A series of direct shear tests using a large-scale constant-normal-stiffness direct-shear testing system was conducted to study the factors that influence the mechanical characteristics of a pile-soil interface (PSI) in clay soil. Interfaces of different roughness (R = 0, 2, 4, and 6 mm) were tested in clay soil with four different water contents with four normal stresses under different shear rates during shearing. Results for the interfacial shear behavior are presented as shear-stress-shear-strain curves, shear strength, and parameters. The results show that (i) the higher the roughness, the higher the shear strength of the PSI. The larger the normal stress, the smaller the roughness effect on the shear strength and parameters of the PSI; and (ii) the higher the water content of the clay soil, the lower the shear strength of the PSI, with maximum cohesion at a water content of 25%. The main influence that increasing the water content has on the shear strength of the PSI is changing the coherence, while the shear rate in this test range has less effect on the shear strength of the PSI. Overall, the mechanical characteristics of the PSI are influenced by roughness, water content, and shear rate, and close attention should be paid to those three factors when analyzing test results.
It is of great significance to study the mechanical properties
of hydrate-bearing sediments for safe and efficient exploitation of
hydrate resources. Considering the lack of studies on clay-bearing
fine-grained reservoirs, submarine clay taken from the Shenhu Sea
in the South China Sea and quartz sand were used to synthesize hydrate-bearing
clayey-silty sediments (HBCS). A series of consolidated-drained tests
were carried out to investigate the effects of hydrate saturation,
effective confining pressure, and their coupling on the mechanical
properties of HBCS. The results show that with the increase in hydrate
saturation and the decrease in effective confining pressure, the stress–strain
curve of the HBCS shows a trend from strain hardening to strain softening.
The peak strength and residual strength increase with the increase
in effective confining pressure and hydrate saturation. The secant
modulus E
50 increases with the increase
in hydrate saturation and shows an irregular change trend with the
increase in effective confining pressure. The contact area between
particles determines the change rule of Secant modulus E
50. With the increase in hydrate saturation, the cohesion
first increased rapidly and then increased slowly. The internal friction
angle increases with the increase in hydrate saturation, but the increase
is small. This indicates that hydrate has a great influence on the
cohesion of sediments, but a small influence on the internal friction
angle.
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