江河水下地层探测技术及设备

应用从美国引进的江河水下地层探测设备StrataBox进行消化吸收和研究,并成功地应用于长江水下示范工程的实地测量,获得了该河段河底以下40m内的沉积物剖面图,提高了我国江河水下地层探测技术和安全监测水平,并为进一步深入研究水库堤坝的病险隐患、河床地质状况和水下工程运用效果提供了准确数据和科学决策依据。

基于BP神经网络的水下岩溶地层盾构掘进参数预测与分析

随着我国城市地铁网的建设,越来越多的隧道将不可避免的穿越水下岩溶区,受制于岩溶地层的复杂性、注浆加固后地层的诸多不确定性,盾构穿越该类地层施工风险极大,而选取合理的盾构掘进参数是确保盾构安全与高效掘进的关键。以长沙地铁三号线盾构穿越水下岩溶段为工程依托,首先通过统计与分析钻探数据,明确了岩溶分布特征;其次,通过输入地层特征参数和隧道特征参数,建立了可输出盾构掘进速度、推力、刀盘扭矩、开挖仓压力、气垫仓压力和同步注浆量等掘进参数的BP神经网络水下岩溶盾构掘进参数预测模型;最后,对样本数据进行了训练,并成功应用于工程实践。研究结果表明:训练的输出值与期望值吻合度较高,构建的BP神经网络模型具有较好的适应性;输出的预测结果能有效反映实际盾构掘进参数的变化趋势,预测值与实际期望值的平均误差均低于13%,在误差可接受范围内。现场应用结果表明,地表沉降在安全范围内,盾构掘进过程中未发生工程事故,盾构掘进参数选取合理,姿态控制较好。研究成果可用于指导水下岩溶盾构隧道工程施工,且该方法的提出也为其他复杂地层盾构掘进参数合理选取提供了新思路。

基于Tesseral2D的水下砂体地震正演计算

基于水下砂层与围岩的波阻抗差异,应用地震波数值模拟软件Tesseral2D建立含有水、粉细砂、砾砂和砾岩的起伏地层模型,在不同的道间距、最小偏移距、子波频率以及不同岩体波速条件下分别对该模型进行正演计算。一般情况下,在震源频率为400 Hz、最小偏移距为5 m、道间距为1 m或2 m时,地震波响应明显、同相轴清晰、干扰波较少,水下地层界面反映良好。进一步结合南京长江第二大桥桥址区的地质资料,建立含有水、淤泥质粉质黏土、粉细砂、砾砂、砂砾卵石和砾岩的水下砂层模型,应用Tesseral2D软件对该模型进行正演研究。结果表明,在震源频率为400 Hz、道间距为2 m以及最小偏移距为5 m时,地震响应能很好地反映水下各岩层界面,特别是能较明显地圈定水下砂层的厚度和分布范围,为实际水下砂体的地震勘探提供理论依据。

苏埃湾海域孤石段盾构施工技术探讨

花岗岩球状风化体(孤石)段盾构施工易造成刀具磨损,甚至刀盘变形,严重时掘进困难。文章对花岗岩球状风化体(孤石)的形成原因、主要组成成分以及形成机理、分布规律进行分析,结合广州、深圳地区地铁盾构施工孤石段常规处理方法,探讨了孤石物探方法及发展,并针对即将在苏埃湾海域开工建设的苏埃通道盾构施工,提出刀具配置、地质预报、水下爆破等施工建议。

