Groundwater Behaviour in Layered Slope Rock Mass And Finite Element Simulation

The paper deals with the relatively weak permeable layer in a layered structure of a slope rock mass and itseffect on groundwater behaviour in the rock mass. When the whole groundwater table is declined in such typeof slope rock mass, the permeability of the relatively weak permeable layer in the middle will be several timeslower than that of the upper and lower permeable layers and consequently the water level in layers of differentpermeability will fall in different rates which will lead to a discontinuous phenomenon of the water body. Amethod of finite element simulation on a vertical two-dimensional profile is suggested for the study of the phe-nomenon and its application to practical situation is described. The calculation result shows that the existingweak permeable layer in a layered slope rock mass exerts unnegligible influence on the variation of water levelin the rock mass of a slope. The result also proves the applicability of the finite element simulation method.     

Geochemical characteristics and source analysis of inflow of mine water in Wang＇ershan Gold Mine, Shandong

Through a systematic observation of water level and temperature, and a comprehensive analysis of the data on major/trace elements, nitrite, hydrogen-oxygen isotopes, the conclusion has been drawn that there are two relatively independent groundwater systems （cool water and hot water）, and the geochemical indicators of hot/cool waters are described. The cool water system is relatively enriched in Ca^2＋, Mg^2＋ and HCO3^-. Its TDS is relatively low, about 1400-1800 mg/L. The hot water system is relatively enriched in K^＋, Na^＋, Cl^- and SO4^2-. Its TDS is relatively high, about 2200-2300 mg/L. The cool water system is enriched in Ba, Ga, Cd, and the hot water system is enriched in B, Ti, Cr, Ni, Cu, Mo, Rb, and Cs, relatively. Especially, the contents of Rb and Cs in the hot water system are more than five times as high as those in the cool water system. The NO3^- contents of cool water discharged from the gold mine are relatively high, and those of hot water are extremely low. The 8D and 8-80 values follow an increasing order of surface water〉mine cool water〉mine hot water. The cool water comes mainly from the lateral supply of phreatic water, while the hot water comes mainly from the vertical supply of deeply circulating structure-fracture water. The ratio of cool water over hot water was estimated to be about 1：1 by a water quality model..     

Isotope analysis of nitrate pollution sources in groundwater of Dong'e geohydrological unit

As nitrate pollution in groundwater has become increasingly serious in recent years, nitrogen isotope was adopted in this paper to define its sources in a typical agricultural area of Dong'e hydrogeological unit. The results show that: Higher content of NO_3~- detected in shallow groundwater is 27.77 mg/L on average and δ15 N content ranges from 7.8‰ to 12 ‰, indicating that shallow groundwater is mainly contaminated by sewage or feces. In contrast, less NO_3~- in deep groundwater(karst water) has an average value of 12.81 mg/L and δ15 N content is between 7.2‰ and 14.3‰, which is closely related to human disturbance as mentioned above. In addition, considering relatively low groundwater quality at some monitoring sites, reasonable fertilization is a better choice in the study area to reduce nitrate source in groundwater.     

Geochemical characteristics and source analysis of inflow of mine water in Wang’ershan Gold Mine, Shandong

Through a systematic observation of water level and temperature, and a comprehensive analysis of the data on major/trace elements, nitrite, hydrogen-oxygen isotopes, the conclusion has been drawn that there are two relatively independent groundwater systems (cool water and hot water), and the geochemical indicators of hot/cool waters are described. The cool water system is relatively enriched in Ca2 , Mg2 and HCO3-. Its TDS is relatively low, about 1400–1800 mg/L. The hot water system is relatively enriched in K , Na , Cl- and SO42-. Its TDS is relatively high, about 2200–2300 mg/L. The cool water system is enriched in Ba, Ga, Cd, and the hot water system is enriched in B, Ti, Cr, Ni, Cu, Mo, Rb, and Cs, relatively. Especially, the contents of Rb and Cs in the hot water system are more than five times as high as those in the cool water system. The NO3- contents of cool water discharged from the gold mine are relatively high, and those of hot water are extremely low. The δD and δ18O values follow an increasing order of surface water>mine cool water>mine hot water. The cool water comes mainly from the lateral supply of phreatic water, while the hot water comes mainly from the vertical supply of deeply circulating structure-fracture water. The ratio of cool water over hot water was estimated to be about 1:1 by a water quality model..     

