Calculation of groundwater head distribution with a close barrier during excavation dewatering in confined aquifer

When pumping is conducted in confined aquifer inside excavation pit(waterproof curtain),the direction of the groundwater seepage outside the excavation changes from horizontal to vertical owing to the existence of the curtain barrier.There is no analytical calculation method for the groundwater head distribution induced by dewatering inside excavation.This paper first analyses the mechanism of the blocking effects from a close barrier in confined aquifer.Then,a simple equation based on analytical solution is proposed to calculate groundwater heads inside and outside of the excavation pit with waterproof curtain(hereafter refer to close barrier)in a confined aquifer.The distribution of groundwater head is derived according to two conditions:(i)pumping with a constant water head,and(ii)pumping with a constant flow rate.The proposed calculation equation is verified by both numerical simulation and experimental results.The comparisons demonstrate that the proposed model can be applied in engineering practice of excavation.

Boundary Element Analysis (Laplace Transform Solution) of Groundwater Unsteady Flow to a Multiple Well System in a Confined Aquifer

The calculations of unsteady flow to a multiple well system with the application of boundary elementmethod (BEM) are discussed. The mathematical model of unsteady well flow is a boundary value problem ofparabolic differential equation. It is changed into an elliptic one by Laplace transform to eliminate time varia-ble. The image function of water head H can be solved by BEM. We derived the boundary integral equation ofthe transformed variable H and the discretization form of it, so that there is no need to discretize the bounda-ries of well walls and it becomes easier to solve the groundwater head H by numerical inversion.

Analytical solution for slope instability assessment considering impact of confined aquifer

An analytical approach was presented for estimating the factor of safety(FS) for slope failure, with consideration of the impact of a confined aquifer. An upward-moving wetting front from the confined water was assumed and the pore water pressure distribution was then estimated and used to obtain the analytical expression of FS. Then, the validation of the theoretical analysis was applied based on an actual case in Hong Kong. It is shown that the presence of a confined aquifer leads to a lower FS value, and the impact rate of hydrostatic pressure on FS increases as the confined water pressure increases, approaching to a maximum value determined by the ratio of water density to saturated soil density. It is also presented that the contribution of hydrostatic pressure and hydrodynamic pressure to the slope stability vary with the confined aquifer pressure.

A Heuristic Approach to Estimating Spatial Variability of Vertical Leakage in the Recharge Zone of the Gambier Basin Tertiary Confined Sand Aquifer, South Australia

The vertical leakage to confined aquifers is rarely quantified in complex settings, where the recharge zone is characterized by both diffuse and preferential flows. In such setting, conventional hydraulic or tracer based estimation of recharge or vertical leakage is problematic, unless the effects of duality of flow regimes are considered. A water balance approach by the use of calibrated groundwater models can be used, as the mass balance is independent of the particular mode of recharge and vertical leakage processes. Here, we adopt a water balance approach to provide a first order assessment of recharge to the unconfined Tertiary limestone aquifer (TLA) and vertical leakage to the Tertiary confined sand aquifer (TCSA) within the Glencoe-Nangwarry-Nagwarry (GNN) recharge zone of the Gambier Basin in South Australia. Despite many studies expressing concern about the impact of land use on recharge to the TLA and vertical leakage to the TCSA, no estimates have been made to quantify the vertical leakage within the GNN recharge zone. In the GNN recharge zone, relatively high recharge to the unconfined aquifer and vertical leakage to the confined aquifer occurs as a result of both diffuse and preferential flow processes. This is due to presence of structural faults and thin or absent aquitard. Within the Hundred of Nangwarry, where 83% of the area is covered with plantation forest, the model calculated recharge to the TLA of 80 mm·year-1, about 44% reduction compared to adjacent non-forested area (144 mm·year-1). Vertical leakage to the TCSA within the Hundred of Nangwarry area is higher (84.5 mm·year-1) than recharge to the TLA. Higher vertical leakage combined with the reduced recharge to TLA resulted in depletion of the TLA storage, as evidenced by drying of the TLA at one locality. In contrast, in plantation forest areas where diffuse recharge is the dominant process (Hundred of Penola), recharge to the TLA is about 19 mm·year-1, a 78% reduction compared to the non-forested areas, a mix of irrigation and dryland pasture. In these areas, vertical leakage to the TCSA is much smaller: 8 mm·year-1 through a thick aquitard. Simulation of a management scenario in which plantation forest is replaced by dryland pasture in the Hundred of Nangwarry results in 135 mm·year-1 recharge to TLA and a 98 mm·year-1 vertical leakage to the TCSA.