Shallow groundwater dynamics in North China Plain

The groundwater level of 39 observation wells including 35 unconfined wells and 4 confined wells from 2004 to 2006 in North China Plain(NCP) was monitored using automatic groundwater monitoring data loggers KADEC-MIZU II of Japan.The automatic groundwater sensors were installed for the corporation project between China and Japan.Combined with the monitoring results from 2004 to 2006 with the major factors affecting the dynamic patterns of groundwater, such as topography and landform, depth of groundwater level, exploitation or discharge extent, rivers and lakes, the dynamic regions of NCP groundwater were gotten.According to the dynamic features of groundwater in NCP, six dynamic patterns of groundwater level were identified, including discharge pattern in the piedmont plain, lateral recharge-runoff-discharge pattern in the piedmont plain, recharge-discharge pattern in the central channel zone, precipitation infiltration-evaporation pattern in the shallow groundwater region of the central plain, lateral recharge-evaporation pattern in the recharge-affected area along the Yellow River and infiltration-discharge-evaporation pattern in the littoral plain.Based on this, the groundwater fluctuation features of various dynamic patterns were interpreted and the influencing factors of different dynamic patterns were compared.

Groundwater Pollution from Underground Coal Gasification

In situ coal gasification poses a potential environmental risk to groundwater pollution although it depends mainly on local hydrogeological conditions. In our investigation,the possible processes of groundwater pollution origi-nating from underground coal gasification (UCG) were analyzed. Typical pollutants were identified and pollution con-trol measures are proposed. Groundwater pollution is caused by the diffusion and penetration of contaminants generated by underground gasification processes towards surrounding strata and the possible leaching of underground residue by natural groundwater flow after gasification. Typical organic pollutants include phenols,benzene,minor components such as PAHs and heterocyclics. Inorganic pollutants involve cations and anions. The natural groundwater flow after gasification through the seam is attributable to the migration of contaminants,which can be predicted by mathematical modeling. The extent and concentration of the groundwater pollution plume depend primarily on groundwater flow ve-locity,the degree of dispersion and the adsorption and reactions of the various contaminants. The adsorption function of coal and surrounding strata make a big contribution to the decrease of the contaminants over time and with the distance from the burn cavity. Possible pollution control measures regarding UCG include identifying a permanently,unsuitable zone,setting a hydraulic barrier and pumping contaminated water out for surface disposal. Mitigation measures during gasification processes and groundwater remediation after gasification are also proposed.

Mining-induced variation in water levels in unconsolidated aquifers and mechanisms of water preservation in mines

Phreatic water resources are widely found in thick unconsolidated surface layers in western China, where water levels respond sensitively and quickly to large-scale underground mining in conjunction with shallow coal seams. Longwall face #32201 of the Bulianta Coal Mine, in the Shendong coalfield was selected as an industrial trail base, where field observations on ground-water levels were conducted when the working face was below a water-rich area. The space-time variation in the behavior of un-consolidated water levels in response to underground mining and its relation with of advance were observed through the field trials. The basic conditions for water preservation in mines are presented and the mechanisms of water preservation in mining analyzed, given the geological condition of two key strata and a severely weathered layer buried in the overburden. The field trails show that water preservation in mining shallow coal seams can be successful under suitable conditions, providing new technology for envi-ronmental protection in the desert coalfields of northwestern China.

Numerical simulation of dewatering thick unconsolidated aquifers for safety of underground coal mining

With an increase of mining the upper limits under unconsolidated aquifers, dewatering of the bottom aquifer of the Quaternary system has become a major method to avoid water and sand inrushes.In the 8th District of the Taiping Coal Mine in south-western Shandong province, the bottom aquifer of the Quaternary system is moderate to excellent in water-yielding capacity.The base rock above the coal seam is very thin in the concealed coal field of the Carboniferous and Permian systems.Therefore, a comprehensive dewatering plan from both the ground surface and the panel was proposed to lower the groundwater level in order to ensure mining safety.According to the hydrogeologic conditions of the 8th District, we established a numerical model so that we could simulate the groundwater flow in the dewatering process.We obtained the simulation parameters from previous data using backward modeling, such as the average coefficient of permeability of 12 m/d and the elastic storage coefficient of 0.002.From the same model, we predicted the movement of groundwater and water level variables and obtained the visible effect of the dewatering project.Despite the overburden failure during mining, no water and/or sand inrush occurred because the groundwater level in the bottom aquifer was lowered to a safe water level.

