上海地区“暗绿色硬土层”的一种特例

我国东部广阔的滨海平原中存在着浅埋的硬塑状态的粘性土层即浅部硬土层,是淤泥质软土地区的良好的地区性持力层。本人曾对其区域特征作过讨论(见1980年第二期“上海地质”),在上海地区其基本特征有三: 1.上部以暗绿色为主,故有“暗绿色硬土层”之称。下部变黄。总厚约十米。上细下粗,由亚粘土渐变为亚砂土或粉砂; 2.多呈硬塑状态,土的固结程度和强度指标较好。如上海港集装箱码头:     

浅层地震横波技术在工程勘察中的应用

本文提供了地震横波反射法及横波速度在工程勘察中的应用实例。采用横波反射技术开展地下各类工程地质的探测与研究,具有波速低、波长小、不受潜水位的影响、波形可极化以及抗干扰能力强等特点。这种尝试对拓宽地震勘探服务领域十分有益。     

地震勘探方法在薄覆盖层区城市活断裂探测中的应用

地震勘探方法是当前探测城市活断层的主要物探方法。在新沂市活断层探测中,由于局部地区覆盖层较薄,单单依靠纵波反射法勘探,只能识别出来自于基岩顶面的反射波。一般情况下,根据地震反射剖面上单个同相轴的变化很难判定断层的准确位置及上断点的埋深。横波反射法分辨率高、分层能力强,能够弥补纵波反射勘探的缺点,因此可以提高勘探的精度;另外,该勘探区内个别断裂两侧存在两种不同年代的地层年代差异较大,两者在速度上有着明显的差异,利用地震层析成像法获得的地震速度剖面,能够反映地下速度结构的变化,可以从另一方面揭示浅埋断层的存在。通过对这几种物探方法取得的成果相互比较和综合分析,并结合地质资料得到了理想的物探成果,取得了良好的勘探效果。     

上海湖沼平原浅层硬土对单桩承载力的影响

从现有计算单桩承载力的方法出发,结合工程实践分析上海湖沼平原地区浅层硬土对预制短桩承载力的影响.上海泻湖沼泽平原地区的地基土层次分布与上海市区滨海平原有较大差别,存在较厚的浅部硬塑态粉质粘土和中密性砂质粉土层(称为浅层硬土),该层土具有压缩性低、承载力高的特点.通过现场静载荷试验比较了按现行规范计算单桩承载力和实测结果的差异,分析了浅层硬土中预制短桩的极限侧摩阻力,讨论了侧摩阻力和静力触探比贯入阻力的关系,所得研究结果可为今后相关场地的类似工程建设提供参考.     

面波联合勘探在深厚覆盖层地区应用实例分析

西南地区河床覆盖层深厚,如何经济快速地获取地基工程场地的横波速度是水利水电工程勘察的重要问题之一。面波勘探技术以其低成本、快捷及受场地条件限制小等优点被广泛应用于浅部横波速度结构探测中。文中采用主动源面波和被动源面波相结合的联合勘探技术对西南某水电站坝址区场地横波速度结构进行了探测,主动源面波法能针对浅部区域进行精确探测,而被动源面波法探测深度更大,两种方法各有优势,相互印证,相互弥补。     

岩溶地区复杂条件下的浅层地震方法应用研究

地震记录质量的好坏极大地影响地震方法解释的可靠程度.在岩溶地区复杂地质条件下,为了获取高质量的记录,合理地选择地震方法,合适地布置测线,尽一切努力来压制干扰,是取得探测成功的关键.探测实例表明,在覆盖层厚度不超过20m的条件下,浅层地震反射法、折射法联合探测可获得良好的地质效果.作为一种有效的探查技术,等偏移横波(SH)反射法具有探测迅速,易于探测土洞、地下岩溶裂隙带的特点.     

