堆石混凝土坝采用分层浇筑的施工工艺,层间界面通过部分堆石外露以提升抗剪性能,使其剪切力学行为复杂,相关认识仍有待深化。开展了450 mm×450 mm×450 mm(长×宽×高)大型直剪试验,结合数字图像相关(DIC)技术,研究了0.25、0.5、0.75、1.0、1.25 MPa这5个法向应力下层面剪切破坏特征及层间堆石对破坏路径的影响机制。结果表明:随法向应力增大,剪切强度、残余强度及峰值位移分别提高了31.02%~86.63%,70.44%~221.78%和14.95%~69.16%,剪切断面均出现露石破坏减少27.5%,HSCC剥落现象增加50%,破坏路径由沿层面平直扩展转为向试件上、下部延伸分叉;应变局部化带由层面逐渐扩展至试件上半块,扩展方式也由单一方向转变为多条弥散型,且应变局部化带宽度逐渐增加;随法向应力提高,层间露石的楔入效应越强,从而影响层面剪切破坏路径。研究结果揭示了法向应力与露石对RFC层面剪切破坏的调控机理,可为层间界面施工质量控制与稳定性评价提供参考。

[Objective] Rock-filled concrete (RFC) dams are generally constructed by means of layered pouring technology. Partial exposure of rock blocks on interlayer interfaces is adopted to effectively enhance the interlayer shear resistance, which consequently leads to highly complex shear mechanical behaviors of interlayer bonding surfaces. At present, the research cognition on the shear failure evolution law and internal mechanical mechanism of RFC interlayer interfaces remains insufficient and needs to be further supplemented and deepened. Aiming at this engineering problem, this study intends to clarify the whole evolution process of interlayer shear failure of RFC under varying normal stress conditions, reveal the influence law of interlayer exposed rock blocks on the initiation, propagation and final development trend of shear failure paths, and explore the synergistic regulation mechanism between normal stress and exposed rock blocks on interlayer shear mechanical properties. [Methods] Large-scale direct shear tests were carried out on cubic (450 mm) RFC specimens. Five typical normal stress levels (0.25, 0.5, 0.75, 1.0, and 1.25 MPa) were set up to simulate different in-situ stress environments of dam interlayers during actual service. Meanwhile, the non-contact full-field deformation monitoring method based on Digital Image Correlation (DIC) technology was synchronously applied. During the whole shear loading process, the surface strain field distribution, micro-crack initiation position, macroscopic crack expansion morphology and interface deformation characteristics of RFC specimens were captured in real time. Combined with macroscopic mechanical test data, the coupling relationship between interlayer exposed rock blocks and shear failure modes was systematically analyzed. [Results] Normal stress exerts a prominent positive influence on interlayer shear mechanical indices. With the increase of normal stress, the interlayer shear strength, residual shear strength and peak shear displacement rise by 31.02%~86.63%, 70.44%~221.78% and 14.95%~69.16% respectively. Obvious variations occur in the morphological characteristics of shear fracture surfaces: the proportion of rock-exposed failure on shear sections decreases by 27.5%, while the spalling phenomenon of highly self-compacting concrete (HSCC) matrix increases by 50%. In terms of macroscopic failure paths, the failure mode transforms from straight planar propagation along the interlayer interface into branched expansion extending towards the upper and lower parts of specimens. The distribution range of strain localization bands gradually expands from the single interlayer interface to the interior of upper specimens, and the strain development pattern changes from unidirectional concentrated distribution to multi-directional dispersed distribution, accompanied by a continuous increase in the width of strain localization bands. Mechanically, higher normal stress can significantly strengthen the wedging and embedding effect of exposed rock blocks distributed on interlayer interfaces, which further dominates and restricts the propagation direction and expansion range of interlayer shear cracks. [Conclusions] This study systematically reveals the intrinsic regulation mechanism of normal stress and interlayer exposed rock blocks on the shear failure behaviors of RFC interlayer interfaces. The quantitative evolution rules of key shear mechanical parameters and the transition law of typical interlayer failure modes under different normal stress states are clearly clarified.