One-dimensional consolidation of visco-elastic aquitard due to withdrawal of deep-groundwater

One-dimensional consolidation of visco-elastic aquitard due to withdrawal of deep-groundwater was studied.Merchant model was used to simulate visco-elastic characteristic of aquitard.General solutions of the governing equation were obtained by applying Laplace transform with respect to time,and then the pore-pressure,strain and deformation of the aquitard could be calculated by Laplace inversion.A case was analyzed to validate the correctness of the present method.Finally,some consolidation properties of the problem were analyzed.Comparison of the average degree of consolidation defined by pore pressure with that defined by settlement shows that they are different and the maximum difference is 22.8%.The influences of parameters of Merchant model and the rate of the water level on the consolidation are great.The smaller the viscosity coefficient is,the later the rate of consolidation decreases.The rate of consolidation is decreased with the decrease of the rate of the water level fall.Therefore,the lagged effect of land subsidence should be considered in the actual project.

Groundwater Waves in a Coastal Fractured Aquifer of the Third Phase Qinshan Nuclear Power Engineering Field

Tidal fluctuations of Hangzhou Bay produce progressive pressure waves in adjacent field fractured aquifers, as the pressure waves propagate, groundwater levels and hydraulic gradients continuously fluctuate. The effect of tidal fluctuations on groundwater flow can be determined using the mean hydraulic gradient that can be calculated by comparing mean ground and surface water elevations.Tidal fluctuation is shown to affect the piezometer readings taken in a nearshore fractured aquifer around the nuclear power engineering field. Continuous monitoring of a network of seven piezometers provided relations between the tidal cycle and the piezometer readings. The relations can be expressed in times of a time and amplitude scaling factor. The time lag and the tidal efficiency factor and wavelength are calculated using these parameters. It provides significant scientific basis to prevent tide and groundwater for the nuclear power engineering construction and safety run of nuclear power station in the future.

Effect of cushion and cover on moisture distribution in clay embankments in southern China

To achieve durability of the embankment in southern China,a method to control the change of moisture content with the cushion and cover was proposed.A finite element model of cushion and cover considering different materials and thicknesses for a typical embankment was built,and 20 numerical analyses of transient seepage in the embankment were simulated.The results show that the sand cushion effectively blocks the effect of groundwater capillary rise and the minimum thickness of the sand cushion is 75 cm without considering the atmospheric environment.With the combination of sand cushion and clay cover,as the thickness of the clay cover increases,the duration time of the moisture content from the initial to relative equilibrium state increases,but the equilibrium moisture content is the same as that of the original embankment.Besides,with the combination of the sand cushion and sand cover,the moisture content inside the embankment remains the same,which is consistent with the optimum moisture content during construction.The combination of 75 cm sand cushion and 30 cm sand cover is a very effective method to block groundwater and atmospheric environment,and achieve the control of the humidity stability of the embankment in southern China.

Numerical Simulation of Land Subsidence at Tanggu District in Tianjin, China

Based on observed data from Tanggu District in Tianjin, a back-propagation neural network (BPNN) model was introduced to predict possible land subsidence due to exploitation of groundwater. According to model estimation under various hypothetical extraction scenarios, patterns of land subsidence at Tanggu District were studied and discussed.The predicted average background land subsidence rate of Tanggu is 9.47 mm/a.The significance of contribution of aquifers to land subsidence descends in order of units Ⅳ,Ⅲ,Ⅴ,Ⅱ.Land subsidence tends to deteriorate with the increase in total extraction rate.

