As a hydrocarbon reservoir rock, shale is generally composed of highly compacted clay particles with submicrometer sizes and includes nanometric porosity and different hard particles, like quartz, pyrite, etc. One of the key reasons for the formation of a complex fracture network via hydraulic fracturing is the multiscale heterogeneity of shale, especially heterogeneity on the microscale. This paper conducted on an experimental investigation of shale and explored the intrinsic relationship between the microstructure, the related mechanical properties at the micrometer level and the anisotropic failure mechanism. Small-scale specimens with micrometer dimensions in the form of cantilever beams with rectangular cross-section were fabricated by means of a focused ion beam (FIB) and tested via bending with a nanoindenter. The load–deflection curves of these bending beams were monitored up to failure, and the tensile strength of the shale composite was directly derived from the load–deflection curves at 474.5 MPa (parallel to the bedding plane) and 168.9 MPa (vertical to the bedding plane). The results show that the strength anisotropy of shale at the micrometer scale is driven by the clay particles and other minerals, and the bonds of these particles. The modulus anisotropy of the shale composite at the microscale is dominated by the orientation of clay particles. Moreover, the shale composite embedded with pyrite exhibited strong softening characteristics.

Damaged adobe masonry is essential to retrofit not only for continued use by less developed populations but also for historical preservation and vernacular landmark maintenance. Coating mortar on adobe can greatly improve the static load-carrying capacity of adobe masonry Wallette. Four retrofitting methods are carried out to enhance the cooperation of mortar and adobe; these four methods focus on the factors of roughness, shear dowel, and mesh size and a novel biological and traditional Chinese binder, sticky rice pulp. The mortar coating with the four bonding enhancement methods can greatly increase both the compressive and lateral load-carrying capacities, with a maximum improvement of 177 and 743%, respectively. The bonding strength has a negative effect on the compressive load-carrying capacity; on the other hand, it has a positive effect on the lateral load-carrying capacity. A range analysis is also carried out, which shows that the shear dowel depth has the greatest effect on both load situations, followed by the wire mesh size.

In this work, one type of commonly used commercial cellulose fibre with lengths ranging from mu m to mm is introduced into cement paste at concentrations of 0.1 wt% to 10 wt% to study its effect on enhancing tensile behaviour and microstructural evolution at the early curing stage. Significantly inhibited hydration due to cellulose fibre incorporation is revealed, and the degree of inhibition increases as the length of the cellulose fibres decreases. Additionally, the degree of hydration calculated by the TGA data of cellulose fibre-incorporated cement paste needs to be calibrated against the mass loss of cellulose fibres during heating because it cannot be directly deduced by the TGA data of pure cellulose fibres. Only mm-scale cellulose fibres significantly improve the post-peak ductility, whereas mu m-scale cellulose fibres have a weak enhancement effect on the post-peak ductility. It is found that cellulose fibres at both the mu m and mm scales can enhance the tensile strength at day 28. Regarding this type of commercial cellulose fibre, it is optimal to adopt the mm-scale cellulose fibres because of their significant effect on improving tensile behaviour.

Chuandou-style timber structures have been widely deployed in rural areas of Southern China; however, their seismic performance has not been fully examined. A shaking table test for a half-scale two-story Chuandou-style timber structure filled with wooden walls was performed first. The slippage of the column root, pull-out of the tenon, and extrusion deformation between the wooden wall and the timber frame were the principal damage patterns. Then, a nonlinear dynamic analysis of a finite element (FE) model of the tested structure was performed, which was established based on a reasonable structural simplification using OpenSees. Two different types of connections between the column root and cornerstone were investigated in detail: hinged connection and rigid connection. The results indicate that the relative errors between the FE modeling and experiments in terms of the first structural natural frequency were 6.5% and 11.3% in the x and y directions, respectively. The rigid connection of the column root negatively affected the dynamic response of the Chuandou-style timber structure compared to the hinged connection. The acceleration amplification factors of each structural layer were greater than 1.0 when the column root was rigidly connected, and the inherent advantages of timber structures in terms of the energy dissipation capacity were seriously diminished. Therefore, the complete rigid fixation method is not recommended for the column root in Chuandou-style timber structures in engineering practice.

Shale contains a certain amount of natural fractures, which affects the mechanical properties of shale. In this paper, a bonded-particle model in particle flow code (PFC) is established to simulate the failure process of layered shale under Brazilian tests, under the complex relationship between layer plane and natural fracture. First, a shale model without natural fractures is verified against the experimental results. Then, a natural fracture is embedded in the shale model, where the outcomes indicate that the layer plane angle (marked as α) and the angle (marked as β) of embedded fracture prominently interfere the failure strength anisotropy and fracture pattern. Finally, sensitivity evaluations suggest that variable tensile/cohesion strength has a changeable influence on failure mechanism of shale, even for same α or/and β. To serve this work, the stimulated fractures are categorized into two patterns based on whether they relate to natural fracture or not. Meanwhile, four damage modes and the number of microcracks during the loading process are recognized quantitatively to study the mechanism of shale failure behavior. Considering the failure mechanism determines the outcome of hydraulic fracturing in shale, this work is supposed to provide a significant implication in theory for the engineering operation.