| The rock slopes are often destabilized by the excavation of road graben,among which the medium dip slopes with the dip angle of 15°～35° account for a large proportion,and are more prone to destabilization by the excavation of road graben than the slow dip slopes.Soft rocks have mechanical characteristics such as low strength,easy to disintegrate and soften by water,and easy to deform by force,which make engineering construction and design more difficult.In this paper,the factors influencing the stability of soft rock slopes with medium dip angle under excavation conditions are discussed by distinguishing the degree of hardness of soft rock by saturated uniaxial compressive strength,and the damage mode is summarized and the determination formula is given.Finally,a case study of a slope site damaged by destabilization due to excavation in the Yibin River Expressway Project was analyzed,and a reasonable construction strategy was discussed based on discrete elements,with the following main research contents and conclusions:The saturated uniaxial compressive strength is used as an index to distinguish the degree of hardness of soft rocks,and the physical and mechanical parameters of rock masses and major joints corresponding to soft rocks with saturated uniaxial compressive strength of 0～15 MPa are estimated by Hoek-Brown damage criterion and Barton-Bandis joint model.150 cases of soft and weak interlayer parameters are summarized by literature collection method,and the parameters satisfy normal distribution,and the expected value is taken as the shear strength parameter of soft and weak interlayer with friction angle of 17° and cohesion of 20 k Pa.The stability of medium-inclined cascading soft rock slopes under excavation conditions is analyzed from the perspective of geometric factors and rock strength,and the damage modes of different slopes are further discussed.Under other conditions,the damage mode gradually evolves from arc-planar sliding damage to cascading planar sliding damage when φ gradually decreases,and the judgment formula is φ=0.9θ+0.35UCS-2.5 for jointed rock slopes andφ=0.7θ+0.1UCS+2.2 for non-jointed rock slopes.Based on circular-planar sliding damage and paralleling planar sliding damage,the main factors are selected with reference to the results of influence factor analysis,the stability under different excavation processes are discussed,and corresponding excavation construction strategies are proposed for different types of slopes according to the safety factors of different slopes under different construction conditions and with reference to slope characteristics such as potential damage range.Based on the Yibin riverine expressway project,a slope damaged by instability due to road graben excavation was used as a case study,and the coordinates and production of slip surface and tension crack were clarified by means of geological mapping and RTK measurement,and a three-dimensional numerical model was established based on ground contours.The physical and mechanical parameters of the rock and joints in the study area were estimated by the empirical judgment method combined with Hoek-Brown damage criterion and Barton-Bandis joint model,and the friction angle of the slip surface was determined to be 17.5° and the cohesive force was 20 k Pa by numerical inversion method,and the landslide evolution analysis was carried out by the obtained parameters,which were compared with each feature of the actual landslide to verify the reasonableness of the parameters.The reasonableness of the parameters was compared with the various characteristics of the actual landslide,and a series of reasons leading to the landslide were summarized,the main reason being the one-time excavation of the slope,and finally a reasonable construction strategy for the study site was discussed based on the discrete element numerical simulation. |
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