安徽亳州市新近沉积粉土性质及其承载力的确定

通过现场勘察和多种原位测试方法,详细地研究了亳州市新近沉积粉土的工程性质,对粉土的地基承载力进行了评价。     

我国老粘土地基承载力问题

一、概述 工业民用建筑地基基础设计规范(TJ7—74)(以下简称规范)和工程地质勘察规范(TJ21—77)[1][2][3]对粘性土按时代、成因和土的工程地质特征分为老粘性土(指第四纪晚更新世(Q_3)及以前沉积的粘性土),一般粘性土(第四纪全新世(Q_4)沉积的粘性土),新近沉积的粘性土(文化期以来新近沉积的粘性土),和几种特殊土(软土、红粘土、人工填土等)。     

天津滨海新区新近沉积土确定及其工程特性研究

基于古海岸线及测年试验分析,对滨海新区上部陆相沉积土的形成年代进行研究,确定了该区新近沉积土的划分原则,并根据成因类型及沉积环境,进一步划分了新近沉积土的类别;根据土层厚度及底板埋深,查清了滨海新区新近沉积土的发育分布规律,并分析评价了该类土的工程特性。结果表明:滨海新区上部陆相沉积土形成年代小于4 000年,应将其划归为新近沉积土,与原新近沉积土共同组成该区新近沉积层;新划分原则下新近沉积土可分为洪泛新近沉积土、古河道新近沉积土及上部陆相新近沉积土三类,其厚度一般在1～2 m,底板埋深一般在3～4 m,工程性质较差,表现为较高含水量、较大孔隙比、较低抗剪强度、较高压缩性,地基承载力普遍在100 kPa左右。     

增城市区冲（洪）积土及残积土的工程地质特征

增城市区的第四纪冲积土及震旦系风化残积土分布普遍，是各类工程建设的地基基础。前者自下而上由两个从粗到细的沉积旋回组成，按沉积物颗粒级配和塑性指标，可分砾砂→粉质粘土→中细砂→粉质粘土；后者主要为砂质粘性土，分为地表和地下两种。其中，地表的第四纪冲积粉质粘土和地表风化残积土可作为３层以下的一秀建筑物的基础持力层；多层及多层以上建筑物的基础，宜选择第四纪冲积的粉质粘土，砾砂层或地下震旦系风化残积土作为     

滑坡冲击作用下的阶地砂质粉土层液化机理

为探究阶地饱和砂质粉土在黄土滑坡冲击荷载作用下的力学机理,选取泾阳南塬典型黄土滑坡LD37为研究对象。通过基本性质测试获取了阶地砂质粉土的物理、水理、颗粒级配和矿物组分等指标。采用自制冲击设备进行了3种饱和度条件下的冲击试验,并对水分迁移和剪切强度变化等问题进行了分析,在此基础上探讨了冲击液化机理。结果表明:冲击荷载会使砂质粉土内部的总应力与孔隙水压力剧增,在应力波的作用下,出现多个峰值,且孔隙水压力在1 s内难以完全消散;80%与90%饱和度的砂质粉土受冲击会在深度方向上形成不同程度的液化,而70%饱和度的砂质粉土受冲击后沿深度方向并未发生液化;砂质粉土发生冲击液化时下部水分会向上部迁移,导致其上部土层含水率骤增,剪切强度骤减;冲击液化过程可划分为初始阶段、冲击挤压阶段和冲击回弹阶段。砂质粉土的冲击液化机理是一种由于快速冲压土体的不排水行为,导致其颗粒原始骨架结构破坏重组,从而引起其内部孔压快速积累的一种液化行为。     

新近沉积粘性土的压缩模量与标准贯入试验锤击数的关系

本文简略论述了新近沉积土的一般特征，通过分析研究大量的试验数据，确定出了新近沉积粘性土的压缩模量Es与标准贯入试验锤击数N值的关系。     

鄂尔多斯盆地富县地区上三叠统延长组砂质碎屑流沉积特征及其油气勘探意义

通过岩芯观测、地震解释和测井分析,结合薄片观察、粒度分析以及各种资料的综合分析,对鄂尔多斯盆地南部富县地区上三叠统延长组沉积相类型及特征进行深入研究,提出长9-长6油层组存在砂质碎屑流沉积。结合盆地沉积背景及其演化规律,探讨了砂质碎屑流沉积的成因机制, 详细论述了砂质碎屑流沉积的沉积特征,建立了砂质碎屑流的沉积模式。研究表明砂质碎屑流砂体主要由块状粉细砂岩和含泥砾粉细砂岩两种成因相构成,其成因是三角洲前缘砂体在外界触发力作用下,滑动崩塌而形成。分析了砂质碎屑流沉积与油气的分布关系,实践表明砂质碎屑流沉积体是下生上储或下储上生的油藏类型,属于典型的岩性油气藏,构成了该区深水区域的良好岩性圈闭储集体。     

