Analysis Of The Reclaimed Land Slope Stability Of The Third Runway At Shenzhen Airport

Shenzhen Bao’an International Airport is the first 4F international airport in China to adopt transit transportation,and also a new era international airport integrating sea,land and air.During the expansion of the airport,the construction of land reclamation from the sea was carried out.As the main peripheral building of the expansion project,the reclaimed land slope is subject to seepage deformation under the action of seawater tide,and the wading landslide seriously endangers the normal operation of the airport navigation and the safety of passengers’ lives and properties.Therefore,it is of great significance to analyze the stability of the reclaimed land slope.Based on the land formation and soft foundation treatment project of the threerunway expansion project of Shenzhen Airport,this thesis obtained the regional tidal water level data through field monitoring and used the Geo-Studio software’s SEEP/W and SIGMA/W modules to simulate the dynamic changes of seepage and deformation of the reclaimed land slope under the tidal hydrodynamic conditions.The SLOPE/W module was used to explore the stability changes of the slope under the three tidal types.Based on this,a new structure for anti-tidal erosion of the land slope with special-shaped revetment is proposed.The main research results of this thesis are as follows.(1)The fluid-solid coupling law of seepage deformation in land slope of reclamation under tidal hydrodynamic conditions is explored.The pore water pressure increases with the rise of seawater level and decreases with the decrease of seawater level.During the rising tide,seawater enters the soil mass,causing a backflow phenomenon inside the land slope.The slope is dominated by compressive stress,with the maximum compressive stress gradually increasing as the seawater level rises,and the direction tends to be parallel to the slope surface.During the ebbing tide,there is a tensile stress effect in the top area of the slope,with tension cracks appearing locally.The shear stress of the soil in the seawater infiltration area is higher than that of the surrounding soil,and there is a phenomenon of stress concentration.The vertical displacement of land slope in different tidal types presents an "S" shape change,which increases with the rise of seawater level and decreases with the decrease of seawater level.The horizontal displacement gradually decreases with the decrease of seawater level and presents negative displacement.The infiltration line inside the land slope decreases outward with the decrease of seawater,and the soil mass tends to move towards the seaside.When the critical conditions are reached,landslide instability is prone to occur.Affected by the tidal difference,the vertical and horizontal displacements of the spring tide are greater than those of the medium and neap tides.(2)The dynamic variation law of seepage stability of land slope under tidal hydrodynamic conditions is analyzed.The stability coefficient of land slope gradually increases with the rise of seawater level and decreases with the decrease of seawater level.During the rising tide,the groundwater level of the land slope gradually rises,and the slope soil mass transitions from unsaturated to saturated state.The water content of the soil mass increases,and the self-weight of the soil mass increases,resulting in an increase in the sliding force of the sliding mass.However,due to the large permeability coefficient of gravel,the hydrodynamic pressure effect within the slope increases,and the water level outside the slope is higher than the groundwater level inside the slope,causing both the hydraulic gradient and the hydrodynamic pressure to point inward,which is conducive to the stability of the slope.During the ebbing tide,the water inside the slope seeps out towards the seaward side,which has a lag effect compared to the change of seawater level.During this process,the dynamic water pressure plays a dominant role.The water level difference inside and outside the slope makes the hydraulic gradient and its dynamic water pressure point towards the outside of the slope,leading to a decrease in slope stability.Under the influence of tidal current,with the acceleration of seawater level decline,the greater the water level difference between the inside and outside of the slope,which is manifested as the lowest stability of the land slope at low tides under the action of spring tides.(3)The new design scheme for anti-tidal erosion of the land slope with specialshaped revetment is proposed.The length of the revetment block is 1.2m,0.4m in its width,0.2m in its thickness,and the front is equipped with a semicircle lock catch with a radius of 0.1m.The action process of seawater on the special-shaped revetment block can be divided into three stages: incidence,circulation and projection.The seawater is easy to generate small circulation in the special-shaped pit to reduce the impact speed and force of the seawater on the reclaimed land slope,so that the wave impact force does not enter the bank slope with the gap between the conventional revetment blocks,thus reducing the erosion damage to the reclaimed land slope.