外文翻译--土方工程的地基勘察与施工

外文翻译--土方工程的地基勘察与施工 毕业 设计 领导形象设计圆作业设计ao工艺污水处理厂设计附属工程施工组织设计清扫机器人结构设计 ,论文， 外文翻译 题目名称:土方工程的地基勘察与施工 院系名称:建筑工程学院 班 级:土木081班 学 号:200801614128 学生姓名:袁巍巍 指导教师:常利武 2012年 3 月 土方工程的地基勘察与施工 保罗?圭格利 爱尔兰岩土工程服务有限公司 摘 要: 当工程场地的处理面积有限且填方工程费用大量增加时，土方工程的地基勘察设计与施工已逐渐地变得重要。由于冰渍土以及含砾粘土的提出使土方工程地基勘察方法的纲要比传统的勘察方法更详细。 本文提出“岩土认证”观点以及对地基勘察与土方工程相结合的优点加以概要说明。 1、引 言 许多爱尔兰含砾粘土的勘察与再利用评价使岩土工程师与道路工程师感到为难。这些冰渍土或含砾粘土主要表现为低可塑性而且还含有从粘土到漂石的不同粒径颗粒。大部分本地粘土与淤泥质土中包含不同比例的砂、砾石、卵石、漂石。颗粒级配控制着土体的行为，而且淤泥使土体性质易受天气变化影响。 土体含水量随着地区不同而不同，从都柏林硬灰黑含砾粘土的7%到中部、西南部或西北部浅灰色含砾粘土沉积物的20%-25%。含砾粘土吸附水的能力建立的较好但土方工程中计划的不恰当常导致其扩大。 一般来说，良好级配的土体对于含水量的轻微变大相当敏感，将导致强度下降或不适合用作工程回填土。许多含砾粘土(尤其中等淤泥质土或良好级配的砂)在选择阶段已经被筛除，但事实上它们能对压缩或强度起到特定的作用。 筛选过程应尽量使用本地土体或者回填区或路堤边性质相对较差的土体，通过仔细评价应加以应用。回填材料必须保持一定的含水量，既不能太湿导致土体不稳定也不能太干以致不能被充分压缩。 高含水量、低强度含砾粘土适用于低路堤回填(相当于2到2.5米的高度)但不适用于没有使用土工织布隔离与回填层的土方回填工程。因此，土方工程承包商充分认识土体的处理特性相当重要，因为许多工程都受到挖掘设备通行能力的影响。 2、传统地基勘察方法 对于道路工程来讲，地基勘察最基本目标是对土体适用性进行类似表6.1的分类，该表源于国家 档案 肢体残疾康复训练教师个人成长档案教师师德档案表人事档案装订标准员工三级安全教育档案 登记处2000年3月版的道路施工 规范 编程规范下载gsp规范下载钢格栅规范下载警徽规范下载建设厅规范下载 。目前大部分道路施工中的地基勘察包含以下提供有关岩土参数的试验方法: ? 取样孔 ? 静压法取样 ? 动力探测 ? 回转钻进 ? 原位测试(标准贯入试验，变水头渗透试验，岩土物理试验等) ?室内试验 评价场地工作的重要性特别是评价土体深部取样区域的适用性时不能过分强调其适用性。静压法取样通常将取样器下沉至要求深度进行取样，并每间隔一米进行取样。 在许多情况下，静压法取样由于卵石、漂石阻碍不能压入非常坚硬的含砾粘土。土样在钻孔内应尽量少扰动，但级配变坏是很正常的，级配变坏将导致土样分类不够精确。 取样孔对于恢复适当尺寸的土样以及观察碎屑岩在卵石、漂石中所占比例来说应该是适当的。因此，详尽且精确的地区描述取样区域以及取样空来说都相当重要，而且还为它们提供了检查土体在钻孔范围以外性质的良机。取样孔也提供了孔壁稳定性的评价以及观察孔壁内水进入时所造成的影响。 一位有经验的岩土工程师或工程地质专家应监督取样孔工作以及土样的恢复。因为土样性质为土样敏感性提供了信息，所以取样时土体性质应被密切关注，尤其是水从小颗粒区域迁移到良好级配区域。而且土体在开挖时的条件为其原位条件提供了一个相对精确的评价。 3、土的分类 土的描述与分类应该依照英国标准5930(1999)进行并依照英国标准1337(1990)进行测试。土的工程描述应基于按粒径大小分级并依照良好级配土的可塑性进行补充。对于许多冰渍土或含砾粘土(混合土)的难点在于其描述与工程性质测试的评价。 关于以前的地基勘察纲要，爱尔兰含砾粘土的粘土与淤泥质土中常由易变比例的砂、砾石、卵石组成。良好级配且含水量为10%-15%的低可塑性土最难进行描述与分类。现在英国标准5930(1999)已认识到描述“混合土”所存在的难点——土的良好级配较之颗粒尺寸对于控制着土的工程性质更优越。 一个关键参数在土分类以及理解过程中经常被低估，该参数就是渗透系数K。检查土的颗粒级配将间接说明土的渗透系数的大小。假如可能，为了准确评价土体的排水特性，三轴单元试验将采用无扰动原状土样或高质量土样进行试验。 低可塑性的中等渗透性含砾粘土(K大约在10-5到10-7米.秒范围内)能经常通过不同排水条件进行“模拟”。其必须在取样区域安装排水边界以及水坑边界或借用钻孔以减少土样的含水量。因此，由于含水量的小量减少，工程性质复杂的冰渍土也能当作合适的工程填土加以应用。 4、土工试验 由于室内试验的许多规定使其被建议用作土的最后试验。土的工程参数列于表6.1，该表源于国家档案登记处2000年3月版的道路施工规范。其中包含以下内容: ? 含水量 ? 颗粒级配 ? 塑 限 ? 加州承载比 ? 密实度(最优含水量) ? 重塑土不排水抗剪强度 当进行室内试验时，大量的关键因素应该被考虑。 ? 密实度.加州承载比.MCV试验土样小于20mm。 ? 含水量测试试样应小于20mm以提供真实有效的对比。 ?压缩时孔隙压力未加以考虑可能导致室内与实际存在相当大的差异。 ?土样测试的准备方法必须被明确规定，而且试验应在指定试验室进行。 进行含砾粘土的含水量测试时必须非常小心谨慎。理想地说，土的含水量应与其粒径有关，而且还有相应的级配 分析 定性数据统计分析pdf销售业绩分析模板建筑结构震害分析销售进度分析表京东商城竞争战略分析 曲线，虽然该曲线不是具有实际应用价值。 在大部分情况下，含水量被应用于密实度被认为是提供了关于建立含砾粘土适用性特征的最好方法。由于含水量能在开挖后快速评价土体的适用性，故强烈建议在取样孔中对其进行测试。因此，含水量刻度能够在实验室内不同含水量增量情况下被采用。土样扰动常发生在搬运过程中，这将对含水量的结果产生重大的影响。 地质科学研究所在进行低可塑性含砾粘土含水量测定时已经土样含水量由于时间的推移(2到7天)存在巨大的差异。许多上述低可塑性含砾粘土表现出与时间相关的含水量变化特性。其变化值主要由于土样取样时的排水条件，土样运移以及其体积的膨胀与土中水的迁移将导致土样破坏或者强度下降。 以上资料对于设计者以及土方工程承包商来说都很重要，因为进行上述规定的测试时它提供了设计者以及土方工程承包商理解土体特性的机会。它能说明在某些情况下先进行排水的所存在的优点。对于混合土来说，对土方工程进行开挖时加快排水工程非常有必要。 含砾粘土的加州承载比测试也需要非常小心谨慎，尤其是开展测试前所采用的准备工作。设计工程师必须意识到这一点，因为准备工作的误差将导致试验结果的明显不同。经验表明，采用2.5或4公斤的锤进行含砾粘土的静态击实将导致超高的孔隙压力，因此将导致加州承载比值变低。被击实含砾粘土的硬化相当重要，因为土的硬化将使孔隙水压力消散。 5、土的工程分类 依照英国标准道路施工规范，一般的粘性填土分类如表6.1如下所示: 2A湿粘性填土 2B干粘性填土 ?2C含石粘性填土 ?2D粉质粘性填土 首先按可接受性进行提供土样特性，然后设计工程师在实验室分类以及工程性质测试基础进行决定土工程分类的上下限。爱尔兰含砾粘土基本上都属于2C含石粘性填土。 道路施工规范612条列出了击实方法。两种现有的规程: ? 原状土样击实 ?重塑土样击实 重塑土样击实被认为最实用，特别是在土方工程合同初期阶段良好的击实控制数据可被利用。检验击实质量时，最小干密度对于合同承包商来说是最有用的。一旦土样被认可或满足工程分类要求，然后原位密度才能进行测定，当土样中含石量较低时，通常采用核子测定仪或换砂试验进行测定。 当布置或击实回填土时，原位干密度能够得到检验，不够密实的地方能够被快速识别并进行击实。该过程要求设计工程师评价击实试验区域的总体密度并估计现场真实的“理论密度”。 6、土工地基勘察方法的补充 传统的勘察方法与规程已在第二部分进行详细介绍。接下来讲述的是有助于道路工程的地基勘察工作方法的几个例子: ? 地基勘察工作分阶段进行，特别是室内测试 ?开挖&深取样孔取样 ?