Environmental Isotopic Characterization of Groundwater and Surface Water in Northeast Missan Province,South Iraq

The present work studies the environmental isotopes assess groundwater characteristics of the different parts of the main aquifer in the northeast Missan Province in south of Iraq.Water samples of groundwater and surface water were collected for two dry and wet seasons during the water year of 2011–2012.The study shows that most of the groundwater in the aquifer falls above the global meteoric water line,and all the samples fall below the Mediterranean meteoric water line,indicating that these samples are a mixture of two water types.The tritium content of these samples supports this conclusion.The overall conclusion of this study indicates that there are two sources of groundwater recharge in the studied area:the ephemeral streams(Teeb and Dewerge) and major precipitation sources.According to the tritium levels at or below one tritium unit(TU) obtained from the water,supply wells are highly confined or "not vulnerable".Overall,the 3H results imply that recent recharge has taken place during the last four to five decades.In the recharge area,the high tritium content in the southern part of the Teeb area suggests that the recharge originates from rapid infiltration of surface runoff.Therefore,the groundwater resources in the study area should be protected from contamination,because it will influence the aquifer in a relatively short period of time if any contamination enters the recharge areas of the aquifer.     

Arsenic Distribution Pattern in Different Sources of Drinking Water and their Geological Background in Guanzhong Basin,Shaanxi, China

To study arsenic(As) content and distribution patterns as well as the genesis of different kinds of water, especially the different sources of drinking water in Guanzhong Basin, Shaanxi province, China, 139 water samples were collected at 62 sampling points from wells of different depths, from hot springs, and rivers. The As content of these samples was measured by the intermittent flowhydride generation atomic fluorescence spectrometry method(HG-AFS). The As concentrations in the drinking water in Guanzhong Basin vary greatly(0.00–68.08 μg/L), and the As concentration of groundwater in southern Guanzhong Basin is different from that in the northern Guanzhong Basin. Even within the same location in southern Guanzhong Basin, the As concentrations at different depths vary greatly. As concentration of groundwater from the shallow wells(50 m deep, 0.56–3.87 μg/L) is much lower than from deep wells(110–360 m deep, 19.34–62.91 μg/L), whereas As concentration in water of any depth in northern Guanzhong Basin is 10 μg/L. Southern Guanzhong Basin is a newly discovered high-As groundwater area in China. The high-As groundwater is mainly distributed in areas between the Qinling Mountains and Weihe River; it has only been found at depths ranging from 110 to 360 m in confined aquifers, which store water in the Lishi and Wucheng Loess(Lower and Middle Pleistocene) in the southern Guanzhong Basin. As concentration of hot spring water is 6.47–11.94 μg/L; that of geothermal water between 1000 and 1500 m deep is 43.68–68.08 μg/L. The high-As well water at depths from 110 to 360 m in southern Guanzhong Basin has a very low fluorine(F) value, which is generally 0.10 mg/L. Otherwise, the hot springs of Lintong and Tangyu and the geothermal water in southern Guanzhong Basin have very high F values(8.07–14.96 mg/L). The results indicate that highAs groundwater in depths from 110 to 360 m is unlikely to have a direct relationship with the geothermal water in the same area. As concentration of all reservoirs and rivers(both contaminated and uncontaminated) in the Guanzhong Basin is 10 μg/L. This shows that pollution in the surface water is not the source of the high-As in the southern Guanzhong Basin. The partition boundaries of the high- and low-As groundwater area corresponds to the partition boundaries of the tectonic units in the Guanzhong Basin. This probably indicates that the high-As groundwater areas can be correlated to their geological underpinning and structural framework. In southern Guanzhong Basin, the main sources of drinking water for villages and small towns today are wells between 110–360 m deep. All of their As contents exceed the limit of the Chinese National Standard and the International Standard(10 μg/L) and so local residents should use other sources of clean water that are 50 m deep, instead of deep groundwater(110 to 360 m) for their drinking water supply.     

Climate change and groundwater conditions in the Mekong Region–A review

Changes in the climatic system introduce uncertainties in the supply and management of water resources. The Intergovernmental Panel on Climate Change(IPCC) predicts an increase of 2 to 4 °C over the next 100 years. Temperature increases will impact the hydrologic cycle by directly increasing the evaporation of surface water sources. Consequently, changes in precipitation will indirectly impact the flux and storage of water in surface and subsurface reservoirs(i.e., lakes, soil moisture, groundwater, etc.). In addition, increases in temperature contribute to increases in the sea level, which may lead to sea water intrusions, water quality deterioration, potable water shortages, etc. Climate change has direct impacts on the surface water and the control of storage in rivers, lakes and reservoirs, which indirectly controls the groundwater recharge process. The main and direct impact of climate change on groundwater is changes in the volume and distribution of groundwater recharge. The impact of climate change on groundwater resources requires reliable forecasting of changes in the major climatic variables and accurate estimations of groundwater recharge. A number of Global Climate Models(GCMs) are available for understanding climate and projecting climate change.These GCMs can be downscaled to a basin scale, and when they are coupled with relevant hydrological models, the output of these coupled models can be used to quantify the groundwater recharge, which will facilitate the adoption of appropriate adaptation strategies under the impact of climate change.     

