Search results

This paper aims to investigate the responses of single piles and pile groups due to tunneling-induced ground movements in a two-layered soil system. The analyses mainly focus on the additional single pile responses in terms of bending moment, lateral deflection, axial force, shaft resistance and pile settlement. Subsequently, a series of parametric studies were carried out to better understand the responses of single piles induced by tunneling. To give further understanding regarding the pile groups, a 2 × 2 pile group with two different pile head conditions, namely, free and capped, was considered.

Using the PLAXIS three-dimensional (3D) software, a full 3D numerical modeling is performed to investigate the effects of ground movements caused by tunneling on adjacent pile foundations. The numerical model was validated using centrifuge test data found in the literature. The relevance of the 3D model is also judged by comparison with the 2D plane strain model using the PLAXIS 2D code.

The numerical test results reveal that tunneling induces significant displacements and internal forces in nearby piles. The magnitude and distribution of internal forces depend mainly on the position of the pile toe relative to the tunnel depth and the distance between the pile and the vertical axis of the tunnel. As the volume loss increases from 1% to 3%, the apparent loss of pile capacity increases from 11% to 20%. By increasing the pile length from 0.5 to 1.5 times, the tunnel depth, the maximum pile settlement and lateral deflection decrease by about 63% and 18%, respectively. On the other hand, the maximum bending moment and axial load increase by about 7 and 13 times, respectively. When the pile is located at a distance of 2.5 times the tunnel diameter (Dt), the additional pile responses become insignificant. It was found that an increase in tunnel depth from 1.5Dt to 2.5Dt (with a pile length of 3Dt) increases the maximum lateral deflection by about 420%. Regarding the interaction between tunneling and group of piles, a positive group effect was observed with a significant reduction of the internal forces in rear piles. The maximum bending moment of the front piles was found to be higher than that of the rear piles by about 47%.

Soil is a complex material that shows differently in primary loading, unloading and reloading with stress-dependent stiffness. This general behavior was not possibly being accounted for in simple elastic perfectly plastic Mohr–Coulomb model which is often used to predict the behavior of soils. Thus, in the present study, the more advanced hardening soil model with small-strain stiffness (HSsmall) is used to model the non-linear stress–strain soil behavior. Moreover, unlike previous studies THAT are usually based on the assumption that the soil is homogeneous and using numerical methods by decoupled loadings under plane strain conditions; in this study, the pile responses have been exhaustively investigated in a two-layered soil system using a fully coupled 3D numerical analysis that takes into account the real interactions between tunneling and pile foundations. The paper presents a distinctive set of findings and insights that provide valuable guidance for the design and construction of shield tunnels passing through pile foundations.

The shield tunnels closely constructed near the foundations have an inevitable influence on the structures, even results in the large settlement or uplift of the structures.

The comparison of structural deformation of three different foundations is presented based on the field monitoring data.

Shield tunnelling parameters vary for the different types of foundations. For the long pile foundations, the recommended speed is 3 to 4 cm/min, the grouting pressure is about 0.3 MPa and the grouting rate ranges from 150 to 180.

The study based on the field monitoring data is rarely reported, especially the topic about the structural deformation of different types of the foundations.

This paper aims to analyse the effect of soft soil grouting on the deformation of the closed shield tunnel with the measured data.

Combining the measured data of vertical, horizontal and convergence deformation of the adjacent tunnel during the grouting construction in foundation pit engineering, the influence of grouting on metro tunnel in soft soil area is analyzed.

The researches indicate that early grouting has the main effect on the horizontal displacement of the tunnel; Due to the disturbing effect of the uninterrupted grouting construction on the soil and the transfer pressure of the rheological soil to the bottom of the tunnel, the tunnel is obviously lifted; And the convergence deformation of the tunnel increases caused by the overburden pressure in the vertical direction, so that the tunnel appears the phenomenon of staggered seam, large opening of bolted joint, damaged segment even leakage of water.

The study based on the field monitoring data is rarely reported, especially the topic about inadvertent grouting in soft soil area is likely to cause severe deformation of adjacent metro tunnel.

Deep excavation in soft clay often causes additional deformations to surroundings. Then, if deformations cannot be predicted reasonably, the adjacent buildings may be threatened by the deep excavation. Based on the good field observations from ten deep excavations in Hangzhou, this paper aims to thoroughly investigate the characteristics of wall deflections and ground settlements induced by deep excavations.

On the basis of good field observation of ten deep excavations, the performances of excavations, supported by contiguous pile in Hangzhou, were studied, and also compared with other case histories.

The maximum wall deflections (dhm) rang mostly from 0.7 to 1.2 per cent H_e, where He is the final excavation depth, larger than those in Taipei and Shanghai. The observed maximum ground settlement in the Hangzhou cases generally ranges from 0.2 to 0.8 per cent H_e. Then, the settlement influence zone extends to a distance of 2.0-4.0 H_e from the excavation. The relatively large movements and influence zones in Hangzhou may be attributed to low stability numbers, large excavation widths and the creep effect. The excavation width is justified to have a significant influence on the wall deflection. Therefore, to establish a semi-empirical formula for predicting the maximum wall deflection, it is necessary to include the factor of excavation width.