使用喷气或聚合物胶质体技术的大直径高质量回转钻进 ? 对可能适合挖方的土样进行小范围击实试验 6.1分段勘察 对于许多大型工程来说，地基勘察工作应分阶段进行已经被提倡许多年了;特别室道路工程更应如此。因为道路工程的大量岩土工程方面数据可在短期内即可使用。大部分的大型地基勘察工程都很少花时间对最初成果进行“消化”和回顾，而且也很少对勘察方法的适用性进行重新评价。 对于土的室内测试，经常准备大量的测试计划，而在最后试验过程中这些计划并未被加以采用。在许多情况下，计划通常都是由经验少的工程师来准备，而经验丰富的工程师进行设计并未包括所准备的计划。 土的工程特性测试不但价格昂贵而且历时长(等同于加州承载比的5个点的测试&每个点的含水量测试超过两个星期)。当土的分类测试(含水量、颗粒级配分析以及阿太堡界限)完成后，才能对岩土数据以及工程特性测试计划进行进一步的分析。假如在取样期间完成了含水量的测试，那么接下来就能立刻获得土的适用性评价。 6.2深取样孔 通常都认为深取样孔的开挖既麻烦又困难，因此设计工程师们都认为该法不够恰当。采用台阶式技术以及水泵抽取地下水在含砾粘土中开挖12米深的深取样孔是可行的。 最近几年，地质科学研究所已经在好几个大型道路地基勘察工程中开挖了12米深的深取样孔。来源于这些深取样孔的宝贵数据使工程师们对土的性质有了更进一步的了解。 专家们都建议在静压法取样和回转钻进后进行深取样孔的开挖，所开挖区域的地下水状况将对深取样孔开挖的可行性起到决定作用。立管以及压力计的安装对地下水状况的了解将起到重大的帮助作用，因而这就是为何把这项工作放在地基勘察过程的后面的缘由。 大量有代表性的土样能够被获得(使用地沟箱)以及对区域抽样进行原位剪切强度测试。通过对附近取样孔的立管或压力计测试结果的比较，取样孔壁的稳定性和地下水状况可以被确定。如果取样孔深度达到惊人的500米时，三个取样孔的费用已经无法估价，还有挖出的土石需要进行小范围的击实试验。 从价值工程的观点来看，开挖以及开挖的复原的费用可以很容易计算出来，一个临时的金额被分配并用于开挖以及开挖的复原。 6.3高质量的大直径回转钻进 该系统要求使用喷气或聚合物胶质体技术的大直径回转钻进技术。用三层取心筒在超载积土层中钻进时，可循环材料被装在塑料芯衬垫中。 低可塑性含砾粘土中的岩芯萃取率相当好(典型的超过90%)。岩芯萃取率越高，那么有关工程地质的记录越详细，越有利于室内试验的试样采集。 在冰堆丘地区，例如在Cavan和Monaghan地区，地质科学研究所发现聚合物胶质体技术的大直径高质量回转钻进已经成功地在该地区非常坚硬的含砾粘土中进行深部取样(静压法取样和取样孔在该地区均失败)。原位测试(十字板，标准贯入等)能在钻孔内进行试验并获得不同地平线下强度与承载力的关系。 使用上述系统，大直径回转钻进的费用比传统的高质量钻进要高出50%到60%，但又从价值工程的角度出发，由于该法所获得的岩土信息质量相当高，所以更值得采用。 6.4小范围击实试验 在地基勘察过程中特别是主要取样剪切区域为“边界适应”土时，小范围击实试验被强烈建议采用。加上实验室数据的确认，设计者能更使土方工程的设计更贴近现实，同时为甲方单位节省相当可观的费用。 击实试验能提供以下资料: 场地实际密度，重塑土剪切强度以及加州承载比 最佳土层厚度以及碾压次数 击实过程中土的灵敏度(静态与动态) 检查车辆通行能力与车辙等级 计划场地内测试垫板的典型尺寸大致为20×10米，厚度可达1.5米。选择的场地应该在取样剪切区域或取土坑附近而且有足够的空间用来堆放材料。正常情况下，土方机械需要履带式开挖机(CAT320或其他型号)，25吨运输车，D6型推土机以及牵引式或机动式碾压机。 由于核子测定仪能快速测定含水量，干密度以及容重，因此建议用该仪器测定击实回填土的原位密度测试。它能够获得一大套有关击实回填土的数据并能对击实度，土层厚度和碾压次数之间关系进行评价。扰动或未扰动击实回填土样能够进行室内测试并确认其场地测得数据(特别是含水量)。根据地质科学研究所的经验，如果计划的好，那么小范围击实试验只需两个工作日既能完成。 7、地基勘察设计的监督 地基勘察承包商与咨询工程师之间的密切联系与相互尊重对于大型道路勘察设计的成功相当重要。一位高级岩土工作者来自上述成员之一能做到以上两点，从而导致地基勘察的方向与范围被转变位考虑区域地层和地基条件。 大型地基勘察设计的特征表明获得数据过程中双方良好的交流与适应非常重要。现场条件会随时发生变化，因而想达到勘察方法与工序两者之间的妥协是不可取的。 从监督方面来看(包括地基勘察承包商与咨询工程师)，为了反对现场勘察工作重复，工作重点应放在现场岩土工程师或工程地质工作者的水平上。 8、岩土认证 英国交通部在1992年准备了一份有关高速公路设计 方案 气瓶 现场处置方案 .pdf气瓶 现场处置方案 .doc见习基地管理方案.doc关于群访事件的化解方案建筑工地扬尘治理专项方案下载 的文件(HD22/92)。该文件指出了地基勘察的设计与报告以及土方工程施工过程中必须使用的工序与认证文件。 道路工程设计方案包括运土方案或复杂岩土特性必须被设计组织—咨询工程师或代理权威认证。岩土工作的专业责任由设计组织负责。 对于这一设计方案，设计组织必须任命一位特许工程师，而该工程师为具有丰富经验的岩土工程师。他(她)职务是岩土联络工程师，主要工作是负责包括工序陈述的准备、报告以及认证所有岩土事务。 HD22/92的1.18节提到“地基勘察工作完工后，设计组织应该提交一份包括所有事实记录、专业承包商的测试结果、承包商或设计组织的解释报告的详细报告与认证”。设计组织应该准备一份土方工程设计报告，该报告为解释设计方有关场地勘察数据以及土方工程设计的详细报告。 项目管理人与岩土联络工程师的联络程度和密切性将很大程度上取决于方案的特性以及勘察于设计过程中遇到的岩土复杂性。 土方工程完工后，要求设计组织准备一份岩土反馈报告。该报告主要陈述土方工程施工中遇到的岩土问题以及正确的处理方法或措施。设计组织准备认证施 工中采取的岩土方法(例如边坡失稳，岩溶特征，采空区，地基改良系统等)。 9、结论 ? 为确保道路NDP岩土勘察工作能被满意执行，地基勘察承包商与咨询工程师之间密切合作是必需的。 ? 许多土在筛选及设计阶段被轻易筛除。希望本文中列举的建议方法能给道路地基勘察设计工程师进行范围与界限等设计时提供帮助。 ? 结合现代化仪器设备，土方工程施工过程中的监测变的非常简单。孔隙水压力，横向与竖向移动能被容易的测得并为土的工程特性提供重要的反馈信息。 ? 地基勘察工作应分段进行，特别是室内试验更为重要，其能对各参数进行恰当的评价。 由于工程垃圾许可执照批准条件变得严格，“取样孔边界”土的处理将? 变得越来越困难而且费用也越来越高。英国地基回填税的出现使得土方工程中对各种土样进行彻底检验以加大其利用程度。对于爱尔兰的岩土工程师与土木工程师来说，它提供了类似的动机与挑战。 ? 同英国国家档案登记处的地基勘察与土方工程处理方法相比，认证方法应该在工程中加以考虑。 DESIGN AND EXECUTION OF GROUND INVESTIGATION FOR EARTHWORKS PAUL QUIGLEY, FGS Irish Geotechnical Services Ltd ABSTRACT The design and execution of ground investigation works for earthwork projects has become increasingly important as the availability of suitable disposal areas becomes limited and costs of importing engineering fill increase. An outline of ground investigation methods which can augment „traditional investigation methods? particularly for glacial till / boulder clay soils is presented. The issue of „geotechnical certification? is raised and recommendations outlined on its merits for incorporation with ground investigations and earthworks. 