Relationship between the Earth tidal factor and phase lag of groundwater levels in confined aquifers and the Wenchuan M_s8.0 earthquake of 2008

This work focuses on variations of the Earth tidal factor and phase lag derived from groundwater observations before and after major earthquakes.It is based on an analysis of the data from four observational wells at boundaries between distinct active blocks of China mainland.These wells are also situated on several active fault zones and have exhibited considerable responses to the Wenchuan Ms8.0 earthquake of 2008 in China.We collected hourly records of water levels of these wells from 2007to 2009 and processed these data for analysis.The tidal factors,phase lags,and phase-difference changes of tidal residuals of each well were calculated.We found that when the Wenchuan quake happened,the tidal factors of the 4 wells were changing rapidly,while their phase lags and phase differences of tidal residuals declined swiftly,which may reflect the stress and strain changes of the well-aquifer system during the seismic generation.

涟水高沟地区承压地下水可更新性研究

为合理开发利用和保护地下水资源,评价区域地下水可更新性成为当前首要解决的问题。本文从定性和定量两个角度进行分析研究,首先从区域水文地质条件与地下水水动力等方面,进行地下水系统划分及特征研究,分析含水层空间结构及补径排条件;其次在收集利用以往测试资料基础上,通过现场采样分析,开展不同水体环境同位素特征研究;最后利用水均衡法计算地下水可更新能力指标。研究结果表明:涟水高沟地区承压水具备地下水补给通道,主要接受上游山区侧向径流补给,且在开发利用过程中不会引发地面沉降等环境地质问题;地下水水龄2万年左右,水循环更新周期上千年,可认为其具有一定的更新能力,不属于难以更新的地下水;同时,地下水的合理开发利用有助于加快地下水循环速率,进一步提高地下水更新能力。

软土深基坑变形及环境影响分析方法与控制技术

随着基坑规模日益增大以及邻近环境设施愈加复杂,合理评估并控制基坑变形及对周边环境影响成为软土基坑工程面临的重要挑战。基于理论分析与工程应用,对软土深基坑变形与环境影响分析方法及控制技术进行了系统研究。首先,在统筹考虑安全与经济的前提下,提出了软土深基坑环境保护等级和变形控制指标,为基坑周边不同类型环境设施的保护提供了依据。其次,系统建立了便于工程应用的基坑变形影响简化分析方法,并提出了基于土体小应变特性的基坑开挖对环境影响的计算分析方法以及确定全套小应变本构模型参数的实用方法,为复杂环境下深基坑环境影响分析提供了重要手段。同时,针对承压水降水影响难以准确量化评估的难题,提出了根据群井抽水试验反演确定关键水文地质参数并评估深层承压水降水对地层和环境变形影响的计算方法,满足了复杂地层承压水降水影响分析的工程需求。此外,还提出了包括支护结构与主体地下结构相结合、数字化微扰动搅拌桩加固、混凝土支撑主动变形控制、承压水控制超深隔渗帷幕等绿色、低碳、环境低影响的基坑变形控制新技术。成果在全国大量工程中成功应用,促进了软土深基坑工程全过程变形影响精细化分析和系统化控制技术的发展,为大规模地下空间的开发利用提供了技术支撑。

基于群井抽水试验的承压含水层水文参数反演分析

城市区域复杂环境条件下的深基坑工程往往涉及复杂的承压水处理问题,当承压含水层深度较大且采用悬挂帷幕结合坑内减压降水方案时,需合理评估承压水降水对周边环境的影响,而其关键是要确定合理的水文地质参数。本文结合位于长江漫滩地貌单元的某深基坑工程,在基坑实施前针对其深厚承压含水层开展了现场群井抽水试验,根据单井抽水试验的解析方法给出了初步的水文地质参数,在此基础上,建立了群井抽水试验的地下水渗流数值分析模型,基于反演分析确定了合理的水文地质参数,为分析基坑承压水降水对周边环境影响提供了直接依据。

