•An improved analytical method for evaluating the responses of shield tunnel due to adjacent excavation is proposed.•The proposed method is verified by three case histories.•The verified method is ...applied to a practical project, construction optimization is also performed.•A series of parametric analyses are conducted.
Adjacent excavations may adversely impact existing shield tunnels. Therefore, evaluating the induced responses of existing tunnels is critical. Previous analytical methods have generally treated shield tunnels as Euler–Bernoulli or Timoshenko beams resting on Winkler or Pasternak foundations to simulate tunnel–soil interactions. However, these methods do not consider excavation–induced disturbance to the surrounding soil and lack sufficient theoretical bases for determining subgrade parameters. This study proposes an improved analytical method that utilizes a Timoshenko beam to simulate a shield tunnel, and that considers the bending and shearing effects on a tunnel. The Vlazov foundation model is introduced to simulate tunnel–soil interactions and to further consider induced disturbance to the surrounding soil. The consistency between the measurements obtained from three case histories and the predictions verifies the proposed method. Then, the verified method is applied to a practical project. Results indicate that the predictions are generally consistent with the in situ measurements. Construction optimizations are also performed to meet the safety requirements and to expedite the construction progress. Finally, parametric analyses are conducted, and their results reveal that the factors, including excavation–tunnel relative distance, ground Young’s modulus and tunnel buried depth, exert considerable influences on the underlying shield tunnel.
•Shield tunnel lining damage induced by soil-water inrush is studied.•Numerical simulation matches with field results reasonably.•Strength reduction method have been applied for the consideration of ...soil loss.•Lessons learned from this incident have been presented.
This paper reports a case study on shield tunnel lining damage induced by soil-water inrush occurred in Tianjin Metro Line 1, China through both field monitoring and numerical simulation. This incident was triggered by the non-watertight boring work of thru holes adjacent to the cross passage between the twin tunnels. Under high hydraulic gradient, the seepage-prone weak zone was formed and extended, then the outburst of soil-water slurry was occurred. Measures including plugging engineering cotton, injecting quick-setting cement and welding partition plate of steel segments, had been taken but in vain. The outburst of soil-water slurry induced soil movement around the cross passage, thus leading to the damage of tunnel lining and ground surface settlement. After sealing the water ingress holes, stabilization methods including surface grouting and inside tunnel back grouting were applied. The mechanisms of segment lining damage and the effectiveness of stabilization are investigated through both numerical simulation and field monitoring data analysis. Lessons learned from this incident have been discussed, thus providing reference for potential shield tunnelling under similar engineering conditions.
A systematic geometric algorithm is developed to generate particle packing with high density, controllable gradation, and uniform spatial distribution for discontinuous deformation analysis (DDA). ...The algorithm incorporates a lattice searching technique to expedite overlap detection and reduce computational costs during particle packing generation. Additionally, a Fourier transformation method is utilized to analytically handle overlap detections on arbitrary irregular boundaries. To evaluate the efficiency and accuracy of the proposed method, a series of comparisons are made between existing methods and the proposed approach. Numerical modelling of engineering problems is conducted using the proposed method and a self-developed numerical program called DDA. The modelling results demonstrate that the proposed particle generation method has wide applications in generating complex particle models for discontinuous numerical analysis. The algorithm exhibits excellent performance in both geometric and numerical analyses, further confirming its efficiency and accuracy.
Article Highlights
A systematic geometric algorithm is developed to generate particle packing with controllable internal characteristics.
The algorithm integrates a lattice searching algorithm to expedite particle generation.
The algorithm incorporates the Fourier transformation method to handle overlap detections on arbitrary irregular boundaries.
When shield tunnelling is in a water-rich sand stratum with poor bearing capacity, instability is easily generated, and even ground collapses may occur. The variation of pore water pressure in a ...water-rich sand stratum during shield tunnelling was analyzed based on a large-scale cross-river shield tunnel in China, which was also investigated by a three-dimensional fluid-solid coupling finite element model. The results show that the influence range of the pore water pressure in front of the excavation face is approximately 2.0 times the excavation diameter and 1.5 times on both sides of the shield. The tunnelling steps would cause obvious variation in the pore water pressure and lead to great disturbance to the surrounding fine sand stratum. The quality of filter cake and the set of support pressure imposes an important impact on the nonlinear variation in the pore pressure, which could cause great disturbance to the stratum. To ensure the safety of the subsequent tunnelling in the fine sand layer, effective treatment should be taken.
