渦北煤礦1.5Mta新井設計含5張CAD圖-采礦工程.zip,煤礦,1.5,Mta,設計,CAD,采礦工程 英文原文 The performance of pressure cells for sprayed concrete tunnel linings C . R . I . C L AY TO N,J. P. VA N D E R B E R G , G . H E Y M A N N, A . V. D. B I C A a n d V. S . H O P E Abstract:The paper examines the factors that affect the performance of tangential cells embedded in shotcrete tunnel linings. New data, derived from field monitoring, numerical modelling,and calibration tests carried out to simulate the embedment and crimping processes, are presented. These suggest that although well-designed embedded total pressure cells will have cell action factors close to unity, they cannot be assumed to provide reasonable estimates of the stresses within sprayed concrete linings, unless the influences of installation effects, temperature changes, shrinkage and subsequent crimping can be taken into account. Keywords: field instrumentation; tunnels. Introduction The pressure cells used for measuring the compressive stresses in shotcrete tunnel linings generally consist of two stainless steel plates with a thin fluid- filled cavity between them. The cavity is connected either to a membrane-type bypass valve or to a vibrating-wire pressure transducer. The use of other direct-stress instruments has been reported in the literature, although infrequently. Pressure cells are typically installed in one of two orientations: radial, to record the stress between the sprayed concrete and the ground surrounding the tunnel; and tangential, to record the hoop stress within the tunnel lining itself. This paper considers only tangential cells. Despite their widespread use in practice, there has been very little research reported in the literature on the use and behaviour of shotcrete pressure cells. Many practitioners remain doubtful of the ability of embedded pressure cells to measure the actual stresses in concrete tunnel linings. In a previous paper reviewing instrumentation for sprayed concrete lined tunnels the present authors noted some of the potential difficulties, stating that it was `extremely unlikely that embedded cells be used for monitoring the actual stress in a tunnel lining'. Yet, potentially, pressure cells are a valuable source of information that might be used to assess whether tunnel design assumptions are justified, and this paper therefore reports the findings of our further research into this important topic. Factors affecting the pressures recorded by tangential pressure cells in tunnel linings Direct stress measurement within any medium is made difficult by the many factors that can affect the results. In the case of tangential pressure cells embedded in shotcrete our recent experiences during tunnel monitoring suggest that these are as follows. Cell properties The cell should be constructed so that the stresses in the shotcrete are not significantly modified by its presence. Since the compressibility of the fluid in the cell is less than the surrounding materials it will under-read, but this can largely be compensated for by making the cell wide and thin. The use of cell fluids such as mercury or oil will affect not only the compressibility of cells but also their temperature sensitivity. Changes in temperature will expand the fluid against the surrounding, relatively rigid cell metal and surrounding concrete, and will produce a change in measured stress. Installation effects The inadvertent formation of cavities around the cell during shotcreting will lead to a soft measurement system, which will subsequently under-read. Incorrect positioning of the cell within the lining, rotating it towards the radial direction, can also cause it to under-read somewhat, because radial stresses are typically less than 10% of