Fluoride contamination in groundwater resources of Alleppey,southern India

Alleppey is one of the thickly populated coastal towns of the Kerala state in southern India.Groundwater is the main source of drinking water for the 240,991 people living in this region.The groundwater is being extracted from a multi-layer aquifer system of unconsolidated to semi-consolidated sedimentary formations,which range in age from Recent to Tertiary.The public water distribution system uses dug and tube wells.Though there were reports on fluoride contamination,this study reports for the first time excess fluoride and excess salinity in the drinking water of the region.The quality parameters,like Electrical Conductivity(EC) ranges from 266 to 3900 μs/cm,the fluoride content ranges from 0.68 to2.88 mg/L,and the chloride ranges between the 5.7 to 1253 mg/L.The main water types are Na-HC03,NaCO_3 and Na-Cl.The aqueous concentrations of F~- and CO_3~(2-) show positive correlation whereas F~- and Ca~(2+) show negative correlation.The source of fluoride in the groundwater could be from dissolution of fluorapatite,which is a common mineral in the Tertiary sediments of the area.Long residence time,sediment-groundwater interaction and facies changes(Ca-HCO_3 to Na-HCO_3) during groundwater flow regime are the major factors responsible for the high fluoride content in the groundwater of the area.High strontium content and high EC in some of the wells indicate saline water intrusion that could be due to the excess pumping from the deeper aquifers of the area.The water quality index computation has revealed that 62%of groundwater belongs to poor quality and is not suitable for domestic purposes as per BIS and WHO standards.Since the groundwater is the only source of drinking water in the area,proper treatment strategies and regulating the groundwater extraction are required as the quality deterioration poses serious threat to human health.     

Geochemical Modelling of Fluoride Concentration in Hard Rock Terrain of Madhya Pradesh, India

The aim of the present study is to locate and decipher the groundwater quality,types,and hydrogeochemical reactions,which are responsible for elevated concentration of fluoride in the Chhindwara district in Madhya Pradesh,India.Groundwater samples,quality data and other ancillary information were collected for 26 villages in the Chhindwara District,M.P.India during May 2006.The saturation index was computed for the selected samples in the region,which suggest that generally most of the minerals are saturated with respect to water.The concentration of fluoride in the region varies from 0.6 to 4.74 mg/l,which is much higher as per the national and international water quality standards.The study also reveals that the fluoride bearing rock formations are the main source of the higher concentration of fluoride in groundwater along with the conjuncture of land use change.Moreover,the area is a hard rock terrain and consists of fractured granites and amygdaloidal and highly jointed compact basalt acting as good aquifer,which is probably enriching the high content of fluoride in groundwater.High concentration of fluoride is found in deeper level of groundwater and it is possible due to rock-water interaction,which requires further detailed investigation.The highly alkaline conditions indicate fluorite dissolution,which works as a major process for higher concentration of fluoride in the study area.The results of this study will ultimately help in the identification of risk areas and taking measures to mitigate negative impacts related to fluoride pollution and toxicity.     

Arsenic pollution of groundwater and its release mechanism in the central part of the Hetao Plain, Inner Mongolia, China

Arsenic pollution of groundwater has become a serious health problem in several regions of the world. Wuyuan County located in the central part of the Hetao Plain, Inner Mongolia, is one of the most severely arsenic polluted areas. Peoples of the county have used groundwater of shallow （12-25 m） tube-well as drinking water. The groundwater is Na-HCO3 and Na-Cl type on the piper plots and aligns with steady Ca ： Mg ratio on cation diagram. The arsenic content in the water is more than 0.2 mg/L and the highest value reaches up to 0.52 mg/L. Drilling data show that Holocene sediments are divided into three zones on the basis of their color appearances; brown, grey and dark gray zones. The strata from 2m to 9-14m under the surface are mainly composed of clay and silt which are impermeable layers. The grey and dark grey zones composed of sand underlie the impermeable bed and the condition of their zones is reductive. At the depth of 30 m near the bottom of drilling, ORP of the groundwater is -300- -400 mV. The dark grey sand changes to yellow in color under the atmosphere. Under reducing environment, the color returns to its original dark grey. The characteristic color is due to amorphous or low-crystalline Fe sulfide coating sand grains. The sediments are of fluvial origin by the Yellow River. The arsenic content in the sediments is rich in fine-grained part and its values are more than 20 mg/kg in clay layer. The highest is 38 mg/kg. X-ray diffraction and macroscopic observation show that the clay layer is made of minerals such as chlorite and illite and contains high quantities of organic matter.     

