巖土工程外文翻譯--先進(jìn)值方法在斜坡穩(wěn)定性分析中的應(yīng)用和限制

1、.成都理工大學(xué)學(xué)生畢業(yè)設(shè)計（論文）外文譯文學(xué)生姓名： 學(xué)號：專業(yè)名稱：巖土工程譯文標(biāo)題（中英文）：中文：先進(jìn)值方法在斜坡穩(wěn)定性分析中的應(yīng)用和限制 英文：Advanced numerical techniques in rock slope stability analysis-applications and limitations譯文出處：17-21 June 2001 Davos, Switzerland pp. 615-624指導(dǎo)老師審閱簽名：外文譯文正文：先進(jìn)值方法在斜坡穩(wěn)定性分析中的應(yīng)用和限制摘 要穩(wěn)定性的定期分析是為了對開挖邊坡（例如明坑采礦法，道路削減等）的安全設(shè)計、功能設(shè)計以及

2、對天然斜坡的平衡條件進(jìn)行評估。分析技術(shù)取決于地形狀況和潛在的崩塌形式，并且要對每種方法論中的不同優(yōu)勢、劣勢、局限性進(jìn)行仔細(xì)考慮。這篇論文是對運(yùn)用在巖石邊坡穩(wěn)定性分析方法的一種回顧。這項(xiàng)分析強(qiáng)調(diào)數(shù)值模擬的近期發(fā)展，其中包括了計算機(jī)可視化、連續(xù)統(tǒng)的運(yùn)用和不連續(xù)統(tǒng)數(shù)值分析的代碼。簡 介當(dāng)代工程師提出了很多關(guān)于巖石及混合巖土斜坡穩(wěn)定性分析的方法；研究內(nèi)容包括從簡單無限斜坡和平面崩塌極限平衡技術(shù)到復(fù)雜的耦合有限極離散元素代碼的有關(guān)問題。除了運(yùn)用大型計算機(jī)和二級編程語言進(jìn)行的涉及臨界面查找程序有關(guān)的分析，人們用圖表表示和運(yùn)用手提計算機(jī)來計算巖石邊坡穩(wěn)定性還不到25年。因?yàn)樵谑袌錾虾茈y買到需要的軟件，所以很

3、大一部分早期的穩(wěn)定性分析程序都來源于內(nèi)部。而現(xiàn)如今，每位工程師都有一臺私人電腦來處理相對簡單的巖石邊坡復(fù)雜數(shù)據(jù)分析?？紤]到當(dāng)今大量數(shù)據(jù)應(yīng)用程序的出現(xiàn)，對于工程師來說，充分理解不同方法內(nèi)在的長處和局限性就顯得尤為重要。例如，即使存在大部分的包括復(fù)雜的內(nèi)部變形和類似于被極限反平衡法要求的二維剛性塊假設(shè)的破碎等因素，極限平衡法在解決巖質(zhì)邊坡工程的問題中仍舊是最常用的方法。包括滑動在內(nèi)的啟動機(jī)制可被分析為極限平衡問題，但是隨之而來的是斜坡的潛變、漸進(jìn)變形、大范圍內(nèi)部變形等問題。在簡單的靜態(tài)分析中，引起最終滑動的因素很復(fù)雜也很容易被忽視。如果上述問題不被解決，那么極限平衡法就可能與簡單巖石崩塌在間斷點(diǎn)有

4、很大聯(lián)系。筆者認(rèn)為，極限平衡法應(yīng)該與數(shù)值模擬相互協(xié)調(diào)來充分發(fā)揮兩者的優(yōu)勢。對當(dāng)今的工程師來說，如果想要證明其盡職盡責(zé)，就一定要展示他所運(yùn)用的工具。其中，正確的工具尤為重要。陳的觀察進(jìn)一步闡明了所有相關(guān)的斜坡分析法在設(shè)計或反分析法中的運(yùn)用的重要性。 “在早些時代，滑坡總被看成是上帝造成的。而如今，尤其是在有人身傷亡和財產(chǎn)損失的時候，律師總是能找到接受懲罰和補(bǔ)償損失的人”。如果斜坡因?yàn)閺?fù)雜機(jī)制（例如流變、內(nèi)部變形和脆性破壞、較弱多土層的液化等等）的出現(xiàn)而崩塌，那么用極限分析法來解決斜坡設(shè)計的問題就足夠了。此外，風(fēng)險評估及其概念的使用使極限分析法在斜坡工程設(shè)計和分析中的作用增強(qiáng)。風(fēng)險評估必須注明斜坡