Fractured zone height of longwall mining and its effects on the overburden aquifers

As mining depth becomes deeper and deeper,the possibility of undermining overburden aquifers is increasing.It is very important for coal miners to undertake studies on the height of fractured zone during longwall mining and the effects of longwall mining on the underground water while mining under surface water bodies and underground aquifers.In order to study this problem,piezometers for monitoring underground water levels were installed above the longwall panels in an American coalmine.Large amounts of pre-mining,during mining and post-mining monitoring data were collected.Based on the data,the heights of fractured zones were obtained and the effects of longwall mining on the underground water were studied.The results demonstrate that when the piezometer monitoring wells had an interburden thickness of less than 72.7 m,the groundwater level decreased immediately to immeasurable levels and the wells went dry after undermining the face of longwall.The height of the fractured zone is 72.7-85.3 m in the geological and mining conditions.The results also show that the calculated values of fractured zones by the empirical formulae used in China are smaller than the actual results.Therefore,it is not always safe to use them for analyses while mining under water bodies.

Exploring Soil Layers and Water Tables with Ground-Penetrating Radar

Ground-penetrating radar (GPR) has been used predominantly for environments with low electrical conductivity like freshwater aquifers, glaciers, or dry sandy soils. The objective of the present study was to explore its application for mapping in subsurface agricultural soils to a depth of several meters. For a loamy sand and a clayey site on the North China Plain, clay inclusions in the sand were detected; the thickness, inclination, and continuity of the confining clay and silt layers was assessed; and a local water table was mapped. Direct sampling (soil coring and profiling) in the top meter and independent measurement of the water table were utilized to confirm the findings. Also, effective estimates of the dielectric number for the site with the dielectric number of moist clayey soils depending strongly on frequency were obtained. Thus, important properties of soils, like the arrangement and type of layers and in particular their continuity and inclination, could be explored with moderate efforts for rather large areas to help find optimal locations for the time-consuming and expensive measurements which would be necessary to detail a model of the subsurface.

Study on effects of longwall mining on the underground water

It is very important for secure mining under water bodies to study the effects of Iongwall mining on the underground water. In order to study this problem, piezometers for monitoring underground water levels were established in an American coalmine. Large amounts of pre-mining and post-mining monitoring data were collected. Based on the data the effects of Iongwall mining on the underground water was studied. The results demonstrate that when the piezometer monitoring wells have an interburden thickness less than 72.7 m, the groundwater level decreases immediately to immeasurable levels and go dry after undermining. The height of the fractured zone in is 72.7-85.3 m in this geological and mining conditions. The results also show that the calculated value of fractured zone by the empirical formulae used in China is smaller than the actual results. Therefore, it is not always safe to use them in analysis of mining under water bodies.

Geochemistry of rare earth elements in groundwater from deep seated limestone aquifer in Renlou Coal Mine,Anhui Province,China

Rare earth element （REE） concentrations were measured by ICP-MS for groundwater collected from deep seated Taiyuan Fm limestone aquifer （from -400 to -530 m） in Renlou Coal Mine, northern Anhui Province, China. It can be concluded that the groundwater is warm （34.0-37.2 ℃） C1-Ca, Na type water with circum-neutral pH （7.35-8.28） and high total dissolved solids （TDS, 1 746-2 849 mg/L）. The groundwater exhibits heavy REEs enrichment relative to light REEs compared with Post Archean Average Shale （PAAS）, as well as their aquifer rocks （limestone）. The enrichment of REEs is considered to be controlled by terrigeneous materials （e.g. zircon） in aquifer rocks, whereas the fractionation of REEs is controlled by marine derived materials （e.g. calcite）, to a less extent, terrigeneous materials and inorganic complexation. The Ce anomalies normalized to PAAS and aquifer rocks are weak, which probably reflects the signature of the aquifer rock rather than redox conditions or pH. The similarities of REE patterns between groundwater and aquifer rocks imply that aquifer rocks play important roles in controlling the REE characteristics of groundwater, and then provide a probability for discrimination of groundwater sources by using REEs.

