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Abstract It is of great significance to evaluate the stress state and mechanical properties of deep rock engineering, by inverting the real-time porosity of rocks. In this study, the triaxial compression tests and real-time ultrasonic velocity tests were conducted on siltstone under different confining pressures. Firstly, a nonlinear model for the evolution of rock ultrasonic velocity with axial strain was proposed, based on the characteristic that the ultrasonic velocity rapidly increases and tends to stabilize. Secondly, a correction coefficient for the ultrasonic velocity of the rock matrix was proposed and the Raymer model was modified. The real-time porosity during triaxial compression of rocks was inverted according to the modified Raymer model and the ultrasonic velocity model. Subsequently, the effective compression coefficient of rocks was calculated based on real-time porosity, and a compaction coefficient was established to describe the compaction effect of cracks and pores. Finally, a new compressive-damage coupled constitutive model for rocks was established, by combining the statistical damage theory and compaction effect.

A stepped cyclic loading test was designed to investigate the stress memory and acoustic emission characteristics of siltstone under different previous stress levels. This study aims to improve the applicability of the acoustic emission in situ stress measurement method in porous weak cementation strata. The stress memory failure range for siltstone and the memory stress correction formula were determined based on characteristic stress value. The analysis of acoustic emission characteristics revealed the failure mechanism of the Kaiser effect of siltstone, and the following conclusions were obtained. Crack initiation stress can serve as the failure criterion for the stress memory effect in siltstone. Therefore, the failure range for the stress memory effect in siltstone can be defined as a previous stress of less than 15.3 MPa and a memory stress of less than 13.7 MPa. The pore compaction process in siltstone and the friction-generated acoustic emission signal during this process negatively affect stress memory. The primary cause of the stress memory effect in rocks is the irreversible development of new internal cracks. The compression rebound effect of primary soft pores in siltstone mainly causes the Kaiser effect to fail. The compression rebound effect of primary soft pores in siltstone is the main reason for the failure of the Kaiser effect. [ABSTRACT FROM AUTHOR]

Our study on the seamounts in the southeast Caroline Plate reveals a formation of a special kind of seamounts in the oceanic basin. These moniliform seamounts link up like the reason of hotspots, but the tectonic factors lead to their formation. The differential motions of the Caroline, North Bismarck, and Pacific plates resulted in the shear stress field by the West Melanesian Trench. The R and R′ faults can be distinguished obviously by seafloor topography. The evolution history of these seamounts can be subdivided into two stages as follows. (a) The R′ faults developed firstly as normal faults to generate ridges on these faults as the release of the underlying sediments. (b) The R faults appeared as shear faults and cut off the ridge from the older R′ faults. These faults can be very deep fractures, which cut through the lithosphere and produced a NW‐trending negative anomaly in isostatic gravity anomaly. As the pressure is released by the R faults, the sediments releasing under the R faults accumulated into these seamounts. The other sections of the R faults performed like a valley because of the leakage of sediments along the faults. Sediments would also release along the R faults to generate ridges when no seamount occurs on the faults. [ABSTRACT FROM AUTHOR]