5、崩塌的結(jié)果和崩塌的可能性; 為了標(biāo)注出所有的崩塌機(jī)率，必須注明對破壞機(jī)理的理解。巖質(zhì)邊坡分析的傳統(tǒng)方法圖表一總結(jié)了在傳統(tǒng)斜坡分析中通常使用的方法，也注明了其優(yōu)缺點(diǎn)。就其本身而論，任何巖質(zhì)邊坡分析的第一步都必須是對巖石學(xué)和巖質(zhì)結(jié)構(gòu)進(jìn)行詳盡的評估。由此來分析現(xiàn)存的間斷點(diǎn)的導(dǎo)向是否會引起巖塊的不穩(wěn)定性。這些評估可以通過實(shí)體技術(shù)和運(yùn)動分析來實(shí)現(xiàn)。例如，程序DIPS (2)可以利用摩擦錐、裂隙和崩塌道路線指標(biāo)以及間斷特性的圖解和統(tǒng)計分析來實(shí)現(xiàn)巖質(zhì)邊坡的運(yùn)動可行性的可視化和檢測。工程師能用這種方法來識別包括單一間斷點(diǎn)和間斷交叉點(diǎn)潛在的滑動崩塌是很重要的。他們不用關(guān)心包括多重節(jié)理組及內(nèi)部變形和破裂而出現(xiàn)的崩

6、塌。在DIPS中定義的間斷點(diǎn)數(shù)據(jù)和節(jié)理組交叉點(diǎn)可以被引入耦合極限平衡代碼(例如SWEDGE (2)來評估反滑動的安全因素(圖 1)。這些程序經(jīng)常并入概率工具，這些工具中的節(jié)理特性和補(bǔ)充道支護(hù)措施可以用來評估他們在安全系數(shù)上產(chǎn)生的影響。所有的極限平衡技術(shù)基于抵抗力和干擾力的比較都有一個共同的方法。為了得到確切的解決方案，所有方法中采取的假設(shè)都一直在變化。圖解分析法用立體圖技術(shù)和塊體理論技術(shù)都可以來評估關(guān)鍵塊體。關(guān)鍵塊體的穩(wěn)定性可以通過極限平衡術(shù)來獲得。如 SAFEX 程序 (3) 和 KBSLOPE (4)所示。圖表1.常用解析法 解析法關(guān)鍵參數(shù)優(yōu)勢劣勢運(yùn)用立體平面和運(yùn)動學(xué)臨界坡和間斷幾何學(xué)；各

7、自的切變強(qiáng)度特征 相當(dāng)簡單實(shí)用并為潛在危險提供原始跡象；有些方法可以對關(guān)鍵塊體進(jìn)行鑒定和分析；也可和其他方法結(jié)合 在一起；可以和數(shù)據(jù)統(tǒng)計技術(shù)相結(jié)合來計算出現(xiàn)危險的可能性和相關(guān)體積只適用于初級和非關(guān)鍵斜坡的設(shè)計.；需要工程分析來確定臨界面；需要和典型的間斷點(diǎn)/聯(lián)合抗剪強(qiáng)度數(shù)據(jù)一起運(yùn)用；首先評估臨界取向,忽視其它的連接特性極限平衡典型幾何和材質(zhì)特征；土塊或巖塊的切變強(qiáng)度參數(shù)(凝聚力和摩擦力)；間斷點(diǎn)切變強(qiáng)度特征；地下水條件；加固特點(diǎn)和外部支持?jǐn)?shù)據(jù)針對失效模型（平面、楔入、坍塌等等）有大量的可用軟件；大都是確定的但是概率性分析的功能增強(qiáng)；可以分析邊坡幾何和材料特性中的安全靈敏度因素；能夠用多種材料、

