水利水電 流體力學 外文文獻 外文翻譯 英文文獻 混凝土重力壩基礎流體力學行為分析

1、文獻出自:Gimenes E, Ferna ndez G. Hydromechanical analysis of flow behavior in concrete gravity dam foundationsJ. Canadian geotechnical journal, 2006, 43(3): 244-259.混凝土重力壩基礎流體力學行為分析摘要：一個在新的和現有的混凝土重力壩的滑動穩定性評價的關鍵要求是對孔隙壓力 和基礎關節和剪切強度不連續分布的預測。本文列出評價建立在巖石節理上的混凝土 重力壩流體力學行為的方法。該方法包括通過水庫典型周期建立一個觀察大壩行為的 數據庫，并用離散

2、元法（DEM）數值模式模擬該行為。一旦模型進行驗證，包括巖 性主要參數的變化，地應力，和聯合幾何共同的特點都要納入分析。斯威土地，Albigna 大壩坐落在花崗巖上，進行了一個典型的水庫周期的特定地點的模擬，來評估巖基上 的水流體系的性質和評價滑動面相對于其他大壩巖界面的發展的潛力。目前大壩基礎 內的各種不同幾何的巖石的滑動因素，是用德國馬克也評價模型與常規的分析方法 的。裂紋擴展模式和相應揚壓力和抗滑安全系數的估計沿壩巖接口與數字高程模型進 行了比較得出，由目前在工程實踐中使用的簡化程序。結果發現，在巖石節理，估計 裂縫發展后的基礎隆起從目前所得到的設計準則過于保守以及導致的安全性過低，不

3、符合觀察到的行為因素。關鍵詞：流體力學，巖石節理，流量，水庫設計。簡介：評估抗滑混凝土重力壩的安全要求的理解是，巖基和他們上面的結構是一 個互動的系統，其行為是通過具體的材料和巖石基礎的力學性能和液壓控制。大約一 個世紀前，Boozy大壩的失敗提示工程師開始考慮由內部產生滲漏大壩壩基系統的揚 壓力的影響，并探討如何盡量減少其影響。今天，隨著現代計算資源和更多的先例， 確定沿斷面孔隙壓力分布，以及評估相關的壓力和評估安全系數仍然是最具挑戰性 的。我們認為，觀察和監測以及映射對大型水壩的行為和充分的儀表可以是我們更好 地理解在混凝土重力壩基礎上的縫張開度，裂紋擴展，和孔隙壓力的發展。圖.1流體力學

4、行為：（一）機械；（二）液壓。5Vnf|injUm本文介紹了在過去20個來自Albigna大壩，瑞士，多年收集的水庫運行周期行 為的代表的監測數據，描述了一系列的數值分析結果及評估了其基礎流體力學行為。 比較了數值模擬和實際行為在實地的監測結果。在此基礎上比較了一系列的結論得出 了基本孔隙壓力在節理巖體的影響可以考慮在其他工程項目，認為那里的巖石節理流 體力學行為應予以考慮。這些項目包括壓力管道，危險廢物處置，以及對流動行為的 控制斷面沿巖石地質遏制依賴的其他情形。流體力學的行為自然對先進設備，機械和個別巖石節理的水力特性的概要。一個對巖石聯合流體力學 行為的更詳細的描述中可以在阿爾瓦雷斯（1

5、997年）和阿爾瓦雷斯（1995年）和在 實驗室調查和數值模擬模型進行了烏鴉和Gale（1985），Gentier（1987年），江崎等 人（1992），和其他人中發現。該水力行為的聯合可以表示為非線性應用之間的有效正應力雙曲線關系， ，并effec ti ve normal Mir或ttnd jointK,1 2V|1ur AV；.1 - fiVn- Tiik 1dll - ni在裝卸，重大的聯合封發生在低有效正應力的地方。該單位的壓力關閉規模迅速 下降，但是，隨著應力水平增加。雙曲線的定義是由初始切線剛度定義，Kni，并聯 合最大的漸近結束，c。這種關系也是非線性，遲滯的卸載條件，直到成為