tangential. Indeed the actual thickness of the lining at the point of installation will also affect the interpretation of the stress measurements. Post-installation factors As noted above, temperature changes can be expected to lead to changes in measured stresses. Shrinkage during the early life of the shotcrete will result in changes in the recorded stress that are not due to external stress changes. Crimping, which is often undertaken to ensure that pressure cells are properly bedded within the shotcrete , can provide a significant offset to the measured pressures. Numerical and physical experiments, and results from monitoring Numerical modelling and physical simulation have been carried out to assess the actual performance of some stress cells used in practice, and to place their performance in the context of other cell designs. Numerical modelling to assess the effects of cell fluid To examine the effect of cell fluid on cell performance two idealised circular cells embedded in a block of concrete were modelled under axisymmetric conditions using the finite element package LUSAS. The geometry of the cells and the material properties modelled are shown in Fig. 1. The 160 mm diameter cell is somewhat larger than many of the cells currently in use, whereas the 80 mm cell is smaller, and was considered by the authors to be likely to have an excessive T/D ratio. In the first numerical experiment the effect of the bulk modulus of the cell fluid was investigated, by applying a constant external axial stress and varying the cell cavity pressure . The bulk modulus equivalent to each cell action factor was calculated by integrating the displacements along the surface of the cell cavity. Fig. 2 shows the considerable influence of bulk modulus on cell action factor, but it also shows that when reasonable cell geometries are used cell action factors remain tolerably close to unity when oil is substituted for mercury. Fig. 1. Geometry of cells and properties of materials used during numerical modelling: (a) idealised pressure cell; (b) geometry modelled; (c) material properties Fig. 2. Effect of bulk modulus of cell fluid on cell action factor Physical simulation Calibration tests were conducted to evaluate the performance of the vibrating-wire mercury-filled pressure cells, in three phases: (a) During the first phase the manufacturer's calibration of the pressure cells was checked by conducting an air pressure calibration on all the cells used.This was done in a 1 m diameter chamber, in the laboratory. (b) The second phase of the experimental work was conducted to investigate whether tangential cells installed under ideal and controlled conditions could produce reliable results. This was done by installing two pressure cells in a precast concrete slab, constructed in the laboratory. (c) The final phase of the experimental work was designed to investigate the performance of the tangential cells under 'working conditions', as well as to investigate ways of installing the cells to improve their performance. This was done by installing tangential pressure cells in shotcrete slabs, formed in a tunnel under working conditions. The cells used for the experimental work were mercury-filled vibrating-wire cells supplied by Geokon, and with a full-scale range of 20 MPa (Fig. 3). All the pressure measurements were calculated using the temperature correction supplied by the manufacturer. Fig. 3. Vibrating-wire mercury-filled concrete stress cell The second phase of the calibration testing was carried out to investigate the performance of the tangential pressure cells under ideal and controlled conditions. For this experiment two cells were embedded in a 25 MPa ready-mix concrete slab, 1.0 