8、加固和地下水概況來建二維和三維斜坡安全性系數(shù)計算沒有指示出不穩(wěn)定性機(jī)制；許多技術(shù)在不同的假設(shè)下都可以運(yùn)用；強(qiáng)壓和完全崩塌是不允許出現(xiàn)的；不用考慮原位應(yīng)力狀態(tài)；紀(jì)律性分析要求明確的輸入數(shù)據(jù)來得到有意義的評估；一般的機(jī)率性分析不會考慮到樣本/數(shù)據(jù)協(xié)方差 落石仿真典型邊坡幾何；巖石塊大小和形狀；恢復(fù)系數(shù)選址結(jié)構(gòu)的實(shí)用工具；可以利用概率性分析 ；二維和三維編碼可以使用實(shí)際設(shè)計圖表在運(yùn)用上的經(jīng)驗(yàn)有限在市場上可買到的極限平衡的計算機(jī)代碼在近幾年已經(jīng)有了很大的進(jìn)步。這包括：有限元法和地下水應(yīng)力分析(如GEO-SLOPEs SIGMA/W, SEEP/W 和 SLOPE/W(6)的二維極限平衡法編碼的集成。三

9、維極限平衡法的發(fā)展(例如 CLARA (7); 3D-SLOPE(8)。概率極限平衡技術(shù)的發(fā)展。· 允許多樣的支持和加固的能力。· 非飽和土抗剪強(qiáng)度標(biāo)準(zhǔn)的混合?？梢暬母叨劝l(fā)展和前處理及后處理的制圖學(xué)。這些編碼在土坡和高度蝕變巖斜坡的分析中起著至關(guān)重要的作用。而在這些斜坡中，離散明確的表面容易發(fā)生滑動。圖2闡明了高嶺土化的花崗巖斜坡崩塌的反分析法中的二維極限平衡程序的運(yùn)用。包括巖塊內(nèi)部的應(yīng)力狀態(tài)和復(fù)雜變形及脆性斷裂影響是極其重要的。數(shù)值模擬技術(shù)也應(yīng)用其中。(如圖2所示). 圖 1. SWEDGE 分析(右)建立在DIPS立體圖輸入的基礎(chǔ)上(LEFT).圖 2. 用極限平衡法

10、對瓷土邊坡進(jìn)行分析來尋求滑動平面（左）和有線差分來模擬剪應(yīng)變發(fā)展（右）石雨模擬器是另一分析法的傳統(tǒng)模式，其中包括用來評估單個墜落方塊的危害的工具。像ROCFALL (2) 的程序用來分析從給定坡面幾何上滾動或彈動的巖塊在速率發(fā)生變化時，滑動巖塊的軌道。在風(fēng)險評估中，經(jīng)過重復(fù)數(shù)量的模擬計算出的塊速度、反彈高度和端點(diǎn)距離等因素都可以在風(fēng)險評估中起到作用。通過效力和阻礙物的動能的影響，石雨模擬器也可以幫助制定補(bǔ)救措施。類似的發(fā)展在編碼中有關(guān)處理崩塌巖塊和快速滑動方面也有體現(xiàn)。它提出適用于流量預(yù)測和擺動運(yùn)行的動態(tài)分析工具。坡度分析的數(shù)值方法許多巖石邊坡穩(wěn)定性存在有關(guān)幾何學(xué)、資料各向異性、非線性性能、

11、原位應(yīng)力和出現(xiàn)幾個耦合過程（例如，孔隙壓力和地震荷載等）的問題。計算機(jī)功能的提高和市場上便宜的數(shù)值模擬代碼的出現(xiàn)意味著潛在石坡崩塌機(jī)制的預(yù)想能夠，或者說在大部分情況下能夠形成巖石邊坡調(diào)查的標(biāo)準(zhǔn)件。石坡穩(wěn)定性分析的數(shù)值方法可以分為三個部分：連續(xù)統(tǒng)、密斷統(tǒng)和混合建模。表格2為現(xiàn)有數(shù)控技術(shù)的摘要。表格2. 數(shù)值分析法解析法關(guān)鍵參數(shù)優(yōu)勢劣勢連續(xù)統(tǒng)建模(例如，有限單元法，有限差)典型邊坡幾何; 本構(gòu)標(biāo)準(zhǔn) (例如， 彈簧、 彈性塑料、 潛變等等); 地下水特征; 表面剪切強(qiáng)度; 原位應(yīng)力狀態(tài).允許物質(zhì)變性和破損；可以模擬復(fù)雜運(yùn)行和機(jī)制； 三維建模性；. 可以模擬地下水和孔隙水壓力的影響；可以評估不穩(wěn)定性參

