毕业设计外文翻译--土方工程的地基勘察与施工(适用于毕业论文外文翻译+中英文对照)

DESIGN AND EXECUTION OF GROUND INVESTIGATION FOR EARTHWORKS 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 constituents which govern the engineering behaviour now takes priority over particle 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 10 5 to 10 7 m s can often be conditioned by drainage measures This usually entails 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 6 1PHASING 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 6 2DEEP 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 6 3HIGH 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 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 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 土方工程的地基勘察与施工土方工程的地基勘察与施工 摘摘 要 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 1 引 引 言言 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