Advanced Tunneling Techniques and Information Modeling of Underground Infrastructure

Rainfall-induced landslides of the flow type in granular soils are among the most complex natural hazards due to the variety of mechanisms which regulate the failure and propagation stages. Among these, debris avalanches are characterised by distinct mechanisms which control the lateral spreading and the increase in soil volume involved during the propagation. Two different stages can be individuated for debris avalanches, i.e. the failure stage and the avalanche formation stage: the former includes all the triggering mechanisms which cause the soil to fail; the latter is associated to the increase of the unstable volume. Regarding these issues, in the literature, either field evidence or qualitative interpretations can be found while few experimental laboratory tests and rare examples of geomechanical modelling are available for technical and/or scientific purposes.

In this paper a contribution is provided about the advanced numerical modelling of the inception of such hazardous debris avalanches. Particularly, the case of the impact of a failed soil mass on stable deposits is considered. This means that a small translational slide occurs; the failed mass causes the soil liquefaction of further material by impact loading; the landslide volume increases inside triangular-shaped areas during the so-called “avalanche formation”, and also soil erosion along the landslide propagation path plays an important role.

To this aim, an innovative numerical technique known as the Material Point Method (MPM) is used. It can be considered as a modification of the well-known Finite Element Method (FEM) particularly suited for large deformations. The continuum body is schematized by a set of Lagrangian points, called Material Points (MPs). Large deformations are modelled by MPs moving through a background mesh, which also covers the domain where the material is expected to move. The MPs carry all physical properties of the continuum such as stress, strain, density, momentum, material parameters and other state parameters, whereas the background mesh is used to solve the governing equations without storing any permanent information. Such advanced approach allows combining a hydro-mechanical coupled approach, any of the well-known soil constitutive models proposed over the years in soil mechanics and a large-displacement formulation.

The numerical analyses are performed adopting 2D geometrical configurations taken from field evidences and previous researches. Triangular 3-noded computational meshes are used, characterized by elements of about 1 m. The interaction between the impacting mass, and then of the propagating flow with the in-situ stable soil is examined, providing important insights about the behaviour of such type of landslide. The results achieved so far are encouraging and show that MPM can properly simulate the inception of debris avalanches and even their complex mechanisms during the impact and the interaction with in-situ stable zones.

Based on the background of the mud shield tunnel engineering in the section between Anfeng Station and Dongxin Station of Line 4 of Nanchang metro, the stress composition of the segment during the shield construction process was analyzed firstly, which was composed of buoyancy, the weight of the segment and the slurry, the viscous resistance of the segment, the friction resistance between the rings, the shear resistance of the bolt and the force of the overlying soil. Secondly, establishing the corresponding mechanical model, wherein: when calculating the viscosity resistance caused by the slurry, the slurry was assumed to be Newtonian; when calculating the overburden pressure, the degree of soil arching effect was considered, and the modified Terzaghi loosening earth pressure calculation was used. Through theoretical analysis of the stress of the segment during the construction phase, the theoretical solution of the amount of the segment from the shield tail to the initial settling of the slurry could be deduced, and then compared the theoretical solution and the basic field monitoring data. Finally, effective anti-buoyancy measures were proposed for the floating of the segments. The result shows that the theoretical solution of the floating amount derived by the calculation model is closer to the actual value, which verifies the feasibility of the calculation model and proposes targeted anti-floating measures based on the force composition of the segment, so as to achieve a good control effect of the upward moving of segments.

During operation of the Yunding Tunnel, the uplift displacement of the invert increases continuously, seriously impacting the safety of the tunnel structure and the normal operation of the railway line. To study the occurrence mechanism and evolution law of invert heave disease of railway tunnel in horizontal layered rock mass, both field investigation and numerical simulations were carried out, and the influence of layer thickness of layered rock mass and horizontal in-situ stresses were discussed. The results show that the deformation characteristic of layered rock mass is the main factor leading to the disease in operating tunnels. Especially in thin-thick to medium-thick layered rock mass and the horizontal in-situ stress of K₀ less than 1.0 or more than 2.0, it is difficult to ensure the stability and safety of bottom structure. Moreover, two proposed treatment schemes were analyzed to evaluate the regulation effect, and the latter scheme was recommended to be used in the project. This study can provide a reference for the treatment of operating tunnel in horizontal layered rock masses.