鄂尔多斯盆地白垩系含水层系统分析

从地下水含水层系统的角度对鄂尔多斯盆地白垩系地下水系统进行了划分和分析。由于下白垩系统保安群为一套陆相碎屑岩建造,岩性复杂,由砂岩、粉砂岩和泥岩组成的频繁交替、重复叠置的多层层状结构,决定了鄂尔多斯白垩系自流水盆地是多层结构的地下水系统。这种重复叠置的多层层状地质结构,决定了地下水含水层系统的多层性、承压性及层与层之间的相对封闭性。根据沉积旋回和含水介质的性质,在全盆地范围内把白垩系地下水系统从上向下划分为：罗汉洞含水岩组、环河含水岩组和洛河含水岩组。通过对这3大含水岩组分别进行了分析认为,洛河含水岩组和环河含水岩组分布范围广、,含水层厚度大、天然资源丰富,是盆地区具供水意义的主要含水岩组。罗汉洞含水岩组因分布面积小,含水层厚度差异大、水质变化大,除陇东地区外,大部分地区供水价值较小。     

重庆歌乐山隧址区地下水同位素组成特征及意义

同位素测试作为一种先进的技术手段在地质科学的各个研究领域得到越来越广泛地应用。运用同位素方法研究流体及矿床成因关系方面取得了较大的进展。目前，环境同位素方法被广泛用于识别地下水系统，研究自然界水循环过程和地下水运动规律。不同成因的地下水具有不同的同位素组成特征，而且氢、氧稳定同位素在低温条件下不与围岩发生同位素交换，放射性同位素变化遵循各自的衰变规律，水中HCO3碳、氧同位素组成与被溶解的碳酸盐岩同位素组成有关。在歌乐山隧道施工涌水对周边地下水系统的影响及环境效应评价过程中，取得许多同位素数据，对该区地下水的同位素特征有了新的认识。文章借助同位素方法探讨了隧址区地下水的补给源、年龄等基本特征。该区地下水主要补给来源为大气降水。碳、氧稳定同位素的研究结果也证实了这一点。对放射性同位素氚研究表明，该区地下水年龄基本都较小，属近期大气降水直接渗入补给。     

山岭隧道工程综合地质勘察方法探讨

山岭隧道工程具有隐蔽性、施工复杂性、地层条件和周围环境不确定性等特点,采用科学的勘察方法,是查明隧道岩土体工程地质条件的有效手段。本文以海淀区西山隧道为依托,针对隧道工程勘察中的关键地质问题,运用工程地质测绘、钻探、工程物探、水文地质勘查等综合勘察方法,有效地查明隧址区的地质构造、岩土体结构和地下水分布特征,全面、客观地评价隧道进出口段边坡及仰坡稳定性、隧道围岩质量与稳定性、隧道涌水量、地应力及有害气体等工程地质问题,并针对不良地质现象提出防治对策,以期为工期紧张、地形困难且日趋增多的山岭隧道工程地质勘察,提供可以借鉴的模式和方法。     

渝湘高速公路正阳隧道塌方治理方案研究

塌方一直是我国隧道建设领域研究的热点问题。从施工过程中冒顶塌方形成经过、产生塌方原因入手,对渝湘高速公路正阳隧道一次塌方事故提出治理方案,认为岩隙渗水作用于覆盖层较薄、渗透性强的松散破碎地段使隧道上方岩土体的自稳能力恶化;通过坍口设置截水沟及多种形式注浆技术,及时加固坍塌体,封堵岩隙渗水。方案效果良好,具有一定借鉴意义。     

Effect of Excavation-Induced Groundwater Level Drawdown on Tunnel Inflow in a Jointed Rock Mass

Analytical and empirical methods used in current engineering practice for estimating inflow rate into a tunnel do not adequately account for the effect of groundwater level drawdown which triggers changes of the flow pattern as well as reductions of the hydraulic head. When there is no reservoir or a large body of water near the tunnel alignment, the groundwater recharge above the tunnel might not be fast enough to avoid a significant excavation-induced water level drawdown. This paper provides analytical methods for estimating groundwater inflow rate taking into account the groundwater table drawdown. The proposed analytical solutions presented here compare well with field observations as well as with results from numerical analysis using distinct element method which can adequately simulate the hydro-mechanically coupled behavior of joints in a rock mass.     

