CAJ | 학술논문

目前国际上普遍认为完整岩体的现场强度近似等于(0.4±0.1)σc ，其中，σc为室内岩石单轴抗压强度。此外，也有学者建议原位岩体的破坏强度，即地下工程围岩的启裂强度，可等价于室内单轴压缩试验或现场微震监测确定的岩石裂隙初始的应力；其原理主要以基于Kirsch解析解或简化的数值模拟(光滑的开挖边界)来近似表达隧道开挖面上的最大切向应力σmax。然而，这些方法均忽略了开挖边界的几何非规则性对计算结果的影响。经论证表明，若考虑开挖面的几何非规则性因素，完整岩体的现场破坏强度并不等于(0.4±0.1)σc ，其破坏强度可高达(0.8±0.05)σc。以加拿大地下实验室Mine-by试验隧道为例，并以该隧道的实际断面形状为几何边界条件，采用有限元软件Phase 2模拟隧道围岩的渐进破坏过程。研究结果表明，当原位岩体强度为0.8σc时，模拟结果与实际观测结果具有很好的一致性。因此，忽略开挖边界的几何非规则性而解读的原位岩体强度(0.4±0.1)σc仅是“等价”强度值，其低估了岩体的实际强度。
목전국제상보편인위완정암체적현장강도근사등우(0.4±0.1)σc ，기중，σc위실내암석단축항압강도。차외，야유학자건의원위암체적파배강도，즉지하공정위암적계렬강도，가등개우실내단축압축시험혹현장미진감측학정적암석렬극초시적응력；기원리주요이기우Kirsch해석해혹간화적수치모의(광활적개알변계)래근사표체수도개알면상적최대절향응력σmax。연이，저사방법균홀략료개알변계적궤하비규칙성대계산결과적영향。경론증표명，약고필개알면적궤하비규칙성인소，완정암체적현장파배강도병불등우(0.4±0.1)σc ，기파배강도가고체(0.8±0.05)σc。이가나대지하실험실Mine-by시험수도위례，병이해수도적실제단면형상위궤하변계조건，채용유한원연건Phase 2모의수도위암적점진파배과정。연구결과표명，당원위암체강도위0.8σc시，모의결과여실제관측결과구유흔호적일치성。인차，홀략개알변계적궤하비규칙성이해독적원위암체강도(0.4±0.1)σc부시“등개”강도치，기저고료암체적실제강도。
It is widely accepted that the field or in-situ strength of massive rocks is approximately (0.4±0.1)σc, whereσc is the uniaxial compressive strength obtained from unconfined laboratory tests. In addition,it has been suggested that the in-situ rock spalling strength,i.e. the strength of the wall of an excavation when spalling initiates,can be set to the crack initiation stress determined from laboratory test or field microseismic monitoring. These findings were based on either Kirsch′s solution or simplified numerical stress modeling(with smooth tunnel wall boundary) to approximate the maximum tangential stressσmax at the excavation boundary. In this article,it is suggested that these approaches ignore one of the most important factors,the irregularity of the excavation boundary. It is demonstrated that the“actual”in-situ spalling strength of massive rocks is not equal to (0.4±0.1)σc ,but can be as high as (0.8±0.05)σc when surface irregularities are considered. It is demonstrated using the Mine-by tunnel notch breakout example that when the realistic“as-built”excavation boundary condition is honored,the“actual”in-situ rock mass strength,given by 0.8σc ,can be applied to simulate progressive brittle rock failure process satisfactorily. We conclude that the interpreted,reduced in-situ rock mass strength of (0.4±0.1)σc without considering geometry irregularity is therefore only an“apparent”rock mass strength.