上海高重建筑物桩基工程地质条件——桩尖持力层的选择和评价

Ⅰ.桩尖持力层分类:上海高重建筑物桩尖持力层大致可归纳为以下三种:1.过去传统习惯,以暗绿色硬土层作为桩尖持力层;2.浅层局部分布的砂性土层(潜水砂层或第一软土层中砂性土夹层);3.由于暗绿色硬土层缺失或建筑物荷重太大,桩打入与暗绿色硬土层相应深度或更深的砂性土层中,甚至有的已打到第一承压水砂层。     

应用于评价活动断层的地震方法技术

以在上海市区开展地震调查深埋活断层的实例,讨论了在都市区强干扰条件下开展断层活动性调查的地震方法技术。认为：在对基岩断层的活动性评价中,反射纵波法根据基岩断层是否向上延伸到第四纪Ｑ３地层内,而剪切波分裂法则根据由Ｑ３地层内界面反射横波确定的各向异性。当基岩断层向第四系延伸幅度较大,即第四纪地层内断层落差较大时,可采用反射纵波法;当基岩断层活动引起的第四纪地层内的断层落差较小,反射纵波法不能对其分辨时,可采用剪切波分裂法     

浅层SH反射波法和多道瞬态面波法 进行联合工程勘察的讨论

针对目前单一工程物探方法调查浅部地质结构的局限性,提出采用弹性波法勘察中研究浅部地质结构的SH波反射勘察和多道瞬态面波法勘察这2种有效手段进行联合勘探,提高其可靠性和精度,并给出了3个实例,指出了在数据采集和处理时应注意的问题。     

AVO技术在识别充填流体溶洞中的应用

寻找到充填流体的大型洞穴是碳酸盐岩油藏预测十分有意义的工作。塔河油田的试验表明,应用AVO技术可以有效地鉴别溶洞是否充填流体。溶洞充填流体之后,由于碳酸盐岩与流体之间存在很大的纵波波阻抗差异会形成强的纵波反射系数;同时,又由于流体内不传播横波,溶洞壁(包括顶低面)是横波的绝对反射界面,因而会形成强的横波反射。换句话说,充填流体溶洞既能形成强的纵波,又能形成强的横波。AVO分析对叠前地震数据进行弹性反演,从中提取出与横波有关的属性来指示充填流体的溶洞。     

The effects of hardpan layers on the water chemistry from the leaching of pyrrhotite-rich tailings material

Column leaching experiments were used to determine the effects of an iron-rich hardpan layer, on the rate of tailings oxidation and the composition of leachate waters, from the Renison Bell tailings dams in western Tasmania, Australia. One-meter-long PVC columns, filled with tailings, cover material (Cassiterite Flotation Tailings) and hardpan samples from the tailings dams, were leached over a period of 14 weeks. Under dry cover conditions, when hardpan was present, the solute loads peaked at 21–49 days (Fe at 2,294 ppm and SO ₄ ^2- at 4,700 ppm), and stabilised at much lower concentrations after 9 weeks. In contrast, the solute loads steadily increased over time in the column where hardpan was absent (SO ₄ ^2- from 1,800 to 3,100 ppm, and Fe from 407 to 1,692 ppm). Under saturated cover conditions, the solute concentrations in the leachate also increased with time (SO ₄ ^2-from 1,900 to 17,000 ppm, and Fe from 480 to 8,500 ppm). The presence of a hardpan layer between the reactive tailings and cover material has been found to improve leachate water chemistry and lessen the rate of sulphide oxidation.     

