KSCE Journal of Civil Engineering最新文献

With the rapid development of urban rail transit systems, the shield tunneling technology has become indispensable for urban tunnel construction. However, the theoretical study of the shield tunneling process is not mature enough in view of the complex mechanical properties of the shield machine and the surrounding soil. In this paper, the attitudinal change behavior of earth pressure balanced shield machines (EPB) during the tunneling process is investigated, and comprehensive theoretical expressions for the normal and frictional forces acting on the shield periphery and cutter face are derived. The discretization equations for the normal forces acting on the shield periphery are given based on the meshing and interpolation method. Based on the above studies, the mechanical equilibrium equations of the shield are established to accurately solve for the shield forces and shield attitude characteristics, as well as to verify the computational accuracy of the theoretical solution. Through the analysis of a practical project involving longitudinal tunneling, it is confirmed that the theoretical calculation model can better reflect the mechanical behavior of the earth pressure balanced shield.

In this study, the ability of regression-based methods, namely conventional regression analysis (CRA) and multivariate adaptive regression splines (MARS), and artificial neural networks (ANNs) method was investigated to model the river dissolved oxygen (DO) concentration. Daily average data for discharge and water-quality (WQ) indicators, which include DO concentration, temperature, specific conductance, and pH, were provided for the monitoring stations USGS 14210000 (upstream) and USGS 14211010 (downstream) in the Clackamas River, Oregon, USA. Eight models were established using different combinations of the input parameters and tested to determine the contribution of each parameter used in the modeling to the performance of the models. The results of the models and methods were compared with each other using several performance statistics. Although the performances of the methods were quite close to each other, the highest estimation performance was obtained from the ANNs method in the testing data sets. According to the performance statistics, Model 8, in which all WQ indicators were included as input parameters, was selected as the optimal model to estimate DO concentration of different periods of the same stations. However, when estimating the DO concentration from one station to another, the highest performance statistics were obtained from Model 8 for upstream and Model 1 for downstream station using the CRA method. For the ANNs method, Model 1 having the single input for both stations was the best model.

Membrane structures are becoming increasingly popular as a solution for covering large spans. Their versatility and short construction time make them an economical solution for temporary or permanent structures. During the structural analysis, the wind effects must be highly considered; however, because of their unique architectural shape, the pressure coefficients are not provided in the design codes. The current paper introduces the wind analysis of an air-inflated membrane structure. The pressure distribution on the external surface of the structure was determined for different wind directions by Computational Fluid Dynamics. The research included mesh sensitivity analysis and the evaluation of different turbulence models. Previous wind tunnel test results validated the numerical simulations. The experimentally and numerically determined pressure coefficient fields and the resulting respective membrane forces and displacements are compared. The presented results show that the CWE analysis can provide a suitable approximation of the WT-based results from a structural point of view. After validation, the numerical model was extended to similar structures with various lengths. The presented results can be used directly in the structural analysis of similarly shaped inflated membranes.

Ground settlement control is a critical aspect in underground projects with shallow overburden. In tunnels with large span, the use of common support elements such as shotcrete and lattice girder are not sufficient in order to provide tunnel stability with acceptable safety factor and additional supporting elements may be required. In this research, the effect of combination of multiple support elements, including shotcrete, fore-poling, nailing, and micro-pile to minimise ground settlements, have been investigated. This case study focuses on the Arash-Esfandiar tunnel, a shallow underground passage located in the northern part of Tehran, Iran with a total length of 1532 m. According to the geotechnical report, ground condition varies from silty sandy gravel to dense clay sand. Finite Element (FE) analyses were performed by assuming different constitutive models i.e., Mohr-Coulomb (MC), Hardening Soil (HS) and Hardening Soil with Small strain stiffness (HSS), to investigate the capability of linear and non-linear models on predicting the surface settlement in the study. The results indicate that axial and bending elements as tunnel support measures concurrently, affects more in ground settlement control. On-site measurements and the results of numerical modelling show a significant effect of removing temporary lattice girder on surface settlements. The research is novel in its application of various constitutive soil models – MC, HS and HSS – to predict surface settlement effects. Comparative analysis of FE results with on-site measurements reveals the significant influence of removing temporary lattice girders on surface settlements. It is found that while the MC model is unable to capture the full complexity of the conditions governing the project and the HS and HSS models demonstrate a higher fidelity in representing the soil behavior during the tunneling process. Whereas on-site measurements indicate a higher impact of excavation stages showing larger deformations. Considering the heights of the walls, during the final stage of excavation the invert didn’t have much effect on surface displacements.

This paper investigated the shear strengths (that is, the ultimate strength, post-ultimate residual strength and failure strength) and shear transfer mechanism of cold joints after experiencing high-cycle fatigue loading and/or precracking. Twelve cold joint push-off specimens with naturally smooth interfaces were cast and tested. Six of these specimens were directly subjected to push-off tests without any prior treatment, serving as control specimens. Two specimens were intentionally precracked, while the remaining four specimens underwent two million constant amplitude load cycles, before the push-off test. Push-off test results indicate that the effect of fatigue loading on shear strengths can be disregarded. Precracking has very little influence upon the residual strength and the failure strength, but it significantly reduces the ultimate strength to a level comparable to the residual strength. Moreover, this paper identified a new interface failure mode and presented complete interface shear load-displacement curves, revealing the shear transfer mechanism at the interface. This mechanism provides a clear explanation for the aforementioned effect on the shear strengths. Besides, building upon this mechanism and through a force-balance analysis, the equations are proposed for predicting the residual strength and failure strength of cold joints, which are found to reliably yield accurate calculation results.

