The Numerical Simulation Research On Construction Mechanics And Surrounding Rock Stability In Tunnel Of The Weak Surrounding Rock

As the development of infrastructural construction in our country and theenlargement of scale of highway tunnels, more and more tunnel of weak surroundingrock has arisen. However, there are many factors that cause the tunnel deformation andcollapses, such as unreasonable technical measures, wrong method of construction, badconstruction process and weak site management. This article will make furtherdevelopment in excavation methods of weak surrounding rock of tunnel and structuralmechanics of tunnel support.In this article engineering geological properties of tunnels with weak surroundingrock, the key factors for tunnels surrounding rock’s stability and deformationcharacteristic are analyzed. This article gives brief summary of excavation methods ofweak surrounding rock of road tunnel. Combining the construction of Luopin tunnel’ssoft surrounding rock, monitoring and measurement results of Luopin tunnel’s typicalcross-section are analyzed.Models are established by the finite element software toanalyze the impact of weak rock tunnel excavation work on the stability of surroundingrock and surrounding rock deformation displacement. The main fruit is listed as follows.①Selecting Luopin tunnel’s soft weak area to make monitoring and measurement,this article makes research on characteristic feature of the typical profile’s surroundingrock displacement-time curve. Results show that the vertical convergence deformationof tunnel’s arch crown is bigger than the horizontal of tunnel’s side wall. the release rateof displacement in down-step’s excavation is faster than the rate in up-step’s excavation.②Using step excavation method CD method and CRD method in shallow coverload part of Luopin tunnel’s soft weak area, this article makes numerical simulation onprocess of excavation and construction. Excavation on the upper of the step excavationmethod, because the span is large and the rise-span ratio is small, in the two lower endsof the steps can make a stress concentration.It is not conducive to bear external load, soit need to support quickly and timely.The supporting strength has to enhance and thecoupling place reinforcement of the up and down of the steps has to draw attention;With the CD method,the surrounding rock of both ends of the wall and primary supportgenerate a big stress concentration and tensile stress and the local damage emergence,using this method, the wall need to use the flexible supporting design;With the CRDmethod, the rapid formation of bearing structure of the surrounding rock isdisadvantageous for the disturbanceand and irresponsible supporting of wall.③According the analyzed results of the above construction methods: all of themethods can ensure construction safety and the displacement of each method can meetthe requirement of criterion; however, we decide to use step method to make excavationand construction measurement considering the time, economic factor and the results ofnumerical simulation. By the comprehensive analysis of measurement data, constructionschedule and economic conditions, etc, choose the most suitable method for this tunnel.