1. INTRODUCTION The investigation and re-use evaluation of many Irish boulder clay soils presents difficulties for both the geotechnical engineer and the road design engineer. These glacial till or boulder clay soils are mainly of low plasticity and have particle sizes ranging from clay to boulders. Most of our boulder clay soils contain varying proportions of sand, gravel, cobbles and boulders in a clay or silt matrix. The amount of fines governs their behaviour and the silt content makes it very weather susceptible. Moisture contents can be highly variable ranging from as low as 7% for the hard grey black Dublin boulder clay up to 20-25% for Midland, South-West and North-West light grey boulder clay deposits. The ability of boulder clay soils to take-in free water is well established and poor planning of earthworks often amplifies this. The fine soil constituents are generally sensitive to small increases in moisture content which often lead to loss in strength and render the soils unsuitable for re-use as engineering fill. Many of our boulder clay soils (especially those with intermediate type silts and fine sand matrix) have been rejected at the selection stage, but good planning shows that they can in fact fulfil specification requirements in terms of compaction and strength. The selection process should aim to maximise the use of locally available soils and with careful evaluation it is possible to use or incorporate „poor or marginal soils? within fill areas and embankments. Fill material needs to be placed at a moisture content such that it is neither too wet to be stable and trafficable or too dry to be properly compacted. High moisture content / low strength boulder clay soils can be suitable for use as fill in low height embankments (i.e. 2 to 2.5m) but not suitable for trafficking by earthwork plant without using a geotextile separator and granular fill capping layer. Hence, it is vital that the earthworks contractor fully understands the handling properties of the soils, as for many projects this is effectively governed by the trafficability of earthmoving equipment. 2. TRADITIONAL GROUND INVESTIGATION METHODS For road projects, a principal aim of the ground investigation is to classify the suitability of the soils in accordance with Table 6.1 from Series 600 of the NRA Specification for Road Works (SRW), March 2000. The majority of current ground investigations for road works includes a combination of the following to give the required geotechnical data: Trial pits Cable percussion boreholes Dynamic probing Rotary core drilling In-situ testing (SPT, variable head permeability tests, geophysical etc.) Laboratory testing The importance of „phasing? the fieldwork operations cannot be overstressed, particularly when assessing soil suitability from deep cut areas. Cable percussion boreholes are normally sunk to a desired depth or „refusal? with disturbed and undisturbed samples recovered at 1.00m intervals or change of strata. In many instances, cable percussion boring is unable to penetrate through very stiff, hard boulder clay soils due to cobble, boulder obstructions. Sample disturbance in boreholes should be prevented and loss of fines is common, invariably this leads to inaccurate classification. Trial pits are considered more appropriate for recovering appropriate size samples and for observing