岩石力学与工程学报
巖石力學與工程學報
암석역학여공정학보
CHINESE JOURNAL OF ROCK MECHANICS AND ENGINEERING
2014年
3期
631-638
,共8页
桩基础%冲切破坏%极限分析%功能方程%安全厚度
樁基礎%遲切破壞%極限分析%功能方程%安全厚度
장기출%충절파배%겁한분석%공능방정%안전후도
pile foundations%punching failure%limit analysis%work-energy equations%safe thickness
岩溶区桩基桩端岩层易发生冲切破坏。针对岩溶区岩体特点引进Hoek-Brown非线性岩石破坏强度准则，并推导得其剪应力的二次抛物线型表达式。基于极限分析上限法原理，确定冲切破坏体的功能方程，并通过变分求极值原理获得冲切破坏体的母线方程，进一步通过微分得到桩端岩层抗冲切安全厚度计算公式。结合岩溶区桩基实践，分析抗冲切安全厚度影响因素的取值范围并进行参数分析，结果表明：(1)冲切破坏体上下直径比d1/d随岩体地质力学分类指标RMR值的增大呈非线性减小，说明岩体质量好的岩溶顶板其冲切所形成的锥形旋转体底部直径小，反之，旋转体底部直径大；(2)根据不同的d1/d及RMR值，初始冲切角为24°～42°；(3)厚径比h/d随RMRαs的增大呈非线性减小，表明岩体质量越好，所需安全厚度也越小；在岩体质量较好(RMR＞65)的情况下，h/d基本在2.5以下。
巖溶區樁基樁耑巖層易髮生遲切破壞。針對巖溶區巖體特點引進Hoek-Brown非線性巖石破壞彊度準則，併推導得其剪應力的二次拋物線型錶達式。基于極限分析上限法原理，確定遲切破壞體的功能方程，併通過變分求極值原理穫得遲切破壞體的母線方程，進一步通過微分得到樁耑巖層抗遲切安全厚度計算公式。結閤巖溶區樁基實踐，分析抗遲切安全厚度影響因素的取值範圍併進行參數分析，結果錶明：(1)遲切破壞體上下直徑比d1/d隨巖體地質力學分類指標RMR值的增大呈非線性減小，說明巖體質量好的巖溶頂闆其遲切所形成的錐形鏇轉體底部直徑小，反之，鏇轉體底部直徑大；(2)根據不同的d1/d及RMR值，初始遲切角為24°～42°；(3)厚徑比h/d隨RMRαs的增大呈非線性減小，錶明巖體質量越好，所需安全厚度也越小；在巖體質量較好(RMR＞65)的情況下，h/d基本在2.5以下。
암용구장기장단암층역발생충절파배。침대암용구암체특점인진Hoek-Brown비선성암석파배강도준칙，병추도득기전응력적이차포물선형표체식。기우겁한분석상한법원리，학정충절파배체적공능방정，병통과변분구겁치원리획득충절파배체적모선방정，진일보통과미분득도장단암층항충절안전후도계산공식。결합암용구장기실천，분석항충절안전후도영향인소적취치범위병진행삼수분석，결과표명：(1)충절파배체상하직경비d1/d수암체지질역학분류지표RMR치적증대정비선성감소，설명암체질량호적암용정판기충절소형성적추형선전체저부직경소，반지，선전체저부직경대；(2)근거불동적d1/d급RMR치，초시충절각위24°～42°；(3)후경비h/d수RMRαs적증대정비선성감소，표명암체질량월호，소수안전후도야월소；재암체질량교호(RMR＞65)적정황하，h/d기본재2.5이하。
The rock stratum at pile tip is prone to punching failare for pile foundation in karst region. The Hoek-Brown nonlinear rock strength criterion has been introduced according to the characteristics of rock mass in the karst region;and then the shear stress of quadratic parabolic expression was obtained. The work-energy equation of punching failure body was established using limit analysis method. Then the generatrix equation of punching failure body was obtained through the variational extremum principle. Furthermore,the calculation formula of safe thickness for the rock stratum anti-punching failure was obtained by differential equation. Combined with the practice of pile foundation in karst area,the value range of main resistant punching shear safety thickness factors affecting were analyzed. Parameter analysis shows that:(1) The top and bottom diameter ratio d1/d of punching failure body decreased nonlinearly along with the increase of RMR value;in other words the bottom conical rotor diameter of punching failure which formed by the good karst roof of rock mass quality is small. Conversely,the greater the diameter at the bottom of the body of revolution. (2) According to the different d1/d and RMR values,the ranges of initial punching angle is between 24°-42°. (3) The ratio of thickness to diameter h/d decreases nonlinearly along with the increase of RMR. That is to say the better the rock mass quality, the smaller the safe thickness. When the rock mass quality is good(RMR>65),the safety thickness h/d is lower than 2.5.