m high, 1.0 m wide and 0.3 m thick. The two cells were tied to a cage constructed from reinforcing bar meshes, which were identical to those in use in the Heathrow Terminal 4 station tunnels. The experimental set-up is shown in Fig. 4, except that in the first set of experiments two bare cells were used. One bare cell and one precast cell were used in a subsequent experiment, described later in this paper. Fig. 4. Layout of cells embedded in concrete panel During the curing period the slab temperature increased to about 32°C, and afterwards decreased slowly over several days. Monitoring was carried out until the cell temperatures reached equilibrium with the laboratory environment (Fig. 5). Fig. 5. Temperatures measured after casting cells in ready-mixed concrete At each load increment the cell readings were observed to stabilise rapidly: creep effects were not apparent. The value of cell action factor was subsequently calculated from pressure cell readings and average applied vertical stresses . The final phase of the experimental work consisted of the evaluation of the tangential pressure cells installed under `working conditions'. This was done by placing two pressure cells in each of two slabs, similar to the above but constructed using shotcrete in a tunnel at Heathrow Terminal 4. Because the results of the experiment on the cells installed in the concrete slab showed that under ideal conditions the cells seem to perform satisfactorily, it was argued that failure under working conditions might result from installation effects. A major difficulty with the installation of tangential pressure cells is ensuring that no voids are formed in `shadow zones' around the cell during shotcreting. It was therefore decided to precast one of the cells in each of the two slabs in a tapered concrete block, designed to prevent the formation of shadow zones (Fig. 6). Fig. 6. Detail of cell cast in precast concrete Discussion Theoretical considerations suggest that a well-designed embedded cell, with high stiffness and a low aspect ratio (T/D), should have a cell action factor close to unity. Our experiments on commercially available cells support this view. The ability of a cell to measure the applied pressure correctly is dependent upon additional factors, however. Offsets due to temperature, crimping and shrinkage must be properly taken into account. The quality of cell installation must be assessed. Although manufacturers routinely supply temperature correction factors for vibrating-wire cells, these correct for the sensitivity of the transducer alone. For a 160 mm radial cell filled with mercury the authors' numerical modelling results suggest that a temperature change of 20°C will produce a pressure change of the order of 2 MPa. Oil-filled cells can be expected to be more temperature sensitive. A 20°C temperature change might produce about a 3 MPa pressure increase, which is of the same order as the tangential stress found in many completed shotcrete tunnel linings. To the authors' knowledge, no estimates of the increase in measured stress induced by shrinkage have ever been reported in the literature. In order to make an initial estimate the data from the authors' laboratory experiments were reprocessed, using only those data obtained when the concrete slabs were unloaded. If crimping is carried out then the zero offset of the cell is permanently altered. In a real installation the absolute pressure can be recovered only if the pressure change during crimping is carefully recorded. It is suggested that, although crimping is unnecessary if cells are well-designed and installation is good, the initial gradient of the crimping curve should provide a good guide to the cell action factor