渤海东部潮流沉积特征及MIS4以来的沉积环境演化

渤海东部发育了典型的潮流沉积,由老铁山水道冲刷槽、辽东浅滩沙脊和渤中浅滩沙席组成。该文基于中国海洋地 质调查最新获取的高分辨率单道地震数据,与水深变化进行对比,将该区的潮流沉积特征与其地震相特征进行精细分析, 同时结合晚第四纪CD5孔的岩性、14C测年和层序地层划分,识别出晚更新世以来的四期层序地层,分别是MIS4以细砂为 主的陆相地层、MIS3以粉砂和黏土为主的滨浅海相沉积地层、MIS2末次盛冰期形成的以粉砂质粘土和细砂质粉砂为主的陆 相沉积地层和全新世（MIS1） 发育的以粉砂质黏土和细砂组成的海相沉积地层。其中全新世地层分别由早期的滨海相沉 积、中期的浅海沉积和晚期的潮流沉积组成。通过这四期层序的研究,揭示了该区MIS4期以来的沉积环境演化。     

淮北平原浅表层沉积土承载力特征及其螺旋板检测评定方法研究

针对淮北平原地区浅表层沉积土典型地质单元,选取代表性试验区域,开展了螺旋板载荷、平板载荷和静力触探等原位测试,分析了含钙质结核黏土、新近沉积粉土、粉砂3种地基的承载力特性,重点探讨了不同类型土体的螺旋板载荷试验p-s曲线特征、承载力特征值确定方法和值域范围,并与静探和平板载荷试验数据进行对比,分析其相关关系和变化规律。研究结果表明:一般性黏土、粉质黏土和粉土的承载力较低,钙质结核黏性土和粉砂的承载力相对较高,值域范围较宽,密实程度是决定粉土、粉砂承载力大小的主要因素。螺旋板载荷试验能较好的反映多元互层地基土体力学性质的变化特征,采用等应变控制法可达到快速、分层检测的目的,并通过等应力控制法对比试验验证了其可靠性。最后通过与平板载荷试验结果进行线性拟合,给出了螺旋板载荷试验确定淮北平原浅表层地基承载力的经验公式。     

上扬子区下寒武统海相页岩岩相类型及沉积模式

上扬子区下寒武统牛蹄塘组页岩是我国南方地区页岩气重要勘探层系之一。通过露头、岩心、薄片、实验测试等资料综合分析,识别了该套页岩岩相类型及相关沉积作用方式,在水体氧化还原条件演变规律分析基础上总结了其沉积演化模式。牛蹄塘组页岩共包含6类岩相：富有机质硅质页岩、含粉砂硅质页岩、粉砂质页岩、黏土质页岩、泥质钙质页岩及粉砂质钙质页岩,主要体现为5种沉积作用方式：砂质机械沉积、钙质化学沉积、硅质生物沉积、泥质絮凝沉积及底流改造沉积。从底到顶,该套页岩表现为一套水体变浅的进积型演化序列,水体还原程度减弱,有机质保存条件变差。牛蹄塘组下段沉积期,盆地相区和陆棚相区分别以硅质生物沉积和钙质化学沉积为主,主体岩相类型为硅质页岩和钙质页岩;上段沉积期,盆地相区和陆棚相区分别以泥质絮凝沉积和砂质机械沉积为主,主体岩相类型为黏土质页岩和粉砂质混合质页岩。提出的牛蹄塘组页岩岩相发育模式及沉积演化规律能为研究区优质页岩的分布预测及页岩气勘探选区评价提供理论依据。     

庐山北麓JL红土剖面粉砂粒级元素地球化学特征及其物源意义

加积型红土是中国南方第四纪环境变化研究的重要陆相载体,其沉积母质显示风成特性,后期经历较强的化学风化。为了明确加积型红土的物质来源,并减弱风化效应对其物源信息的影响,本文提取了庐山北麓JL红土剖面(厚18.46 m)部分样品的粉砂组分(4~63 μm),分析其元素地球化学特征,并通过元素比值及物源判别指数等方法讨论其蕴含的物源信息。结果显示:1)粉砂粒级化学组成中SiO2、Al2O3和Fe2O3三者的含量可达84.29%,K2O、Na2O、CaO和MgO四者含量仅1.30%,与全岩相比SiO2含量增高,Al2O3和Fe2O3含量明显降低,风化指数CIA值(74.02%)明显低于全岩样品(85.00%);微量元素中,粉砂粒级相对全岩Cu、Zn、Rb、Sr、Cr、La等含量降低,Y、Zr含量则略高。2)Na2O/Al2O3与K2O/Al2O3及Na2O/K2O与CIA的散点图中,粉砂粒级样点间的集聚程度明显降低,暗示风化效应在一定程度上被削弱。此外以洛川黄土和长江河漫滩沉积物为端元的物源指数计算表明,全岩样品消除粒级效应后的物源指数(PIw)与粉砂粒级物源指数(PIfs)吻合度较好,进一步验证了粉砂粒级地球化学特征在削弱风化效应方面的有效性。3)JL剖面上部黄棕色土的PIfs值为0.45,物源上更接近北方黄土,剖面中下部的网纹红土PIfs值为0.57,物源更接近长江沉积物。结合TiO2/Al2O3、Zr/Y、Hf/Ti等元素比值,JL剖面自下而上近源物质的贡献略有减少,远源物质的贡献则趋于增加,这可能意味着晚第四纪以来东亚冬季风不断增强的过程。     

