土木工程专业外文翻译---土方工程的地基勘察与施工

1、design and execution of ground investigation for earthworks abstractthe 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 outl

2、ine 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 earth

3、works.1. introductionthe 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 boul

4、ders. 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 t

5、he 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 sensi

6、tive 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 pla

7、nning 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 embank

8、ments. 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 su

9、itable 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 earthmo

10、ving 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

11、 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 testingthe importance of phas

12、ing 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,

13、 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 appropri

14、ate 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. tri

15、al 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

16、 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. engineering performan

17、ce testing of soilslaboratory 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) remou

18、lded undrained shear strengtha 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

19、 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 co

20、ntent 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 c

21、haracteristics 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 ca

22、n occur during transportation to the laboratory and this can have a significant impact on the resultant mcvs.igsl has found large discrepancies when performing mcvs in the field on low plasticity boulder clays with those carried out later in the laboratory (2 to 7 days). many of the aforementioned l

23、ow plasticity boulder clay soils exhibit time dependant behaviour with significantly different mcvs 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

24、 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

25、 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 c

26、ompaction 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.4.

27、 engineering classification of soilsin 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 cohesivethe material properties required for acceptability are given and the design engineer then determines th

28、e 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 compactionend product com

29、paction 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 mat

30、erial 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 rec

31、ognised 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.5. supplementary ground investigation methods for earthworksthe more traditional methods and procedures hav

32、e 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

33、 drilling using air-mist or polymer gel techniques 译文： 土方工程的地基勘察与施工摘 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、

34、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

35、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，该表源于国家档案登记处2000年3月版的道路施工规范。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

36、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。