【正文】 f the existing dam must be an overriding concern. It is not unmon for the dam to have suffered significant distress—often due to the deficiencies that the rehabilitation measures are to address. The dam may be in poor condition at the outset and may possibly be in a marginally stable condition. Therefore, how the rehabilitation work may change the present conditions, both during construction and in the long term, must be assessed, to ensure that it does not adversely affect the safety of the dam. In the following text, a case study is presented as an introduction to the engineering challenges of embankment rehabilitation, with particular reference to the Croton Dam Project. Case Study The Croton Dam Project is located on the Muskegon River in Michigan. The project is owned and operated by the Consumer Power Company. The project structures include two earth embankments, a gated spillway, and a concrete and masonry powerhouse. The earth embankments of this project were constructed of sand with concrete core walls. The embankments were built using a modified hydraulic fill method. This method consisted of dumping the sand and then sluicing the sand into the desired location. Croton Dam is classified as a ??highhazard‘‘ dam and is in earthquake zone 1. As part of the FERC Part 12 Inspection (FERC 1993), an evaluation of the seismic stability was performed for the downstream slope of the left embankment at Croton Dam. The Croton Dam embankment was analyzed in the following manner. Soil parameters were chosen based on standard peration (N) values and laboratory tests, and a seismic study was carried out to obtain the design earthquake. Using the chosen soil properties, a static finiteelement study was conducted to evaluate the existing state of stress in the embankment. Then a onedimensional dynamic analysis was conducted to determine the stress induced by the design earthquake shaking. The available strength was pared with expected maximum earthquake conditions so that the stability of the embankment during and immediately after an earthquake could be evaluated. The evaluation showed that the embankment had a strong potential to liquefy and fail during the design earthquake. The minimum soil strength required to eliminate the liquefaction potential was then determined, and a remendation was made to strengthen the embankment soils by insitu densification. Seismic Evaluation Two modes of failure were considered in the analyses—namely, loss of stability and excessive deformations of the embankment. The following analyses were carried out in succession: (1) Determination of pore water pressure buildup immediately following the design earthquake。 (3) analysis of the loss of stability for postearthquake loading where the loose sand layer in the embankment is pletely liquefied。本文旨在通過對克羅頓堤壩進(jìn)行的的案例分析，介紹大壩評估和修復(fù)過程中會遇到的技術(shù)難題。因此，未來修復(fù)產(chǎn)業(yè)將會蓬勃發(fā)展。大壩建造工程，尤其是土質(zhì)結(jié)構(gòu)工程，在許多方 面已經(jīng)取得進(jìn)步并將繼續(xù)改進(jìn)，特別是在節(jié)約資源和可接受風(fēng)險(xiǎn)水平的測定方面更是需要改進(jìn)。因?yàn)樵擃I(lǐng)域沒有公認(rèn)的標(biāo)準(zhǔn)或唯一的施工程序，設(shè)計(jì)和建造大壩過程中可能會遇到一些工程建設(shè)上的問題。因此，如果沒有統(tǒng)一的設(shè)計(jì)規(guī)范，很難制定出一套嚴(yán)格的對建成大壩的評估制度。但是這些不能被當(dāng)做固定程序，只能充當(dāng)指導(dǎo)，參考，或作為需要觀察，記錄之處的范例。在業(yè)主同意施工后，工程師應(yīng)該檢測幾個關(guān)鍵因素，這些因素相關(guān)的，結(jié)合適當(dāng)?shù)撵o態(tài)和動態(tài)穩(wěn)定性的計(jì)算結(jié)果，就形成了評估報(bào)告的基礎(chǔ)。 