can provide theoretical basis and technical support for large-scale engineering construction and prevention of karst geologic disasters in karst stone mountainous areas in the northern Guangxi. Keywords: dolomite and limestone; structural features; corrosion characteristics; northern Guangxi

The phenomenon of rocky desertification is obvious in karst plateau of Guizhou, China, and the distribution area of slight–medium–severe rocky desertification is very large in Zhenfeng–Guanling–Huajiang, Guizhou. To explore the cause of formation and development of rocky desertification in the region, the karst development mechanism and characteristics were studied by the method of indoor dissolution test and microscopic analysis. The results show that the dissolution and karst features of carbonate rocks are closely related to geological structure, hydrogeological conditions, and lithology. The dissolution rate is the most affected by the chemical composition and mineral composition, followed by the pore structure and the particle feature. The dissolution rate of carbonate is in positive proportion with the calcite content, while it decreases with increasing content of dolomite. In the same chemical composition, the rock with the finer grains has a faster surface dissolution rate. In addition, the erosion amount will change with the pore aperture and connectivity. Karst morphology is mainly affected by the microstructure and mineral assemblage characteristics of carbonate rocks. In this rocky desertification area, bare rock over a large area will be further eroded, which will form the stone bud, stone forest. At the same time, the hydrodynamic effect of groundwater will erode the rock deeply, and the depression, karst funnel, or deep valley will appear gradually.

Rocky desertification induced by soil erosion is a serious geological hazard in the karst regions of southwestern China. This paper made a research on small watersheds of Chengjiang River in Gongcheng County, Guilin City, Guangxi Province, analyzed the causes and trends of soil erosion in the regions by comparing rocky desertification areas in 1991, 2006 and 2015, and proposed countermeasures against soil erosion based on the above analysis. This research provides a basis for restoring ecological environments and preventing soil erosion in small watersheds of karst regions.

The dolomite in the Yuntai Mountain, Shibing, Guizhou, China constitutes the gentle stratum, affected by several weathering processes. It is coupled with a vertical joint development, which makes it easy to form the collapse and stone peaks corroded by running water. The aim of this paper is to study the effects of weathering processes of dolomite outcropping in the Yuntai Mountain (Shibing, Guizhou, China). This work shows the dolomite’s physical and mechanical characteristics, microscopic characteristics of rock and pore structure based on chemical and minero-petrographic analyses. The findings indicate that the dolomite in this region is gray, pure quality and hard-packed superfine grain to fine grain. Mass surface voids suggest that the dolomite’s pass is small and has more pore throat. Its grain cementation is relatively poor. The degree of rock weathering is relatively high. The mechanical strength is lower than that of the surrounding limestone. This work shows how the macro–micro characteristics of the dolomite affect the formation of collapse and stone peaks. This work further focuses on the study of the cone-shaped peak cluster basement and the upper tower-shaped stone peaks, which are the most important features of this region.

The Guang-Qing freeway reconstruction and extension project is located in Guangdong province, China, extending from Guangzhou city to Qingyuan city. The total project length is 57.6 km, 33 km of which is in a karst area where sinkhole collapses are common. Therefore, there were concerns about the safety and security of the roadbed, bridge piles, and other structures associated with the original roadway. The study addresses karst development, covering layer (overburden), and external factors that contribute to catastrophic sinkhole collapse along the project. The study found that the formation of sinkhole collapses is affected significantly by the degree of karst development and soil characteristics, including thickness. Collapses may be triggered directly by external factors that disturb the natural equilibrium. Such factors include heavy rainfall that impacts soil and groundwater conditions, as well as vibration and groundwater flow disruptions that are caused by pile construction and other engineering activities. Prevention measures were adapted to local conditions and optimized based upon safety, reliability and cost-effectiveness.

The characteristics of coastal zones are controlled by the geological structure and properties of rock and soil mass, and accordingly they can be classified into several categories. In this paper, six important problems confronted in coastal geological environment were discussed: (1) earthquake and tsunami; (2) seawater invasion; (3) coast erosion and sedimentation; (4) coastal subsidence; (5) climate—geological disaster chain control; and (6) sea level change. In the West Coast Economic Zone with the core being Fujian Province, China, some coastal cities, such as Fuzhou, Xiamen, Quanzhou, are affected by the Minjiang, Jiulongjiang and Jinjiang rivers. This paper discusses the geological environment of these cities, and the significant connection with the river ecology. A conceptual framework was proposed for developing a sustainable ecological river and a water-front city with ecological civilization.