Räumliche Charakterisierung der hydraulischen Leitfähigkeit in alluvialen Schotter-Grundwasserleitern: Ein Methodenvergleich

For groundwater transport modeling on a scale of 10–100 m, detailed information about the spatial distribution of hydraulic conductivity is of great importance. At a test site (10×20 m) in the alluvial gravel-and-sand aquifer of the perialpine Thur valley (Switzerland), four different methods were applied on different scales to assess this parameter. A comparison of the results showed that multilevel slug tests give reliable results at the required scale. For its analysis, a plausible value of the anisotropy ratio of hydraulic conductivity (K _v /K _h ) is needed, which was calculated using a pumping test. The integral results of pumping tests provide an upper boundary of the natural spectrum of hydraulic conductivity at the scale of the test site. Flowmeter logs are recommended if the relative distribution of hydraulic conductivity is of primary importance, while sieve analyses can be used if only a rough estimate of hydraulic conductivity is acceptable.     

Impact d’une galerie étanche peu profonde sur l’écoulement d’une nappe

While many studies have been achieved on the interactions between groundwater and deep tunnels, in order to identify the evolution of pore pressure around the structure and to characterize the flow to its leaky parts, few studies have dealt with the impact of the carrying out of an impervious gallery in a shallow aquifer. The induced change in the piezometric level of the aquifer and the one in the hydraulic gradient of the flow however can, in this case, have significant consequences, in particular when the linear structure is located in an urban environment. This paper investigates, in steady state, the case of a straight tunnel having a horizontal axis perpendicular to the direction of the regional groundwater flow and a circular or square cross section. The aim is to determine the additional lost head Δh _s due to the tunnel (i.e. additional to that resulting from the regional flow, supposed to be uniform with a hydraulic gradient i ₀). In the context of a horizontal confined aquifer having a thickness 2B and of a tunnel of radius R located in the middle part of the aquifer, an analogy can be established with the flow above a hydraulic threshold resulting from a local rise of the elevation of the base of an aquifer, having a thickness B, on a width 2R and with a vertical maximum amplitude R. When neglecting the vertical component of the hydraulic gradient compared to its horizontal component, analytical solutions are developed for various hydraulic threshold shapes (rectangular, triangular and circular), based on the equivalence with a local change in the transmissivity of an aquifer keeping a constant thickness. The corresponding formulas take the form: $ {\frac{{\Updelta h_{s} - \Updelta h_{0} }}{{\Updelta h_{0} }}} = f(a) $ , with $ a = {\frac{R}{B}} $ and Δh ₀ = 2Ri ₀. The use of these formulas shows that the additional lost head Δh _s due to the hydraulic threshold is proportional to i ₀ and that, for values of the ratio a < 0.5, the change in the piezometric surface is small. These conclusions are therefore limited by the fact that the vertical conductivity is supposed to be very large. In order to remove this hypothesis, numerical simulations are achieved using the MODFLOW code. It is considered a confined aquifer of length 2L = 110 m and thickness B = 10 m, a ratio $ a = {\frac{R}{B}} = 0.25 $ and a horizontal hydraulic conductivity $ K_{H} = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . In the case of an isotropic medium ( $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} = 1 $ ), the simulations allow to check the linearity of the relationship between Δh _s and i ₀, with therefore a homogeneous variation in the proportionality coefficient compared to analytical solutions. Simulations also reveal that, in the case considered, the width of influence upstream and downstream L _i , corresponding to a value of the vertical component of the hydraulic gradient <1% of i ₀, is below 5.5R for the three hydraulic threshold shapes, and that it was few influenced by the hydraulic gradient i ₀. In the case of an anisotropy of the horizontal and vertical hydraulic conductivities, simulations reveal the significant importance of the anisotropy ratio $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} $ when it is more than 1, the most common case, and indicate that the proposed analytical solutions give an asymptotic value of $ {\frac{{\Updelta h_{s} }}{{\Updelta h_{0} }}} $ for the isotropic case and for the values of the component α < 1. In the context of an unconfined aquifer, the hydraulic threshold model is not directly applicable. The model studied, using the Dupuit-Forchheimer assumption, is the one of a water table aquifer with a sloped base (slope value: p ₀). The simulations focus on an aquifer of length 2L = 85 m, with a tunnel of circular cross section having a diameter 2R = 5 m, bottom of which is located 5 m above the base of the aquifer, the isotropic hydraulic conductivity being equal to $ K = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . The definitions of water heights d ₀ and d between the water table and the top of the tunnel are given in Fig. 7. The water table can be located above (fully submerged tunnel) or below (partially emerged tunnel) the top of the tunnel. The difference d ₀ ? d represents the half of the additional lost head Δh _s due to the tunnel. Simulations are performed for various values of p ₀ and d ₀. They provide the values of i ₀, d and Δh _s . In the case of a fully submerged tunnel (d > 0), a significant rise of the water table upstream of the tunnel is obtained only for high values of the hydraulic gradient (5 and 10%), but, even in this case, it remains less than the tenth of the wetted height of the aquifer h _m . It is also highlighted that the ratio $ {\frac{{\Updelta h_{s} }}{{i_{0} }}} $ varies as a linear function of (R + d) and that, in the studied case, there is no influence of the tunnel for d ≥ 4R. In the case of a partially emerged tunnel (d < 0), the aquifer is locally confined under the tunnel. It is suggested that an equivalence is possible with the case of a confined aquifer having a thickness equal to the wetted height in the unconfined aquifer. This is verified with one of the simulations. In the case of a partially emerged tunnel, the change in the water table due to the tunnel remains low.     

