土方工程的地基勘察与施工毕业论文外文翻译

《土方工程的地基勘察与施工毕业论文外文翻译》由会员分享，可在线阅读，更多相关《土方工程的地基勘察与施工毕业论文外文翻译（20页珍藏版）》请在装配图网上搜索。

1、附录附录：Design and Execution of Ground Investigation For EarthworksPAUL QUIGLEY, FGSIrish Geotechnical Services LtdAbstractThe design and execution of ground investigation works for earthwork projects has become increasingly important as the availability of suitable disposal areas becomes limited and c

2、osts 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 fo

3、r incorporation with ground investigations and earthworks.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 plastici

4、ty 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 ca

5、n 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

6、 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 西安工业大学学士学位论文type silts and fine sand

7、 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

8、 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 u

9、se 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 projec

10、ts this is effectively governed by the trafficability of earthmoving equipment.2. Tradtional 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 f

11、or 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 te

12、sts, geophysical etc.) Laboratory testingThe 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 reco

13、vered 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 in

14、accurate 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 opportu

15、nity 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

16、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 accura

17、te assessment of its in-situ condition.3. Soil ClassificationSoil 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 plasticit

18、y 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 c

19、lay 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 param

20、eter (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 (U100s) or good quality cor

21、e 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 cu

22、t 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 SoilsLaboratory testing is very much dictated by the proposed end-use for the soils

23、. 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 strengthA number of key factors should be borne in mind when scheduling labo

24、ratory 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. Preparati

25、on 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

26、 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 a

27、s 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 res

28、ultant 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 low plasticity boulder clay soils exhibit time dependant behaviour with significantly different MC

29、Vs 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

30、 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 boulde

31、r 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

32、 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 SoilsIn accordance with the NRA SRW, general cohesive fill is cate

33、gorised 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 the upper and lower bound limits on the basis of the laboratory classification and engineering perf

34、ormance 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 compaction is considered more practical, especially when good compaction control data becomes availa

35、ble 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,

36、 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 fiel

37、d densities with the laboratory compaction plots and evaluate actual with theoretical densities.6. Supplementary Ground Investigation Methods For EarthworksThe more traditional methods and procedures have been outlined in Section 2. The following are examples of methods which are believed to enhance

38、 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 s

39、uitable cut material6.1 PhasingPhasing 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

40、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 ju

41、nior 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 c

42、lassification 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 MCVs are performed during trial pitting then a good assessment of the soil suitability

43、 can be immediately obtained.6.2 Deep Trial PitsThe 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 techniq

44、ues 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 r

45、ecommended 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 piezomete

46、rs 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

47、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

48、 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.6.3 High Quality Large Diameter Rotary Core DrillingThis system entails the use of large diameter ro

49、tary 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 9

50、0%). 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 st

51、iff / hard boulder clay soils for deep road cut areas (where cable percussion boreholes and trial pits have failed to penetrate). In-situ testing (vanes, SPTs etc) can also be carried out within the drillhole to establish strength and bearing capacity of discrete horizons.Large diameter rotary drill

52、ing 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.6.4 Small-Scale Compaction TrialsThe undertaking of small-scale

53、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 cos

54、t 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 p

55、ad 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

56、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 t

57、o 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). IGSLs experien

58、ce 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 roa

59、d 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 me

60、ans 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 shoul

61、d be on the quality of site-based geotechnical engineers, engineering geologists as opposed to quantity where work is duplicated.8. Geotechnical CertificationThe Department of Transport (UK) prepared a document (HD 22/92) in 1992 for highway schemes. This sets out the procedures and documentation to

62、 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 responsibili

63、ty 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

64、 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 interpretati

65、ve report produced either by the specialist contractor or DO”. The DO shall then prepare an Earthworks Design Report this report is the Designers 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 g