of the installed cell, with high crimping gradients indicating satisfactory cells. The pressure increases caused by crimping can be eliminated by subtracting them from the values subsequently recorded. Conclusions Using numerical and physical experiments, coupled with field observations, this paper has for the first time attempted a rational assessment of the many factors that may lead to embedded shotcrete pressure cells misreading. The data suggest that, unless installation defects are present, the cell action factors of well-designed shotcrete pressure cells are likely to be near to 1. However, other factors need to be taken into account before embedded pressure cell data can be used to determine the true stress in a tunnel lining. Temperature changes immediately after cell placement will be large, and, coupled with the high rate of shrinkage that occurs during the early life of shotcrete, will prevent satisfactory stress measurement during this period. Seasonal temperature changes will cause further changes in pressure cell readings. Strains due to shrinkage of the shotcrete may also significantly increase the measured stresses. Our data suggest that it is possible to predict the temperature sensitivity of the shell/shotcrete system using numerical modelling. Field data, laboratory measurement and estimates based upon an analytical approach are in good agreement. After temperature changes due to cement hydration have ceased, the shape of the crimping curve can be used to assess the quality of cell installation. However, the crimping procedure will generate offset pressures that may be of the same order of magnitude as the actual pressure to be measured in most shotcrete linings. Measurements made after the crimping procedure is completed must be corrected by subtracting the pressure increase observed during crimping. If shadow zones cannot be prevented during installation then the use of precast cells may be advantageous, although the cell action factor of the installation will be modified. The various factors influencing the measurement of the absolute stress in a shotcrete lining cannot be taken account of when routinely interpreting pressure cell data, without the benefit of careful calibration, numerical estimates of thermal sensitivity, and experimental determinations of the effects of shrinkage. We have shown that the effects of temperature, shrinkage and crimping will probably be large, and of the order of the stresses to be measured. However, the cell action factors of well-designed and well-installed pressure cells will be close to unity and, as we have shown, it should be possible to take account of the effects of temperature changes and shrinkage, to estimate the quality of the installation, and to correct forcrimping offset. Despite the potential difficulties the authors believe that tangential pressure cells can still be useful in many tunnelling applications, but only provided great care is taken in the interpretation of their measurements. Acknowledgements The authors gratefully acknowledge the support of Heathrow Express, Mott MacDonald Consulting Engineers, and the Engineering and Physical Sciences Research Council of the UK, and the help of Mr J. Barrie Sellers, President of Geokon, Inc.,USA, in reviewing the manuscript. The work described in this paper forms part of a wider research programme now being carried out by the University of Southampton, UK, into the behaviour of SCL tunnels. 中文譯文 噴射混凝土巷道應力測量儀的性能 C.R.I.克萊頓，J.P.范德伯格，G.霍曼，A.V.D.哈曼和V.S.霍普 摘要：本文研究了影響噴射混凝土巷道應力測量儀性能的因素。新數據通過實地檢測、數字模擬、模擬埋設標定試驗和褶曲變化進程等進行派生的表達。這些數據表明，雖然精心設計的應力測量儀測出的數據很接近圍巖整體運動規(guī)律，但是它們不能被假定為對噴射混凝土巷道圍巖應力提供了合理的估計，除非將安裝影響、溫度變化、圍巖收縮及后續(xù)的褶曲變化等因素考慮在內。 