the proportion of clasts to matrix and sizes of cobbles, boulders. Detailed and accurate field descriptions are therefore vital for cut areas and trial pits provide an opportunity to examine the soils on a larger scale than boreholes. Trial pits also provide an insight on trench stability and to observe water ingress and its effects. A suitably experienced geotechnical engineer or engineering geologist should supervise the trial pitting works and recovery of samples. The characteristics of the soils during trial pit excavation should be closely observed as this provides information on soil sensitivity, especially if water from granular zones migrates into the fine matrix material. Very often, the condition of soil on the sides of an excavation provides a more accurate assessment of its in-situ condition. 3. SOIL CLASSIFICATION Soil description and classification should be undertaken in accordance with BS 5930 (1999) and tested in accordance with BS 1377 (1990). The engineering description of a soil is based on its particle size grading, supplemented by plasticity for fine soils. For many of our glacial till, boulder clay soils (i.e. „mixed soils?) difficulties arise with descriptions and assessing engineering performance tests. As outlined previously, Irish boulder clays usually comprise highly variable proportions of sands, gravels and cobbles in a silt or clay matrix. Low plasticity soils with fines contents of around 10 to 15% often present the most difficulties. BS 5930 (1999) now recognises these difficulties in describing „mixed soils? – the fine soil onstituents which govern the engineering behaviour now takes priority over particle c size. A key parameter (which is often underestimated) in classifying and understanding these soils is permeability (K). Inspection of the particle size gradings will indicate magnitude of permeability. Where possible, triaxial cell tests should be carried out on either undisturbed samples (U100?s) or good quality core samples to evaluate the drainage characteristics of the soils accurately. Low plasticity boulder clay soils of intermediate permeability (i.e. K of the order of -5 to 10-7 m/s) can often be „conditioned? by drainage measures. This usually entails 10 the installation of perimeter drains and sumps at cut areas or borrow pits so as to reduce the moisture content. Hence, with small reduction in moisture content, difficult glacial till soils can become suitable as engineering fill. 4. ENGINEERING PERFORMANCE TESTING OF SOILS Laboratory testing is very much dictated by the proposed end-use for the soils. The engineering parameters set out in Table 6.1 pf the NRA SRW include a combination of the following: Moisture content Particle size grading Plastic Limit CBR Compaction (relating to optimum MC) Remoulded undrained shear strength A number of key factors should be borne in mind when scheduling laboratory testing: Compaction / CBR / MCV tests are carried out on < 20mm size material. Moisture content values should relate to < 20mm size material to provide a valid comparison. Pore pressures are not taken into account during compaction and may vary considerably between laboratory and field. Preparation methods for soil testing must be clearly stipulated and agreed with the designated laboratory. Great care must be taken when determining moisture content of boulder clay soils. Ideally, the moisture content should be related to the particle size and have a corresponding grading analysis for