12、數(shù)的影響；計算機(jī)軟件的發(fā)展在合理的時間內(nèi)在計算機(jī)上建立復(fù)雜模型；可以結(jié)合蠕變；可以結(jié)合動態(tài)分析運(yùn)用著必須訓(xùn)練有素、經(jīng)驗(yàn)豐富并且遵循良好的造型實(shí)踐。應(yīng)該意識到模型和軟件是限制因素(例如，邊界效應(yīng)、網(wǎng)格的縱橫比、對稱度 硬件記憶限制) 普遍輸入的貧瘠數(shù)據(jù)的可用性必需輸入數(shù)據(jù)沒有經(jīng)過定期測量； 不能夠模擬高度節(jié)理巖石的效果； 由于運(yùn)行時間受限，靈敏度分析很難完成。密斷統(tǒng)建模(例如， 離散單元, 分立元件)典型邊坡 和間斷幾何;完整的本構(gòu)標(biāo)準(zhǔn); 間斷剛度和切變強(qiáng)度; 地下水特征; 原位應(yīng)力狀態(tài)允許彼此的塊變形和塊移動；可以模擬復(fù)雜運(yùn)行和復(fù)雜機(jī)制 (復(fù)合材料、間斷運(yùn)行和液壓機(jī)械及動態(tài)分析)；能夠評估不穩(wěn)

13、定性參數(shù)變化的影響同上，使用者必須經(jīng)驗(yàn)豐富才能遵守好的模擬；和上述的普遍局限性一樣；需要注意縮放效果；需要模擬典型間斷幾何 (間距, 持久性等等)；節(jié)理特性可使用的的數(shù)據(jù)有限 (例如 jkn, jks).混合物/耦合模擬列出獨(dú)立模型的輸入?yún)?shù)的組合耦合有限元/離散單元模型能夠模擬節(jié)理和層狀媒介上的完整的裂縫延伸和斷裂復(fù)雜問題需要高端內(nèi)存容量；在實(shí)踐中相對來說有較少的經(jīng)驗(yàn)；需要持續(xù)校準(zhǔn)和限制連續(xù)統(tǒng)建模連續(xù)統(tǒng)建模最適合應(yīng)用于由大量完整巖石、軟弱巖石、類土或嚴(yán)重斷裂的巖塊構(gòu)成的斜坡。大多數(shù)連續(xù)統(tǒng)代碼有含離散斷裂的設(shè)備，如斷層和層面。但是不適用于不均介質(zhì)的分析。石坡穩(wěn)定性中的連續(xù)統(tǒng)方法包括有線差分法和

14、有限元素法。Hoek et al. (10)談到了其顯著的優(yōu)勢和劣勢。這兩種方法在石坡分析中都有廣泛的應(yīng)用。 近幾年，絕大多數(shù)已發(fā)布的連續(xù)統(tǒng)石坡分析都運(yùn)用到了二維有限差分代碼： FLAC (11).此代碼為本構(gòu)模型描述巖體和合并不穩(wěn)定運(yùn)行、耦合水機(jī)制和動力模型提供了多種選擇。圖3顯示的是FLAC在表面煤礦斜坡的失穩(wěn)損壞中的應(yīng)用。二維連續(xù)統(tǒng)代碼假定平面應(yīng)變條件，但對于有不同結(jié)構(gòu)巖石學(xué)和地勢的非齊次石坡并不十分有效。類似FLAC3D (11) 和 VISAGE (12)等三位連續(xù)統(tǒng)代碼最近的出現(xiàn)使工程師能夠用臺式電腦從事石坡的三維分析。圖 4為瓷土邊坡的FLAC三維分析的例子，它包括沿著擊打面修改

15、的不同的區(qū)域。圖 3. FLAC 表面煤礦斜坡的失穩(wěn)損壞的模型圖 4. FLAC 瓷土邊坡的三維模型盡管二維和三維連續(xù)統(tǒng)代碼在描述石坡崩塌機(jī)制方面十分有效，工程師也有責(zé)任仔細(xì)考慮并證實(shí)它們是否是石塊的代表。若石坡控制失敗機(jī)制的多重節(jié)理組構(gòu)成，那么運(yùn)用密斷統(tǒng)模型的方法就很適合。密斷統(tǒng)模擬密度統(tǒng)方法認(rèn)為石坡由剛性組合或變形塊構(gòu)成，從而將它視為間斷巖體。分析包括滾動和主要被聯(lián)合正常和聯(lián)合剪切剛度控制的巖石間斷的開或關(guān)。密斷統(tǒng)建模構(gòu)成最常使用的石坡分析數(shù)字方法，最受歡迎的是離散單元分析法 (13)。假設(shè)存在有石坡的位移的條件下，如 UDEC (11)的離散單元代碼運(yùn)用力位移定律來指明變形聯(lián)合界塊和牛頓

