Research On Inversion Of Mechanical Parameters Of Weak Surrounding Rock And Optimization Of Support Scheme For Hydraulic Tunne

During the tunnel construction process,the mechanical parameters of the surrounding rock are the key factors in the tunnel design and construction.Especially in the construction of soft rock tunnels,due to the low strength of the surrounding rock,poor quality of the rock mass,and high support strength,the accuracy of obtaining the mechanical parameters of the surrounding rock will directly affect the stability evaluation of the tunnel and the design of the support structure,rationality.Parameter inversion is a commonly used method to obtain the mechanical parameters of surrounding rock.In the process of parameter inversion,the analytical method,numerical simulation method and experimental method are mainstream to invert the mechanical parameters of surrounding rocks.However,due to the complexity of the soft rock occurrence environment,its anisotropy is more significant.Thus,conventional methods require a lot of computing resources and time.It is difficult to truly reflect the real parameters of the rock mass for the research results.And it is also hard to provide effective guidance for the support design and stability evaluation of the tunnels.Based on this,this study relies on the 1# branch tunnel of the Wuzhuang Village Tunnel of the Central Yunnan Water Diversion Project and mainly takes the Class IV surrounding rock section as the research object.To be close to the mechanical parameters of the surrounding rock of the actual monitor section,it provides a theoretical basis for the support scheme optimization.The main achievements are as follows:(1)According to the value range of mechanical parameters of Class IV surrounding rock in the actual engineering geological survey and design report,a comprehensive scheme of parameter design combined with four methods,such as Latin hypercube sampling technology.The design of mechanical parameters such as deformation modulus,internal friction angle,and cohesion of surrounding rock can fill the entire distribution interval.And in the generated 1000 sets of mechanical parameter data,the average value of each parameter is close to its interval value,and the sample design is effective.(2)According to the relationship between the deformation value of the surrounding rock and the mechanical parameters of the surrounding rock in Wuzhuangcun Tunnel 1#branch tunnel(soft rock tunnel)of the Central Yunnan Water Diversion Project,a hybrid model EO using the balance optimizer algorithm to optimize Light GBM is proposed.-Light GBM,used to invert mechanical parameters such as deformation modulus,internal friction angle,and cohesion of surrounding rock.Among them,the EO-Light GBM model is used to invert the mechanical parameters of the surrounding rock in 10 sections,such as CX43+230 in the actual project,and the mechanical parameters obtained by the inversion are input into the FLAC3 D program for analysis and calculation.The calculated results are highly consistent with the actual deformation values of the project,and the maximum average error is 6.44%,which further verifies the rationality and accuracy of the EO-Light GBM model.(3)This study also discusses the applicability of calculation methods for equivalent parameters of different support structures in tunnel support simulation.The support simulation effects of the two equivalent parameter methods are discussed respectively.Comparing the calculated displacements of 10 sections,such as CX43+230 at the actual project,it is closer to the actual support when the equivalent method-1 in this paper used to equivalent the parameters of the steel arch support in the current situation.(4)Based on the above research results,after the inversion of the specific surrounding rock mechanical parameters,the actual support situation on the site was simulated,and a specific optimization scheme was given in combination with the reserved deformation in the design.Taking the CX43+230 and CX43+430 sections as examples,the row spacing between the steel arches in the CX43+230 section can be optimized from1.0m to 1.2m,and the steel arches in the CX43+430 section support is optimized from1.0m to 1.1m.And from the three aspects of economic benefit,social benefit and environmental benefit,it analyzes the influence of support scheme optimization on different aspects of benefits.In summary,through the comprehensive use of the EO-Light GBM parameter inversion model and FLAC3 D numerical simulation software,the inversion obtained from the surrounding rock mechanical parameters of 10 research sections,and based on the inversion obtained from surrounding rock mass mechanical parameters,realized the analysis of Optimization of tunnel support structures.All the results of this study can provide a reference for the inversion of mechanical parameters of surrounding rock in soft rock tunnels and the optimal design of support.And it has higher guiding significance for mine support with small mining section.