direct comparison, although this is not always practical. In the majority of cases, the MCV when used with compaction data is considered to offer the best method of establishing (and checking) the suitability characteristics of a boulder clay soil. MCV testing during trial pitting is strongly recommended as it provides a rapid assessment of the soil suitability directly after excavation. MCV calibration can then be carried out in the laboratory at various moisture content increments. Sample disturbance can occur during transportation to the laboratory and this can have a significant impact on the resultant MCV?s. IGSL has found large discrepancies when performing MCV?s in the field on low plasticity boulder clays with those carried out later in the laboratory (2 to 7 days). Many of the aforementioned low plasticity boulder clay soils exhibit time dependant behaviour with significantly different MCV?s recorded at a later date – increased values can be due to the drainage of the material following sampling, transportation and storage while dilatancy and migration of water from granular lenses can lead to deterioration and lower values. This type of information is important to both the designer and earthworks contractor as it provides an opportunity to understand the properties of the soils when tested as outlined above. It can also illustrate the advantages of pre-draining in some instances. With mixed soils, face excavation may be necessary to accelerate drainage works. CBR testing of boulder clay soils also needs careful consideration, mainly with the preparation method employed. Design engineers need to be aware of this, as it can have an order of magnitude difference in results. Static compaction of boulder clay soils is advised as compaction with the 2.5 or 4.5kg rammer often leads to high excess pore pressures being generated – hence very low CBR values can result. Also, curing of compacted boulder clay samples is important as this allows excess pore water pressures to dissipate. 5. ENGINEERING CLASSIFICATION OF SOILS In accordance with the NRA SRW, general cohesive fill is categorised in Table 6.1 as follows: 2A Wet cohesive 2B Dry cohesive 2C Stony cohesive 2D Silty cohesive The material properties required for acceptability are given and the design engineer then determines the upper and lower bound limits on the basis of the laboratory classification and engineering performance tests. Irish boulder clay soils are predominantly Class 2C. Clause 612 of the SRW sets out compaction methods. Two procedures are available: Method Compaction End-Product Compaction End product compaction is considered more practical, especially when good compaction control data becomes available during the early stages of an earthworks contract. A minimum Target Dry Density (TDD) is considered very useful for the contractor to work with as a means of checking compaction quality. Once the material has been approved and meets the acceptability limits, then in-situ density can be measured, preferably by nuclear gauge or sand replacement tests where the stone content is low. As placing and compaction of the fill progresses, the in-situ TDD can be checked and non-conforming areas quickly recognised and corrective action taken. This process requires the design engineer to review the field densities with the laboratory compaction plots and evaluate actual with „theoretical densities?. 