Characteristics of water contamination in abandoned coal mines:a case study on Yudong River area,Kaili,Guizhou Province,China

The seasonal and spatial changes in the chemical composition of the water in abandoned mine drainages and rivers in Yudong River area in the years of 2017-2018 were analyzed.The effects of mine water drainage on the seasonality and physicochemical properties of the river water after mine closure were evaluated,and the feasibility of irrigation using river water and the degree of pollution to farmland were assessed using the Water Quality Standard for Farmland Irrigation.The results show that the mine water has low pH value(<3.5-4)and high levels of total hardness,SO_(4)^(2−),Fe,Al,and Zn.In addition,the pH of the mine water is negatively correlated with the presence of other metal ions.The correlation coefficient between the chemical oxygen demand(COD)and Fe reached 0.989.While the pollution levels of Pinglu and Baishui rivers were low,the confluence region of the two rivers was seriously polluted.However,only the levels of Fe and Cd slightly exceeded the Surface Water Environmental Quality Standard after the confluence of Yudong and Chongan rivers.Overall,the heavy pollution type of the confluent river is consistent with mine water pollution.The water quality is slightly better in the dry season compared than in the high-water period.Sulfate and Fe content decreased by 39 and 16 mg/L,respectively,and Cd content decreased two-fold.Despite these findings,this study shows that from 2017 to 2018,the pH and Cd content of the rivers at the confluence exceeded the irrigation limit and the water quality continued to deteriorate,which may pose a soil contamination risk.Long-term use of the river for irrigation water may cause toxic elements such as Cd,Fe,Mn,SO_(4)^(2−),Al,and F-to enter the food chain,thereby endangering the life and health of villagers in Yudong River area.

Study on ascending mining roadway layout of close distance coal seams in deep mine

To solve the problems appeared in mining process of No.2 seam, the ascending stress-releasing mining method was adopted. Studying on the reasonable layout of actual mining roadway in upper coal seams is the precondition of successful ascending mining. By using ＂device of leak measuring by blocking up double ends＂, it detected the height of overburden water flowing fractured zone originated from sub-coal seams mining. Thus it proved that the actual mining roadway of No.2 upper ascending seam was located in the smooth sagging zone. On the basis of analyzing the stress-releasing effect of sub-coal seams mining to upper coal seams by using RFPA software, it analyzed the stability of up-face coal seams and the reasonable location of starting cut in up-face coal seams. It also analyzed the reasonable gateway location in upper coal seams, which ensured the crossheading in upper coal seams out of the effect of sub-coal work face mining by using theory of underground pressure. Meanwhile, the reasonable pillars dimensions in upper coal seams by building the structure mechanics model of stope were researched. It can make the roadway driven along next goaf to be located in low stress zone, and be beneficial to keeping roads stable owing to less stress of surrounding rock. Finally, it tested the rationality of the layout method of roads in upper coal seams by engineering field measurement in 3221 working face.

Stability control of gob-side entry retained under the gob with close distance coal seams

In multi-seam mining,the interlayer rock strata between the upper coal seam(UCS)and the lower coal seam(LCS)appear damage and strength weakening after mining the UCS.Ground stability control of the gob-side entry retaining(GER)under the gob with close distance coal seams(CDCS)is faced with difficulties due to little attention to GER under this condition.This paper focuses on surrounding rock stability control and technical parameters design for GER under the gob with CDCS.The floor rock strata damage characteristics after mining the UCS is first evaluated and the damage factor of the interlayer rock strata below the UCS is also determined.Then,a structural mechanics model of GER surrounding rock is set up to obtain the main design parameters of the side-roadway backfill body(SBB)including the maximum and minimum SBB width calculation formula.The optimal SBB width and the water-to-cement ratio of high water quick-setting material(HWQM)to construct the SBB are determined as 1.2 m and 1.5:1.0,respectively.Finally,engineering trial tests of GER are successfully carried out at#5210 track transportation roadway of Xingwu Colliery.Research results can guide GER design under similar mining and geological conditions.

Measurement of overburden failure zones in close-multiple coal seams mining

In the Kaiping Coal field,mining of five coal seams,located within 80 m in the Kailuan Group,#5,#7,#8,#9 and#12 coal seam,is difficult due to small interburden thickness,concentrated stress distributions,high coal seam metamorphism,and complex geological conditions.By using the ZTR12 geological penetration radar(GPR)survey combined with borehole observations,the overburden caving due to mining of the five coals seams was measured.The development characteristics of full-cover rock fractures after mining were obtained from the GPR scan,which provides a measurement basis for the control of rock strata in close multiple coal seam mining.For the first time,it was found that the overburden caving pattern shows a periodic triangular caved characteristic.Furthermore,it is proposed that an upright triangular collapsed pile masonry and an inverted triangular with larger fragments piled up alternately appear in the lower gob.The research results show that the roof structure formed in the gob area can support the key overlying strata,which is beneficial to ensure the integrity and stability of the upper coal seams in multiple-seam mining of close coal seams.

Study on the economic mining method for the close quarter coal seams with thin rock sheet

The paper presents the mining method for the close quarter coal seams with thin rock sheet, that is mining the low coal seam, recovering the top coal seam after putting down the roof rock of the low coal seam. Practice has proved that in recovering the top coal outside the face width after the rock between seams falls naturally or is demolished, the technology is simple, easy to operate and does not make a great demand for technical equipment. In the process of recovering the top coal, the low seam support could not be affected seriously, and two seams mining could be coordinated. Compared with the individual mining method, this mining method can produce a better economic benefit.