6、有效正 應力為零（圖1a）。Knl和tc的價值觀通過對實驗數據的回歸分析來估計的。對于自然和花崗巖裂 隙，這些參數都是相互關聯的下列限制范圍之間的阿爾瓦雷斯等。（1995年）：25店*吧i 2W*這里Km的單位是M pa/日m，七 的單位是日m粗糙關節展覽最大規模的聯合最高和最低的封閉初始關節僵硬，關節光滑而有最 低mc和最大的Kni巖石的共同特點是液壓行為之間的線性關系液壓孔徑，ah，它控制流動規模， 關閉和機械聯合，AVn，用于水平應力。液壓孔繪制相應的聯合與關閉（圖1b），以 獲取攔截線，aho，起始水力孔徑，邊坡系數和耦合，f，而“刻畫了聯合流體力學 行為，i. e，兩者在液壓機械孔徑

7、由于孔徑的變化變化的關系，鑒于其中%是剩余的水力孔徑對于給定的巖石節理，兩者之間是有粗糙度及耦合系數的關系，因為f的分布和 沿關節面流道曲折而定。對于理想的平行板，以在整個關節面單流道，f= 1.0.對于集 中流道蜿蜒穿過關節面，f1.0。因此，用經典的立方定律表示通過巖石節理流率：其中Q是流量；氣是水的單位重量；A是沿巖石節理頭部下降;u是水（11.005 x10-3p.s）的動力粘度；a是聯合液壓孔徑而g是形狀因子，由水流幾何而定。直 流地下G=W/L（其中W和L是寬度和長度，分別聯合），為不同徑向流，G =2n/lnG成 其中r和re分別為內外圓柱面半徑。裂隙巖體滲透性隨深度變化另外，巖

8、體等效滲透，公里，可以以同樣的形式作為修改后的定律，或在液壓口 徑計算，同樣的形式占關節間距，S:5靖三（次門如）以3，在裂隙巖體滲透性的變化，由于覆蓋層和圍應力，計算。1 - 3。巖體的滲透 性，K，理論的深度關系的結果高達1000米，采用當量。5載于圖2。孔的液壓隨 覆蓋減少強調在巖體滲透性，隨深度的增加，從10-3 cm/s到附近10-8的水面在600 厘米深度/秒-1000米的結果估計巖體滲透性得到假設f= 1.0，L = aho和kni= 10二成，這是在實驗室測試中 取得的值與（阿爾瓦雷斯等al.1995）相似，巴西在這一測試中描述位置的花崗巖編 隊部分。覆蓋層講估計使用的是26.

9、0 kN/m3單位重量。在這種情況下，它的假設是 橫向和縱向應力大致相同（土壓力系數Ko =1.0），這也被認為將在巴西的測試位置 的火成巖地層的代表，但其他價值在原位強調可以預計，如對高e.g., for Ko1.0，垂 直節理將有較大的滲透率。在深露天礦在巴西花崗巖開采項目獲得的場滲透率測量在圖2中繪制與理論的 關系比較。聯合間距從鉆孔巖心觀察值都在數米范圍內，從而產生了一個5米間距是 常數的計算假設。阿霍的價值在300 -1000 U m范圍被用來確定公里=f的理論關系（z） 的，其中Z是深度，以實地測量和比較這兩個鉆孔測量值相對滲透率在100至200米深處的高，可能表明的一個區或剪 切

10、節理巖帶更多的存在。所測巖石滲透率穩步下降，在深度的增加，然而，它們的值 與對應的巖體滲透性的理論與模型估計趨勢良好。典型液壓孔徑400 -500 Um的和后關節僵硬=K NI 10V的雙曲線關系，與三菱商 事和匕c =七。似乎同意這些結晶巖體觀測場行為良好。圖.2 .裂隙巖體滲透性隨深度的關系。-洞 1-F-u iyi(i_f io 偵 fHydraulic canductivity4 5 二E Efo雖然真正的流體力學節理巖體的行為是需要考慮具體的地點和地質因素，該方法 提供了一個框架，但在設計階段，其中巖石資料尚未提供大規模滲透。Hydro mechanical analysis of

