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 control of surface heaving has been of interest in major applications of compaction grouting such as ground improvement and settlement compensation works. Some studies generalize compaction grouting as heave-inducing and thus the corresponding soil improvement increases with depth, while others do not. Effective planning of compaction grouting requires assessment of whether it is heave-inducing and understanding the effects of confining stresses on its mechanisms and effectiveness. Unfortunately, little effort has been made in this regard. The current paper addresses these issues through physical modeling of compaction grouting using a large-scale double-wall calibration chamber and injection system capable of injecting the stiff compaction grouts. The results of twenty-one test cases conducted under well-controlled conditions are presented, discussed, and compared with the results of actual compaction grouting. The confining stresses as represented in terms of the vertical stress (sigma V) and coefficient of earth pressure at rest (K0). The presented results and discussions show the reliability of the adopted modeling. Empirical correlations that engineers can use to predict the occurrence of surface heaving as well as pre-heaving compression of soil, surface heave, creep deformation, and residual increase of K0 for given confining stresses are newly introduced. The results of developed correlations show good comparison with those of actual compaction grouting. Implications for actual compaction grouting are also presented.

The paper presents the evolution of the bearing capacity of a pile model in calibration chamber after the application of a cyclic axial loading at a large number of cycles. This work is a part of the French research project ANR-SOLCYP which aims to understand the mechanisms governing the evolution of the bearing capacity of piles up to a very large number of cycles (105 cycles). The experimental study consists in using a calibration chamber in which axial cyclic loading is applied to pile model jacked into sand under a large number of cycles, up to 105, while measuring the axial shaft capacity before and after the cyclic sequence. Some key parameters have been investigated such as the cyclic displacement amplitude, the level of applied consolidation stress and the density index of the soil. It was found that after a large number of cycles of cyclic axial loading, the post-cyclic bearing capacity of the piles is significantly improved. Results analysis indicated that the mechanism of densification of the soil around the pile led to improve pile capacity.