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1、編號(hào)： 時(shí)間：2021年x月x日 書山有路勤為徑，學(xué)海無涯苦作舟 頁碼：第10頁 共10頁 混凝土重力壩基礎(chǔ)流體力學(xué)行為分析 摘要：一個(gè)在新的和現(xiàn)有的混凝土重力壩的滑動(dòng)穩(wěn)定性評價(jià)的關(guān)鍵要求是對孔隙壓力和基礎(chǔ)關(guān)節(jié)和剪切強(qiáng)度不連續(xù)分布的預(yù)測。本文列出評價(jià)建立在巖石節(jié)理上的混凝土重力壩流體力學(xué)行為的方法。該方法包括通過水庫典型周期建立一個(gè)觀察大壩行為的數(shù)據(jù)庫，并用離散元法（DEM）數(shù)值模式模擬該行為。一旦模型進(jìn)行驗(yàn)證，包括巖性主要參數(shù)的變化，地應(yīng)力，和聯(lián)合幾何共同的特點(diǎn)都要納入分析。斯威土地，Albigna大壩坐落在花崗巖上，進(jìn)行了一個(gè)典型的水庫周期的特定地點(diǎn)的模擬，來評估巖基上的

2、水流體系的性質(zhì)和評價(jià)滑動(dòng)面相對于其他大壩巖界面的發(fā)展的潛力。目前大壩基礎(chǔ)內(nèi)的各種不同幾何的巖石的滑動(dòng)因素，是用德國馬克也評價(jià)模型與常規(guī)的分析方法的。裂紋擴(kuò)展模式和相應(yīng)揚(yáng)壓力和抗滑安全系數(shù)的估計(jì)沿壩巖接口與數(shù)字高程模型進(jìn)行了比較得出，由目前在工程實(shí)踐中使用的簡化程序。結(jié)果發(fā)現(xiàn)，在巖石節(jié)理，估計(jì)裂縫發(fā)展后的基礎(chǔ)隆起從目前所得到的設(shè)計(jì)準(zhǔn)則過于保守以及導(dǎo)致的安全性過低，不符合觀察到的行為因素。 關(guān)鍵詞：流體力學(xué)，巖石節(jié)理，流量，水庫設(shè)計(jì)。 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(jié)構(gòu)是一個(gè)互動(dòng)的系統(tǒng)，其行為是通過具體的材料和巖石基礎(chǔ)的力學(xué)性能和液壓控制。大約一個(gè)世紀(jì)前，Boo

3、zy大壩的失敗提示工程師開始考慮由內(nèi)部產(chǎn)生滲漏大壩壩基系統(tǒng)的揚(yáng)壓力的影響，并探討如何盡量減少其影響。今天，隨著現(xiàn)代計(jì)算資源和更多的先例，確定沿?cái)嗝婵紫秹毫Ψ植迹约霸u估相關(guān)的壓力和評估安全系數(shù)仍然是最具挑戰(zhàn)性的。我們認(rèn)為，觀察和監(jiān)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(chǔ)上的縫張開度，裂紋擴(kuò)展，和孔隙壓力的發(fā)展。 圖.1流體力學(xué)行為：（一）機(jī)械;（二）液壓。 本文介紹了在過去20個(gè)來自Albigna大壩，瑞士，多年收集的水庫運(yùn)行周期行為的代表的監(jiān)測數(shù)據(jù)，描述了一系列的數(shù)值分析結(jié)果及評估了其基礎(chǔ)流體力學(xué)行為。比較了數(shù)值模擬和實(shí)際行為在實(shí)地的監(jiān)測結(jié)果。

4、在此基礎(chǔ)上比較了一系列的結(jié)論得出了基本孔隙壓力在節(jié)理巖體的影響可以考慮在其他工程項(xiàng)目，認(rèn)為那里的巖石節(jié)理流體力學(xué)行為應(yīng)予以考慮。這些項(xiàng)目包括壓力管道，危險(xiǎn)廢物處置，以及對流動(dòng)行為的控制斷面沿巖石地質(zhì)遏制依賴的其他情形。 流體力學(xué)的行為自然 對先進(jìn)設(shè)備，機(jī)械和個(gè)別巖石節(jié)理的水力特性的概要。一個(gè)對巖石聯(lián)合流體力學(xué)行為的更詳細(xì)的描述中可以在阿爾瓦雷斯（1997年）和阿爾瓦雷斯（1995年）和在實(shí)驗(yàn)室調(diào)查和數(shù)值模擬模型進(jìn)行了烏鴉和Gale（1985），Gentier（1987年），江崎等人（1992），和其他人中發(fā)現(xiàn)。 該水力行為的聯(lián)合可以表示為非線性應(yīng)用之間的有效正應(yīng)力雙曲線關(guān)系，,并聯(lián)合