16、運(yùn)動第二定律的相互作用。UDEC 特別適用于包括節(jié)理媒介的問題，并且廣泛應(yīng)用于滑坡和表面礦山邊坡的調(diào)查研究。也可以模擬地下開采、地震、 地下水壓力等因素對石塊滑動和變形的影響。圖 5 為發(fā)生在加拿大亞伯達(dá)的重大巖滑F(xiàn)rank Slide的分析。Benko和Stead詳細(xì)描述了這次模擬調(diào)查 (14)并且舉例說明了在巖滑開始的山坡腳下的地下采礦可能產(chǎn)生的影響。圖 6 舉例說明了在發(fā)生在加拿大亞伯達(dá)Luscar煤礦的主要崩塌不穩(wěn)定模型的作用。這項(xiàng)分析能夠模擬地下采礦從底層到表面的基礎(chǔ)屈曲面的前進(jìn)發(fā)展 (15)。通過采用可見和不可見斜坡的數(shù)值分析的程序模型能夠?yàn)榻窈蟮牟傻V規(guī)劃提供有價值的信息。圖 5.

17、 Frank Slide的原理截面 (左) 和 UDEC模型沿著表面和節(jié)理顯示的剪切(右).圖 6. 表層煤礦斜坡的屈曲崩塌UDEC模型工程師必須注意到離散單元分析法的的結(jié)構(gòu)輸入必須是典型的。Hencher et al. (16)舉例說明了在預(yù)測破壞機(jī)理的表層間距的重要性。Stead和Eberhardt (17)展示了不連續(xù)面狀態(tài)在表層煤礦斜坡的實(shí)效故障的重要性。 需要強(qiáng)調(diào)的通過調(diào)節(jié)模型結(jié)構(gòu)來調(diào)整手提電腦上的調(diào)節(jié)低隨機(jī)存取存儲器的做法可能會導(dǎo)致不典型的結(jié)果，例如運(yùn)用不典型間斷間距的做法。假設(shè)必須隨著實(shí)地觀測和可能邊坡儀器數(shù)據(jù)的變化而變化。隨著3DEC (11)等三維間斷代碼的發(fā)展這將變得更加精

18、確。 只有斜坡的三維特征是精確可信的，結(jié)果才能被認(rèn)為是具有代表性的。這反過來也需要大量而深入的事先現(xiàn)場調(diào)查。由Shi (18)發(fā)展的斷點(diǎn)變性分析法 DDA也在間斷巖體建模和巖滑及崩塌的使用上取得了巨大的成就。離散單元法和顆粒流的應(yīng)用為密斷統(tǒng)代碼近期的發(fā)展，例如： PFC2D/3D (11). T 能將巖體描述成通過摩擦滑動接觸相互作用的一系列吸附劑顆粒。粒子群能夠通過指定粘合強(qiáng)度結(jié)合在一起，從而模擬聯(lián)合界塊。這種方法的主要優(yōu)點(diǎn)就是石坡中的強(qiáng)壓將會以一種近似的方式削弱粒子模擬和巖石的完全斷裂之間的連接。許多作者已經(jīng)用密斷統(tǒng)和連續(xù)統(tǒng)方法來提供石坡分析的有益方法。Board et al. (21)

19、舉例說明了650米高的露天礦邊坡內(nèi)的復(fù)雜變形的分析。Chile 運(yùn)用FLAC和UDEC的聯(lián)合方法。 同樣地，Benko和Stead (14)運(yùn)用FLAC進(jìn)行 Frank Slide的初步調(diào)查，用UDEC做深入研究。通過將每種方法做為工具在全面石坡分析中提供了一個階梯，從而使后者從極限平衡法、連續(xù)統(tǒng)和間斷統(tǒng)分析中的得到完整的結(jié)果?；旌霞夹g(shù)在石坡分析中混合方法的應(yīng)用變得越來越廣泛。這包括比如軟件中采用的GEO-SLOPE (6)等極限平衡穩(wěn)定分析和有限單元地下徑流和壓力分析的混合方法?；旌蠑?shù)值模型在包括耦合邊界離散單元法和耦合邊界應(yīng)對措施的地下巖土工程中，混合數(shù)值模型的運(yùn)用已有相當(dāng)長的一段時間。

