Influences of hydrate layered distribution patterns on triaxial shearing characteristics of hydrate-bearing sediments

Hydrate distribution patterns have significant influences on the mechanical parameters and failure mechanism of the hydrate-bearing sediments (HBS), which remains further investigation at the current state. In this paper, we carried out a series of tests to analyze the mechanical properties of HBS when hydrate is distributed horizontally in laminary mode. The HBS specimens are made of two different hydrate-saturated layers, which are the lower hydrate-saturated sub-layer and the higher hydrate-saturated sub-layer. The experimental results indicate that, whether the sediment shows strain-softening or strain-hardening behavior during shearing is mainly determined by the low hydrate-saturated sub-layer. The cohesion of the HBS is closer to the low hydrate-saturated sub-layer, while the internal friction angle is more approaching to the high hydrate-saturated sub-layer. Under the condition of the same average hydrate saturation, the strength parameters of the HBS with layered hydrate distribution are affected by the height ratio, which is defined as the height ratio of the low hydrate-saturated sub-layer and the high hydrate-saturated sub-layer. The peak strength increases linearly, while the Young's modulus increases logarithmically, with the increase in height ratio. Furthermore, the existence of a low hydrate-saturated layer would reduce the peak strength of the whole HBS. This study provides a theoretical reference for the controlling mechanisms of strength weakening during natural gas hydrate development. •Mechanical characteristics of sediments with hydrate layered distribution is investigated.•The layer with lower hydrate saturation determines failure mode of the whole sediment.•Existence of low hydrate-saturated layer weakens the failure strength of the reservoirs.•The effect of layered hydrate distribution should be considered in evaluating hydrate related engineering geohazards.