Friction resistance usually constitutes one of the two main components for the calculation of required jacking force. This paper provides a new approach to predict the friction resistance of slurry ...pipe jacking. First, the existing prediction equations and their establishment methods and essential hypotheses used were carefully summarized and compared, providing good foundations for the establishment of the new model. It was found that the friction resistance can be uniformly calculated by multiplying an effective friction coefficient and the normal force acting on the external surface of the pipe. This effective friction coefficient is introduced to reflect the effect of contact state of pipe-soil-slurry, highly affected by the effect of lubrication and the interaction of pipe-soil-slurry. The critical quantity of pipe-soil contact angle (or width) involved may be calculated by Persson’s contact model. Then, the equation of normal force was rederived and determined, in which the vertical soil stress should be calculated by Terzaghi’s silo model with parameters proposed by the UK Pipe Jacking Association. Different from the existing prediction models, this new approach has taken into full consideration the effect of lubrication, soil properties (such as internal friction angle, cohesion, and void ratio), and design parameters (such as buried depth, overcut, and pipe diameter). In addition, four field cases and a numerical simulation case with various soils and design parameters were carefully selected to check out the capability of the new model. There was greater satisfaction with the measured data as compared to the existing models and the numerical simulation approach, indicating that the new approach not only has higher accuracy but is also more flexible and has a wider applicability. Finally, the influence of buried depth, overcut, and pipe diameter on the friction resistance and lubrication efficiency were analyzed, and the results can be helpful for the future design.
Impact loads widely exist in practical engineering and often cause cumulative damage and cracks or even fracture failure of concrete structures with their repeated long-term action. This experimental ...research is conducted on the damage evolution characteristics of concrete under impact loads by regarding C50 nonreinforced concrete as the research object and using a self-developed drop-weight device with electromechanical impedance measurement technology. Results show the following. (1) Under low-energy impact, concrete damage has long continuous development process and remarkable cumulative effects. An apparently sudden break characteristic appears before failure. Under high-energy impact, concrete damage accumulates rapidly, and piezoceramic patch signals grow linearly. (2) The root mean square deviation (RMSD) of the concrete increases exponentially with impact times. Particularly, when the RMSD exceeds 0.075, the concrete damage process enters the rapid development stage and approaches the critical failure state. (3) Under the experimental conditions in this study, the relationship between the ultimate impact times (damage life) and impact heights of the concrete samples shows the development trend of the power function. The above results can provide reference for the research on service life prediction methods of concrete structures under impact loads.
During deep foundation pit construction, the structural clearance intrusion, which is caused by the complex formation conditions and the inefficient drilling equipment, is usually detected due to the ...vertical deviation of piles. To meet construction requirements, pile parts intruding into the structural clearance are supposed to be excised. However, the sectional flexural strength of the pile is bound to decrease with partial excision, which would reduce the bearing capacity of the enclosing structure during construction. In this paper, a theoretical derivation of the normal sectional flexural strength of the partially excised circular pile is proposed. The derivation adopts the assumption of the plane section and steel ring equivalence and can be solved by the bisection method. Furthermore, the calculation method is applied to the pile evaluation of a practical engineering; also, the method is verified by the numerical method. The application results show that the excision of rebar and pile’s sectional area will cause a rapid linear decline in the sectional flexural strength. After excising 18 cm radial thickness of the circular pile (ϕ800 mm) and 6 longitudinal rebars, the sectional flexural strength of the pile decreases to 58% from the origin, which cannot meet the support requirement. The analysis indicates that pile reinforcements must be carried out to maintain the construction safety.