20、近期的發(fā)展包括運(yùn)用FLAC3D及PFC3D (22)的耦合粒子流和有限差分析法。在例如管道斜坡?lián)p壞的現(xiàn)象和高地下水壓力對弱巖質(zhì)邊坡的影響的調(diào)查中，這些混合方法都表現(xiàn)出了巨大的潛力。包含自適應(yīng)網(wǎng)格重構(gòu)的有限/離散單元分析法都是可用的。這些方法運(yùn)用有限元網(wǎng)格來描繪石坡或聯(lián)合界塊。這和離散單元模型一起能夠模擬包括節(jié)理在內(nèi)的變形。如果石坡內(nèi)的壓力超過了有限單元法中的失效準(zhǔn)則，那么就會產(chǎn)生裂痕。格化允許裂縫通過有限單元格的增殖，從而進(jìn)行模擬。Hybrid codes with 混合編碼和適合的重嚙合程序已經(jīng)被廣泛應(yīng)用在強(qiáng)烈壓裂的模擬和表層煤礦爆炸、礦產(chǎn)磨、擋土墻崩塌和地下巖層開中 (24)。 作者目前正

21、在研究能夠模擬多樣斜坡崩塌過程的代碼。發(fā)展前景在計算上可以廣泛使用最先進(jìn)的數(shù)值模擬代碼來進(jìn)行復(fù)雜山體滑坡的分析。如果擴(kuò)大這些方法的收益，那么現(xiàn)場采集技術(shù)能能有效促進(jìn)設(shè)計能力的進(jìn)步是十分重要的。在過去十年間，大部分當(dāng)前數(shù)據(jù)收集方法并未發(fā)生太大的變化，并仍旨在極限平衡分析。必須收集巖體特征、儀表裝置和地下水的數(shù)據(jù)來實(shí)現(xiàn)石坡?lián)p壞機(jī)制的模擬。職業(yè)工程師和研究員必須努力是自己的思想超越臺式計算機(jī)的使用，迎接并行計算機(jī)飛速發(fā)展的技術(shù)。幾十年前，由于數(shù)據(jù)無法人工或用計算機(jī)計算，工業(yè)工程師需要在主機(jī)計算機(jī)上操作斜坡分析?，F(xiàn)存的模擬是為了充分利用和發(fā)展自適應(yīng)網(wǎng)格重構(gòu)和三維耦合模型。當(dāng)個人電腦不足夠的時候我們必須

22、運(yùn)用并行計算機(jī)。工廠已經(jīng)將這種方法應(yīng)用于底下鉀肥礦井的三維模擬和儲油層的假設(shè)中。在接下來的十年里，我們在模擬完全故障處理從開始經(jīng)過流動再到沉積方面具有極大的潛能。這將我們對基低風(fēng)險評估有更嚴(yán)謹(jǐn)?shù)睦斫?。虛擬實(shí)體程序的出現(xiàn)使工程師更以有力的生動有效地方式傳達(dá)仿真的結(jié)果。為了提供必不可少的驗(yàn)證，質(zhì)量/數(shù)量的輸入數(shù)據(jù)和建模所用的儀表數(shù)據(jù)隨之的改進(jìn)都是十分重要的。 ; ADVANCED NUMERICAL TECHNIQUES IN ROCK SLOPE STABILITY ANALYSIS APPLICATIONS AND LIMITATIONSABSTRACT Stability analyses

23、are routinely performed in order to assess the safe and functional design of an excavated slope (e.g. open pit mining, road cuts, etc.), and/or the equilibrium conditions of a natural slope. The analysis technique chosen depends on both site conditions and the potential mode of failure, with careful

24、 consideration being given to the varying strengths, weaknesses and limitations inherent in each methodology. This paper presents a review of numerical techniques used in rock slope stability analysis emphasising recent developments in numerical modelling, including advances in computer visualisatio

