In the design process of bridges, especially long-span bridges, it is often necessary to consider the tonnage of ships to and from to determine the design height of the bridge, which often increases the construction difficulty and construction period of the bridge.
Introduction 1.1 research purpose: from the current situation and development trend of subsea tunnel construction abroad, certain experience has been accumulated in subsea tunnel construction, but there is no precedent for building large-section tunnel in rich water and soft stratum.
The cross section of XX subsea tunnel is large, the surrounding rock is soft, and the geological conditions are complex.
The double side heading method is the construction method adopted under the condition that the surface settlement is particularly strict.
The displacement boundary condition of the model is the displacement constraint in the X direction on the left and right sides of the tunnel; Z-direction displacement constraint is given on the bottom surface; The longitudinal boundary surface (excluding the boundary surface of the opening) is given the displacement constraint in the Y direction.
The model range is taken as 50m from the bottom to the surface, 50m from the left and right sides of the tunnel, and 50m from the tunnel entrance.
In the model, 8-node hexahedral elements are used for grid division, the Mohr Coulomb model is used for the stratum and pipe shed reinforcement area, and the linear elastic model is used for the tunnel structure.
Therefore, according to the actual situation of the subsea tunnel, only the CD method or the CRD method is considered.
The statistical results of a large number of construction examples show that the preferred order of construction methods in controlling settlement is: double side heading method, CRD method, CD method, reserved core soil bench method and bench method; In terms of controlling horizontal displacement, the construction methods are selected in the following order: CRD method, double side heading method, CD method, temporary closed bench method of upper half section, and bench method; From the perspective of construction progress and economy, the preferred order is: bench method, reserved core soil bench method, CD method, CRD method and double side wall heading method.
The excavation span is 16.74m and the excavation height is 12.261m.
The reasonable construction method is determined after comprehensive consideration; (2) Six different working conditions and two different processes are designed to conduct numerical simulation on the three-dimensional deformation state of the stratum during excavation under various working conditions, analyze and summarize the deformation and instability laws, and optimize the step distance and process between each part of CRD construction method on this basis; (3) The principle of deformation distribution control is applied to tunnel construction to determine the control target value, and the deformation is controlled within the safe range through monitoring feedback and step-by-step control; (4) Study the mechanism of the foot lock bolt, conduct numerical simulation of the construction effect of the foot lock bolt, systematically study its force and deformation laws, and optimize the design and construction methods of the foot lock bolt; (5) The catastrophe model of interaction between initial support and surrounding rock is established, and the catastrophe instability of surrounding rock is studied by using the stiffness of initial support and the weakening stiffness of surrounding rock.
2.2 engineering and geological overview: the subsea section of XX tunnel is 4200m long, and the average overburden thickness of the shoal section is 7.35m.
2.3 FLAC3D is used to calculate and analyze the settlement caused by the excavation of CD method and CRD method at the tunnel entrance.
The model is divided into 16900 elements and 18438 element nodes..
Therefore, this topic combines the characteristics of complex geological conditions, large excavation section and no mature experience for reference of XX subsea tunnel, It is of great practical significance to conduct in-depth research on the construction methods, settlement control and auxiliary construction methods of soft stratum, summarize a set of technologies and methods suitable for the construction of soft stratum, large section and subsea tunnel, and use the research results to guide the construction and optimize the design.
1.2 research content this topic is closely combined with the construction of XX subsea tunnel, and is studied through on-site monitoring, numerical calculation and theoretical analysis.
However, the existence of the subsea tunnel solves this problem well.
Study on the construction settlement control of CRD method and CD method in shallow shoal Section 2.1 construction methods of shallow buried long-span soft rock tunnel in recent years, engineering examples at home and abroad show that there are many methods for tunnel construction under various geological conditions, but there are six basic construction methods suitable for large-section tunnel: bench method, temporary closed bench method of upper half section, CD method, CRD method, side wall heading method and spectacle method (double side wall heading method).
The CD and CRD construction methods are respectively modeled and calculated, and the numerical simulation analysis and comparison are carried out.
Source: the copyright of Zhulong forum belongs to the original author.
2.
This chapter simulates and compares the two construction methods.
What are the main construction technologies of the subsea tunnel, What can we also apply to other projects? 1、 Research on construction stability control of subsea tunnel in soft stratum 1.
The strata passing through are mainly filling soil, clay, sandy loam and biotite granite, which are class V surrounding rocks.
The mechanism of grouting behind the wall is explained theoretically, and the effect of filling grouting on settlement control is verified by field monitoring.
(1) The numerical method is used to simulate the soil layer and construction conditions at the site.
The bench method is difficult to apply.