复杂巨厚第四纪松散沉积层地区深基坑降水三维渗流场数值模拟——以上海地铁4~#线董家渡段隧道修复基坑降水为例

针对长江三角洲地区分布有复杂巨厚第四纪松散沉积层,且具有较高的承压水位,其深基坑降水的模拟、预测难度大。以上海地铁4#线董家渡段隧道修复基坑降水为例,建立基坑降水三维渗流模型,并采用有限差分数值模拟方法,模拟在多层含水层复合存在、含水层最深底板埋深达150 m、基坑周围挡水连续墙埋深达65 m、抽水井埋深达59 m、抽水井过滤器埋深为44～59 m及30口抽水井联合降水情况下,基坑中心下伏第2承压含水层中部降压段水位降至埋深43.35 m时的地下水复杂流动状态。经后续工程验证,该结果正确、可靠,该理论用于模拟预测此类地区深基坑降水引起的地下水流场变化具有较高的可信度。     

武汉高承压水区域深基坑降水的设计与施工

武汉长江两岸属Ⅰ级阶地,地质条件差,环境复杂,承压水位高,且承压水与长江水有联系。随着基坑开挖深度的增加,降水越来越重要,总结了高承压水软土地区深基坑减压降水的设计与施工技术,并讨论了由于降水引起地表沉降的规律及计算方法。     

复杂地层中基坑降水引发的水位及沉降分析与控制对策

在深大基坑工程中,若止水帷幕设置不合理,基坑内外水力联系将不能被完全截断,这样基坑内降水不但会引起坑外土体沉降,还会引发围护结构变形。在天津地铁5号线某车站基坑工程中,由于场地地层较为复杂,含水层不连续且存在大量透镜体,因此在开挖前进行了预降水试验,判断基坑内外水力联系。文章通过对预降水试验进行数据分析得出,该基坑内外承压含水层连通,且各含水层存在水力联系,原设计的落底式止水帷幕未能彻底截断承压含水层,造成了较大的围护结构变形与显著的建筑物沉降。因此,当场地承压含水层构造较为复杂时,应当在勘察阶段进行场地抽水试验,或者在基坑开挖前进行预降水试验,以全面掌握场地水文地质情况及基坑内外含水层水力联系。同时预降水前应在坑外合理设置回灌井,避免降水引发坑外沉降,并提前施工基坑第一道水平支撑,增加围护结构抗侧移刚度,减小降水引发的围护结构变形。     