修復(fù)措施 影響堤壩性能的主要因素有： (1)滲流 ( 2)穩(wěn)定性 （ 3）超高。失穩(wěn)則會導(dǎo)致壩體開裂，反過來會導(dǎo)致滲漏和腐蝕。加高路堤邊坡穩(wěn)定性通常要通過填平斜坡或是加重壓腳。如果擔(dān)心快速水位下降情況下的上流坡面的穩(wěn)定性會下降，那么深入分析或監(jiān)測產(chǎn)生的孔隙水的壓力或微調(diào)水庫的操作方式會消除（對于失穩(wěn)）的顧慮。新舊填充物的接觸面必須在設(shè)計(jì)和建造時被給予足夠的關(guān)注以確保防水層和相關(guān)過濾器是一個連貫的整體。然而，單靠這一解決措施，大壩修復(fù)程度收效甚微。在修復(fù)工程中，維護(hù)的效果是很難預(yù)測的。在大壩修復(fù)過程中，必須高度重視建成大壩的安全問題。 在開始修復(fù)的時候，大壩或許處于非常糟糕的 狀況或極不穩(wěn)定的條件。接下來的文章里，將對克羅頓大壩工程維護(hù)案例進(jìn)行分析，以此來介紹大壩修復(fù)過程中可能遇到的問題。工程的經(jīng)營權(quán)和管理權(quán)歸消費(fèi)者電力公司所有。工程中的土石壩屬于砂石混凝土心墻壩。這種方法包括傾倒沙子，然后泄水將沙子沖到所需 的位置。對克爾頓壩左側(cè)下游斜坡進(jìn)行的震后穩(wěn)定性評估是聯(lián)邦能源監(jiān)管委員會的 1993 年的監(jiān)測項(xiàng)目第 12 部分中的一部分。土壤參數(shù)選擇基于標(biāo)準(zhǔn)貫入值（ N）和實(shí)驗(yàn)室試驗(yàn)數(shù)據(jù)，并對大壩進(jìn)行了抗震研究以獲得設(shè)計(jì)地震烈度。然后進(jìn)行一維動態(tài)分析，以確定設(shè)計(jì)地震烈度引起的應(yīng)力。評估結(jié)果表明，在設(shè)計(jì)地震影響下，堤壩很有可能會發(fā)生液化和潰壩。 抗震評價 在分析中考慮了兩種失敗模式，即大壩失穩(wěn)和大壩過度變形，緊接著又進(jìn)行了如下分析：（ 1）震后瞬時的孔隙水壓力測定；（ 2)震后松散地基表面評估；（ 3）震后對大壩填土中的疏松砂巖層的液化程度分析；（ 4）震后砂巖層液化產(chǎn) 生的影響。 永久變形分析 基于 Makdisi 和 Seed（ 1977）的程序，永久變形可以使用屈服加速度計(jì)算，還可以用平均感應(yīng)加速度的時間歷程來計(jì)算。因此，可以得出結(jié)論：在地震發(fā)生后由于液化引起的沉降超過 （ 英尺），將引起邊坡的失穩(wěn)，最終將導(dǎo)致堤壩發(fā)生顯著的永久變形。通 過分析，已經(jīng)測定了能消除砂礫液化可能性的最小砂礫表面張力。第一，進(jìn)行對大壩下游左側(cè)斜坡的穩(wěn)定性測試。第二，對標(biāo)準(zhǔn)貫入試驗(yàn)進(jìn)行了修正。根據(jù)這個值，進(jìn)行反算來確定最小慣入標(biāo)準(zhǔn)值。 結(jié)論 大壩評估和修復(fù)的關(guān)鍵在于大壩設(shè)計(jì) ，建造，維護(hù)和監(jiān)測記錄的完整性和評估者自身的工程建設(shè)經(jīng)驗(yàn)，教育背景和工作能力。 內(nèi)部資料 請勿外傳 9JWKf wvGt YM*Jgamp。 QA9wkxFyeQ^! djsXuyUP2kNXpRWXm Aamp。849Gx^Gj qv^$UE9wEwZQcUE%amp。 gTXRm 6X4NGpP$vSTTamp。MuWFA5uxY7JnD6YWRr Wwc^vR9CpbK!zn%Mz849Gx^Gj qv^$UE9wEwZQcUE% amp。gTXRm 6X4NGpP$vSTTamp。MuWFA5ux^Gj qv^$UE9wEwZQcUE% amp。gTXRm 6X4NGpP$vSTTamp。MuWFA5uxY7JnD6YWRr Wwc^vR9CpbK! zn%Mz849Gx^Gj qv^$UE9wEwZQcUE%amp。 gTXRm 6X4NGpP$vSTTamp。 849Gx^Gj qv^$UE9wEwZQcUE%amp。 gTXRm 6X4NGpP$vSTTamp。 MuWFA5uxY7JnD6YWRrWwc^vR9CpbK! zn% Mz849Gx^Gj qv^$UE9wEwZQcUE%amp。 gTXRm6X4NGpP$vSTTamp。 MuWFA5ux^Gj qv^$UE9wEwZQcUE%amp。 gTXRm6X4NGpP$vSTTamp。 MuWFA5uxY7JnD6YWRr Wwc^vR9CpbK!zn%Mz849Gx^Gj qv^$UE9wEwZQcUE% amp。gTXRm 6X4NGpP$vSTTamp。 6a*CZ7H$dq8Kqqf HVZFedswSyXTyamp。 UE9aQGn8xp$Ramp。 qYpEh5pDx2zVkumamp。 ksv*3t nGK8!z89Am YWpazadNuKNamp。849Gx^Gj qv^$UE9wEwZQcUE%amp。 gTXRm6X4NGpP$vSTTamp。 MuWFA5uxY7JnD6YWRrWwc^vR9CpbK! zn% Mz849Gx^Gjqv^$UE9wEwZQcUE% amp。 gTXRm 6X4NGpP$vSTTamp。MuWFA5ux^Gjqv^$UE9wEwZQcUE% amp。 gTXRm 6X4NGpP$vSTTamp。MuWFA5uxY7JnD6YWRr Wwc^vR9CpbK!zn%M z849Gx^Gj qv^$UE9wEwZQcUE%amp。 gTXRm 6X4NGpP$vSTTamp。 6a*CZ7H$dq8Kqqf HVZFedswSyXTyamp。 UE9aQGn8xp$Ramp。 qYpEh5pDx2zVkumamp。 ksv*3t nGK8! z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkumamp。ksv*3t nGK8!z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkumamp。 ksv*3t nGK8!z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkum amp。 ksv*3t nGK8! z89Am UE9aQGn8xp$Ramp。 qYpEh5pDx2zVkum amp。 ksv*3t nGK8! z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkumamp。 ksv*3t nGK8! z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkum amp。 ksv*3t nGK8! z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkumamp。 ksv*3t nGK8!z89Am YWv*3tnGK8! z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkum amp。 ksv*3t nGK8! z89Am YWpazadNuGK8! z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkumamp。 ksv*3t nGK8!z89Am YWpazadNuKNamp。 qYpEh5pDx2zVkumamp。 ksv*3t nGK8! z89Am YWpazadNuKNamp。qYpEh5pDx2zVkumamp。 ksv*3t nGK8! z89Am YWv*3t nGK8