5、， 在裝卸，重大的聯(lián)合封發(fā)生在低有效正應(yīng)力的地方。該單位的壓力關(guān)閉規(guī)模迅速下降，但是，隨著應(yīng)力水平增加。雙曲線的定義是由初始切線剛度定義，，并聯(lián)合最大的漸近結(jié)束，。這種關(guān)系也是非線性，遲滯的卸載條件，直到成為有效正應(yīng)力為零（圖1a）。 和的價(jià)值觀通過對實(shí)驗(yàn)數(shù)據(jù)的回歸分析來估計(jì)的。對于自然和花崗巖裂隙，這些參數(shù)都是相互關(guān)聯(lián)的下列限制范圍之間的阿爾瓦雷斯等。 （1995年）： 這里的單位是M pa/m， 的單位是m 粗糙關(guān)節(jié)展覽最大規(guī)模的聯(lián)合最高和最低的封閉初始關(guān)節(jié)僵硬，關(guān)節(jié)光滑而有最低和最大的 巖石的共同特點(diǎn)是液壓行為之間的線性關(guān)系液壓孔徑，，它控制流動(dòng)規(guī)模，關(guān)閉和機(jī)械聯(lián)

6、合，，用于水平應(yīng)力。液壓孔繪制相應(yīng)的聯(lián)合與關(guān)閉（圖1b），以獲取攔截線，，起始水力孔徑，邊坡系數(shù)和耦合，，而“刻畫了聯(lián)合流體力學(xué)行為，i. e，兩者在液壓機(jī)械孔徑由于孔徑的變化變化的關(guān)系，鑒于 其中是剩余的水力孔徑 對于給定的巖石節(jié)理，兩者之間是有粗糙度及耦合系數(shù)的關(guān)系，因?yàn)閒的分布和沿關(guān)節(jié)面流道曲折而定。對于理想的平行板，以在整個(gè)關(guān)節(jié)面單流道，f= 1.0.對于集中流道蜿蜒穿過關(guān)節(jié)面，f<1.0。 因此，用經(jīng)典的立方定律表示通過巖石節(jié)理流率： 其中Q是流量; 是水的單位重量; 是沿巖石節(jié)理頭部下降;μ是水（11.005×p?s）的動(dòng)力粘度; 是聯(lián)合液壓孔徑而G是形狀因子，由水

7、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(lián)合），為不同徑向流，G =2π/ln(re/),其中和re分別為內(nèi)外圓柱面半徑。 裂隙巖體滲透性隨深度變化 另外，巖體等效滲透，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(jì)算，同樣的形式占關(guān)節(jié)間距，S: 在裂隙巖體滲透性的變化，由于覆蓋層和圍應(yīng)力，計(jì)算。 [1] - [3]。巖體的滲透性，K，理論的深度關(guān)系的結(jié)果高達(dá)1000米，采用當(dāng)量。 [5]載于圖2?？椎囊簤弘S覆蓋減少強(qiáng)調(diào)在巖體滲透性，隨深度的增加，從 cm/s到附近的水面在600厘米深度/秒 - 1000米的結(jié)果 估計(jì)巖體滲透性得到假設(shè)f= 1.0，=和

8、= 10，這是在實(shí)驗(yàn)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(duì)部分。覆蓋層講估計(jì)使用的是26.0 kN/m3單位重量。在這種情況下，它的假設(shè)是橫向和縱向應(yīng)力大致相同（土壓力系數(shù)Ko = 1.0），這也被認(rèn)為將在巴西的測試位置的火成巖地層的代表，但其他價(jià)值在原位強(qiáng)調(diào)可以預(yù)計(jì)，如對高e.g., for Ko<1.0，垂直節(jié)理將有較大的滲透率。 在深露天礦在巴西花崗巖開采項(xiàng)目獲得的場滲透率測量在圖2中繪制與理論的關(guān)系比較。聯(lián)合間距從鉆孔巖心觀察值都在數(shù)米范圍內(nèi)，從而產(chǎn)生了一個(gè)5米間距是常數(shù)的計(jì)算假設(shè)。阿霍的價(jià)值在300 -1000μm范圍被用來確定公

9、里= f的理論關(guān)系（z）的，其中Z是深度，以實(shí)地測量和比較 這兩個(gè)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(gè)區(qū)或剪切節(jié)理巖帶更多的存在。所測巖石滲透率穩(wěn)步下降，在深度的增加，然而，它們的值與對應(yīng)的巖體滲透性的理論與模型估計(jì)趨勢良好。 典型液壓孔徑400 -500μm的和后關(guān)節(jié)僵硬= 10V的雙曲線關(guān)系，與三菱商事和= 似乎同意這些結(jié)晶巖體觀測場行為良好。 圖.2.裂隙巖體滲透性隨深度的關(guān)系。 雖然真正的流體力學(xué)節(jié)理巖體的行為是需要考慮具體的地點(diǎn)和地質(zhì)因素，該方法提供了一個(gè)框架，但在設(shè)計(jì)階段，其中巖石資料尚未提供大規(guī)模滲透。

