| Before the completion of the Hong Kong-Zhuhai-Macao Bridge,immersed tunnels in China were built in inland rivers.For the immersed tunnel located in the inland river,the slope stability of foundation trench is not emphasized due to good geological conditions,low wave strength and small amount of back silting.However,the long-distance submarine immersed tunnel engineering represented by Shenzhen-Zhongshan immersed tunnel has a series of problems,such as poor geological conditions,high-intensity waves,large amount of back silting.For long-distance submarine immersed tube tunnel engineering,the slope stability of foundation trench controls the safety of the entire project.Relying on Shenzhen-Zhongshan immersed tunnel project,this article studied the slope stability of foundation trench under static water condition,back silting action and wave action by means of measurement experiment of back silting in trial trench and numerical simulation.The main research contents and results of this paper are as follows:(1)The variation with time and space of the back silting is obtained by experiments.The results show that the horizontal distribution of back silting is obviously different,which shows that the amount of back silting at the bottom of trial trench,the north slope and the south slope decreases in sequence.The vertical distribution of back silting was uneven,which shows that the thickness of back silting from top to bottom is decreasing.The amount of back silting varies greatly throughout the year,which shows that the amount of back silting is large in flood season,but small in dry season,and the back silting gradually becomes compact,which leads to the increase of its density.(2)The research shows that the finite element limit equilibrium method can analyze the instability mechanism of slope more thoroughly from stress-strain state,safety factor and potential slip surfaces.It is especially suitable for stability analysis under external load.Based on the finite element limit equilibrium method,the factors affecting the stability of foundation trench slope under hydrostatic condition are studied.The results show that there are obvious differences in the stability of rock,sand,clay and silt slopes,so more attention to the stability of silt slopes should be paid.The slope safety factor decreases with the increase of slope height or gradient,and the safety factor has a linear relationship with slope coefficient.(3)Based on the experimental results of trial trench,numerical models is established to study the stability of foundation trench slope under the action of back silting.The research show that the stability of foundation trench slope is mainly controlled by the back silting and the stability of back silting can be significantly improved by desilting with slope.The safety factor of back silting decreases with the increase of back silting thickness,the increase of desilting gradient,the increase of slope height,the increase of slope gradient or the decrease of back silting's shear strength.(4)Based on the linear wave theory,the wave force is equivalent to quasi-static load.The influence of wave on the stability of foundation trench slope is deeply analyzed from safety factor,potential slide surface and deformation.The results show that the influence of wave on silt slope is much greater than that on sand or clay slope.The safety factor of slope fluctuates with time and when the wave crest is above the top of the slope,the safety factor is minimized.The safety factor of foundation trench slope decreases with the decrease of foundation trench's depth and the increase of wave length or wave height.(5)Relying on practical engineering,the conclusions are verified.Through studying the effects of wave in different recurrence periods,it is concluded that the conventional wave has little effect on the stability of foundation trench slope,but the huge wave in the recurrence period of more than 100 years will lead to a significant decrease in the safety factor of foundation trench slope. |
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