•A detailed FDEM numerical method to simulate mechanical and fracturing responses of heterogeneous geomaterials with irregular inclusions is systematically developed.•A computational geometry method ...named CWSVM is proposed to control mesh quantity and quality.•A signed-distance-field-based discrete element method (SDF-DEM) is employed to approach the natural allocation and orientation of inclusions.•A combined constitutive model is proposed to consider the shearing hardening behaviour for the cohesive elements.•Effects of the interface strength on the mechanical and fracturing behaviours of inclusion-containing geomaterials are extensively discussed.
In this paper, a detailed FDEM approach to simulate the mechanical and fracturing responses of heterogeneous geomaterials with irregular inclusions is systematically developed. The inclusion surface morphology is first obtained through 3D scanning techniques. A computational geometry method, the curvature-weighted sphere Voronoi method (CWSVM), is adopted to control the mesh quantity and quality and ensure the efficiency and accuracy of the FDEM numerical model. A signed-distance-field-based discrete element method (SDF-DEM) is employed to approximate the natural distribution and orientation of inclusions. Heterogeneous geomaterials with large inclusion contents (such as 60% and 70%) are generated effectively and efficiently through this approach. Next, to model the fracturing process, a finite discrete element method (FDEM) model is developed by integrating cohesive elements into the mesh in a fast and efficient manner. In addition, a combined constitutive model is proposed to consider the shear-hardening behaviour of the cohesive elements. The proposed numerical approach is verified through comparison with experimental results, including the shape of inclusions and mechanical responses of geomaterials. The results demonstrate that both satisfactory precision and low calculation costs can be achieved using the proposed algorithm. The consequent simulation performance is verified through comparisons of observations and numerical results with experimental results for failure patterns and mechanical behaviours. In addition, the effects of the strength of the interfaces between the inclusions and matrix on the mechanical and fracturing characteristics of inclusion-containing geomaterials are analysed quantitatively. The mechanical strength decreases rather than increases with increasing content of inclusions when the interface strength is less than the matrix strength.
The electromechanical impedance (EMI) technique based on the PZT transducer, in the past twenty years of research progress, has demonstrated its potential for cost-effective and high damage-sensitive ...structural health monitoring. This paper presents an application of EMI technique for damage evolution investigation of initial damaged tunnel invert concrete under high traffic cyclic loading. In the tests, six different levels of initial damage inside the specimens, as the influencing factor, were firstly created by applying a certain number of impacts with a free-falling iron ball. Then, these specimens were applied typical mechanical boundaries similar to that of tunnel invert concrete by an installation specially designed. Finally, the traffic cyclic loading carefully determined was exerted by the MTS815 hydraulic zero-control testing system, to investigate the evolution characteristic of piezoelectric signature of the PZT sensor. The experimental result shows that the conductance signature follows a consistent rightward shifting with the number of cycles increasing, and the larger the initial damage of the specimen, the more obvious the rightward shifting. It indicates that, in general, the traffic cyclic loading is not large enough to make the microcracks propagate to fatigue failure in tunnel invert concrete even if there is a large initial damage. On the contrary, with special mechanical boundaries, the local nominal stiffness of tunnel invert concrete will gradually increase. This phenomenon may be interpreted as an effect of generalized damage recovery. A new damage index, with values between 0 and 1, was then defined to quantify the damage level for quantitative analysis. It was found that the damage recovery behaviors for different initial damaged specimens can be well and uniformly described by an empirical expression, which may be helpful for the damage assessment of tunnel invert concrete under high traffic cyclic loading in the future.
This paper performs an extensive literature survey and example investigation on the stabilisation of slurry wall trenches during the construction of diaphragm wall panel trenches, and the failure ...modes of slurry wall trench instability, the stability theoretical analysis models and methods, the slurry formation and its protection mechanism, the influence of related factors on slurry wall trench stabilisation, and other related problems are summarized and analyzed emphatically. And then, based on the limit equilibrium analysis method, the mechanical models of the overall stability and local stability of the trench wall are established, respectively, and the design method of slurry unit weight is derived to ensure the stability of the trench wall. Furthermore, an example application shows that the established slurry unit weight design method is reliable. At last, this paper also proposes the focus and direction for follow-up work, that is, to construct an accurate and effective theoretical analysis model of slurry wall trench instability considering the influence of multiple factors and the calculation method of the slurry cake and its mechanical or mathematical relationship with slurry quality.
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