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Subsurface fluid injection and extraction can reactivate faults and induce earthquakes. In current research, faults are typically described as symmetrical structures and the presence of asymmetric structures is often overlooked. The reality is that numerous asymmetric faults exist within the Earth's crust. The architectural and permeability characteristics of fault zones differ significantly between symmetrical and asymmetrical faults. These differences may have a great influence on fault stability during fluid injection or extraction. In this study, the impact of fault zone structures on fluid-induced slips and seismic activity were investigated through numerical analysis. The findings indicated that symmetrical faults were more likely to induce larger slips and earthquakes during various subsurface fluid operations. For asymmetric faults, larger induced slips occurred when fluid was operated in a hanging wall reservoir than in a footwall reservoir. In symmetrical faults, the opposite was true. When evaluating the stability of a fault in subsurface fluid engineering, the fault structure and fluid pattern and their combined effects must be considered comprehensively. [ABSTRACT FROM AUTHOR]

Cement solidification was a widely used method to broaden the resource utilization of dredged sludge. However, the organic matter in sludge limit the application of cement solidification. The fulic acid (FA) was used to simulate the natural organic matter in sludge. With the increase in FA content, the sludge gradually changed from low-liquid-limit clay to high-liquid-limit clay. The unconfined compression test showed that the strength of cement-solidified dredged sludge (CDS) decreased with FA content. The influence mechanism of the FA on cement solidification was revealed by a water content test, a hydration heat test, scanning electron microscopy, and thermogravimetric analysis. FA hindered the conversion of pore water to combined water and reduced the hydration heat inside CDS. The FA in sludge weakened the internal bond within CDS by hindering the development of C-S-H gel from spheroidal to flake. At the same time, the final amount of hydrates such as C-S-H, C-A-H and AFt also decreased in the CDS containing FA. The weakening mechanism of FA on the strength of CDS can be attributed to three aspects: (1) FA adsorbed on the surface of cement minerals and hindered the contact between cement minerals and pore water; (2) acidic FA reduced the pH of the pore liquid in CDS; (3) the carboxyl and hydroxyl functional groups of FA adsorbed calcium ions in pore liquid through ion coordination. [ABSTRACT FROM AUTHOR]

The unconfined compressive strength (UCS) of sludge with different consistency limits solidified by cement was investigated. The results showed that under the condition of constant initial water content, a higher liquid index of soil resulted in higher UCS. A novel strength-evaluation model based on the ratio of the liquid index to the cement content was developed, and the prediction deviation of the model was within 30%. The influence mechanism of the consistency limit of sludge on the cement solidification was revealed by scanning electron microscopy, mercury intrusion porosimetry, X-ray diffractometer and thermogravimetric analysis. For the cement-solidified dredged sludge (CDS) with a lower liquid index, a large amount of hydrate was interlaced with each other and wrapped soil particles, promoting the formation of a dense structure. For the CDS with a higher liquid index, hydrates such as C-S-H and ettringite challenged each other to play the role of "cementing particles" and "filling pores", resulting in the formation of the porous structure. The mineralogical analyses confirmed that more C-S-H gels and ettringites were generated in the CDS with a lower liquid index, but less calcite was formed due to its denser structure. In engineering applications, reducing the liquid index by adjusting the consistency limit can improve the strength performance of CDS. [ABSTRACT FROM AUTHOR]

Cement-stabilized dredged sediment (CDS) when used as a new road construction material cannot only solve the problem of abandoned sediment disposal, but also effectively save natural soil resources. This study aimed to evaluate the strength and permeability of CDS and establish corresponding prediction models from the perspective of a stabilization mechanism. The soil–water composition and pore size distribution were investigated by the nuclear magnetic resonance (NMR) technique. The results demonstrated that more liquid pore water inside the CDS specimen transformed into combined water with cement hydration. The amount of combined water, which essentially characterized the hydration process of cement, presented a linear relationship with log (t). The cementation and filling action of hydrates resulted in the transformation of large pores into smaller ones, hence the optimal pore size decreased with an increasing curing period and cement content. The stress–strain curves and hydraulic conductivity were determined based on unconfined compression and flexible wall penetration tests, respectively. The unconfined compressive strength increased exponentially with the amount of combined water, and the functional correlations of hydraulic conductivity and micropore parameters were established. The reliability of the NMR technique as a new method to study the microscopic evolution mechanism of the strength and permeability of CDS was further verified by scanning electron microscopy and mercury intrusion porosimetry tests. [ABSTRACT FROM AUTHOR]

The multivariate range function of the high-speed maneuvering target induces modulations on both the envelop and phase, i.e., the range cell migration (RCM) and Doppler frequency migration (DFM) which degrade the long-time coherent integration used for detection and localization. To solve this problem, many long-time coherent integration methods have been proposed. Based on mechanisms of typical methods, this paper names two signal processing modes, i.e., processing unification (PU) mode and processing separation (PS) mode, and presents their general forms. Thereafter, based on the principle of the PS mode, a novel long-time coherent integration method, known as the generalized dechirp-keystone transform (GDKT), is proposed for radar high-speed maneuvering target detection and localization. The computational cost, energy integration, peak-to-sidelobe level (PSL), resolution, and anti-noise performance of the GDKT are analyzed and compared with those of the maximum likelihood estimation (MLE) method and keystone transform-dechirp (KTD) method. With mathematical analyses and numerical simulations, we validate two main superiorities of the GDKT, including (1) the statistically optimal anti-noise performance, and (2) the low computational cost. The real radar data is also used to validate the GDKT. It is worthwhile noting that, based on closed analytical formulae of the MLE method, KTD method, and GDKT, several doubts in radar high-speed maneuvering target detection and localization are mathematically interpreted, such as the blind speed sidelobe (BSSL) and the relationship between the PU and PS modes. [ABSTRACT FROM AUTHOR]