Influence of hardpan layers on arsenic mobility in historical gold mine tailings

Hardpans, or cemented layers, form by precipitation and cementation of secondary minerals in mine tailings and may act as both physical and chemical barriers. Precipitation of secondary minerals during weathering of tailings can sequester metal(loid)s, thereby limiting their release to the environment. At Montague Gold Mines in Nova Scotia, tailings are partially cemented by the Fe arsenate mineral scorodite (FeAsO₄·2H₂O). Previous studies have shown that the formation of scorodite can effectively limit aqueous As concentrations due to its relatively low solubility (<1 mg/L at pH 3–4) and high As content (43–52 wt.% As₂O₅, this study). Co-existing waters and solids were sampled at Montague Gold Mines to identify present-day field conditions influencing scorodite precipitation and dissolution, and to better understand the mineralogical and chemical relationship between hardpan and tailings. In addition to scorodite, hardpan cements were found to include amorphous Fe arsenate and Fe oxyhydroxide. Nearly all hardpan is associated with historical arsenopyrite-bearing concentrate which provides a source of acidity, As⁵⁺ and Fe³⁺ for secondary mineral precipitation. Pore waters sampled from the hardpan have pH values ranging from 2.43 to 7.06. Waters with the lowest pH values also have the highest As concentrations (up to 35.8 mg/L) and are associated with the most extensive hardpan and greatest amount of weathered sulfide. Samples from areas with discontinuous hardpan and less sulfide have near-neutral pH and lower As concentrations. Detailed petrographic observations indicate that the identity and stability of As-bearing secondary minerals depends on the continued availability of sulfide concentrate. The results of this study are being used to develop remediation strategies for highly weathered, hardpan-bearing tailings that consider the stability of both primary and secondary minerals under various cover scenarios.     

Influence of climate, mineralogy and mineral processing on the weathering behaviour within two, low-sulfide, high-carbonate, gold mine tailings in the Eastern Desert of Egypt

Despite its importance within environmental management strategies, little concern is shown to sulfide oxidation and/or hardpan formation at neutral pH where dry condition prevails. Two gold mine tailings in Egypt, El Sid and Barramiya, were studied for their geochemical/mineralogical properties, and climate influence on hardpan formation. The tailings are characterised by homogeneous silt-sized sediments (>42%), have high carbonate, predominantly as calcite for El Sid and dolomite-ankerite for Barramiya, and low-sulfide contents, chiefly as pyrite, galena and sphalerite for El Sid, and arsenopyrite–pyrite for Barramiya. El Sid is characterised by high average concentrations of Pb (2,758 mg/Kg) and Zn (2,314 mg/Kg), its lower part dominated by mafics, overlaid by granitoids. Barramiya has higher As (average 2,836 mg/Kg) content and represents a mixture of mica-schists/mafics-ultramafics. During field investigations, no hardpans were identified, only bassanite and gypsum were found at the surface of El Sid tailings, forming thin layers and desiccation crack fillings. Column experiments showed a thin crust consisting of gypsum, halite and sodium sulfate formed at the top of the column of El Sid tailings after 2 weeks, this was not recognized in the column from Barramiya. The homogenous thickened tailings deposition in both areas did not favour hardpan formation, since the critical amounts of reacting sulfides were never achieved in individual lamina, due to missing mineral/grain size fractionation. The high-temperature/low-water availability, characteristic for desert climate regions did not allow significant sulfides oxidation. Therefore, both tailings will suffer from continuous erosion and spreading out of contaminants to the environment for a prolonged period of time by sporadic flash floods.     

Quantifying time scales of pedogenic calcrete formation using U-series disequilibria

Time scales of pedogenic calcrete development are quantified by subsampling carbonate from within a mature (stage V) pedogenic calcrete profile from southeast Spain and dating the material by U-series disequilibria. The location of the earliest and latest cements can be estimated by comparing previous studies of calcrete morphological development with micromorphological analysis of the study profile. Carbonate was sampled and dated from three locations within the profile: (1) below the lower surface of clasts within the hardpan (representing the earliest cement present—207±11 ka), (2) from the centre of cement filled pores within the hardpan (reflecting the final plugging of the calcrete hardpan—155±9 ka) and (3) from the laminar calcrete overlying the hardpan (representing the latest cement—112±15 ka). These results show that the hardpan took between 73 and 31 ka to form, whilst the mature stage V profile took between 121 and 69 ka to form. This is the first time that rates of mature calcrete development have been established by direct radiometric dating of the authigenic carbonate. The technique is appropriate for dating mature calcretes in dryland regions worldwide and offers the opportunity of increasing our understanding of the spatial and temporal variability in rates of pedogenic calcrete development.     