10、 Hydromechanical analysis of flow behavior in concrete gravity dam foundations Abstract: 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

11、 discontinuities. This paper presents a methodology 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

12、 a distinct element method (DEM) numerical model. 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

13、 Albigna Dam, Switzer land, founded on granitic 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 pre

14、sent within the dam foundations was also evaluated 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 t

15、hose from simplified procedures currently used 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 t

16、he observed behavior. Key words: Hydromechanical, 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 th

17、e mechanical and hydraulic properties of concrete 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.

18、. Today, with modern computational resources and much 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

19、 large dams on well mapped and adequately instrumented 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

20、 :(a) mechanical;(b)hydraulic. This paper presents behavior 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 hydromecha

21、nical behavior of its foundations. Comparisons are made between results 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 m

22、ay be considered in other engineering projects, where the hydromechanical 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. H

23、ydromechanical behavior of natural joints A brief summary of the state-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 investi

24、gations in laboratory and numerical model simulations carried out by Raven 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,， and joint closure,

25、 During 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,, and the asymptote maximum joint closure, .

26、 This relationship is also nonlinear and hysteretic for the unloading condition until effective normal stresses become zero (Fig.1a). The values of and are estimated by regression analysis on experimental data. For natural and induced fractures in granite, these parameters are interrelated and ran

27、ge between the following limits Alvarez et al. (1995): Where is in M pa/m and is in m Rough joints exhibit the largest joint maximum closure and the lowest initial joint stiffness, whereas smooth joints have the lowest and the largest The hydraulic behavior of the rock joint is characterized

28、by the linear relationship between hydraulic aperture,, which controls the magnitude of flow, and mechanical joint closure, , which depends on stress levels. Hydraulic apertures are plotted versus their corresponding joint closure (Fig.1b)to obtain the line intercept, ,initial hydraulic aperture, a

29、nd the coupled slope coefficient, ,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 Where is the residual hydraulic aperture. For a given rock joint, there is a relationshi

30、p 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 surface, f=1.0.For concentrated flow channels meandering across the joint surfa

31、ce, f<1.0. Hence, the classic cubic law expresses flow rate through a rock joint: Where Q is the flow rate; is the unit weight of the water; is the head drop along the rock joint; μ is the dynamic viscosity of the water(1.005×Pa·s ); Is the joint hydraulic aperture; and G is the shape factor, w

32、hich depends on the geometry of flow. For straight flow, G=W/L (where W and L are the width and length, respectively, of the joint); and for divergent radial flow, G=2π/ln (re/), where and re are the borehole and external cylindrical surface radiuses, respectively. Jointed rock mass permeability c

33、hange with depth Alternatively, 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 joints, S: Changes in jointed rock mass permeability due to overburden and confining stresses w

34、ere 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 apertures with increasing overburden stresses results in a rock mass permeability that decreases with an

35、 increase in depth from cm/s near the surface to cm/s at depths of 600– 1000 m. The rock mass permeability estimates were obtained assuming f=1.0, = and =10, which are representative of the values obtained in laboratory tests carried out in granitic formations(Alvarez et al.1995)similar to those

36、 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 vertical stresses are about the same (coefficient of earth pressure at rest Ko=1.0), which are also considered to be represe

37、ntative of the igneous formations at the Brazil test location, but other values of in situ stresses could be estimated, e.g., for Ko<1.0, vertical joints would have larger permeabilities. Field permeability measurements obtained in Packer tests at a deep open-pit mining project in granitic rock in

38、Brazil are also plotted in Fig.2 for comparison with the theoretical relationship. Values of joint spacing observed from borehole cores are in the range of a few meters, and thus a constant spacing of 5m was assumed in the computations. Values of aho in the range of 300–1000μm were used to determine

39、 the theoretical relationships of km=f (z), where z is the depth, and compare with field measurements. Measured permeability values in the two boreholes are relatively high at depths between 100 and 200m, probably denoting the presence of a sheared zone or a zone of more jointed rock. The measured

40、rock permeabilities decrease steadily with an increase in depth, however, and their values correspond well with the theoretical trend of rock mass permeability estimated with the model. Typical hydraulic apertures of 400–500μm and joint stiffness following a hyperbolic relationship with =10V mc and

41、= seem to agree well with observed field behavior for these crystalline rock masses. Fig.2.Theoretical jointed rock mass permeability relationship with depth. Although real Hydromechanical behavior of jointed rock masses is site specific and depends on geologic factors, which need to be taken into account, the proposed approach provides a framework to estimate rock mass permeability during design stages where information is not yet available. 第 10 頁 共 10 頁