Multi-scale Evaluation Of Construction Safety Risk Of Ningbo Metro Station Under The Coupling Effect Of Complex Factors

With the increasing load of urban public transportation,the subway has become the main means to expand the urban underground space.Although China’s urban subway construction has made great achievements,due to the long construction period,complex construction technology,and many unforeseen risks in the construction of subway stations,construction accidents often occur during project construction.In fact,a coupled system of complex factors can lead to security risks.The soft soil characteristics of Ningbo make it very likely to cause risk accidents due to the excessive deformation of the station foundation pit under the coupling effect of multiple risk factors.Therefore,based on the engineering background of Ningbo Metro Honglian Station,this paper studies the coupling characteristics of construction risk factors and analyzes the deformation monitoring data of A1 foundation pit during the excavation stage.FLAC3 D was used to establish a numerical model of A1 foundation pit,and the calculation results were compared with the monitoring data to verify the accuracy of the model.Then use the numerical model to analyze the sensitivity of the risk factors,and finally use the multiscale analysis method to evaluate the project risk.It mainly includes the following four aspects:(1)The coupling characteristics of the construction safety risk factors of Ningbo subway station were explored.For t he Ningbo Urban Rail Transit Honglian St at io n Project,t he WBS-RBS met hod is used t o ide nt ify r isk fact ors.And use t he ISM model t o est ablish t he r isk fact or coupling relat ionship net work.It can be found t hat t here is a coupling relat io nship bet ween t he r isk fact ors.Under t he coupling effect of t he r isk fact ors,a causal pat h will be for me d,leading t o t he occurrence o f a safet y accident.Then t he coupling st rengt h bet ween t he r isk fact ors is calculat ed t hrough t he cloud model and t he coupling degr ee model,and it can be found t hat t he coupling syst em is in a high-st rengt h coupling st at e.(2)The field monitoring data of foundation pit deformation of Ningbo Metro Honglian Station were analyzed.First,t he layout of t he mo nit or ing po int s o f t he A1 foundat io n pit o f t he Honglian St at io n is explained.Furt her more,t he mo nit or ing dat a o f t he ground set t lement,t he hor izont al displacement o f t he ground connect ing wall,and t he support ing axial force at different locat io ns dur ing t he excavat io n st age of t he foundat ion pit were analyzed.It can be found t hat t he maximu m set t lement o f t he so il out side t he r ight wall r eaches-22.87 mm.The maximu m hor izo nt al displacement of t he enclosure st ruct ure appears at t he excavat io n dept h o f t he foundat ion pit at 22.5m,reaching 57.27 mm.T he support axia l force value fluct uat es in t he range of 900～3600k N.Co mb ined wit h t he act ua l working condit io ns,t he axial force change curve is analyzed fro m five st ages.(3)A numerical model for the deformation analysis of the A1 foundation pit of Ningbo Metro Honglian Station was established.Relying on t he A1 foundat ion pit pro ject of Ningbo Met ro Honglian St at io n,t he finit e element analys is so ft ware FLAC3D6.0 is used t o carry out t he numer ical mo deling o f t he A1 foundat io n pit excavat ion st age.The calculat io n result s of t he horizont al disp lacement of t he wall,t he sur f ace set t lement and t he support axial force are ext ract ed for research,and t he calculat io n result s are co mpared wit h t he mo nit or ing dat a.It can be found t hat t he simulat io n result s are consist ent wit h t he monit or ing result s for t he dist r ibut ion law o f sur face subsidence,and t he maximu m values are bot h around 15 m.For t he changing t rend o f t he hor izo nt al displacement of t he envelope st ruct ure,t he simu lat ion result s are t he same as t he mo nit or ing result s.Regarding t he numer ical value,t he simulat io n resul t s are smaller t ha n t he mo nit or ing result s.S elect ing t he concret e support axial force for analys is,it can be found t hat t he simulat io n result s and t he monit or ing result s ar e consist ent in t he change t rend,and t he t wo are also relat ively consist ent in nu mer ical value.It can be seen t hat t he simu lat io n of t he support st ruct ure by t he numer ical model can bet t er restore t he scene sit uat ion.(4)The multi-scale evaluation of the construction safety risks of Ningbo Metro Honglian Station has been realized.First,t he defor mat ion cont rol syst em o f deep foundat ion pit s in Ningbo area is int roduced.Based on t he obt ained numer ical model,t he sensit ivit y analysis o f four t ypes of r isk fact ors is obt ained.T he fuzzy co mprehensive evaluat ion met hod is used t o evalua t e t he project risk,and t he pro ject r isk value is 67.1592,which is high r isk.Taking t he r isk fact ors of so il elast ic modulus and over-excavat io n dept h as examples,t he mult i-scale evaluat io n of engineer ing pro ject r isks under t he act ion of single fact or and t he coupling act ion of t wo fact ors are carried out respect ively.It can be found t hat when t he t wo fact ors are coupled,t he defor mat ion of t he foundat ion pit will be aggravat ed,and t he r isk of t he pro ject will incr ease sharply.