6. SUPPLEMENTARY GROUND INVESTIGATION METHODS FOR EARTHWORKS The more traditional methods and procedures have been outlined in Section 2. The following are examples of methods which are believed to enhance ground investigation works for road projects: Phasing the ground investigation works, particularly the laboratory testing Excavation & sampling in deep trial pits Large diameter high quality rotary core drilling using air-mist or polymer gel techniques Small-scale compaction trials on potentially suitable cut material PHASING Phasing ground investigation works for many large projects has been advocated for many years – this is particularly true for road projects where significant amounts of geotechnical data becomes available over a short period. On the majority of large ground investigation projects no period is left to „digest? or review the preliminary findings and re-appraise the suitability of the methods. With regard to soil laboratory testing, large testing schedules are often prepared with no real consideration given to their end use. In many cases, the schedule is prepared by a junior engineer while the senior design engineer who will probably design the earthworks will have no real involvement. It is highlighted that the engineering performance tests are expensive and of long duration (e.g. 5 point compaction with CBR & MCV at each point takes in excess of two weeks). When classification tests (moisture contents, particle size analysis and Atterberg Limits) are completed then a more incisive evaluation can be carried out on the data and the engineering performance tests scheduled. If MCV?s are performed during trial pitting then a good assessment of the soil suitability can be immediately obtained. DEEP TRIAL PITS The excavation of deep trial pits is often perceived as cumbersome and difficult and therefore not considered appropriate by design engineers. Excavation of deep trial pits in boulder clay soils to depths of up to 12m is feasible using benching techniques and sump pumping of groundwater. In recent years, IGSL has undertaken such deep trial pits on several large road ground investigation projects. The data obtained from these has certainly enhanced the geotechnical data and provided a better understanding of the bulk properties of the soils. It is recommended that this work be carried out following completion of the cable percussion boreholes and rotary core drill holes. The groundwater regime within the cut area will play an important role in governing the feasibility of excavating deep trial pits. The installation of standpipes and piezometers will greatly assist the understanding of the groundwater conditions, hence the purpose of undertaking this work late on in the ground investigation programme. Large representative samples can be obtained (using trench box) and in-situ shear strength measured on block samples. The stability of the pit sidewalls and groundwater conditions can also be established and compared with levels in nearby borehole standpipes or piezometers. Over a prominent cut area of say 500m, three deep trial pits can prove invaluable and the spoil material also used to carry out small-scale compaction trials. From a value engineering perspective, the cost of excavating and reinstating these excavations can be easily recovered. A provisional sum can be allocated in the ground investigation and used for this work. HIGH QUALITY LARGE DIAMETER ROTARY CORE DRILLING This system entails the use of large diameter rotary core drilling techniques using air mist or polymer gel flush. Triple