Search

In the mining process of a coal seam containing a fault structure, due to the influence of mining stress, the rock mass inside the fault zone and between the fault and the coal pillar that is preserved to prevent fault activation is prone to producing damage and activation. This study is focused on this problem. Based on the analysis of the failure, activation and movement of the rock mass in front of the fault body and the coal wall, extended finite element numerical simulation software is adopted to study the stress evolution and deformation failure rules of a coal seam containing a fault floor. In particular, the dynamic response process (including slip velocity, slip distance and friction force) of the fault structure under mining conditions is monitored, and then the turning and failure process of the fault structure is analysed. However, an analogue modelling is reformed. A similar material analysis model is established to monitor the displacement field changes near the fault during the mining process, obtain the movement rules of the fault zone and surrounding rock mass during the mining process, and then verify the reliability of the numerical simulation results. The research results can provide references for exploring the coupling movement rules between the fault and the work area for production in the mining process of coal seam stopes, as well as prevention before water inrush under the influence of the fault and treatment after water inrush.

Based on laboratory experiments, the paper researches the effect of polyvinyl alcohol (PVA) content on the performance of fly ash-based cement grouting materials. The test results show that the addition of PVA has limited effect on the initial and final setting time and brings a certain but minor delay on the appearance of the hydration peak period. It enhances cement hydration during the hydration slow down period. The impermeability of PVA to the grouting material is obviously improved, and it increases with the growing amount of PVA content. PVA improves the flexural strength and compressive strength of the sample block to varying degrees, and the improvement on flexural strength is more obvious than that on the compressive strength. It has a significant effect on the mechanical properties of the grouting material and can effectively improve the rock mass’s hydraulic coupling characteristics. It also has great application value and practical significance for the prevention and control of water hazards in deep coal stopes.

Renewable energy-based microgrids play a critical role in future smart grids. Due to the uncertainties of renewable generations, the microgrids face potential risk of load shedding during operation. To address this problem, we propose a contract-based approach to enhance the resilience of microgrids. Specifically, in the framework, the microgrids who may not be self-efficient to meet their local demands can purchase the needed power from their connected microgrids by signing a contract that specifies the power price in advance. We leverage a principal-agent model to capture the energy trading relationships between the microgrids through a resilience as a service (RaaS) paradigm. By focusing on the incentive compatible and individual rational constraints of the service requester, the service provider designs the optimal contracts for the transactive resilience that yields the largest payoff despite the incomplete information. We characterize analytical solutions of the optimal contracts for several scenarios where the service requester has various options on its hidden actions. Numerical simulations are used to illustrate and corroborate the obtained results.

In this study, the feasibility of using municipal solid waste incineration fly ash (MSWIFA) as additive for the strengthening of pretreated cement-stabilized soil was evaluated. Results indicated that the leaching concentrations of chromium and lead in MSWIFA after the water washing process and addition of 4% ferrous sulphate were reduced by 67% and 89%, respectively, which was lower than the limit value of Identification standard for hazardous waste (GB 5085.3-2007). After pretreatment, MSWIFA samples with ratios of 5% and 10% were blended into cement-stabilized soil with ordinary Portland cement (OPC) content of 10%, 15% and 20%. The unconfined compressive strength (UCS), internal friction angle and cohesion of the cement-stabilized soil increased with OPC and pretreated MSWIFA (PFA) content. The same effect was observed on UCS after the addition of 10% PFA as replacement of 5% OPC. In the subsequent X-ray powder diffraction test, scanning electron microscopy and leaching tests, the leaching concentrations of heavy metals in cement-stabilized soil became far lower than the limit value under the synergistic effects of the physical encapsulation of hydration products and stabilization of chemical agents. The incorporation of PFA as a supplementary material can effectively accelerate the formation of hydration products and can thus provide cleaner options for foundation reinforcement.

The use of calcium solutions is a cost-limiting factor for bio-cement production from microbially induced carbonate precipitation (MICP). The aim of this article is to analyse the feasibility of using recycled calcium sources to solidify sand, including oyster shells, scallop shells and eggshells, by comparing the physical and mechanical properties and microstructural characteristics of solidified sand with different recycled calcium sources and chemical calcium nitrate. The results show that oyster shells have the optimal effect on MICP, with values of permeability, dry density, unconfined compressive strength and calcium carbonate precipitation of 1.12 × 10−4 m s−1, 2.09 g cm−3, 1454.6 kPa and 15.28%, respectively. Strength values of bio-cemented sands made from different recycled calcium sources in this article range from 845.1 to 1454.6 kPa. According to the SEM and XRD analysis, calcium carbonates originating from the above recycled calcium sources precipitate as globular vaterite, whereas the precipitation from calcium nitrate is a cluster mixture of vaterite and calcite. Oyster shells, scallop shells and eggshells derived from kitchen waste, which is more economical and environmentally friendly than calcium nitrate, can be applied as recycled calcium solutions in MICP.

The structural planes existing in natural rock mass can control the failure process of rock mass. Based on the progressive response-stability failure process of a single fracture interface, the relationship between progressive response and material failure of composite rock mass is discussed. The method of friction contact plane analysis in PANDAS numerical analysis software is applied to explore the correlation between the movement and mechanical properties of composite rock mass under external forces. The motion index is mainly represented by the sliding speed and distance of the contact surface, while the mechanical properties are mainly explained by the normal contact force, the friction of the contact surface, the friction coefficient and the material damage. The relationship between these six variables illustrates the progressive response relationship during the movement of the composite rock mass. Based on the static and progressive characteristics of the progressive response process of deep rock mass engineering, the failure evolution law and energy dissipation law of composite rock mass loading process and the synergistic failure characteristics of composite rock mass are discussed. The scientific problems that need to be studied in the structure, deformation and failure of deep rock mass are put forward. The reference is provided for the failure law of fractured rock mass in water inrush process under the influence of mining, as well as fault plate material and the study of mechanical state of rock mass in fault fracture zone.

In this paper, we consider a linear-quadratic-Gaussian defending assets differential game (DADG) where the attacker and the defender do not know each other's state information while they know the trajectory of a moving asset. Both players can choose to observe the other player's state information by paying a cost. The defender and the attacker have to craft both control strategies and observation strategies. We obtain a closed-form feedback solution that characterizes the Nash control strategies. We show that the trajectory of the asset does not affect both players' observation choices. Moreover, we show that the observation choices of the defender and the attacker can be decoupled and the Nash observation strategies can be found by solving two independent optimization problems. A set of necessary conditions is developed to characterize the optimal observation instances. Based on the necessary conditions, an effective algorithm is proposed to numerically compute the optimal observation instances. A case study is presented to demonstrate the effectiveness of the optimal observation instances.