非达西效应下不稳定承压-无压井流的有限差分解

在深部煤矿开采工程中,为了避免出现涌水现象,通常利用矿井排水使承压含水层水位低于采矿工作面,以确保煤炭开采的安全。因此,为了揭示承压含水层定流量抽水引起的不稳定承压-无压转换机理,提出了基于有限差分的非达西效应影响下不稳定承压-无压流的数值模型。该模型以Izbash方程为基础,提出了一种新的线性化方法来处理非达西问题,并进一步研究了非达西效应下非达西指数、准渗透系数和储水系数比对水位降深与无压区发展的影响。结果表明:在抽水期间,非达西指数和准渗透系数越大,则承压区的水位降深越大,无压区的水位降深越小,发生承压-无压转换的时间越晚;承压区的水位降深与储水系数比之间呈负相关关系,储水系数比越大意味着承压区存在较大的弹性储水量,对抽水井的补给水量也越大,导致水位降深越小。

煤层底板下隐伏陷落柱的滞后突水机理

应用有限元数值计算方法,模拟研究了含隐伏陷落柱煤层底板在采动应力扰动和高承压水共同作用下陷落柱活化、裂隙萌生、裂隙扩张、突水通道贯通形成的全过程,通过对损伤场、变形场、应力场和渗流场的解读,对突水通道进行时空基准标定,并就陷落柱发育高度、承压水水压力大小对突水滞后时间的影响进行了分析探讨,从岩体在长期的环境影响、载荷作用下损伤演化、物理力学性能退化的角度,揭示了煤层底板下隐伏陷落柱的滞后突水机理.

海河流域平原深层地下水补给特征及其可利用性

针对海河流域平原区的第四系深层地下水可利用性问题,分析了深层地下水资源有限性的特点,其补给资源只是浅层地下水的0.07倍,弹性储量资源也只是浅层地下水储量资源的0.10倍,表现出类似石油和天然气的非再生特征。从其补给模式和^(14)C年龄分布特点论证了深层地下水资源有限和非再生的自然属性,同时通过论述该区深层地下水开发利用现状和国外发达国家的情况,阐明了深层地下水资源的社会人文属性和时代特征,提出了深层地下水作为一种具有非再生性特征的资源,其在人类社会文明与经济发展历史进程中,从“生存的原始性利用”至“协调发展的文明利用”,必然要经历“初始高速发展的资源掠夺性利用”和“理性发展的反思性利用”两个阶段;上述两个阶段是深层地下水发挥其“资源”历史作用的重要时期的观点。提出了有序、适度、阶段性利用海河流域深层地下水资源的战略和可利用指标与合理利用方案,强调过度开采和全面禁用深层地下水都是不正确的观点。

含隐伏断层煤层底板损伤演化及滞后突水机理分析

基于对采动岩体流固耦合作用的力学响应以及底板岩体强度退化机制的认识,针对承压水体上采煤的岩体水力学模型,对底板隔水岩体的长期强度特征进行了分析,并用数值方法再现了含隐伏小断层底板在采动应力扰动和高承压水共同作用下采动裂隙形成、小断层活化、扩张、突水通道最终贯通形成的全过程。通过对损伤演化、应力场和渗流场的解读,揭示了开采扰动及水压驱动下完整底板由隔水岩层到突水通道的演化机理,对突水通道进行时空基准标定,并着重就小断层发育高度、承压水水压力大小对隔水底板的损伤演化模式及突水滞后时间的影响关系进行了分析探讨,从岩体强度退化及损伤演化机制的角度,为承压水体上采煤底板滞后突水的机理分析提供了一些新的认识。

地下水对地基基础工程的危害及事故预防

很多地基基础工程事故都和地下水有关。地下水受季节性降水的影响、地下水的流动性及水位的变化、施工引起的地下水排水路径改变及地下水的承压性等是造成很多地基基础工程事故的原因,应引起工程人员的高度重视。结合多起由地下水原因导致的工程事故实例,阐明地下水对地基基础工程的危害,并给出相应的事故预防措施。

含断层煤层底板突水通道形成过程的仿真分析

基于对断层形态、产状要素、力学性质复杂性及断层诱发突水机制的认识,针对承压水上采煤的含断层岩体水力学模型,通过有限元数值仿真再现了含断层煤层开采底板采动裂隙形成、断层活化到突水通道形成的全过程。通过对损伤演化、应力场和渗流场的解读,揭示开采扰动及水压驱动下完整底板由隔水岩层到突水通道的演化机制。数值分析结果显示:断层本身的物理力学性质及断层的产状要素,包括断距和倾角等,对煤层底板的相对安全性都具有重要的影响。最后结合现场地质、水文地质调查及数值仿真结果对一工程实例进行突水机制分析,为承压水上采煤底板突水的机制分析及防治提供一些新的认识。

