Study On Mechanism Of Dam Slope Leakage And Treatment Measures Of Chendong Tailing Pond

Tailings pond is a subsidiary facility of mine concentrator production.There were 18,000 tailings dams worldwide in 2020,of which 3,500 were in operation.In the past decades,there are a lot of safety accidents of tailing ponds at home and abroad,including pipe surge,sand leakage,shaft toppling,slope sliding,flood overtopping and even dam collapse.In these accidents,there were some major accidents that have resulted in hundreds of deaths and injuries.There are two main causes of tailings pond dam collapse: flood overtopping and dam slope sliding.Flood overtopping is usually caused by overdesigned flood,insufficient drainage capacity or blockage,while dam slope sliding is mainly caused by high phreatic line and steep dam slope.The phreatic line is known as the “lifeline” of tailings dam,and its minimum burial depth in the dam slope is clearly stipulated in the 《Code for Design of Tailings Pond Facilities》(GB50863-2013)and the《Safety technical regulations for the tailing pond》(AQ 2006-2005).Therefore,in the daily safety management of tailings pond,the depth of phreatic line is an extremely important control index.During the operation of Chendong tailings pond in the Guangdong province,there were ever abnormal phenomena of high phreatic line and slope surface leakage,while the water level of the tailing pond and the slope degree of the dam ware within the normal range.The reason of abnormal leakage could not be explained by the conventional seepage theory analysis at that time.In order to ensure the safety of tailings pond and the normal production of enterprises,this paper had carried out a special study on the leakage problem of the tailings dam.By means of geological survey,in-situ excavation exploration,phreatic line observation and seepage calculation,comprehensive and detailed research were performed to explore the mechanism of slope leakage of Chendong tailings dam.Based on the revealed mechanism of the leakage,the corresponding measures for shallow soil drainage through the blind ditch network was designed.After this measure was adopted in construction,the phreatic line of dam body dropped down rapidly,and no leakage occurs on slope surface,thus the problem of dam slope leakage was solved effectively.The research work and achievements are summarized as follows:(1)The topography and geology of the tailings pond,the surrounding environment,the characteristics of the dam body and drainage system,and the safety condition of the dam body are comprehensively analyzed.According to the seepage situation and the depth of the the phreatic line,the abnormal leakage phenomena and patterns appearing in the upper dam slope are clarified.This kind of slope surface leakage of tailing dam is not common,and there is no relevant regulations to cover it in the present technical specification of tailings pond in China.(2)Through the targeted geological investigation and excavation inspection,combined with the seepage calculation and the analysis of the phreatic line observation data,it is revealed that the the main reason of the dam slope leakage is the historical clay embankment in the dam slope.The clay embankment forms a “soil nail” retaining dam in the tailings sand,and the back seepage water from ore drawing and infiltrated rainfall accumulates in the shallow tailings upstream of the retaining dam,forming a “surface stagnant water layer”with high water content.It is just the “surface stagnant water layer” that causes the surface seepage of tailings dam slope.At the same time,the stagnant water fell into the pressure measuring tube,so that the water level of the pressure measuring tube rose a lot,resulting in the illusion of high phreatic line.(3)Based on the revealed causes of dam slope leakage,the measure to excavate the blind channels in the clay embankment was taken to drain out the stagnant water in the dam slope.After construction,the leakage phenomenon of the dam slope surface was eliminated,and the phreatic line return to the normal state.The treatment measures had been successful,providing a good example for other tailing ponds to solve similar problems,and providing a scientific basis for the improvement of tailing ponds related specifications.