Study On Seismic Fragility And Safety Risk Of Anchored Sheet Pile Retaining Wall

Earthquake-induced landslides lead to not only direct economic losses and casualties but also traffic interruption,causing great inconvenience to the earthquake relief work.Anchored sheet pile retaining wall can effectively improve the stress state of rock and soil mass and enhance the stability of slopes by exerting active restraints on slopes,so they are widely used in slope supporting engineering.However,it has been a new problem in the seismic design of anchored sheet pile retaining wall as to whether the anchored sheet pile retaining wall will be damaged in earthquakes and what the risk of damage at all levels are.The concept of performance-based seismic design is introduced into the seismic research of slopes supported by anchored sheet pile retaining wall in this study.By combining theoretical analysis and numerical simulation,the dynamic coupling effect of wall-soil-anchor is discussed,the dynamic finite element model of anchored sheet pile retaining wall is established,the seismic fragility and safety risk are studied,and the seismic safety of anchored sheet pile retaining wall is evaluated.The main research contents and results are as follows:?1?In the framework of limit equilibrium theory,the seismic active earth pressure of retaining wall is transformed into a function optimization problem with two Lagrangian constants as unknowns according to the variational principle.The magnitude of seismic active earth pressure,the action point position and the corresponding slip surface shape of retaining wall under different displacement modes are studied.The results show that the limit equilibrium variational method can effectively estimate the magnitude of seismic active earth pressure and the interval of action point position under all possible displacement modes of retaining wall,which can provide reference for seismic design of anchored sheet pile retaining wall.?2?The mechanical model of the entire pullout process of soil anchors is established based on a softening shear model of the anchor-soil interface and a load transfer model of the anchoring section.The pullout process of anchors is calculated numerically with the help of Matlab.The results show that the present study accurately simulates the entire pullout process of anchors,obtains a complete load-displacement curve,determines their ultimate bearing capacity,and lays a foundation for the subsequent seismic design and dynamic analysis of anchored sheet pile retaining wall.?3?The components of slopes supported by anchored sheet pile retaining wall are equivalent to solid members,and the corresponding constitutive laws of the members are given.Based on OpenSees,the dynamic finite element model of anchored sheet pile retaining wall is established,and its static and dynamic response is analyzed.The results show that the shear force of the retaining wall is generally distributed in an inverted"S"shape under static force,and the maximum shear force appears near the excavation surface;the horizontal displacement increases gradually from the bottom to the top of the wall.With the increase of PGA,the cumulative displacement of the retaining wall increases more and more greatly;at the same time,the peak shear force of the retaining wall also increases and is much larger than the shear force under static load;the acceleration amplification coefficient of soil increases with the increase of slope height,and it was positively correlated with PGA.Within the range of tensile strength,the axial force of anchor is proportional to PGA;after reaching the tensile strength,the anchor gradually fails,its axial force decreases,and the residual strength decreases with the increase of PGA.?4?The cumulative displacement index?_CDIDI of the wall top is selected as the engineering demand parameter.A large number of ground motions are selected for dynamic time-history analysis of anchored sheet pile retaining wall based on PEER database.And its probabilistic seismic demand model is established by cloud analysis and multiple-strip analysis,respectively.The results show that the median values of engineering demand obtained by cloud analysis and multiple-strip analysis increase linearly with the increase of ground motion intensity.The median value of engineering demand obtained by cloud analysis is a straight line,while the median value obtained by multiple-strip analysis is a piecewise straight line.And the logarithmic standard deviation obtained by cloud analysis is a fixed value,while the logarithmic standard deviation obtained by multiple-strip analysis changes with the change of earthquake intensity.?5?According to the failure mode analysis of the retaining structure,combined with the damage state and use condition of anchored sheet pile retaining wall under seismic action,the seismic performance of anchored sheet pile retaining wall can be divided into four levels,namely,basic intact,minor damage,moderate damage and severe damage.And three limit states of minor damage LS1,moderate damage LS2 and severe damage LS3 can be obtained.The viscous damping?is assumed to follow a normal distribution,and all other parameters follow a logarithmic normal distribution,such as elastic modulus of reinforcementE_s,elastic modulus of concreteE_c,weight?,cohesion c and internal friction angle?of cohesive soil;the random IDA method based on point estimation can provide the seismic capacity for each limit state,which are close to the existing research results,indicating that the method is suitable for the probabilistic seismic capacity analysis of anchored sheet pile retaining wall.?6?The probabilistic seismic demand model and probabilistic seismic capacity model are convoluted to deduce the analytic fragility function of anchored sheet pile retaining wall,and the corresponding seismic fragility curve is obtained by means of Matlab.According to the seismic fragility curve,the failure probability of anchored sheet pile retaining wall at each level under different earthquakes?small,medium and large earthquakes?is obtained.The results show that the seismic fragility curve is generally distributed in an"S"shape;from minor damage to severe damage,the curve gradually becomes flat,that is,the failure probability becomes smaller and smaller for the same earthquake intensity.Under the action of small earthquakes,the structure remains basically in good condition and there is little possibility of damage.In middle earthquakes,there's a possibility of damage at all levels in the structure,but mainly minor damage.In major earthquakes,the possibility of structural damage at all levels is greatly increased,but it is within a controllable range.?7?On the basis of probabilistic seismic demand analysis and seismic capacity analysis,the classical power function of seismic risk is introduced and the analytical function of seismic safety risk is established.The annual average failure probability of each limit state and the failure probability at all levels of damage during the service period are calculated,and then the seismic safety of anchored sheet pile retaining wall is evaluated.The results show that the seismic safety risk of anchored sheet pile retaining wall in each limit state is slightly greater than the seismic demand risk due to the uncertainty of structural capacity.The probability of minor damage of anchored sheet pile retaining wall in the 50-year base service period is 11.9%?5-point estimation method?and 9.5%?7-point estimation method?respectively,far less than 63.2%.The probability of moderate damage is 2.9%?5-point estimation method?and 2.7%?7-point estimation method?respectively,both less than 10%.The probability of severe damage is 1.2%?5-point estimation method?and 1.3%?7-point estimation method?respectively,both less than 2%,meeting the three levels of seismic fortification.