高速公路桥梁岩溶地基应力应变响应机制

On the Stress-strain Response Mechanism of Karst Foundation of Highway Bridges

贵州高速公路桥梁具有跨度大、高度高、荷载大等显著特点,为了研究喀斯特地区高速公路桥梁复杂岩溶地基破坏模式,利用离散元数值模拟法模拟串溶和鹰嘴岩现象桥梁岩溶地基应力应变响应机制.以桐新高速第2标段芭蕉湾特大桥左幅4c-2桩基的串溶现象、枇杷洞大桥右幅6-0鹰嘴岩现象为案例,通过主动式声呐系统探测桥梁桩基下岩溶的空间位置和分布,并利用离散单元法进行数学建模,然后通过PFC颗粒流软件进行加载过程应变应力响应机制进行模拟分析,最后利用结构近似分析法对模拟结果进行验证分析.分析表明:芭蕉湾特大桥桩底在0.68,1.73 m处分布了2个高度为0.62,1.03 m的溶洞情况下,在设计荷载27000 kN作用下,地基会出现挤压隆起和碎裂形成的整体破坏模式;枇杷洞大桥右幅6-0桩底在桩底鹰嘴岩现象时,在设计荷载18000 kN作用下,会存在地基地层挤压碎裂和桩基不均匀沉降,从而导致地基破坏和失稳的局部剪切破坏模式.并且,根据结构近似分析法,虽然2个工点岩溶洞室的厚跨比大于0.5满足理论要求,但是其抗弯和抗剪验算均未通过,因此,判定其在桥梁设计荷载作用下,地基不稳定.通过模拟分析和理论计算分析结论,为桐新高速岩溶地基处理提供数据支撑和决策依据.

Guizhou expressway bridges are featured by large span,high height and high load.In order to study the complex karst foundation failure mode of expressway bridges in karst areas,the discrete element numerical simulation method is used to simulate the stress-strain response mechanism of bridge karst foundation under the phenomena of series dissolution and olecranon rock.The project takes the cross dissolution phenomenon of the 4c-2 pile foundation on the left side of the Bajiaowan Extra Large Bridge in the second section of the Tongxin Expressway and the 6-0 olecranon rock phenomenon on the right side of the Pipaodong Bridge as case studies.By using an active sonar system to detect the spatial position and distribution of karst under the bridge pile foundation,and using the discrete element method for mathematical modeling,the PFC particle flow software is used to simulate and analyze the strain stress response mechanism during the loading process.Finally,the structural approximation analysis method is used to verify and analyze the simulation results.Analysis results show that under the condition of two karst caves with heights of 0.62 m and 1.03 m distributed at 0.68 m and 1.73 m respectively at the bottom of the pile of the Bajiaowan Grand Bridge,the foundation will exhibit an overall failure mode of compression uplift and fragmentation under the design load of 27000 kN.When the bottom of the 6-0 pile on the right side of the Loquat Cave Bridge is exposed to the phenomenon of eagle beak rock at the bottom of the pile,under the design load of 18000 kN,there will be local shear failure modes such as ground layer compression fragmentation and uneven settlement of the pile foundation,leading to foundation failure and instability.According to the structural approximation analysis method,although the thickness to span ratio of the two rock cave chambers at the construction site is greater than 0.5,which meets the theoretical requirements,their bending and shear resistance calculations have not passed.Therefore,it is determined that the foundation is unstable under the design load of the bridge.It has provided data support and decision-making basis for the karst foundation treatment of Tongxin Expressway through simulation analysis and theoretical calculation analysis conclusions.