關鍵詞：實地檢測；巷道 1前言 用來測量噴射混凝土巷道壓縮應力的應力測量儀（以后簡稱測力儀）通常由兩個不銹鋼板組成，兩個板之間有一個充滿液體的管。這個管一般和一個膜式旁路閥門或一個弦式壓力傳感器連接。在文獻中，也提到了一些其他測量應力的器材的作用，雖然不常見。測力儀通常安裝在兩個方向之一：徑向，記錄噴射的混凝土與巷道圍巖之間的應力；切向，記錄巷道內的切應力。本文認為只有切向應力。 雖然它們在實踐中廣泛使用，但在研究報告文獻中很少有介紹噴射混凝土巷道測力儀的使用和作用。很多學者仍然保留著對嵌入式測力儀能夠測量噴射混凝土巷道實際應力的性能的懷疑。在前一篇審查噴射混凝土巷道測力儀性能的文章中，作者指出了一些潛在困難，特別說明嵌入式測力儀用于監(jiān)測巷道實際應力是極不可能的。然而，潛在的測力儀是一種寶貴的信息，可能被用來評估巷道設計假設是否合理，因此，這篇文章在這個重要的項目中報告了我們進一步研究的成果。 2切向測力儀測量巷道應力的影響因素 由于很多因素可以影響結果，所以在任何媒體中直接測量都很困難。在切向測力儀嵌入混凝土的情況下，在巷道監(jiān)測過程中，我們最近的經驗表明如下所示。 2.1測力儀特性 測力儀應該被改進，以便巷道中的壓力不會被它的存在而受到明顯改變。當測力儀中的流體的可壓縮性小于周圍材料，它會讀不出數據，但這可以在很大程度上通過將測力儀變寬變長的方法來彌補。測力儀中的流體（如汞或油）的使用不僅會影響測力儀的可壓縮性，而且會影響他們的溫度敏感性。溫度的變化將促使流體對抗環(huán)境、相對剛性的測力儀金屬和周圍的混凝土，并且會使測量的應力產生變化。 2.2安裝影響 噴漿過程中，在測力儀周圍無意形成的空隙會導致一個松軟的測量環(huán)境，這就會使測量儀讀不出數據。不正確安裝的測量儀，旋轉它往徑向，有時也會導致讀不出數據，這是因為徑向應力一般比切向應力小10%。事實上，實際安裝時的襯砌厚度也會影響應力測量的結果。 2.3安裝后的影響因素 如上所述，溫度的變化將會導致實測應力變化。早期噴漿中的收縮過程導致應力記錄的變化不取決于外部應力的變化。經常進行褶曲以確保測力儀正常嵌入巷道內，可以提供一個明顯的偏移測量應力。 3數字模擬與物理實驗和檢測結果 數字和物理模擬實驗已進行，用來評估一些測力儀在實踐中的性能，并且將這些性能用于一些其它測力儀的設計中去。 3.1數字模擬實驗評估壓力計流體的影響 為了檢驗測力儀中流體對測力儀性能的影響，參照實驗——將兩個圓形測力儀以軸對稱方式嵌入混凝土塊中，使用有限元包LUSAS進行測定。測力儀的幾何結構和材料屬性參照圖如圖1所示。160毫米直徑的測力儀比許多目前正使用的測力儀要大一點，而80毫米直徑的要小一點，作者認為可能是T/D比較大。在第一個數字模擬實驗中，通過應用一個恒定的外部軸向應力和不同的測力儀管內應力，調查了測力儀流體體積彈性模量的影響。體積彈性模量相當于通過整體的測力儀管曲面位移計算每一個應力單元。圖2顯示了應力變化因素體積彈性模量的相當大的影響力，但同時還顯示了當應用合理的幾何形狀時，在用汞替代油的情況下，應力單元變化情況仍和整體一致。 圖1 測力儀的幾何結構和用于實驗的材料屬性 圖2 測力儀流體體積彈性模量的影響因素 3.2物理模擬實驗 用來評估弦式汞應力測力儀性能的校準測試分為三個階段： 1）在第一階段，通過對所有使用的測力儀進行一個空氣壓力試驗來檢查制造商校準過的測力儀。這個實驗是在實驗室中一個1米直徑的空間中進行的。 2）實驗工作的第二階段是研究測力儀在理想和能控制的條件下安裝，到底哪個能得出可靠的結果。這通過在實驗室中構建的預制混凝土板中安裝兩個測力儀來進行。 3）最后一個階段是調查切向測力儀在工作條件下的性能，以及研究如何通過改變安裝方法來改善測力儀的性能。這通過在處于工作條件下的巷道中形成的混凝土板中安裝切向測力儀來實現。 用于實驗的弦式汞測力儀都質優(yōu)價廉，而且測量范圍達到20兆帕（如圖3）。所有的應力測量都通過制造商提供的溫度修正來進行計算。 圖3 弦式汞應力測量儀 校準實驗的第二階段是研究切向測力儀在理想和現實條件下的性能。在這個實驗中，將兩個測力儀嵌入拌好的混凝土板中，這個板高1.0米，寬1.0米，厚0.3米。兩個測力儀被綁定到一個用鋼筋加固的網格籠中，這個籠和希思羅機場4號站隧道中所使用的是完全相同的。實驗設置如圖4所示，只是在第一組實驗中使用了兩個原裝的測力儀。本文稍后會介紹，在隨后的實驗中使用了一個原裝測力儀和一個預制的測力儀。 在固化階段，鋼坯溫度增長到32°C，在隨后的幾天，溫度緩緩下降。監(jiān)測一直進行到測力儀溫度和實驗室環(huán)境平衡為止（如圖5）。 圖4 嵌入混凝土板中測力儀的布局 圖5 測力儀嵌入混凝土后的溫度變化 隨著每個增量的加載，測力儀的讀數迅速穩(wěn)定：蠕變影響不明顯。隨后通過測力儀讀數和提供的垂直應力的平均值來計算測力儀單位應力值。實驗的最后階段包括對處于工作條件下的切向測力儀性能的評估。將兩個測力儀分別放在兩個板中，和上述的相似，但使用的是希思羅機場4號站隧道的混凝土板。因為這個實驗的結果表明在理想條件下，測力儀似乎表現得更讓人滿意，有人認為在工作條件下會失敗可能是安裝影響所導致的。安裝切向測力儀的一大困難是確保在處于混凝土中的測力儀周圍沒有空隙所形成的“陰影區(qū)”。因此，當局決定在一個圓錐形的混過凝土塊中預制兩個測力儀中的一個，旨在防止形成“陰影區(qū)”（如圖6）。 圖6 嵌入混凝土中的測力儀的詳細信息 4討論 理論思考表明一個精心設計的具有高剛性和低長寬比（T/D）的嵌入式測力儀應該有一個單元接近整體。我們對商業(yè)上可用的測力儀的實驗支持這一觀點。然而，一個測力儀能正確測量所施加的應力的能力取決于其它因素。除了溫度的影響，褶曲和壓縮的偏移量也必須適當地考慮在內。必須評估測力儀的安裝質量。 雖然制造商經常為弦式測力儀提供溫度修正，但他們僅僅是對傳感器靈敏度進行了校正。對于160毫米直徑的汞測力儀，作者的數字模擬實驗結果表明溫度每變化20°C，測出的結果會有2兆帕的變化。油測力儀有望有更高的溫度敏感性。20°C的溫度變化可能產生約3兆帕應力的增加，這是在很多已完成的噴射混凝土巷道中發(fā)現的切應力變化的共同規(guī)律。 據作者所知，在已報告的文獻中，沒有因收縮導致已測應力增加的評估。為了使作者從實驗室實驗中得到的初步估計數據得到進一步的處理，當混凝土板卸載時僅用這些提到的數據。 如果進行褶曲，則測力儀的零偏移量會永久改變。在實際安裝中，只有仔細記錄褶曲過程中的應力變化，才能使絕對應力恢復。有人建議，雖然當測力儀經過精心設計，且安裝不出錯時，褶曲是不必要的，但是褶曲曲線的起始梯度應該為安裝好的測力儀提供一個很好的指南，并且褶曲高梯度標示令人滿意的測力儀。褶曲產生的應力增量可以通過隨后的記錄值減去增量來消除。 5結論 通過數字和物理模擬實驗，再加上實地觀測，本文第一次嘗試對眾多影響因素進行理性的評估，這些因素可能會導致對噴射混凝土巷道測力儀做出錯誤判斷。 數據表明，除非安裝缺陷存在，精心設計的測力儀的應力單元值才可能和1接近。然而，只有將其它因素考慮在內之后，嵌入式測力儀得到的數據才能用于確定巷道中的真實應力。 在測力儀布局增大后，溫度會馬上發(fā)生變化，再加上早期發(fā)生在混凝土中的高頻率收縮運動，溫度變化將會給這個時期令人滿意的測量造成困擾。季節(jié)溫度變化將會對測力儀讀數造成進一步的影響。由于混凝土收縮產生的應力也可能使測量的應力大大增加。我們的數據表明，預測使用數字模擬的噴混凝土系統(tǒng)的溫度敏感性是可能的。實測數據、實驗室測量和基于一種解析方法的估算達成了一致。 在水泥水化引起的溫度變化停止后，褶曲曲線的形狀可以用來評估測力儀的安裝質量。然而，褶曲過程將會產生可能和多數巷道中實測應力同一個數量級的應力偏移量。褶曲過程結束后，測量的數據必須通過減去觀測褶曲過程中產生的應力增量進行修正。如果測力儀安裝過程中不能阻止陰影區(qū)的形成，那么使用預制測力儀會更有利，雖然這會使測力儀的安裝因素改變。 當按慣例解釋測力儀數據時，影響噴射混凝土巷道絕對應力測量的各種數據可以不用考慮在內，不包括小心校準、熱靈敏度的數據估算及收縮影響的實驗測定的好處。我們已經說明了溫度、收縮和褶曲的影響可能會很大，包括要測量的應力的順序。不過，精心設計和安裝合理的測力儀應力單元會接近整體，如我們所示，應該盡可能將溫度和收縮的影響考慮在內，評估安裝質量，修正褶曲偏移量。盡管有很多的潛在困難，作者扔堅信切向測力儀在很多巷道的應用程序中是有作用的，但只有在測量中非常認真才能讓它實用。 6鳴謝 作者衷心感謝希思羅機場快遞、莫特 · 麥克唐納咨詢工程師、英國工程與自然科學研究委員會的支持，以及J.巴里 · 塞勒先生的幫助，感謝他們對本文的大力支持。本文描述的實驗形成了一個更廣泛的研究項目，目前被英國南安普頓大學提出，用于研究SCL巷道的表現形式。