土方工程的地基勘察與施工畢業(yè)論文外文翻譯1

DESIGN AND EXECUTION OF GROUND INVESTIGATION FOR EARTHWORKS PAUL 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 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. 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 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 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 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 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 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 (U100s) 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.土方工程的地基勘察與施工保羅圭格利愛爾蘭巖土工程服務(wù)有限公司摘 要：當(dāng)工程場地的處理面積有限且填方工程費(fèi)用大量增加時(shí)，土方工程的地基勘察設(shè)計(jì)與施工已逐漸地變得重要。由于冰漬土以及含礫粘土的提出使土方工程地基勘察方法的綱要比傳統(tǒng)的勘察方法更詳細(xì)。 本文提出“巖土認(rèn)證”觀點(diǎn)以及對(duì)地基勘察與土方工程相結(jié)合的優(yōu)點(diǎn)加以概要說明。1、引 言許多愛爾蘭含礫粘土的勘察與再利用評(píng)價(jià)使巖土工程師與道路工程師感到為難。這些冰漬土或含礫粘土主要表現(xiàn)為低可塑性而且還含有從粘土到漂石的不同粒徑顆粒。大部分本地粘土與淤泥質(zhì)土中包含不同比例的砂、礫石、卵石、漂石。顆粒級(jí)配控制著土體的行為，而且淤泥使土體性質(zhì)易受天氣變化影響。土體含水量隨著地區(qū)不同而不同，從都柏林硬灰黑含礫粘土的7%到中部、西南部或西北部淺灰色含礫粘土沉積物的20%-25%。含礫粘土吸附水的能力建立的較好但土方工程中計(jì)劃的不恰當(dāng)常導(dǎo)致其擴(kuò)大。一般來說，良好級(jí)配的土體對(duì)于含水量的輕微變大相當(dāng)敏感，將導(dǎo)致強(qiáng)度下降或不適合用作工程回填土。許多含礫粘土（尤其中等淤泥質(zhì)土或良好級(jí)配的砂）在選擇階段已經(jīng)被篩除，但事實(shí)上它們能對(duì)壓縮或強(qiáng)度起到特定的作用。篩選過程應(yīng)盡量使用本地土體或者回填區(qū)或路堤邊性質(zhì)相對(duì)較差的土體，通過仔細(xì)評(píng)價(jià)應(yīng)加以應(yīng)用?；靥畈牧媳仨毐３忠欢ǖ暮浚炔荒芴珴駥?dǎo)致土體不穩(wěn)定也不能太干以致不能被充分壓縮。高含水量、低強(qiáng)度含礫粘土適用于低路堤回填（相當(dāng)于2到2.5米的高度）但不適用于沒有使用土工織布隔離與回填層的土方回填工程。因此，土方工程承包商充分認(rèn)識(shí)土體的處理特性相當(dāng)重要，因?yàn)樵S多工程都受到挖掘設(shè)備通行能力的影響。2、傳統(tǒng)地基勘察方法對(duì)于道路工程來講，地基勘察最基本目標(biāo)是對(duì)土體適用性進(jìn)行類似表6.1的分類，該表源于國家檔案登記處2000年3月版的道路施工規(guī)范。目前大部分道路施工中的地基勘察包含以下提供有關(guān)巖土參數(shù)的試驗(yàn)方法： 取樣孔 靜壓法取樣 動(dòng)力探測 回轉(zhuǎn)鉆進(jìn) 原位測試（標(biāo)準(zhǔn)貫入試驗(yàn)，變水頭滲透試驗(yàn)，巖土物理試驗(yàn)等） 室內(nèi)試驗(yàn)評(píng)價(jià)場地工作的重要性特別是評(píng)價(jià)土體深部取樣區(qū)域的適用性時(shí)不能過分強(qiáng)調(diào)其適用性。靜壓法取樣通常將取樣器下沉至要求深度進(jìn)行取樣，并每間隔一米進(jìn)行取樣。在許多情況下，靜壓法取樣由于卵石、漂石阻礙不能壓入非常堅(jiān)硬的含礫粘土。土樣在鉆孔內(nèi)應(yīng)盡量少擾動(dòng)，但級(jí)配變壞是很正常的，級(jí)配變壞將導(dǎo)致土樣分類不夠精確。取樣孔對(duì)于恢復(fù)適當(dāng)尺寸的土樣以及觀察碎屑巖在卵石、漂石中所占比例來說應(yīng)該是適當(dāng)?shù)?。因此，詳盡且精確的地區(qū)描述取樣區(qū)域以及取樣空來說都相當(dāng)重要，而且還為它們提供了檢查土體在鉆孔范圍以外性質(zhì)的良機(jī)。取樣孔也提供了孔壁穩(wěn)定性的評(píng)價(jià)以及觀察孔壁內(nèi)水進(jìn)入時(shí)所造成的影響。一位有經(jīng)驗(yàn)的巖土工程師或工程地質(zhì)專家應(yīng)監(jiān)督取樣孔工作以及土樣的恢復(fù)。因?yàn)橥翗有再|(zhì)為土樣敏感性提供了信息，所以取樣時(shí)土體性質(zhì)應(yīng)被密切關(guān)注，尤其是水從小顆粒區(qū)域遷移到良好級(jí)配區(qū)域。而且土體在開挖時(shí)的條件為其原位條件提供了一個(gè)相對(duì)精確的評(píng)價(jià)。3、土的分類土的描述與分類應(yīng)該依照英國標(biāo)準(zhǔn)5930（1999）進(jìn)行并依照英國標(biāo)準(zhǔn)1337（1990）進(jìn)行測試。土的工程描述應(yīng)基于按粒徑大小分級(jí)并依照良好級(jí)配土的可塑性進(jìn)行補(bǔ)充。對(duì)于許多冰漬土或含礫粘土（混合土）的難點(diǎn)在于其描述與工程性質(zhì)測試的評(píng)價(jià)。關(guān)于以前的地基勘察綱要，愛爾蘭含礫粘土的粘土與淤泥質(zhì)土中常由易變比例的砂、礫石、卵石組成。良好級(jí)配且含水量為10%-15%的低可塑性土最難進(jìn)行描述與分類?，F(xiàn)在英國標(biāo)準(zhǔn)5930（1999）已認(rèn)識(shí)到描述“混合土”所存在的難點(diǎn)土的良好級(jí)配較之顆粒尺寸對(duì)于控制著土的工程性質(zhì)更優(yōu)越。一個(gè)關(guān)鍵參數(shù)在土分類以及理解過程中經(jīng)常被低估，該參數(shù)就是滲透系數(shù)K。檢查土的顆粒級(jí)配將間接說明土的滲透系數(shù)的大小。假如可能，為了準(zhǔn)確評(píng)價(jià)土體的排水特性，三軸單元試驗(yàn)將采用無擾動(dòng)原狀土樣或高質(zhì)量土樣進(jìn)行試驗(yàn)。低可塑性的中等滲透性含礫粘土(K大約在10-5到10-7米.秒范圍內(nèi))能經(jīng)常通過不同排水條件進(jìn)行“模擬”。其必須在取樣區(qū)域安裝排水邊界以及水坑邊界或借用鉆孔以減少土樣的含水量。因此，由于含水量的小量減少，工程性質(zhì)復(fù)雜的冰漬土也能當(dāng)作合適的工程填土加以應(yīng)用。6