库水位循环下岸坡-桥梁桩基相互作用致损机理

库水位循环作用下,库岸边坡岩土体物理力学性质劣化,引起岸坡变形、滑移,将对桥梁基础、桥墩及上部结构产生不同程度损伤,甚至会导致桥梁上部结构落梁、垮塌。针对重庆万州长江二桥库岸边坡失稳致灾问题,采用FEM-SPH(finite element method-smoothed particle hydrodynamics)转换耦合算法建立了岸坡-桥梁三维有限元模型,结合桥位处地质勘测数据模拟了变动水位条件下岸坡变形、滑移、失稳全过程,揭示了岸坡滑移与桥梁桩基相互作用机理,研究了桥墩偏位规律及下部结构失效模式。结果表明：以滑动带有限元网格悉数转换为SPH(smoothed particle hydrodynamics)粒子作为岸坡失稳判据,FEM-SPH转换耦合算法能够更直观、准确地模拟库岸边坡从变形、滑移至失稳全过程;桥位处岸坡将在第16、20次水位升降循环过程中发生失稳破坏;随着岸坡变形、滑移、失稳演化,桥墩偏位呈“缓增-激增”的变化趋势;岸坡发生第2次失稳时,桩基础在土-岩交界面上部发生剪切破坏,破坏面与水平面夹角约为60°。

Damage mechanism and failure mode of bank slope-bridge pile foundation interaction under reservoir water level cycle

Under the action of the reservoir water level cycle, the physical and mechanical properties of the reservoir bank slope deteriorate, causing bank deformation and slippage, which will produce different degrees of damage to the bridge foundation, piers and superstructure, and even lead to the bridge superstructure falling and collapsing. Aiming at the problem of instability of the bank slope of a Yangtze River Bridge in the Three Gorges Reservoir area, a three-dimensional finite element model of bank slope and bridge was established by using the FEM-SPH conversion coupling algorithm. Combined with the geological conditions of the bridge location, the whole process of bank slope deformation, slippage and instability under changing water level conditions is simulated, the interaction mechanism between bank slope slippage and bridge pile foundation is revealed, and the deflection law of bridge piers and the failure mode of the substructure are studied. The results show that: Taking the sliding zone finite element meshes all converted into SPH particles as the bank slope instability criterion, the FEM-SPH conversion coupling algorithm can more intuitively and accurately simulate the whole process of the reservoir bank slope from deformation, slippage to instability. The bank slope at the bridge location will be destabilized during the 16th and 20th water level rise and fall cycles. With the evolution of bank deformation, slippage and instability, the bridge pier deflection shows a trend of "slowly increasing-surge". When the second instability occurs on the bank slope, the pile foundation undergoes shear failure at the upper part of the soil-rock interface, and the angle between the failure plane and the horizontal plane is about 60°.