青藏铁路巴索曲特大桥沙害形成原因分析

Analysis of Formation Causes of Sand Disasters on Basuoqu Bridge of Qinghai-Tibet Railway

通过现场调查与数值仿真分析,从沙物质来源与风场变化两方面分析巴索曲特大桥风积沙害的形成原因。结果表明:青藏铁路巴索曲特大桥两侧积沙主要来源于湖滨沉积物、巴索曲及桑曲冲积物、湖岸边大片固定沙丘及岩石风化物;桥梁两侧积沙的直接原因是梁体改变了其周围的风沙流场,破坏了风沙流的平衡状态,导致部分区域风速减小,气流携沙能力降低,沙粒沉积在梁体两侧;桥梁两侧积沙的间接原因是梁底设计净空过小,导致梁体对气流的扰动程度过大,虽然沙粒更容易通过梁底,但两侧更容易积沙;与简支梁相比,同等条件下箱梁两侧更不易积沙,同时背风侧的积沙区域距梁体越远,清沙周期越长,防护费用越小。

Through on-the-spot investigation and numerical simulation,the formation causes of aeolian sand disasters on Basuoqu Bridge were analyzed from sand material source and wind field change.The results showed that the aeolian sands on both sides of Basuoqu bridge of the Qinghai-Tibet Railway were mainly from lakeside sediments,alluvial deposit from Basuoqu and Sangqu,fixed sand dunes on the shores of the lake and weathered rocks.The direct cause of aeolian sand formation on both sides of the Basuoqu bridge lay in the bridge beam′s change of sand flow field around the bridge,which destroyed the balanced state of wind sand flow,and caused reduction of local wind speed and airflow carrying capacity,and deposition of the sands on both sides of the beam.The indirect cause was the beam′s high degree of disturbance on the airflow due to small designed clearance of the beam bottom.Although the sand was easier to pass through the beam bottom,it was more likely to accumulate along both sides of the bridge.Compared with simple beam under the same condition,blown sand may not easily accumulate on both sides of the box girder.The farther the blown sand region of the leeward side was from the beam and the longer the sand cleaning cycle,the lower the protection cost was.