Multi-Step Combined Control Technology for Karst and Fissure Water Inrush Disaster During Shield Tunneling in Spring Areas

Shield tunneling in highly fractured karst water-rich conditions easily results in water inrush disaster or even causes the roof of the karst caves to collapse. Severe water inrush disasters have occurred during the EPB (earth pressure balance) shield machine of the Jinan Metro Line R1 advanced through a karst and fissure groundwater-rich limestone ground in the spring area. To cope with the extreme water inrush risk, a multi-step combined control technology was put forward. First, a detailed geological exploration was carried out by ahead geophysical prospecting using high-density resistivity method, geological radar, etc., and geological borehole drilling was conducted from the ground surface before excavation. As a result, the distribution orientation, size, fissure development degree, and water inflow channel within the surrounding rock of the karst caves were detected. Second, multi-step grouting was performed to reinforce the surrounding rock, including pre-grouting treatment and filling rock blocks to the big karst caves from the ground surface, multiple grouting with a small amount of inert slurry each time inside the tunnel, and secondary circumferential hoop grouting at the shield tail. Third, the tunneling process was optimized, including optimizing the tunneling parameters, making full use of the air-pressurized tunneling technology of the EPB to press bentonite into the fractures around the excavation cabin to seal the fissure water, and using the drainage system of EPB and muck improvement technology to reduce the water inrush disaster. Meanwhile, shield protection slurry technology is applied to cutter inspection and replacement in the pressurized chamber under dynamic water flow environment of the spring terrain. The practice shows that the water inrush on the tunnel face is obviously alleviated after the shield machine advanced into the grouting area. According to statistics, the water inflow on the tunnel face decreases from about 4 m3/h before treatment to less than 0.3 m3/h after the abovementioned control, and the water seepage between the segmental linings reduces to almost zero. The average advance rate increased from 3 m/day without stopping or even zero when the shield machine needs to shut down 2–3 days for drainage to about 6 m/day. In addition, the treatments prevented the shield machine from jamming and the head descending disaster. This study provided a reliable control method for shield tunneling through the karst and fissure water-rich area and played an essential role in protecting the spring water.

Transformation Process of Five Water in Epikarst Zone: A Case Study in Subtropical Karst Area

Five water stand for five forms existence models of water. In Karst area, Five water means precipitation, groundwater, evapotranspiration water, soil water, and overland flow. The complicated water-bearing hydrogeological media and the inhomogeneous water storage structure leads to low efficiency of water utilization. To reveal intricated water resources transformation in karst areas, a typical epikarst zone was selected. The Five water and their conversion processes were studied and the transformation models was built based on the long-term positioning observations. The results show that: (1) Overland flow can be generated when precipitation reaches 6 mm and lasts for 6 h. Under light and moderate rainfall (LMR) conditions, less than 6% of the precipitation is converted to overland flow. Under heavy rainfall and rainstorm (HRR) conditions, the conversion rate is 3.5%-6%. (2) Under the condition of LMR, there are 2%-3.5%, 40%-60% and 25%-35% that transformed to vegetation water, soil water and groundwater respectively, while it is 1.5%-2.2%, 25%-30% and 32%-50% under the condition of HRR. (3) The proportion of precipitation was transformed to soil water is 20%-70%. (4) The conversion rate of groundwater and karst fissure water for LMR conditions are 8%-15% and 10%-15%, and that for HRR is 15%- 20% and 20%-35%. (5) The proportions of different degrees of precipitation transformed into vegetation transpiration and evaporation water are 1.5%-3.5% and 6%-9%, respectively. (6) Generally, about 0%-4% of the precipitation is converted into overland flow, 20%-70% into soil water, 25%-50% into karst groundwater, and 1%-10% into evaporative water.

Laboratory Study On Mechanical Response And Failure Mechanism of Red-Bed Soft Rock Under Water-Rock Interaction

Red-bed soft rock is a geomaterial that displays special deformation and failure characteristics. The stability of red-bed slopes can be negatively impacted by water and stepped excavation disturbance; however, there is limited research regarding the mechanical behavior and failure characteristics of red-bed soft rock under the action of water-rock hydro-mechanical coupling. In this study, to explore the mechanical response and failure mechanisms of red-bed soft rock under coupled water-rock hydro-mechanical action, a visual experimental platform based on digital radiography and a multi-level loading device was constructed. Angiography was used to visualize the rock fracture process by replacing fissure water with a contrast medium. Multi-level loading was applied to cubic red-bed mudstone samples, and acoustic emission signals, stress, flow rate, and digital radiography images were collected during the failure process. An original image processing method based on Hough transform and a convolutional neural network was used to segment and extract cracks from the imagery, and fissure water flow characteristics, rock mechanical response, and crack evolution were analyzed in detail (Liu et al., 2015; Lv et al., 2013, 2014). Results showed that when the Felicity ratio FR was lower than 1.2, water could induce secondary "water-damaged cracks" in the red-bed samples. Study findings were used to highlight the importance of improved early-warning methods for rainfall-induced landslides at an engineering scale. The original experimental platform proposed and evaluated in this study provides a new and powerful tool to investigate the mechanical behavior of different rock types under the action of water-rock hydro-mechanical coupling at a laboratory scale. These findings will facilitate improved disaster prevention strategies for red-bed geological bodies.