我国主要平原盆地地下水资源可持续利用的几点思考

本文根据近年来的最新调查资料,针对长期以来地下水开发实践中存在的主要问题,提出加快调整深层承压水开采布局、充分开采利用浅层水和改变西北内陆盆地水资源利用方式的建议。

巴丹吉林沙漠湖泊及其下游地下水同位素分析

本文通过环境同位素水化学等分析方法研究了祁连山北侧、龙首山、巴丹吉林沙漠、古日乃、拐子湖和额济纳盆地的泉水和井水的来源 ,揭示了巴丹吉林沙漠等下游地区的地下水来自于祁连山降水的补给 ,平均补给高程为 330 0m ,祁连山顶部存在大片裸露的灰岩地层 ,雪水融化后沿着喀斯特地层或山前大断裂补给到深部 ,穿过龙首山直接补给到巴丹吉林沙漠及其下游地区 ,在沙漠湖泊中发现的钙华与钙质胶结证明地下水经过了石灰岩地层 ,承压水通过越流补给到浅部含水层 ,通过蒸发量计算得到的地下水补给量接近 6× 10 8m3 /a,承压水中地下水的年龄为 2 0～ 30a。

油气田区承压含水层地下水污染机理及其脆弱性评价

根据研究区地质构造及水文地质概况,分析了研究区承压含水层地下水有机污染的机理,建立了针对该地区承压含水层地下水污染脆弱性评价指标体系,并应用神经网络技术作为评价体系中参数的赋权方法;由ANN与GIS耦合技术得到的研究区承压含水层地下水污染脆弱性区划图比较好地符合研究区的实际情况。

海河流域中东部平原区深层地下水补给与释水机制探讨——兼谈深层地下水资源可利用性

通过对近30年以来海河流域中东部平原区深层地下水实际开发利用状况的分析,阐明了深层地下水资源实际利用的特殊性;从深层地下水的自然属性出发,通过对深层地下水补给与释水机制及其开采过程中激发释水效应的剖析,揭示了深层地下水自然释水和开采条件下释水的规律,提出了便于实际应用的广义“深层地下水释水”理念。在此基础上,论证了深层地下水储量资源的可利用性。

松散承压含水层水文地质参数分区及水流场数值模拟

为了揭示华北型煤田松散承压含水层水文地质参数及其对地下水流数值模拟的意义，以安徽淮北煤田宿南矿区祁东煤矿松散层承压第四含水层（简称“四含”）为研究示范，对多个影响因素综合分析，采用层次分析一模糊综合评价法，对研究区四含水文地质参数进行分区，合理确定各分区的水文地质参数，并用于采煤情景下地下水流动态数值模拟。数值模拟结果表明：祁东煤矿2008-2012年浅部煤层开采过程中四含地下水流场没有明显改变，但南北分区水头差逐年增大，地下水流向始终从南向北，而且在井田北部水力梯度逐渐减小，在井田南部水力梯度逐渐增大，南北区以倾角为60°-70°、断距为10～320m的魏庙断层为分界线，基岩中大倾角与大落差断层的出现是引起上覆松散承压含水层水力梯度异常的根本原因。

人类活动对内蒙古托克托县浅层地下水NO_3~–-N污染的驱动作用

地下水NO_3~–-N污染已成为当今世界上一个日趋严重的环境问题和社会问题。本文在水文地质调查基础上,应用地质统计学方法对所采集样品测试数据进行了分析,结果表明呼和浩特市托克托县浅层地下水NO_3~–-N分布极不均匀,NO_3~–-N含量大于20 mg/L的地下水分布面积占全区总面积的72.1%,广泛分布于古城镇以南的区域。少数井点地下水NO_3~–-N含量已大于100 mg/L,最高达304.6 mg/L,已发展成为硝酸型地下水。通过采用水质解析法和化学平衡法分析地下水NO_3~–-N污染来源,揭示了人类污水灌溉、粪便堆放、化肥施用等活动对托克托县地下水NO_3~–-N污染有重要的驱动作用。