25、n and the use of continuum and discontinuum numerical modelling codes.INTRODUCTION The engineer today is presented with a vast range of methods for the stability analysis of rock and mixed rock-soil slopes; these range from simple infinite slope and planar failure limit equilibrium techniques to sop

26、histicated coupled finite-/distinctelement codes. It is less than 25 years since most rock slope stability calculations were performed either graphically or using a hand-held calculator, the exception being advanced analyses involving critical surface searching routines performed on a mainframe comp

27、uter and Fortran cards. The great majority of early stability analysis programs were in-house with very little software being available commercially. Today, every engineer has access to a personal computer that can undertake with relative ease complex numerical analyses of rock slopes. Given the wid

28、e scope of numerical applications available today, it has become essential for the engineer to fully understand the varying strengths and limitations inherent in each of the different methodologies. For example, limit equilibrium methods still remain the most commonly adopted solution method in rock

29、 slope engineering, even though most failures involve complex internal deformation and fracturing which bears little resemblance to the 2-D rigid block assumptions required by most limit equilibrium back-analyses. Initiation or trigger mechanisms may involve sliding movements which can be analysed a

30、s a limit equilibrium problem, but this is followed by or preceded by creep, progressive deformation, and extensive internal disruption of the slope mass. The factors initiating eventual sliding may be complex and not easily allowed for in simple static analysis. Not withstanding the above comments,

31、 limit equilibrium analyses may be highly relevant to simple block failure along discontinuities. It is the authors view that limit equilibrium techniques should be used in conjunction with numerical modelling to maximize the advantages of both. The engineer today, if he is to demonstrate due-dilige

32、nce, must show he has used both all the tools at his disposal and, more importantly, the correct tools. The argument for the use of all relevant available slope analysis techniques in a design or back-analysis is crystallized by the observation of Chen (1), “In the early days, slope failure was alwa

33、ys written off as an act of God. Today, attorneys can always find someone to blame and someone to pay for the damage especially when the damage involves loss of life or property”. The design of a slope using a limit equilibrium analysis alone may be completely inadequate if the slope fails by comple

34、x mechanisms (e.g. progressive creep, internal deformation and brittle fracture, liquefaction of weaker soil layers, etc.). Furthermore, within slope engineering design and analysis, increased use is being made of hazard appraisal and risk assessment concepts. A risk assessment must address both the

35、 consequence of slope failure and the hazard or probability of failure; both require an understanding of the failure mechanism in order that the spatial and temporal probabilities can be addressed.CONVENTIONAL METHODS OF ROCK SLOPE ANALYSIS Table 1 provides a summary of those techniques that are rou

36、tinely applied in conventional slope analyses together with their inherent advantages and limitations.As such, the first step in any rock slope stability analysis must be a detailed evaluation of the lithology and rock mass structure. From this follows the necessity to determine if the orientation o

37、f the existing discontinuity sets could lead to block instability. This assessment may be carried out by means of stereographic techniques and kinematic analysis. For example, the program DIPS (2) allows for the visualisation and determination of the kinematic feasibility of rock slopes using fricti

38、on cones, daylight and toppling envelopes, in addition to graphical and statistical analysis of the discontinuity properties. It is essential that the engineer is aware that such approaches recognise potential sliding failures involving single discontinuities or discontinuity intersections. They do

39、not cater for failure involving multiple joints/joint sets or internal deformation and fracture. Discontinuity data and joint set intersections defined in DIPS, however, can be imported into companion limit equilibrium codes (e.g. SWEDGE (2) to assess the factor of safety against sliding (Figure 1).

40、 The seprograms often incorporate probabilistic tools, in which variations in joint set properties and added support measures can be assessed for their influence on the factor of safety. All limiting equilibrium techniques share a common approach based on a comparison of resisting forces/moments mob

41、ilized and the disturbing forces/moments. Methods vary, however, in the assumptions adopted in order to achieve a determinate solution. Graphical analysis using stereonet techniques can also be carried out using block theory techniques to assess critical keyblocks. The stability of such keyblocks ca

42、n then be assessed using limit equilibrium methods such as in the SAFEX program (3) and KBSLOPE (4).Table 1. Conventional methods of analysis (after (5).Analysis methodCritical input parametersAdvantagesLimitationsStereographic and KinematicCritical slope and discontinuity geometry; representative s