Seasonal Differences in Water-Use Sources of Impatiens hainanensis (Balsaminaceae), a Limestone-Endemic Plant Based on “Fissure-Soil” Habitat Function

The southwestern mountains of Hainan Island are the southernmost region with tropical karst landform in China. The frequent alternation of dry and wet seasons leads to the loss of the mineral nutrients of limestone, creating karst fissure habitats. Plants living in karst fissure habitats for long periods of time have developed local adaptation mechanisms correspondingly. In the paper, hydrogen–oxygen stable isotope technology was applied to determine the water-use sources of Impatiens hainanensis in the dry and wet seasons, hoping to expound the adaptation mechanism of I. hainanensis in karst fissure habitats to the moisture dynamics in the wet and dry seasons. In the wet season (May to October, 2018), the air humidity is relatively high in the I. hainanensis habitat; in the dry season (November 2018 to April 2019), there is a degree of evaporation. In the wet season, fine-root biomass increases with soil depths, while coarse-root biomass decreases with soil depths; in the dry season, fine-root biomass is lower and coarse-root biomass is higher compared with the wet season. It was found that the average rainfall reached 1523 mm and the main water-use sources were shallow (0–5 cm) and middle (5–10 cm) soil water, epikarst water, and shallow karst fissure water during the wet season; the average rainfall reached 528 mm, and the deep (10–15 cm) soil water and shallow karst fissure water were the main water-use sources during the dry season. Fog water has a partial complementary effect in the dry season. The differences in the distribution of root biomass and each source of water in the wet and dry seasons of I. hainanensis also reflect the different water-use strategies of I. hainanensis in the wet and dry seasons. In both dry and wet seasons, I. hainanensis formed a water-use pattern dominated by soil water and shallow fissure water (0–15 cm) under the influence of the “fissure-soil-plant” system in the karst region.

ASSESSING THE VALUE OF GROUNDWATER REVENUES AND DETERMINATION OF OPTIMUM RATES IN MAKASSAR CITY

Ground water is defined as water that is in the ground and is water that moves and is present in the spaces between the grains of soil that make it up and rock crevices, where the initial part is called layer water and the latter is called fissure water. Water is one of the natural elements that are needed in the life activities of living things, especially humans. The purpose of this study is to assessing the value of groundwater revenues and determine of optimum rates in Makassar City. Data analysis method used is the analysis of groundwater value by referring to the Minister of Energy and Mineral Resources Regulation No.20 of 2017 concerning Guidelines for Establishing Groundwater Revenue Value and the marginal cost pricing method. The results showed that the average revenue of groundwater in Makassar City was IDR.690,276,939.35 with an average tax of IDR.138,055,387.87. The value of groundwater is quite high when compared to the revenue value of groundwater that has been determined by the Makassar City government at this time. The results of determining the optimum rates obtained for the user group 1 is IDR.9,661.96 per m3 per month, the user group 2 is IDR.13,973.63 per m3 per month, the user group 3 is IDR.10,866.67 per m3 per month, and the user group 4 is IDR.4,255.56 per m3 per month. Whereas the beneficiary group 5 has a higher average groundwater utilization cost when compared to the PDAM water rates. The results of research can become policy basis of the Makassar City local government in determining the value of groundwater.

A Discussion of Reinforcement Timing Optimization for Main Inclined Shaft Roadway with Water Seepage

The infiltration and physical and chemical effects of fissure water often have a degrading effect on the strength and bearing capacity of the surrounding rock of the roadway. With the increase of the time of water infiltration, the roadway deformation increases exponentially, resulting in a higher risk of roadway destruction. In this paper, targeting at the supporting and protection issues associated with the main inclined shaft during the water-drenching, a numerical simulation method was established to evaluate the impact of the fissure water on the deformation of the surrounding rock of the roadway, and a solution to control the top water in main inclined shafts by grouting was proposed. Through the numerical simulation method, the effective penetration range of the slurry in the surrounding rock and the variation of the tunnel deformation with the grouting timing were studied. A method of combining numerical simulation with on-site monitoring to determine a reasonable grouting timing was proposed. The field application suggests that grouting at a reasonable timing can effectively control the influence of seepage water from the roof crack of the main inclined shaft on the deformation of the roadway surrounding rock, improve the integrity of the roadway surrounding rock, increase the bearing capacity of the support, and maintain the safety and stability of the roadway surrounding rock of the main inclined shaft. Furthermore, this study can provide insightful references to the grouting reinforcement adopted by similar main inclined shafts.

Oxidation of black shale and its deterioration mechanism in Xujiaping rockslide, Southwestern China

<p>The water-rock chemical interaction of black shale interbedded with limestone along the bedding slip zone and its deterioration to the surrounding rock mass in Xujiaping rockslide is studied. As an important rock-forming mineral in black shale, pyrite is known for being easily oxidized to produce sulfuric acid in water, and sulfuric acid is a significant factor that leads to the dissolution of minerals. Significant number of erosion pits on the limestone were found and many geochemical phenomenon such as extremely low pH fissure water and the secondary mineral phases were investigated. Rock and water samples from this site were analyzed to determine mineralogy, chemical composition and hydrochemistry. The results indicate that many major elements and heavy elements are dissolved, such as Fe, Mn, Si, Zn, Ni, Al, S, Mg, Ca, Na, K, Co and Sr, because of the strong dissolution ability of acid water from black shale.The acid water migrates along the slip zone to exposed surface of cliff and fractures, where it evaporates to form the secondary mineral phases including melanterite, rozenite, szomolnokite, and gypsum etc. The water-rock chemical interaction in Xujiaping rockslide is a combination of dissolution, oxidation, dehydration, and neutralization reactions. Besides, the deterioration mechanism is expanded on two aspects: (1) rock-forming minerals, carbonate minerals especially are prone to be dissolved by sulfuric acid from oxidation of black shale in the slip zone; (2) the crystallization volume expansion of minerals precipitated, which leads to the further expansion and deformation of fractures.</p>