11、flow behavior in concrete gravity dam foundationsAbstract: A key requirement in the evaluation of sliding stability of new and existing concrete gravity dams is the prediction of the distribution of pore pressure and shear strength in foundation joints and discontinuities. This paper presents a meth

12、odology for evaluating the hydromechanical behavior of concrete gravity dams founded on jointed rock. The methodology consisted of creating a database of observed dam behavior throughout typical cycles of reservoir filling and simulating this behavior with a distinct element method (DEM) numerical m

13、odel. Once the model is validated, variations of key parameters including litho logy, in situ stress, joint geometry, and joint characteristics can be incorporated in the analysis. A site-specific simulation of a typical reservoir cycle was carried out for Albigna Dam, Switzer land, founded on grani

14、tic rock, to assess the nature of the flow regime in the rock foundations and to evaluate the potential for sliding surfaces other than the dam-rock interface to develop. The factor of safety against sliding of various rock wedges of differing geometry present within the dam foundations was also eva

15、luated using the DEM model and conventional analytical procedures. Estimates of crack propagation patterns and corresponding uplift pressures and factors of safety against sliding along the dam-rock interface obtained with the DEM were also compared with those from simplified procedures currently us

16、ed in engineering practice. It was found that in a jointed rock, foundation uplift estimates after crack development obtained from present design guidelines can be too conservative and result in factors of safety that are too low and do not correspond to the observed behavior.Key words: Hydromechani

17、cal, jointed rock, flow, dam design.Introduction: Evaluating the safety of concrete gravity dams against sliding requires an understanding that rock foundations and the structure above them are an interactive system whose behavior is controlled by the mechanical and hydraulic properties of concrete

18、materials and rock foundations. About a century ago, the failure of Boozy Dam prompted dam engineers to start considering the effect of uplift pressures generated by seepage within the dam-foundation system and to explore ways to minimize its effect. Today, with modern computational resources and mu

19、ch more precedent, it is still most challenging to determine the pore-pressure distribution along foundation discontinuities to assess pertinent stresses and evaluate factors of safety. It is our opinion that observing and monitoring the behavior of large dams on well mapped and adequately instrumen

20、ted foundations can bring important insights for a better understanding of factors controlling joint opening, crack propagation, and pore-pressure development in foundations of concrete gravity dams.Fig.1.Hydromechanical behavior of natural joints :(a) mechanical;(b)hydraulic.This paper presents beh

21、avior representative of cycles of reservoir operation in the last 20 years collected from monitored data of Albigna Dam, Switzerland, and also describes the results of a series of numerical analyses carried out to assess the hydromechanical behavior of its foundations. Comparisons are made between r

22、esults of numerical modeling and the actual behavior monitored in the field. Based on these comparisons, a series of conclusions are drawn regarding basic pore-pressure buildup mechanisms in jointed rock masses with implications that may be considered in other engineering projects, where the hydrome

23、chanical behavior of jointed rock should be considered. Such projects include pressure tunnels, hazardous waste disposal, and other situations dependent on geologic containment controlled by flow behavior along rock discontinuities.Hydromechanical behavior of natural jointsA brief summary of the sta

24、te-of-the-art of mechanical and hydraulic behavior of individual rock joints is presented here. A more detailed description of rock joint Hydromechanical behavior can be found in Alvarez(1997)and Alvarez et al.(1995)and in investigations in laboratory and numerical model simulations carried out by R

25、aven and Gale (1985), Gentier (1987),Esaki et al.(1992),and others.The mechanical behavior of the joint can be represented by a nonlinear hyperbolic relationship between the applied effective normal stress, n, and joint closure, 京neffec ti ve normal stress, a.nd joint closu :jt a yy 武 *| I | 磯=11,11