西南地区隧道工程条件下岩溶地下水系统变化特征分析

岩溶山区越岭长大隧道的施工不可避免地会使当地的岩溶水系统发生改变,如地下水水位的下降、地表泉点的漏失等。基于隧道工程对岩溶地下水系统边界条件、排泄状况等天然特征的影响,依据西南地区岩溶地下水系统主要特征及隧道工程特点,考虑隧道工程条件下影响岩溶地下水系统特征的主要因素,对岩溶类型(岩溶含水岩组的埋藏条件)、构造特征、补给特征、岩溶水径流方式与隧道工程特点相组合的模式下的岩溶地下水系统的变化进行特征分析,并将岩溶地下水系统的变化归纳为3种类型。据此,选择研究区金汁河地下水系统作为典型研究对象,假设3种隧道穿越方案,将不同隧道穿越方案下的岩溶地下水系统与天然岩溶地下水系统进行对比分析,归纳概述其变化特征,最后对各隧道方案下的涌水量及其涌水危险性进行初步预测及评价。     

Mechanism of the Mudstone Tunnel Failures Induced by Expansive Clay Minerals

Expansive clay minerals can be a serious threat to underground rock structure because of their swelling behavior when absorbing water. Roof and wall collapse as well as large deformation were observed in Xiaotun Coal Mine, Guizhou Province, China. This paper studies the characteristics of expansive clays in order to understand the mechanism of the mudstone tunnel failures in the mine. The physical and mechanical properties of the tunnel surrounding rock samples, including mudstone, silty mudstone, argillaceous siltstone and fine sandstone were determined. X-ray diffraction analysis was conducted to determine the mineralogical composition while the scanning electron microscope was used to examine the internal structure of the different samples. The results indicate that the illite–smectite and the montmorillonite are the main minerals composing the rock samples. A series of micro-cracks and pores occur in the samples which suggest a good hydraulic conductivity. The results indicate that the mudstone has poorer mechanical properties in comparison to the fine sandstone. Also, the Flac3D numerical simulations were conducted and it was shown that the large deformations were consistent with the field observation due to weak mechanical properties of the surrounding rock under seepage action especially with the increase of water head and porosity. It is concluded that internal structure and mechanical strength of the mudstone is weakened by the illite–smectite and the montmorillonite mineral content as well as the combined action of underground water causing physical disintegration.     

Groundwater Effect on Faulted Rock Mass: An Evaluation of Modi Khola Pressure Tunnel in the Nepal Himalaya

Groundwater has a negative impact not only in construction activity, but also in stability of a tunnel. Severity increases particularly in tunnels passing through fault gouge and breccia, where rock material is completely crushed and extremely weak. Instantaneous collapse and excessive plastic deformation is most likely in tunnels passing through such zones. Often, ‘flowing’ conditions may prevail if groundwater is mixed in the rock mass. This paper presents one such tunnel case in the Nepal Himalaya; i.e. the Modi pressure tunnel. This pressure tunnel passes through a tectonic fault consisting of gouge material. High deformation in the tunnel was observed while excavating the tunnel through the fault. Based on the tunnel deformation that was actually measured, the paper first back-calculates the rock mass strength by analytical approach. Then, the extent of in-situ stress condition in the area is determined by numerical modeling for the rock mass with no ground water in consideration. The ground water effect is then analyzed. We found that the effect of ground water with a static head <1.5 bar pressure may increase the deformation by up to a maximum of 30 %. Finally, we briefly discuss uncertainties related to the input parameter study and used methodologies.     

渗流作用下黄土含水率变化特征及对隧道工程的影响

富水黄土隧道施工开挖后含水率增加对隧道工程施工影响较大,前人建立了多种以黄土含水率为指标的工程措施判别标准,但对于黄土含水率的变化原因及时空变化特征缺乏系统研究。银西高铁驿马一号隧道不同工况下含水率的变化特征表明,自然渗流状态下隧道洞身黄土含水率平均为25.9%,局部为软塑;施工排水阶段受渗涌水影响,黄土含水率平均上升到31.3%,下拱腰上升到32.2%,引起了隧底软化、掌子面滑塌失稳、围岩稳定性变差等问题;采取地表降水后,黄土含水率下降为25.4%,改善了黄土的物理性质,确保了隧道施工安全与进度;水位恢复后,黄土含水率平均上升到29.4%,拱顶与上拱腰变化较小,下拱腰达到了37.2%。研究认为地下水渗流变化将使得隧道洞身黄土含水率变幅达15%～33%,通过控制地下水渗流作用可以达到隧道安全施工的目的。