43、hear strength characteristics.Relatively simple to use and give an initial indication of failure potential. Some methods allow identification and analysis of critical keyblocks. Links are possible with other analysis methods. Can be combined with statistical techniques to indicate probability of fai

44、lure and associated volumes.Only really suitable for preliminary design or design of non-critical slopes. Need to determine critical discontinuities that requires engineering judgement. Must be used with representative discontinuity/joint shear strength data. Primarily evaluates critical orientation

45、s, neglecting other important joint properties.Limit EquilibriumRepresentative geometry and material characteristics; soil or rock mass shear strength parameters (cohesion and friction);discontinuity shear strength characteristics; groundwater conditions; reinforcement characteristics and external s

46、upport data.Wide variety of software available for different failure modes (planar, wedge, toppling, etc.). Mostly deterministic but increased use of probabilistic analysis. Can analyse factor of safety sensitivity to changes in slope geometry and material behaviour. Capable of modelling 2-D and 3-D

47、 slopes with multiple materials, reinforcement and groundwater profiles.Factor of safety calculations give no indication of instability mechanisms. Numerous techniques available all with varying assumptions. Strains and intact failure not allowed for. Do not consider in situ stress state. Probabilis

48、tic analysis requires well-defined input data to allow meaningful evaluation. Simple probabilistic analyses may not allow for sample/data covariance.Rockfall SimulationRepresentative slope geometry; rock block sizes and shapes; coefficient of restitution.Practical tool for siting structures. Can uti

49、lise probabilistic analysis.2-D and 3-D codes availableLimited experience in use relative to empirical design charts.Considerable advances in commercially available limit equilibrium computer codes have taken place in recent years. These include:· Integration of 2-D limit equilibrium codes with

50、 finite-element groundwater flow and stress analyses (e.g. GEO-SLOPEs SIGMA/W, SEEP/W and SLOPE/W(6).· Development of 3-D limit equilibrium methods (e.g. CLARA (7); 3D-SLOPE(8).· Development of probabilistic limit equilibrium techniques.· Ability to allow for varied support and reinfo

51、rcement.· Incorporation of unsaturated soil shear strength criteria.· Greatly improved visualisation, and pre- and post-processing graphics. These codes are extremely relevant in the analysis of soil slopes and highly altered rock slopes, where sliding takes place on discrete well-defined

52、surfaces. Figure 2 illustrates the use of the 2-D limit equilibrium program SLOPE/W in the back-analysis of a failure in a kaolinised granite slope. Where it is necessary to include the stress state within the rock mass and the influence of complex deformation and brittle fracture, numerical modelli

53、ng techniques should be used (e.g. Figure 2). Figure 1. SWEDGE analysis (RIGHT) based on DIPS stereonet input (LEFT).Figure 2. Analysis of China clay slope using limit equilibrium to find the critical slip plane (LEFT) and finite-difference to model shear strain development (RIGHT). Rockfall simulat

54、ors, another conventional form of analysis, include tools used to assess hazards of individual falling blocks. Programs such as ROCFALL (2) analyse the trajectory of falling blocks based on changes in velocity as rock blocks roll and bounce over a given slope geometry. Other factors solved for inclu

55、de block velocity, bounce height and endpoint distance, which can be analysed statistically over a repeated number of simulations to aid in a risk assessment. Rockfall simulators can also assist in determining remedial measures by calculating the effectiveness and kinetic energy of impact on barrier

56、s. Similar developments that deal with failed rock blocks and rapid slides include Hungrs (9) DAN code, which proposes a dynamic analysis tool suited for the prediction of flow and runout behaviour.NUMERICAL METHODS OF SLOPE ANALYSIS Many rock slope stability problems involve complexities relating t

57、o geometry, material anisotropy, non-linear behaviour, in situ stresses and the presence of several coupled processes (e.g. pore pressures, seismic loading, etc.). Advances in computing power and the availability of relatively inexpensive commercial numerical modelling codes means that the simulatio

58、n of potential rock slope failure mechanisms could, and in many cases should, form a standard component of a rock slope investigation. Numerical methods of analysis used for rock slope stability may be conveniently divided into three approaches: continuum, discontinuum and hybrid modelling. Table 2 provides a summary of existing numerical techniques.Table 2. Numerical methods of analysis (after (5).Analysis methodCritical input parametersAdvantagesLimitationsContinuum Modelling (e.g. finiteelement, finitedifference)Representative slope geometr