Sliding Stability Analysis Of Gently Inclined Submarine Slope On Basis Of Stress State

With the increase of marine resources development strength and offshore facilities, the harm of submarine slope instability appeared gradually, submarine slope stability analysis has become a research focus in the current marine geotechnical engineering problems.Submarine slope sliding instability mode is generally divided into infinite slope sliding and limited slope sliding. This paper analyzes the influence of the slope angle and wave action into the unit of the direction of the potential failure surface of soil. On basis of the characteristics of the submarine gentle slope under wave action, a stress analysis method is proposed to analyze sliding stability of the submarine slope according to the soil stress state at the slip surface.For submarine infinite and finite gentle slope, the paper compares the difference between stress analysis method and traditional calculation method, and analyzes the characteristics of sliding instability by stress analysis method.Late, with wave-induced stability analysis on submarine finite gentle slope based on stress station, the paper analyses the finite sliding stability of silt seabed at the Yellow River Estuary.The paper mainly gets the following conclusion:With the increase of slope angle, soil unit of principal stress rotation will occur, For cohesionless soil slope,and when the slope angle achieves internal friction angle, unit of potential failure surface of soil will be parallel to slope surface, namely the finite slope sliding will turn into infinite slope sliding; For the submarine slope, because of wave action, when the slope angle is less than internal friction angle, the finite slope sliding mode has turned into infinite slope sliding mode.For submarine gentle infinite slope, A case study of a submarine infinite slope has been conducted by the limit equilibrium method and the proposed stress analysis method,the results have shown that the factor of safety by the stress analysis method is greater than that of the limit equilibrium method, and the difference of the two methods tends to become larger with increase of depth of the slip surface, Poisson ratio of the soil deposit and dip angle of the infinite slope.For a submarine infinite slope with gentle dip angle under wave action, it may probably slides along a slip zone rather than a single slip surface;furthermore, the depth of the maximum shear stress does not indicate the most instability location of the infinite slope.For submarine gentle finite slope, A case study shows that the safety coefficient of the stress analysis method of safety coefficient is greater than the Henkel method and Okusa method,and calculation result of Henkel method is similar to Okusa method, and with the increase of the poisson ratio of soil and the slope angle, the difference of calculation result between Okusa method and he stress analysis method. With the increase of half chord length of the potential sliding surface l, the stability coefficient value of submarine gentle finite slope changes like wave, and the half chord length of the most dangerous sliding surface is about 3L/16;Under the action of transient wave, when instability sliding of the saturated gentle finite slope seabed occurs, the most dangerous sliding surface will be symmetrical about wave node, and the instability of slope sliding uphill section is located at peak, and downhill section is located in the wave trough; Considering the cumulative pore water pressure, when instability sliding of the saturated gentle finite slope seabed occurs,the composite sliding surface is not symmetrical about wave node, but slightly offset in the direction of the trough.For submarine slope of soft soil at the Yellow River Estuary, with the increase of the depth of the water, the minimum undrained shear strength to keep soil slope stability increases first and then decreases, and the depth of the necessary minimum undrained shear strength reached maximum for 8m water depth, showing that slope is most likely to occur instability for 8m water depth; With the increase of the depth of sliding surface,the minimum undrained shear strength to keep soft soil slope stability increases first and then decreases, this corresponds with the wave stress changing with the depth of the seabed. When the undrained shear strength of soil is more than 5.2 kPa, the soft soil slope instability sliding at the Yellow River Estuary generally will not occur;when instability sliding of soft slope seabed occurs, the composite sliding surface is generally symmetrical about wave node.For submarine slope of silt soil at the Yellow River Estuary, silt seabed slopes will be liquefied when water depth is less than 5m. With the increase of the depth of the water, the critical wave action time when the soil begins to liquefy decreases first and then increases, and the soil is most likely to occur liquefication for 8m water depth; For the water depth of 8m, when the wave action time within a certain range, the depth of the critical slip surface of silt soil slope is greater than its maximum liquefaction depth; Considering the cumulative pore water pressure, silt composite sliding surface of slope instability is not symmetrical about wave node, but slightly offsets in the direction of the trough about 0.04 L.