Prediction of long-term settlements of subway tunnel in the soft soil area

Nowadays, the issue of predicting soil settlement has gradually become an important research area. The theory of predicting soil settlement under static load is comparatively mature, while the method of predicting soil settlement under dynamic loading is still at the exploratory stage. This paper aimed to find a suitable model to satisfy the prediction of long-term settlements of subway tunnel. The settlement monitoring data of Subway Line 1 in Shanghai were taken as the case. In this paper, current nonlinear prediction methods of settlement were summarized. The fitting method was introduced and applied in the settlement data of Shanghai subway tunnel; correlation coefficient r of the fitting results can keep a high level in most cases, illustrating the validity of segmentation simulation. Two kinds of prediction methods and its utilizing methods were introduced in this paper, i.e., Grey Model (1, 1) and Auto-Regressive and Moving Average Model (n, m). The settlement trend of Subway Line 1 in Shanghai was predicted by GM (1, 1) and ARMA (n, m) model. The results show that ARMA (n, m) model is more precise than the GM (1, 1). As a new method in settlement prediction field, ARMA (n, m) model is prospective in the future.     

Influence of geology in the geochemistry signature of Itacolomi State Park waters,Minas Gerais-Brazil

In all geological scenarios, mineral water reactions will affect the water chemistry. As such, water resources in different rocks commonly involve different hydrogeological compartments. The aim of this work is to evaluate the influence of geology in the geochemistry signature of Itacolomi State Park waters. To do so, a survey of the geological units in the area was carried out, a geological/stratigraphic division was made, and its correlation with the main geological events was determined. Using the advantages of GIS, all the catchments were delimited. Based on this division, near 30 stream and lake segments were chosen for analyses. In each point, all physiochemical properties of the water were measured, and samples were collected to determine the concentrations of major and trace elements by ICP–OES. The dynamics of the Itacolomi State Park rock-soil and stream water solutions suggest that mixing of drainage waters from different bedrock and soil sources regulates stream water physical–chemical parameters and solute concentrations. The analytical data showed a clear correlation between the chemical compositions of the solute and the geological characteristics of the catchment. Units that are covered by iron oxide hardpan (Manso unit) and iron-banded formations (Custódio unit) show a large amount of soluble elements, including high values of Fe and Mn. On the other hand, the presence of high values of Al and K (Itacolomi unit) are a direct consequence of the presence of quartzite associated with low pH values.     

Morphology and stratigraphic relationships of the Wiluna hardpan in arid Western Australia

Over much of arid Western Australia a red and brown hardpan occurs on broad plains; it may lie either on the surface or buried beneath a shallow mantle of soil. It is proposed that, because of its lithological character and its considerable thickness and extent, it should be given the name of Wiluna Hardpan. The proposed type section is north of Wiluna, near Bulloo Downs homestead, where headward erosion of the Ashburton River is exposing sections 30 m deep. Although both ferruginous and calcareous cement may be present, Wiluna Hardpan is largely indurated with silica. It is younger than laterite, but broadly contemporaneous with calcrete and Robe Pisolite. Initially it was probably geographically restricted by a coincidence of suitable conditions of low relief and a climate resulting in episodic flooding and desiccation. Its present distribution is partly controlled by current erosional and depositional processes.     

瞬态瑞雷波法在上海地区成层加固地基检测中的应用

阐述瞬态瑞雷波的发展及基本理论,着重介绍了瞬态瑞雷波法在上海地区检测成层加固地基的有效性。     

上海地区地震放大效应的初步探讨

上海地区地震反应敏感,经常出现烈度异常,究其原因主要与深厚松散堆积层的地震放大效应有关,本文主要从井下基岩与地表土层的地动位移、地震烈度及加速度峰值几方面论述了上海地区的土层地震放大效应。     

上海及其周边地区高耸建筑物抗震设计中卓越周期的评价与选择

根据上海及周边地区地质构造、地震活动的历史和动力参数实测资料,通过分析研究,提出上海地区剪切波和卓越周期的经验计算法。