川西山区某公路拱桥变形破裂成因及处理措施探讨

Study on the mechanism and treatment for the deformation and failure of a highway arch bridge in the coteau areas of West Sichuan

川西山区某公路桥为一长16m的双曲偏心单孔坡条石拱桥,横跨于一小型冲沟上。东侧桥基为强-中风化钙质泥岩,西侧桥基置于一多期泥石流堆积体斜坡上(未做特殊处理)。1996年建成通车后,1997年桥身开始出现裂缝,到1999年已发展成为一座危桥,且变形破裂迹象呈进一步发展的趋势。在这个过程中,为了缓解这一趋势并彻底查清变形破裂成因,以便为危桥的全面整治提供科学依据。先后进行了桥体及周边边坡变形破裂迹象的调查、桥体三维位移长期监测、桥基灌浆加固及效果检测、周围地质环境勘察以及地质灾害危险性评价等工作。文章在大量勘察、试验以及监测数据的基础上,运用工程地质的基本分析方法,并引入结构力学理论及断裂动力学理论,对该公路拱桥的变形破裂成因进行了深入地分析和探讨。研究表明,双曲偏心拱的桥身结构不能与周边复杂的地质环境相适应是桥体变形破裂的根本原因。西侧斜坡体侧向主动土压力和两桥台间的不均匀沉降是拱桥变形破裂的起因和触发因素。而桥面间歇性动荷载作用则是促使桥体已有裂纹进一步扩展的主要原因。针对桥体的病害原因,为危桥整治提出了将原拱桥桥身结构改为对桥基变形适应性强的桥梁结构,将西侧较软弱的桥基进行灌浆加固。

The bridge on the highway in the west Sichuan is a hyperbolic and eccentric single\|span stone arch bridge which is 16 meter long and strides over a small gulch.The east bridge foundation is the intensely\|moderately weathered calcareous mudstone,while the west one is put on a slope which is composed of multi\|periods of debris flow(haven't made special treatments).After built and opened to traffic in 1996,minute cracks were found in the bridge in 1997.When the time came to 1999,it had developed into a dangerous bridge and the deformation and failure phenomena had the trend to develop further.During the time,in order to slow down the trend and find out the cause which is the base for thorough treatments on the bridge,a series of work were finished successively,such as investigating the deformation\|failure phenomena of the bridge and the ambient slopes,the long\|term monitoring for the bridge′s three dimensional displacement,grouting to reinforce the foundation and the effect checking,the exploration of the peripheral geology environment and the evaluation of the geological hazard danger.\;Combining the author′s practice on the site and basing on abundant datum on exploration,test and monitoring,the paper analyses and discusses the mechanism for the deformation and failure of the highway arch bridge by using the fundamental analyzing methods of engineering geology and introducing the theory of structural mechanics and dynamic fracture mechanics.In this paper,the fact that the hyperbolic and eccentric arch structure can not get adapted to the complicated geology environment is brought forward as the ultimate cause for the deformation and failure and the authors think that the lateral active earth pressure of the west slope and the unequal settlement between the abutments are the orginal and triggering cause,and what is more,the further spreading of the existent cracks owe a great part to the intercepted dynamic load from the bridge deck.At last,according to the mechanism,the comprehensive treatment measures are made for the dangerous bridge,that is substituting girder bridge structure for the original arch structure,which can be better adapted to the abutment′s deformation,grouting to reinforce the weaker ground in the west,adding base girders to link both of the abutments so as to enhance the whole stiffness of the bridge and setting vertical column piles on the side of the west abutment.