Effect of ammonium on the hydraulic conductivity of geosynthetic clay liners

Hydraulic conductivity and swell index tests were conducted on a conventional geosynthetic clay liner (GCL) containing sodium-bentonite (Na-B) using 5, 50, 100, 500, and 1000 mM ammonium acetate (NH₄OAc) solutions to investigate how NH₄⁺ accumulation in leachates in bioreactor and recirculation landfills may affect GCLs. Control tests were conducted with deionized (DI) water. Swell index of the Na-B was 27.7 mL/2 g in 5 mM NH₄⁺ solution and decreased to 5.0 mL/2 g in 1000 mM NH₄⁺ solution, whereas the swell index of Na-B in DI water was 28.0 mL/2 g. Hydraulic conductivity of the Na-B GCL to 5, 50, and 100 mM NH₄⁺ was low, ranging from 1.6–5.9 × 10^?11 m/s, which is comparable to the hydraulic conductivity to DI water (2.1 × 10^?11 m/s). Hydraulic conductivities of the Na-B GCL permeated with 500 and 1000 mM NH₄⁺ solutions were much higher (e.g., 1.6–5.2 × 10^?6 m/s) due to suppression of osmotic swelling. NH₄⁺ replaced native Na⁺, K⁺, Ca²⁺, and Mg²⁺ in the exchange complex of the Na-B during permeation with all NH₄⁺ solutions, with the NH₄⁺ fraction in the exchange complex increasing from 0.24 to 0.83 as the NH₄⁺ concentration increased from 5 to 1000 mM. A Na-B GCL specimen permeated with 1000 mM NH₄⁺ solution to chemical equilibrium was subsequently permeated with DI water. Permeation with the NH₄⁺ converted the Na-B to “NH₄-bentonite” with more than 80% of the exchange complex occupied by NH₄⁺. Hydraulic conductivity of this GCL specimen decreased from 5.9 × 10^?6 m/s to 2.9 × 10^?11 m/s during permeation with DI water, indicating that “NH₄-bentonite” can swell and have low hydraulic conductivity, and that the impact of more concentrated NH₄⁺ solutions on swelling and hydraulic conductivity is reversible.     

上海某枢纽基坑工程浅层承压水回灌试验分析

随着上海城市建设进程的不断推进,深大基坑大量涌现,同时因城市立体空间设施的密集化,使得基坑周边环境趋于复杂,在此背景下因浅层承压水降水而引起的工程性地面沉降事故不断发生,给社会带来了巨大的经济损失。地下水人工回灌是控制因降水引起的工程性地面沉降的方法之一,目前地下水人工回灌系统主要应用于深层承压水的回灌。本文通过上海某地第一承压含水层的回灌试验,研究分析了浅层承压含水层回灌井的结构、回灌过程中地下水的流态变化规律、水土应力变化及对控制地面沉降作用的效率,证明了浅层承压水回灌在基坑环境保护中的可行性。试验研究对基坑建设中的地下水浅层承压水回灌系统的设计和施工有重要的指导意义。     

悬挂式止水帷幕基坑降水控制措施研究

为了优化深基坑降水控制技术,以天津某地铁换乘站基坑降水为背景,利用有限差分软件Visual Modflow,对基坑开挖降水引起的基坑内外地下水水位变化进行数值模拟计算,模拟计算结果与监测数据基本吻合。同时,在此模拟计算基础上对止水帷幕插入深度、降水井的抽水速率、滤水管插入承压含水层深度及降水时间等几种控制措施在降水控制中所发挥的作用进行深入研究。结果表明,降水过程中止水帷幕深度插入比宜达到1:0.9～1:1之间,滤水管插入承压含水层深度宜控制在0.5～0.7倍含水层厚度区间范围内,降水井抽水速率的大小需根据以上两种措施确定后再进行优化。此研究结果不但能有效减少基坑降水对周围环境的影响,还能保护地下水资源,节约工程造价。     