26、 ,j or AV； =S一I -3nf -K -Wn 皿yn A in rmcDuring loading, significant joint closure takes place at low effective normal stresses. The magnitude of the closure per unit of stress decreases rapidly, however, as the stress level increases. The hyperbola is defined by the initial tangent stiffness,Kni, an

27、d the asymptote maximum joint closure, 匕* . This relationship is also nonlinear and hysteretic for the unloading condition until effective normal stresses become zero (Fig.1a).The values ofKni and 匕* are estimated by regression analysis on experimental data. For natural and induced fractures in gran

28、ite, these parameters are interrelated and range between the following limits Alvarez et al. (1995):5/V 2。沖*Where Kni is in M pa/ 日 m and 匕* is in 日 mRough joints exhibit the largest joint maximum closure and the lowest initial joint stiffness, whereas smooth joints have the lowest 匕* and the larges

29、t KniThe hydraulic behavior of the rock joint is characterized by the linear relationship between hydraulic aperture, ah, which controls the magnitude of flow, and mechanical joint closure, 京n , which depends on stress levels. Hydraulic apertures are plotted versus their corresponding joint closure

30、(Fig.lb)to obtain the line intercept, aho ,initial hydraulic aperture, and the coupled slope coefficient, f ,which characterizes the hydromechanical behavior of the joint ,i. e., the relationship between changes in hydraulic aperture due to changes in mechanical aperture, given by皿二,也匕h 5Where ahr i

31、s the residual hydraulic aperture.For a given rock joint, there is a relationship between roughness and the coupled coefficient, because f depends on the distribution and tortuosity of flow channels along the joint surface. For ideal parallel plates, with a single flow channel along the entire joint

32、 surface, f=1.0.For concentrated flow channels meandering across the joint surface, f1.0.Hence, the classic cubic law expresses flow rate through a rock joint:Q = eEMMWWhere Q is the flow rate; 7 w is the unit weight of the water; is the head drop along the rock joint; is the dynamic viscosity of th

33、e water(1.005 X 10 -3 Pa *s ); ah Is the joint hydraulic aperture; and G is the shape factor, which depends on the geometry of flow. For straight flow, G=W/L (where W and L are the width and length, respectively, of therrjoint); and for divergent radial flow, G=2n/ln (re/ /), where i and re are the

34、borehole and external cylindrical surface radiuses, respectively.Jointed rock mass permeability change with depthAlternatively, the rock mass equivalent permeability, km, can be expressed in the same form as the modified cubic law, or in terms of hydraulic aperture, to account for spacing of the joi

35、nts, S:5 靖三S門叩)京3，Changes in jointed rock mass permeability due to overburden and confining stresses were calculated using eqs. 1 - 3.The results of a theoretical relationship of rock mass permeability, k, for depths up to 1000 m, using eq. 5 are presented in Fig.2.The reduction of hydraulic apertur

36、es with increasing overburden stresses results in a rock mass permeability that decreases with an increase in depth from 10 一3 cm/s near the surface to 10-8 cm/s at depths of 600- 1000 m.The rock mass permeability estimates were obtained assuming f=1.0,匕* = 腥 andkni =10 VOTC33, which are representat

37、ive of the values obtained in laboratory tests carried out in granitic formations(Alvarez et al.1995)similar to those of the Brazilian test location described in this section. Overburden stresses were estimated using a unit weight of 26.0 kN/m3.In this case it was assumed that horizontal and vertica

38、l stresses are about the same (coefficient of earth pressure at rest Ko=1.0), which are also considered to be representative of the igneous formations at the Brazil test location, but other values of in situ stresses could be estimated, e.g., for Ko1.0, vertical joints would have larger permeabilities.Field permeability measurements obtained in Packer tests at a deep open-pit mining project in granitic rock in Brazil are also plotted in Fig.2 for comparison with the theoretical relationship. Values of joint spacing observed from borehole c