Influence of Hydrate Exploitation On Stability of Submarine Slopes

The decomposition of natural gas hydrate will reduce the cementation effect of hydrate and produce ultra-static pore pressure, which will change the mechanical characteristics of the reservoir. Eventually, a series of geological disasters could be triggered, of which the submarine landslide is a typical example. In order to analyze the stability of hydrate-bearing submarine slopes and to explore the internal relationship between hydrate decomposition and submarine landslides, a “two-step reduction method” was described in this paper. This method was based on a strength reduction approach, which can be used to assess the effects of the initial geostress balance and hydrate decomposition on substrate strength reduction. This method was used to reveal the essence of hydrate decomposition and then a joint operation mode of multi-well was proposed. The internal relationship between hydrate decomposition and submarine landslides were analyzed in detail. And the development process and mechanism of submarine landslide were deeply discussed. The results showed that hydrate decomposition is a dynamic process of stress release and displacement, where the “stress inhomogeneity” distributed along the slope is transformed into “displacement inhomogeneity”. We concluded that hydrate decomposition could trigger a submarine landslide, especially along a sliding surface. The formation of submarine landslide is a gradual development process, and presents the dual characteristics of time and space.

Analysis of Stress Inhomogeneous Coefficient of a Continuous Rigid Frame Bridge during Construction Stage

The box section which can meet the requirements of wider deck is widely used in the construction of continuous rigid frame bridge. However, the shearing force lag is very obvious, which causes the inhomogeneous distribution of stress in the cross section, and it may threaten the safety of the bridge structure when it is serious. Taking a continuous rigid frame bridge located in Yunnan, China as an example, this paper establishes the finite element calculation model of the bridge to analyze the stress inhomogeneity in the construction stage. The results show that the shear lag coefficient of the section is constantly changing during the dynamic process of construction, with the increase of the length of the cantilever, the shear lag coefficient gradually converges to 1; prestress is the most important factor that causes the lateral inhomogeneity of the positive stress.

Scaling laws for segregation forces in dense sheared granular flows

In order to better understand the mechanism governing segregation in dense granular flows, the force experienced by a large particle embedded in a granular flow made of small particles is studied using discrete numerical simulations. Accurate force measurements have been obtained in a large range of flow parameters by trapping the large particle in a harmonic potential well to mimic an optical tweezer. Results show that positive or negative segregation lift forces (perpendicular to the shear) exist depending on the stress inhomogeneity. An empirical expression of the segregation force is proposed as a sum of a term proportional to the gradient of pressure and a term proportional to the gradient of shear stress, which both depend on the local friction and particle size ratio.