The densification of surrounding soil from compaction grouting for the compaction-grouted soil nail is a significant merit to improve the pullout force. However, few studies was conducted to quantify the contribution of the compaction grouting to the pullout force, thus, a semi-analytical model was proposed. First, a hyperbolic model considers the soil-grout bulb (soil nail) interface behavior was established, and an energy transfer analysis model of a soil nail with grout bulb was proposed by combining the energy method and the hyperbolic model. Second, the semi-analytical model was verified based on the result of physical model test. Third, parametric study was conducted to evaluate the influence of the key parameter of the hyperbolic model on the pullout force with grouting process and those without.

Hybrid mono-bucket foundations with ballast and skirt are employed to support offshore wind turbines (OWTs) in East China, with the advantages in capacity and efficient installation. The prediction of soil resistance during the penetration is critical in the design of mono-buckets, but few studies focused on the installation in silty soil. Two methods on predicting the penetration resistance are introduced based on soil parameters and in-situ CPT results, respectively. A modification on the friction angle of silty soil is made to account for the effect of the cohesion on the skirt-soil interface. A comparison is then carried out between the prediction results and prototype installation data to verify the methods and calibrate the coefficients in the equations. The back-analysis according to the field installation data shows that the accuracy of the first method is improved by the modification, and the second method based on the in-situ CPT data has a higher reliability with reasonable coefficients.

Standard Penetration Test (SPT) is the most commonly used field test in any geotechnical investigation campaign. Although SPT provides quite useful information on the nature and type of the subsurface strata, owing to its inherent operating mechanism, SPT incorporates several limitations. During the dynamic impact of the SPT hammer during the testing/sampling, there is a tendency of the breakage of the cementation and disturbance of the structure in the partially-cemented soils. Breakage of cementation and similar disturbance to the soil structure may mask some of the essential information required for the choice of geotechnical design parameters for the in-situ strata. Such partially-cemented soils are prevalent in the semi-arid regions of the world such as eastern Saudi Arabia. Cone Penetration Test (CPT) is another penetration-based field test employed, usually, deployed as a secondary test for the geotechnical explorations. Due to the pseudo-static penetration mechanism of the cone during CPT testing, this test is capable of quite closely recording the information pertinent to the undisturbed structure of the soil. Therefore, CPT can be classed as an essential complementary test to SPT for the development of the representative in-situ design subsurface profile. This paper discusses several case studies from eastern Saudi Arabia, in which the precise interpretation of the CPT provided the essential complementary information that augmented the results from the SPT in developing the accurate and field representative subsurface design profiles.

Because of the advantages of fast detection speed and no need for traffic control, the rapid detection vehicle based on camera technology is more suitable for the detection of apparent diseases in high-grade highway tunnels. However, this type of rapid detection vehicle basically uses visible light illumination, which has defects such as interfering with the normal driving of other vehicles in the tunnel. Therefore, a rapid detection vehicle for tunnel cracks using infrared supplementary light and its tunnel crack measurement technology based on digital images are introduced. Furthermore, in order to ensure the accuracy of crack detection of fast detection vehicle, it is necessary to calibrate the accuracy. In this paper, a new calibration method is proposed for the shortcomings of the existing calibration methods crack of detection accuracy. As an example, the rapid tunnel inspection vehicle based on the infrared band imaging technology is calibrated and compared with the other tunnel rapid inspection vehicles using visible light illumination. It is found that the calibration method is suitable for the calibration of the crack detection accuracy of tunnel rapid inspection vehicles with infrared or visible light illuminated. It also has the advantages of conforming to the actual environment of the operating tunnel, not affecting the traffic operation, small image processing workload, high accuracy, repeatable calibration, etc., and is further verified and reliable by the operating road tunnel, which meets the requirements of the relevant specifications for the accuracy of crack detection.

In this paper, the three-dimensional reconstruction of the tunnel point cloud is carried out based on the polynomial fitting method. Due to some shortcomings, a method of constructing a curved surface by region is introduced to analyze its fitting accuracy and fitting effect. For the tunnel vault with larger (or large) curvature, a B-spline interpolation method is used to reconstruct the tunnel, and for the arch waist, a polynomial fitting method is used to optimize the fitting method in different regions. Finally, the application of fitting results is prospected on this basis.