The relevant literature concentrated on the characteristics of deep excavations supported by the contiguous pile wall in Hangzhou soft clay can rarely be found. Based on the ten deep excavations with good field observation in Hangzhou, the characteristics of wall deflection and ground settlements were comprehensively studied for the first time, which can provide some theoretical support for similar projects.

This study aimed to address a gap in subcontractor management by focusing on previously unexplored complexities surrounding subcontractor management in developing countries. While past studies concentrated on selection and relationships, this study delved into how effective subcontractor management impacts project success.

This study used the Bayesian Network analysis approach, through a meticulously developed questionnaire survey refined through a piloting stage involving experienced industry professionals. The survey was ultimately distributed among participants based in Accra, Ghana, resulting in a response rate of approximately 63%.

The research identified diverse components contributing to subcontractor disruptions, highlighted the necessity of a clear regulatory framework, emphasized the impact of financial and leadership assessments on performance, and underscored the crucial role of main contractors in Integrated Project and Labour Cost Management with Subcontractor Oversight and Coordination.

Previous studies have not considered the challenges subcontractors face in projects. This investigation bridges this gap from multiple perspectives, using Bayesian network analysis to enhance subcontractor management, thereby contributing to the successful completion of construction projects.

The purpose of this study is to investigate the effect of presence of buried flexible pipe on the bearing capacity of shallow footing. First, a model study is performed where shallow footing model is tested for its load settlement behavior, with and without the existence of buried PVC pipe lying vertically below the base of the footing.

The experimental set-up consisted of a steel box filled with sand at two different relative density values [RD = 50 per cent (medium dense) and RD = 80 per cent (dense sand)] and vertical load was applied on the model footing through hydraulic jack and reaction frame arrangement connected with a proving ring. Test results are verified numerically using commercially available finite element code PLAXIS 2D. With due verification, a parametric study has been conducted, numerically, by varying the range of input parameters, such as unit weight, angle of internal friction, diameter of buried conduit and the Elastic modulus of the soil to assess the pre cent reduction in the capacity of the foundation soil because of the presence of underlying buried flexible pipe.

Results show that for each footing, there exists a critical depth below which the presence of the buried conduit has negligible influence on the footing performance. When the conduit is located above the critical depth, the bearing capacity of the footing varies with various factors, such as geotechnical parameters of soil and location and diameter of the buried conduit.

It is an original paper performed to assess the presence of buried flexible pipe on the bearing capacity of the shallow footing.

Continua and discontinua coexist in natural rock materials. This paper aims to present an improved approach for addressing the mechanical response of rock masses based on the combined finite-discrete element method (FDEM) proposed by Munjiza.

Several algorithms have been programmed in the new approach. The algorithms include (1) a simpler and more efficient algorithm to calculate the contact force; (2) An algorithm for tangential contact force closer to the actual physical process; (3) a plastic yielding criterion (e.g. Mohr-Coulomb) to modify the elastic stress for fitting the mechanical behavior of elastoplastic materials; and (4) a complete code for the mechanical calculation to be implemented in Matrix Laboratory (MATLAB).

Three case studies, including two standard laboratory experiments (uniaxial compression and Brazilian split test) and one engineering-scale anti-dip slop model, are presented to illustrate the feasibility of the Y-Mat code and its ability to deal with multi-scale rock mechanics problems. The results, including the progressive failure process, failure mode and trajectory of each case, are acceptable compared to other corresponding studies. It is shown that, the code is capable of modeling geotechnical and geological engineering problems.

This article gives an improved FDEM-based numerical calculation code. And, feasibility of the code is verified through three cases. It can effectively solve the geotechnical and geological engineering problems.

This paper aims to investigate the creep behaviour of the recently developed Sn–8Zn–3Bi–xSb (x = 0, 0.5, 1.0 and 1.5) low temperature lead-free solder alloys.

An in-house compressive test rig was developed to perform creep tests under stresses of 20–40 MPa and temperature range 25°C–75 °C. Dorn power law and Garofalo hyperbolic sine law were used to model the secondary creep rate.

High coefficient of determination R² of 0.99 is achieved for both the models. It was found that the activation energy of Sn–8Zn–3Bi solder alloy can be significantly increased with addition of Sb, by 60% to 90 kJ/mol approximately, whereas the secondary creep exponent falls in the range 3–7. Improved creep resistance is attributed to solid solution strengthening introduced by micro-alloying. Creep mechanisms that govern the deformation of these newly developed lead-free solder alloys have also been proposed.

The findings are expected to fill the gap of knowledge on creep behaviour of these newly developed solder alloys, which are possible alternatives as lead-free interconnecting material in low temperature electronic assembly.