基于易损性评价的耿马县城避震疏散通道连通性评价研究

Research on Connectivity Evaluation of Seismic Evacuation Channel in Gengma County Based on Vulnerability Evaluation

山地小城镇避震疏散通道震后连通性直接关系到受灾群众能否安全转移、救灾工作能否顺利展开。本文以地震高发的滇西山地小城镇耿马傣族佤族自治县县城(下称耿马县城)为研究对象,以沿街建筑易损性灰色度评价测算各路段的连通概率值,分析在不同地震烈度下避震疏散通道的连通性。研究表明:耿马县城发生地震烈度为7度及以下地震灾害时,整体避震疏散通道网络连通度较好,随着地震烈度的增大,避震疏散通道网络连通度下降,甚至有部分避震疏散通道不能连通。因此,在地震灾害发生前,应进行避震疏散通道的连通性的评估,并根据评价结果有效布置救灾物资,加固改造连通性差的避震疏散通道。

The seismic evacuation channels are important lifelines for the safe transfer of urban residents and disaster relief after earthquake,and their connectivity assessments are important work of earthquake risk assessment in urban areas.The connectivity of seismic evacuation channels in small mountain towns has a direct impact on the safe displacement of the affected people and whether the disaster relief work can be carried out smoothly.In general,the connectivity probability of evacuation channel is affected by the vulnerability of buildings,slopes and bridges on both sides of the road,and the random probability of each factor is independent of each other.However,in some circumstances,such as building collapse is due to slope instability,and it may also be related to each other.The research object is Gengma County,a small mountainous town in western Yunnan.Based on the field investigation of the existing road data,according to the screening criteria of seismic evacuation channels,combined with the requirements of road grade and red line width in the study area,the network system of seismic evacuation channels in the study area turns out to be the main and secondary trunk roads,roads in communities,temporary passages that meet the evacuation conditions,and the outlet roads.The connectivity probability of the evacuation channel is affected by the vulnerability of the building,the slope and the bridge.Therefore,the link can be regarded as a series of the building unit,the slope unit and the bridge unit.Due to the uncertainty of the failure correlation of each basic unit,the connectivity probability method is used to study the connectivity of evacuation channel based on the vulnerability assessment of each unit.Firstly,all the buildings(structures)on the evacuation channels are investigated.There are eight types of buildings:multi-storey masonry structure(1-5 floors),multi-storey masonry structure(more than 6 floors),bottom frame anti-seismic wall masonry structure,frame structure(≤24 m),frame structure(24 m),seismic wall structure,civil stone structure and single story industrial workshop.It found out the weak sections which could not reach the effective width after the buildings on both sides or(one side)collapsed in opposite direction.The buildings(structures)were identified as the buildings(structures)in need of vulnerability assessment.Similarly,the slopes requiring vulnerability measurement are determined.Since there is no bridge in the study area,no bridge is assessed.Then,the vulnerability of each unit under different seismic intensity is measured by grey degree evaluation method of building vulnerability by experts and slope vulnerability calculation method.Finally,the connectivity probability of evacuation channel under different seismic intensity is calculated by using the connectivity probability method.It is basically reliable to take the connection probability of 50%as the evacuation channel.In other words,when Pst≥to 50%,the evacuation channel is basically reliable,and it is connected in the network analysis;when Pst<50%,the evacuation channel is unreliable,and it is disconnected when analyzing the network of the evacuation channel.In this way,the network diagram of evacuation channel under different earthquake intensity can be obtained.The results show that when the earthquake intensity of Gengma County is seven degree or less,the connectivity of the whole evacuation channel network is better,and the connectivity between the disaster area and the evacuation site as well as that among the evacuation sites can be ensured.When the earthquake intensity is eight degree,the connectivity of the whole evacuation channel network decreases,and a small number of disaster stricken points cannot be connected with the evacuation sites and among the evacuation sites.When the earthquake intensity is nine degree,the connectivity of evacuation channel is lower,and the connectivity between the disaster points and the evacuation sites and that among the evacuation sites cannot be secured.When earthquake disaster occurs in small towns located in mountainous areas,the higher the seismic intensity level,the lower the overall connectivity of the evacuation channel network.Therefore,before the occurrence of earthquake disaster,we should do a good job in the risk assessment of the evacuation channel under different earthquake intensity,and put forward the corresponding disaster prevention and relief plan.According to the connectivity evaluation data of the evacuation channel,we should effectively arrange the relief materials,reinforce and reconstruct the poor connectivity evacuation channel.After the occurrence of earthquake disaster,the disaster victims can be transferred from one place to another according to the actual situation,which is conducive to the rescue work after the disaster.