上海地铁11号线徐家汇站深基坑降水数值模拟

承压水是基坑工程施工主要风险源之一,基坑降水是地铁站建设经常采取的措施。承压水降水设计应综合考虑水位降深要求、承压含水层厚度、降水井深度、止水帷幕深度等因素,通常采用数值模拟方式进行计算分析。本文以上海地铁11号线徐家汇站深基坑降水工程为例,根据场地工程地质和水文地质条件、地铁站围护结构设计深度和基坑开挖深度,建立地下水渗流三维数学模型,通过单孔和群孔抽水试验资料反求水文地质参数,结合场地初始条件和边界条件,采用Visual Modflow有限差分法对基坑降水进行模拟,数值模拟结果与地下水位实际监测数据十分吻合,为地铁工程深基坑降水设计提供了指导作用。     

广州地铁燕塘站基坑降水的三维渗流场有限元分析

基坑降水是地铁深基坑工程施工设计所关注的重点问题,尤其要关注基坑降水后的三维渗流场分布、降水效果和渗透稳定等。本文采用了潜水承压水稳定渗流场理论和改进的截止负压法对广州地铁燕塘站深基坑降水后的三维渗流场进行了有限元分析。研究了布置不同抽水井和帷幕灌浆等多个工况的渗流场分析和基坑涌水量。研究结果表明,采用抽水井和对承压含水层进行灌浆帷幕的设计方案,深基坑降水后的渗流场和地基的渗透比降满足设计要求。     

基坑开挖及降水引起的地表沉降预测

以随机介质理论、渗流理论和土体压密理论为基础,探讨了一种新的基坑开挖及降水引起的地表沉降的计算方法。推导了基坑降水渗降漏斗曲线方程及考虑水的渗流作用的基坑周边土体中有效应力的计算公式,并由此导出了考虑渗流作用的基坑降水地表沉降计算公式,再利用叠加原理,得到最终的由开挖和降水引起的地表沉降分布计算公式。工程实例分析计算结果表明,距基坑周边8～10m范围以内,基坑开挖和降水引起的地表沉降基本相当,而距坑周20m以外的地表下沉主要由降水引起,因此基坑降水引起的地表下沉不容忽视。本文推导的计算方法能充分反映基坑降水对周边地表下沉的影响,是一种计算基坑开挖及降水引起的地表沉降的有效方法。     

Performance of the bearing reinforcement earth wall as a retaining structure in the Mae Moh mine,Thailand

In this research, a Bearing Reinforcement Earth (BRE) wall with a residual clay stone backfill was successfully implemented as an alternative truck ramp support for an on-site crusher plant in the Mae Moh mine, Thailand. The performance of the BRE wall during and after the end of construction as well as during the service state was evaluated in terms of, settlement, bearing stress, lateral movement, lateral earth pressure and tension force in the reinforcements. Bearing reinforcement is a cost-effective inextensible earth reinforcement, which is composed of a longitudinal member and transverse members. The maximum settlement at the end of construction (20 days) was about 5 mm. The installation of the truck ramp (10 days after the end of construction) resulted in an immediate settlement of about 2 mm. The final settlement due to the backfill, truck ramp and truck load after 270 days was found to be uniform due to the contribution of bearing reinforcement and was approximately 25 mm. The bearing stress which was uniformly distributed was found to increase rapidly with construction time, which was in agreement with the relatively uniform settlements. The lateral wall movement at the front and lateral sides at the end of construction was very small with the maximum movement (at the top of the wall) found to be less than 10 mm. As such, the ratio of lateral movement to height (δ/H) was found to be approximately 0.12%, which was lower than the allowable value of 0.4%. With this low δ/H and the insignificant change in the measured settlement and lateral movement during service, the BRE wall was considered to have a very high stability. The coefficients of lateral earth pressure, K and depth relationship were proposed based on the analysis of measured maximum tensile force in the reinforcements. The maximum tension plane of the BRE wall could be represented by the coherent gravity hypothesis. Using the proposed K and maximum tension plane, the internal stability of the BRE wall was furthermore examined. A proposed method of designing the BRE wall with claystone backfill was also proposed.     