Tunnel drainage systems are crucial design factors in tunnels because the accumulation of groundwater at the back of linings can affect tunnel safety. Geotextiles are used to facilitate the dissipation of pore-water pressure. However, chemical agents in the water can lead to clogging as tunnels age. In this study, laboratory tests and image analysis, namely Secondary Scanning Microscopy (SEM) and Energy-dispersive X-ray Spectrometry (EDS), were conducted to assess the drain performance of five geosynthetic materials: four geocomposites and one three-layered Non-Woven Needle-Punched (NWNP) geotextile. Calcium carbonate (CaCO₃) in liquids affects the discharge capacity of drains, and this capacity decreases with increasing confining pressure. NWNP geotextile is the most vulnerable to confining pressure as it lacks a core. The reason behind the significant decrease in the discharge capacity of NWNP geotextile is clarified based on the SEM analysis. EDS analysis investigated the major composition of the clogged materials, revealing that the primary components are carbon, oxygen, and calcium. Advanced imaging techniques can be utilized to gain a deeper understanding of the underlying mechanisms. The results of this study can aid in the design and maintenance of engineering systems, especially tunnel drainage systems, that incorporate geosynthetic materials.

Ground deformation induced by frost heave is a matter of concern in cold region engineering construction since it affects surrounding structures. Frost heave, which is related to the heat-water-stress interaction, is a complicated process. In this study, a heat-water-stress coupling model was established for saturated frozen soil under different stress levels to quantify the water redistribution, heat transfer, frost heave, and water intake. An empirical formula for the soil permeability considering the confining and deviator pressures was employed as an indispensable hydraulic equation in the coupling model. The Drucker-Prager yield criterion matched with the Mohr-Coulomb criterion was employed in the force equilibrium equation to investigate the deformation due to the deviator and confining pressures. The anisotropic frost heave during unidirectional freezing was further considered in the coupling model by introducing an anisotropic coefficient. Subsequently, based on the above coupling relationship, a mathematical module in COMSOL Multiphysics was applied to calculate the governing equation numerically. Finally, the proposed model was validated through an existing frost heave experiment conducted under various temperature gradients and stress levels. The results of the freezing front, water redistribution, water intake, and frost heave ratio predicted using the proposed model were found to be consistent with the experimental results.

This study addresses the issue of localized ground subsidence and its effect on buried pipelines. Timoshenko beam model, placed on a Pasternak foundation, is used to analyze the internal force response of buried pipelines under foundation subsidence. The load on the pipeline, resulting from localized ground subsidence, is assumed to be symmetric. The load distribution on the buried section of the pipeline is represented using a McLaurin series. Analytical solutions for the deflection and bending moment of the pipeline under arbitrary symmetrical loading are derived based on the theory of elastic foundation beams. Additionally, the accuracy of the analytical solutions is verified through comparisons with experimental studies, finite element analysis, and existing theories. In the analysis, the shear modulus of the Timoshenko beam is set to infinity, resulting in the degeneration of the model into the Euler-Bernoulli beam. The effect of the shear modulus and diameter-span ratio (D/l) of the Timoshenko beam is investigated in the parameter analysis, and the applicability for both beam models is determined. The results indicate that, for buried pipelines with a diameter-span ratio greater than 0.1, the Timoshenko beam model provides more accurate deflection calculations than the Euler-Bernoulli beam model.

Facing the insufficient shear-bearing capacity of Hollow Core Beam (HCB), the High-performance Concrete (HPC) and shear steel rebars were proposed by the authors. However, investigations of the maximum diagonal crack width of the strengthened HCB specimens were scarce. Simultaneously, there were no details for the shear failure mechanism of the complex interface between HCB and HPC. For this reason, the failure modes and stirrup stress were first investigated. A simple model of maximum diagonal crack width of the strengthened HCB specimens was suggested. The maximum deviation of predictive value and test result was within 3%. Secondly, a modified truss-arch model of strengthened HCB specimen was proposed, considering the tensile behavior of the HPC. The average ratio of estimated and experimental results was 1.02. Finally, the shear-bearing capacity of strengthened HCB specimens was suggested considering the shear contribution of the HPC, shear steel rebars and interface bonding force. Compared with the previous shear test results reported by the authors, the maximum deviation was within 1%. To validate the accuracy of the formula, the other HCB specimen was used to evaluate the maximum deviation within 5%. It can be concluded that the proposed formula agrees well with the test results.

Poor procurement and management practices can negatively affect subconsultant bidding interest and contract performance. Subconsultants tolerate these practices until a tipping point is reached, at which point their willingness to bid decreases and their contract performance declines. In this study, personnel from four engineering consultant firms and seven subconsultants in Taiwan were interviewed to investigate the effects of their outsourcing and procurement practices on the bidding interest of subconsultants. Outsourcing records spanning 3 years were retrieved from an engineering consultant firm and used to identify the aforementioned tipping points. The findings suggest that inviting many subconsultants to bid lowers their response rate and contract performance, without reducing the contract award price. In addition, when the maximum award price falls below the minimum price acceptable to subconsultants, resulting in the inability to achieve a one-time bidding scenario, even if the engineering consultant firms subsequently increase the maximum award price and successfully contract, the subconsultants’ sentiment remains unrecoverable. Finally, a novel remainder analysis mechanism is proposed to reveal the reasons why some contracts are not awarded in the first round and evaluate whether the reasonableness of the maximum award price setting by engineering consultant firms.