对北京地区新近沉积土的判别认识

新近沉积土自上世纪50年代被认识并引起工程界重视,目前在实际工作中的判别分析仍存在难点。为加强认识,通过比较总结前人的知识经验,并结合笔者在北京地区从事岩土工程勘察的实践,阐述了北京地区新近沉积土的基本特征与分布,着重探讨了其主要物理力学性质及地基承载力等工程特性,并对其定性、定量判别方法作了总结讨论。     

The need for Quaternary geological knowledge in geotechnical engineering

Engineering geology, like geotechnical engineering, is a new scientific subject in Denmark. Experience in the period since 1924 is laid down in the Danish Code of Practice for Foundation Engineering, which states that the geological conditions establish the foundation class and must be determined as early as possible during the soil investigations by experienced geologists and engineers. The consequences are illustrated by some examples from geotechnical investigations performed at the Danish Geotechnical Institute:
• The economic foundation of a small wooden building on the brink of a postglacial lake and fiord basin at Vedbæk.
• The deep excavation for and foundation of a huge commercial center at Lyngby situated in the middle of a tunnel valley with more than 12 m late- and postglacial organic deposits, based on design and control in the high foundation class.
• The engineering geological modelling of the Quaternary development in the Danish North Sea. Applied geology plays an increasing part in geotechnical engineering as a prerequisite for economic and safe technical solutions. The future use of geological and geotechnical data bases will bring Quaternary geological knowledge into focus.     

The engineering-geological characteristics and classification of the major superficial soils of the Niger Delta

A study of the engineering geological properties, distribution and classification of the major superficial soils of the Niger Delta was carried out as part of a study programme to provide the much needed information and data for the infrastructural development of the region. Four major superficial soil groups were recognized on the basis of similarity in geotechnical, geological and geomorphological characteristics. The soils are generally fine grained and their geotechnical properties revealed that they are essentially clays with varying proportions of sand, silt and organic matter. The clay, silt and organic contents increase seawards. The values of the various geotechnical parameters are mainly influenced by the amounts of clay (and/or sand) and organic matter.     

微生物矿化作用改善岩土材料性能的影响因素

基于微生物诱导碳酸钙沉淀作用（MICP）的土体改性技术近年来在岩土工程领域引起了人们的广泛关注。该技术在改善岩土材料的强度、刚度、抗液化、抗侵蚀及抗渗透性等性能的同时,还能维持土体良好的透气性和透水性,改善植物的生长环境。由于微生物矿化作用涉及一系列生物化学和离子化学反应,固化过程中的反应步骤较多,因此,MICP固化效果受许多因素的制约与影响。基于大量文献资料,系统总结了细菌种类、菌液浓度、温度、pH值、胶结液配比及土的性质等关键因素对微生物改善岩土材料性能的影响,讨论了这些影响因素的优化方式和未来的研究方向,主要得到了以下几点结论：菌种类型、菌液浓度、温度、pH、胶结液性质会从微观上影响碳酸钙的晶体类型、形貌和尺寸,进而在宏观层面影响岩土体的胶结效果;菌液浓度尽可能高、温度在20～40℃间、pH值在7.0～9.5左右、胶结液浓度在1 mol/L以内的因素条件对微生物加固岩土体具有较好的效果。上述范围内的低温、较高的pH值、低浓度胶结液有助于提高土体的抗渗性,而高温、较低的pH值以及中高浓度胶结液有助于提高土体的强度;MICP加固土体的有效粒径范围为10～1 000 ?m,相对密度越大、级配越好则加固效果越好。分步灌浆法、多浓度相灌注法及电渗灌浆法有助于提高土体固化均匀性,0.042 (mol/L)/h以下的注浆速度有利于提高胶结液利用率,砂土试样的灌浆压力一般在10～30 kPa之间,粉黏土试样的灌浆压力不宜超过110 kPa,过高的灌浆压力会破坏土体结构,降低固化效果。     

基于现行规范的粉土定名分析与探讨

根据现行规范对粉土定名的规定,从工程实践角度,通过对粉土、黏性土的室内试验、原位测试和野外鉴别结果进行综合分析,论述了在不同的液限标准下,同一种土可能定出不同的名称.因不同类型土的物理力学性质存在较大差异,如粉土具有流变性和触变性等对工程极为不利的特性,因此土层定名错误会误导设计和施工,危及工程安全.     