考虑承压含水层间越流的地下水回灌现场试验研究

当场地存在多层层间有一定水力联系的承压含水层时,基坑内降水可引发基坑止水帷幕墙底以下的承压含水层的水头下降,并相应引起坑外多个含水层水位降低,若对所有层进行回灌则将导致成本大幅提高,此时可对某一层回灌,通过越流对其他含水层进行水位补给。通过在天津地铁某车站基坑所在场地开展抽水试验、单井回灌试验、先抽后灌试验对基坑内外的水力联系、不同含水层间的水力联系和隔层回灌的效果进行了研究。结果表明,由于各含水层间之间有一定水力联系导致竖向越流补给较强,基坑内疏干降水可引起坑外承压含水层水头下降并引起坑外地层沉降。对基坑外第Ⅰ微承压含水层进行回灌可有效对其上部潜水层和下部第Ⅱ-1承压层的水头起到抬升作用,通过隔层回灌从而控制其水位下降导致的坑外沉降。对第Ⅰ承压含水层进行回灌对基坑外第Ⅱ-2承压层水位抬升也有一定的作用,但是尚不足以使其因基坑内降水引起的坑外水位下降值完全恢复,建议结合设置此层的备用回灌井以控制其水位下降。     

Hydraulische Modellierung und die Ermittlung des repräsentativen Elementarvolumens (REV) im Kluftgestein

The objective of the following study is the development of a method for the evaluation of the hydraulic conductivity and the representative elementary volume (REV) in fractured rock aquifers, which can be used for the hydraulic modelling of large-scale fractured systems. Two-dimensional stochastic discrete fracture networks were simulated for the evaluation of hydraulic conductivity. Due to the strongly variable fracture density in the considered area, a sensitivity study was performed which examined three various fracture densities according to their hydraulic properties. The flow behaviour in the discrete fracture networks is described with the cubic law. The hydraulic modelling in the fractured rock showed that an REV could not be determined for all discrete fracture networks. With one exception, an REV with a size of 10 m × 10 m could be determined for discrete fracture networks with a medium (P₂₁ = 13.1 m^–1) and high fracture density (P₂₁ = 16.9 m^–1). In contrast, no REV could be found for discrete fracture networks with a low fracture density (P₂₁ = 5.1 m^–1).     

Classification and assessment of rock mass parameters in Choghart iron mine using P-wave velocity

Engineering rock mass classification,based on empirical relations between rock mass parameters and engineering applications,is commonly used in rock engineering and forms the basis for designing rock structures.The basic data required may be obtained from visual observation and laboratory or field tests.However,owing to the discontinuous and variable nature of rock masses,it is difficult for rock engineers to directly obtain the specific design parameters needed.As an alternative,the use of geophysical methods in geomechanics such as seismography may largely address this problem.In this study,25 seismic profiles with the total length of 543 m have been scanned to determine the geomechanical properties of the rock mass in blocks Ⅰ,Ⅲ and Ⅳ-2 of the Choghart iron mine.Moreover,rock joint measurements and sampling for laboratory tests were conducted.The results show that the rock mass rating(RMR) and Q values have a close relation with P-wave velocity parameters,including P-wave velocity in field(V_(PF)).P-wave velocity in the laboratory(V_(PL)) and the ratio of V_(PF) V_(PL)(i.e.K_p = V_(PF)/V_(PL).However,Q value,totally,has greater correlation coefficient and less error than the RMR,In addition,rock mass parameters including rock quality designation(RQD),uniaxial compressive strength(UCS),joint roughness coefficient(JRC) and Schmidt number(RN) show close relationship with P-wave velocity.An equation based on these parameters was obtained to estimate the P-wave velocity in the rock mass with a correlation coefficient of 91%.The velocities in two orthogonal directions and the results of joint study show that the wave velocity anisotropy in rock mass may be used as an efficient tool to assess the strong and weak directions in rock mass.     