A Modified DRASTIC Approach to Shallow Groundwater Vulnerability in the West Lake Watershed in Hangzhou, China

The quality of shallow groundwater in the West Lake watershed wasinvestigated form March to July 2000. Integrating with BlacklandGRASS GIS system, the DRASTIC model was used to compile the ground-water vulnerability map. A land use factor was added to the DRASTICmodel and the modified model (LDRASTIC0 increased the accuracy ofprediction form 26.9/100 to 51.3/100. The vulnerability map showedthat the lowly, moderately and highly susceptible area predictedoccupied about 11.6/100, 70.9/100 and 17.5/100 of the wholewatershed, respectively. Compared with the observed values of nitrateand electric conductivity, the LDRASTIC index improved the Pearsoncorrelation coefficients form -0.010 to 0.237 and 0.380 to 0.503;Both the improved coefficients were significant at the 0.01 level.The modified DRASTIC analysis showed a Great potential as a screeningtool for policy decision-making in groundwater management.

Hydrochemical characteristics of aquifers in Northern Gezira State,Central Sudan

This paper presents an assessment of the hydrochemical characteristics of groundwater in Northern Gezira State, Central Sudan. The approaches followed here include the chemical analyses for major ions chemistry and construction of hydrochemical maps of total dissolved solids (TDS), sodium (Na +), bicarbonate (HCO 3 -), and chloride (Cl -) ions. The hydrochemical characteristics of the groundwater in each aquifer and management consideration are discussed. Sources of major ions in groundwater are analyzed. The hydrochemical maps of important species are constructed. The relationship of groundwater to use is elaborated. High concentrations of the chemical and hydrochemical constituents and the occurrence of calcretes (CaCO 3) in upper zones suggest a long history of evaporation and increasing leachates.

Iron and Manganese in Groundwater of Rrogozhina Aquifer, Western Albania

This paper aims to advance previous studies on the iron and manganese content in groundwater of Rrogozhina aquifer （western Albania） and to show the factors which control the content of both iron and manganese in groundwater of this aquifer. Rrogozhina aquifer represents an important groundwater source of the country whose relevance was highly increased during recent years because of the demographic expansion in this region. This is a typically multi-layered artesian aquifer which consists of sandstone and conglomerate with high heterogeneous permeability. The groundwater mostly belongs to HCO3-Mg-Ca hydrochemical type. The content of soluble iron and manganese in groundwater ranges from 0.004 mg/L to 0.7 mg/L, and from 0.0 mg/L to 1.147 mg/L, respectively. Deeper the groundwater occurs and longer the distance from the recharge zone, higher is the content of Fe2＋ in groundwater due to gradual depletion of Oe in groundwater. The content of iron is higher than that WHO and EU recommended, which were 21% and 25% respectively, while the content of manganese were 17% and 23%, respectively. Abstraction of groundwater with high quantities by deeper wells would be accompanied by increase of dissolved iron and manganese content in groundwater which should be treated （with aeration） in order to decrease the content of these two elements in the water before using it.

Boussinesq equation-based model for flow in drainage layer of highway

In order to study the water flow in the drainage layer of highway under steady-state condition, one-dimensional （1D） Boussinesq equation-based model with Dupuit-Forchheimer assumption was established and the semi-analytical solutions to predict the water-table height were presented. In order to validate the model, a two-dimensional （2D） saturated flow model based on the Laplace equation was applied for the purpose of the model comparison. The water-table elevations predicted by ID Boussinesq equation-based model and 2D Laplace equation-based model match each other well, which indicates that the horizontal flow in drainage layer is dominated. Also, it validates the 1D Boussinesq equation-based model which can be applied to predict the water-table elevation in drainage layer. Further, the analysis was conducted to examine the effect of infiltration rate, hydraulic conductivity and slope of drainage layer on the water-table elevation. The results show that water-table falls down as the ratio of Is to K decreases and the slope increases. If the aquifer becomes confined by the top of drainage layer due to the larger ratio of Is to K or smaller slope, the solution presented in this work can also be applied to approximate the water-table elevation in unconfined sub-section as well as hydraulic head in the confined sub-section.