Ensuring safe extraction is a prerequisite for the development of deep-sea resources. As an in-situ exploration technique, cone penetration test (CPT) can accurately analyze the physical, strength, and deformation characteristics of deep-sea sediments and hydrate reservoirs after data interpretation, thereby ensuring the safe extraction of deep-sea resources. CPT calibration chamber (CCC) testing is considered one of the most effective means to determine the correlation between lab measurement values of soil and its undisturbed mechanical properties. Currently, the stress conditions of the CCCs that have been established are limited in scope and insufficient to simulate the high-stress field conditions of deep-sea sediments as well as the high-pressure and low-temperature conditions where deep-sea hydrates occur. Therefore, based on the traditional CCC, this article independently developed a high-pressure and temperature-controlled CCC with a type of boundary condition one (BC1), which can be used to simulate the process of CPT penetrating marine sediments (including the in-situ environment of hydrate reservoirs). This CCC features a maximum loading force of 200 KN at the top and 150 KN at the bottom. With a maximum confining and pore pressure of 25 MPa, and a temperature range from -15 degrees C to room temperature, it can effectively replicate in-situ effective stress, pore pressure, and temperature conditions necessary for hydrate formation. The maximum sample size is 300 mm in diameter and 600 mm in height, and two sizes of CPT probes (2 cm2 and 5 cm2) can be replaced to test the boundary effect. To verify the feasibility of the CCC, a series of CPT penetration experiments were conducted on silty sediments under highpressure and temperature-controlled conditions in the established CCC. It was found that cone tip and friction resistance increase with the increase of effective stress. This CCC contributes to establish the relationship between CPT data and various mechanical properties of marine sediments, and providing theoretical support for evaluating the stability of marine hydrate reservoirs during exploitation.

The traction force of the tracked miner is primarily determined by the shear characteristics of deep-sea sediments. The influence of different parameters on the shear characteristics of deep-sea sediments and the particles change law of the soil-track interface are discussed. By constructing the relationship between the particles horizontal displacement and residual shear strength, a novel shear rheological damage model of deep-sea sediments considering the influence of grounding pressure is proposed, and the microscopic mechanism of shear displacement of deep-sea sediments is explained. The results show that the peak shear strength and residual shear strength increase significantly with the increase of grounding pressure, track length, grouser height and shear speed. Moreover, the particles within the soil-track interface move along the lower right of the vehicle operating direction during the shearing process under different working conditions, the change of particle spacing shows a non-linear trend, and a quantitative equation for the horizontal deformation of soil-track interface under the experimental conditions is constructed. Additionally, the new shear model has a high level of accuracy in fitting with the experimental data, the internal particle migration changes on the soil-track interface can be divided into four characteristics: compaction, failure, deformation and translation.

This study establishes a coupled thermo-hydro-mechanical dynamic model(THMD) for saturated porous sediments under the eccentric motion of a deep-sea mining vehicle, considering the characteristics of deep-sea sediments. We applied the method of complex Fourier series expansion to simplify the coupled equations into ordinary differential equations and obtained the complex Fourier series expansion forms of various physical quantities of sediments during the eccentric movement of the mining vehicle. The undetermined constants are determined based on boundary conditions, yielding a series representation of the solution for THMD of deep-sea sediments. Subsequently, the solution was utilized to investigate the influence of mining vehicle parameters on the dynamic response of deep-sea sediments. This study demonstrates that the vertical displacement, vertical stress, and excess pore water pressure of sediments increase as the speed of the mining vehicle increases. Furthermore, the vertical displacement, vertical stress, and excess pore water pressure increase with the increment of load amplitude, and the differences in the curves at different eccentricities gradually become larger as the load amplitude increases. The proposed model can be applied to geotechnical engineering problems in saturated porous foundations, providing a necessary theoretical basis and analytical approach.