tube core drilling is carried out through the overburden soils with the recovered material held in a plastic core liner. Core recovery in low plasticity boulder clay has been shown to be extremely good (typically in excess of 90%). The high core recovery permits detailed engineering geological logging and provision of samples for laboratory testing. In drumlin areas, such as those around Cavan and Monaghan, IGSL has found the use of large diameter polymer gel rotary core drilling to be very successful in recovering very stiff / hard boulder clay soils for deep road cut areas (where cable percussion boreholes and trial pits have failed to penetrate). In-situ testing (vanes, SPT?s etc) can also be carried out within the drillhole to establish strength and bearing capacity of discrete horizons. Large diameter rotary drilling costs using the aforementioned systems are typically 50 to 60% greater than conventional HQ core size, but again from a value engineering aspect can prove much more worthwhile due to the quality of geotechnical information obtained. SMALL-SCALE COMPACTION TRIALS The undertaking of small-scale compaction trials during the ground investigation programme is strongly advised, particularly where „marginally suitable? soils are present in prominent cut areas. In addition to validating the laboratory test data, they enable more realistic planning of the earthworks and can provide considerable cost savings. The compaction trial can provide the following: Achievable field density, remoulded shear strength and CBR Establishing optimum layer thickness and number of roller passes Response of soil during compaction (static v dynamic) Monitor trafficability & degree of rutting. A typical size test pad would be approximately 20 x 10m in plan area and up to 1.5m in thickness. The selected area should be close to the cut area or borrow pit and have adequate room for stockpiling of material. Earthwork plant would normally entail a tracked excavator (CAT 320 or equivalent), 25t dumptruck, D6 dozer and either a towed or self-propelled roller. In-situ density measurement on the compacted fill by nuclear gauge method is recommended as this facilitates rapid measurement of moisture contents, dry and bulk densities. It also enables a large suite of data to be generated from the compacted fill and to assess the relationship between degree of compaction, layer thickness and number of roller passes. Both disturbed and undisturbed (U100) samples of the compacted fill can be taken for laboratory testing and validation checks made with the field data (particularly moisture contents). IGSL?s experience is that with good planning a small-scale compaction trial takes two working days to complete. 7. SUPERVISION OF GROUND INVESTIGATION PROJECTS Close interaction and mutual respect between the ground investigation contractor and the consulting engineer is considered vital to the success of large road investigation projects. A senior geotechnical engineer from each of the aforementioned parties should liase closely so that the direction and scope of the investigation can be changed to reflect the stratigraphy and ground conditions encountered. The nature of large ground investigation projects means that there must be good communication and flexibility in approach to obtaining data. Be prepared to compromise as methods and procedures specified may not be appropriate and site conditions can quickly change. From a supervision aspect (both contractor and consulting engineer), the emphasis should be on the quality of site-based geotechnical engineers, engineering geologists as opposed to quantity where work is duplicated. 