Hydrogeology of Al-Lith Sabkha,Saudi Arabia

In Saudi Arabia, coastal sabkhas cover extensive areas along the coasts of the Red Sea and Arabian Gulf in addition to the continental sabkhas scattered in many places inland. Al-Lith sabkha is one of the typical coastal sabkhas located along the Red Sea coast. Sabkhas, in general, pose a number of geotechnical problems and need to be carefully investigated before being urbanized.A generalized geologic section in Al-Lith sabkha indicates a salty crust at the surface followed by yellowish brown silt and silty sand, olive gray silt and sandy silt and bottomed by coralline reefal limestone. Within this succession, there are several isolated lenticular bodies of sandy silt, silty sand and shelly silty sand. The clay minerals constituting the fine-grained portion of the soil are, in decreasing order, kaolinite, illite and montmorillonite in addition to minor chlorite.The depth to groundwater in 17 observation wells ranged from 0.18 to 1.81 m with a maximum fluctuation of 0.60 m between summer and winter. The permeability of the top silt layer was found to be very low with an average of 5.4×10⁻⁴ m/day. A pumping test was performed in a deep well penetrating the coralline limestone. The measured permeability is 1.1×10² m/day and the estimated storage coefficient is 4×10⁻⁵.Soil water evaporation was measured using a lysimeter constructed with undisturbed soil samples having different depths to the water level. The rate of evaporation ranges from 2.8 to 27.8 ml/day decreasing with an increase in depth to the water level.Groundwater samples were analyzed for their major anions and cations. Salt concentrations show a general increase toward the sea except for the calcium and carbonates that show a landward increase. The groundwater could be classified as a Cl+SO₄ brine. The salinity of the groundwater was determined at different depths in the pumping well and was found to be low in the top 4 m. It sharply increases until it reaches a value approximately 10 times the salinity of the top layer indicating groundwater intermixing with freshwater and salt-water intrusion. The change in the salinity during pumping was erratic but within a range of 2%.     

青藏高原多年冻土区沼泽草甸土壤CH_4产生速率研究

用实验室培养法对青藏高原多年冻土区沼泽草甸土壤不同温度条件下的CH4产生速率进行了研究.结果表明：CH4产生速率与温度之间呈现显著的指数关系,整个土壤剖面平均CH4生成速率和CH4生成速率初始值随温度的变化具有显著的相似性,都表现出随温度的升高而增加规律,0℃、5℃、18℃时的CH4生成速率分别是-18℃时的5.7、1...     

Abrasion-derived sediments under intensified winds at the latest Pleistocene leading edge of the advancing Sinai-Negev erg

Quaternary desert loess and sandstone-loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion. In the northern Sinai-Negev desert carbonate terrain, only sand abrasion in active erg could have produced the large quantities of quartzo-feldspathic silts constituting the late Quaternary northwestern Negev loess. In the continuum of source (medium to fine sand of dunes) to sink (silts in loess) the very fine sand is unaccounted for in the record. This weakens the sand abrasion model of silt formation as a global process. Here, we demonstrate that, as predicted by experiments, abrasion by advancing dunes generated large quantities of very fine sand (60-110 μm) deposited within the dune field and in close proximity downwind. This very fine sand was generated 13-11 ka, possibly synchronous with the Younger Dryas under gusty sand/dust storms in the southeastern Mediterranean and specifically in the northern Sinai-Negev erg. These very fine sands were washed down slope and filled small basins blocked by the advancing dunes; outside these sampling basins it is difficult to identify these sands as a distinct product. We conclude that ergs are mega-grinders of sand into very fine sand and silt under windy Quaternary and ancient aeolian desert environments.     

上海市第四系的工程地质研究

通过２０余项工程代表性的钻孔岩芯分析,对比了上海市１２０ｍ以浅晚第四纪各沉积层的成因类型,形成时代,岩性及其物理力学性质,并按地基工程要求。编制了“地基土层次名称表”。表中将沉积层划分为１２个工程地质层及众多亚层。在此基础上,参照已有２０００多项工程勘察资料,编制成多时段１：５万古地理图,从而摸清了本区各土层的空间分布规律及其结构变化特征。根据地层结构差异,编制了 桩基工程地质分区图”,阐述了天然地基和三个不同桩基区岩土工程地质条件及应用中需注意的事项,为上海市工程勘察、设计和麓工提供了可靠的科学依据。