第四纪松散沉积层地下水疏降与地面沉降三维全耦合数值模拟

针对第四纪松散沉积层地下水疏降引起的地面沉降问题,以比奥固结理论为基础,考虑土体的非线性特征及土的渗透性随应力状态的动态变化,将地下水渗流场和土体应力场耦合起来,建立了地下水疏降与地面沉降变形的水土全耦合三维数学模型,并采用三维有限元数值分析方法,以上海市地铁四号线董家渡段隧道修复深基坑降水为例,模拟预测了基坑中心水位降至标高-23.4 m时基坑周围地下水渗流场与地面沉降变形场的分布特征。该模型稳定性好,收敛速度快,能模拟复杂三维地质体和整个基坑降水工程的结构,具有重要的工程实用价值。     

松散承压含水层地区深基坑降水三维渗流与地面沉降耦合模型

以上海环球金融中心基坑降水为例,根据基坑降水过程中有效应力和孔隙水压力的转化关系,建立了基坑降水与地面沉降的耦合模型,并采用有限差分数值模拟方法,模拟了在多层含水层复合存在、含水层最深底板埋深达145 m、基坑周围挡水连续墙埋深达34 m、抽水井埋深达55 m、抽水井过滤器埋深为34～55 m,单井抽水量为1420 m3/d的8口抽水井联合降水情况下,基坑中心下伏第Ⅰ承压含水层上部降压段水位降至埋深26 m时的地下水复杂流动状态及其地面沉降特征。经后续工程验证,该结果正确、可靠,该理论用于模拟预测此类地区深基坑降水引起的地下水流场变化及其地面沉降具有较高的可信度。     

上海第⑨层承压水的短滤管减压井试验研究

上海第二、第三承压水降水及其导致的环境沉降是目前深层地下空间开发中的技术难点,采用短滤管减压井可以增加滤管底与截水帷幕底之间的高差,有助于控制坑外降深和沉降.在上海张江硬X射线工程现场,采用气举反循环工艺成井,进行了不同滤管长度减压试验井的现场抽水试验,对不同滤管长度下减压试验井产生的第二、第三承压含水层的降深进行比较...     

抗突涌稳定验算公式分析

基坑底承受高水头承压含水层水压力作用时需要进行抗突涌稳定验算,抗突涌稳定验算对基坑降水设计具有重要影响,决定了水头降低的程度,从而决定了降水井的布置和最终地面沉降值。规范中的抗突涌稳定验算公式基于压力平衡理论,Terzagh i针对砂土基坑的抗突涌稳定验算公式经推导具有与规范公式相同的形式。规范公式具有使坑底土体有效应力大于零、被动区小主应力大于零和水力坡降大于临界水力坡降的含义。     

Stiffness parameters of municipal solid waste

This paper presents results of the deformability parameters of municipal solid waste (MSW) determined through laboratory (oedometer and triaxial tests) and in situ tests [standard penetration tests (SPT) and cone penetration tests (CPT)], as well as by a monitoring system including topographic control marks, open-tube piezometers, earth and pore pressure cells and inclinometer tubes with magnetic settlement plates and spiders. The studied landfill is located in a textile industry area, and was landfilled with some direct waste (10 %) and mostly pre-treated waste (90 %, from composting and triage). The influence of: the waste age, construction phase of the landfill and confining stress on the results of stiffness modulus, lateral waste pressure coefficient at-rest (K ₀) and Poisson’s ratio (ν) are presented, as well as an attempt to establish correlations to estimate MSW stiffness modulus from SPT and CPT tests. The results indicate the increases of K ₀ and ν with the average effective confining stresses during the first 2 years of the post-construction phase, reaching maximum values of 0.7 for K ₀ and 0.4 for ν, and then decreasing gradually until stabilizing at values of around 0.23–0.48 for K ₀ and around 0.19–0.32 for ν. The stiffness modulus values determined by different methods are consistent with each other and corroborate the fact that typical values for MSW are low. These values are between 0.4 and 2 MPa for a mean confinement stress of about 50 kPa, and tend to increase linearly with the increase of the confinement stress. The correlations established with SPT and CPT tests are of the same type as usually proposed for granular soils; however, the constant values are significantly lower than the lowest values reported for normally consolidated sandy soils.