8. GEOTECHNICAL CERTIFICATION The Department of Transport (UK) prepared a document (HD 22/92) in 1992 for highway schemes. This sets out the procedures and documentation to be used during the planning and reporting of ground investigations and construction of earthworks. Road projects involving earthmoving activities or complex geotechnical features must be certified by the Design Organisation (DO) - consulting engineer or agent authority. The professional responsibility for the geotechnical work rests with the DO. For such a project, the DO must nominate a chartered engineer with appropriate geotechnical engineering experience. He/she is referred to as the Geotechnical Liaison Engineer (GLE) and is responsible for all geotechnical matters including preparation of procedural statements, reports and certificates. Section 1.18 of HD 22/92 states that “on completion of the ground investigation works, the DO shall submit a report and certificate containing all the factual records and test results produced by the specialist contractor together with an interpretative report produced either by the specialist contractor or DO”. The DO shall then prepare an Earthworks Design Report – this report is the Designer?s detailed report on his interpretation of the site investigation data and design of earthworks. The extent and closeness of the liaison between the Project Manager and the GLE will very much depend on the nature of the scheme and geotechnical complexities discovered as the investigation and design proceed. After the earthworks are completed, a geotechnical feedback report is required and is to be prepared by the DO. This addresses the geotechnical issues and problems encountered during the construction earthworks and corrective action or measures taken. Certificates are prepared by the DO to sign off on the geotechnical measures carried out (e.g. unstable slopes, karst features, disused / abandoned mine workings, ground improvement systems employed, etc). 9. CONCLUSIONS Close co-operation is needed between ground investigation contractors and consulting engineers to ensure that the geotechnical investigation work for the roads NDP can be satisfactorily carried out. Many soils are too easily rejected at selection / design stage. It is hoped that the proposed methods outlined in this paper will assist design engineers during scoping and specifying of ground investigation works for road projects. With modern instrumentation, monitoring of earthworks during construction is very straightforward. Pore water pressures, lateral and vertical movements can be easily measured and provide important feedback on the performance of the engineered soils. Phasing of the ground investigation works, particularly laboratory testing is considered vital so that the data can be properly evaluated. Disposal of „marginal? soils will become increasingly difficult and more expensive as the waste licensing regulations are tightened. The advent of landfill tax in the UK has seen thorough examination of all soils for use in earthworks. This is likely to provide a similar incentive and challenge to geotechnical and civil engineers in Ireland in the coming years. A certification approach comparable with that outlined should be considered by the NRA for ground investigation and earthwork activities.