Numerical Analysis of a Tunnel in Residual Soils

This paper presents results of an elastoplastic finite element back analysis of a shallow tunnel through residual soils. The tunnel was constructed as part of the expansion of the underground transit system in the city of S?o Paulo, Brazil. A comprehensive laboratory testing program on undisturbed soil samples was performed in order to characterize the stress–strain–strength behavior of the residual soils. Results from this laboratory testing program were used to calibrate a nonassociated elastoplastic constitutive model utilized to reproduce the behavior of the residual soils under stress paths typical of underground excavation. A stress transfer method is proposed to simulate, using a two-dimensional finite element analysis, the response of the soil mass to the three-dimensional advancement of a tunnel excavation. Comparisons are presented between monitored displacements from an instrumented section of the Paraíso tunnel, empirical predictions, and the results of a finite element back analysis. Good agreement is achieved between the displacements obtained from field instrumentation data and the empirical and numerical results.     

Problem-Centered Approach in a Numerical Methods Course

This paper is an illustration of using a problem-centered approach in an undergraduate course in numerical methods. The problem used in the course was first encountered in a research project that related to the assembly procedure of the fulcrum of bascule bridges. It involved the study of the fulcrum assembly procedure where a trunnion cooled in a dry-ice/alcohol mixture for shrink fitting became stuck halfway in the hub before full insertion could take place. The solution of the problem and its implementation involved numerical solutions of mathematical procedures taught in a typical numerical methods course. The effect of the problem-centered approach in the classroom was quantitatively and qualitatively surveyed over a two-semester period. The results indicate very high student satisfaction in helping them: acquire basic knowledge and skills; reinforce information presented in class, reading assignments, and problem sets; learn to clearly formulate a specific problem and then work it through to completion; develop generic higher-order thinking and problem solving skills; and develop a sense of competence and confidence and see the relevance of the course material to their major.     

Validation of a New 2D Failure Mechanism for the Stability Analysis of a Pressurized Tunnel Face in a Spatially Varying Sand

A new two-dimensional (2D) limit analysis failure mechanism is presented for the determination of the critical collapse pressure of a pressurized tunnel face in the case of a soil exhibiting spatial variability in its shear strength parameters. The proposed failure mechanism is a rotational rigid block mechanism. It is constructed in such a manner to respect the normality condition of the limit analysis theory at every point of the velocity discontinuity surfaces taking into account the spatial variation of the soil angle of internal friction. Thus, the slip surfaces of the failure mechanism are not described by standard curves such as log-spirals. Indeed, they are determined point by point using a spatial discretization technique. Though the proposed mechanism is able to deal with frictional and cohesive soils, the present paper only focuses on sands. The mathematical formulation used for the generation of the failure mechanism is first detailed. The proposed kinematical approach is then presented and validated by comparison with numerical simulations. The present failure mechanism was shown to give results (in terms of critical collapse pressure and shape of the collapse mechanism) that compare reasonably well with the numerical simulations at a significantly cheaper computational cost.     

Empirical Analysis of the Learning Curve Principle in Prestressed Concrete Piles

The principle of learning curves can be applied in construction for the prediction of the time/cycle of future work, work performance levels, and other performance measures. Learning curve principles can be effectively utilized in litigation cases where production is compromised by delays. The objective of this study was to determine if learning curves could be used to accurately predict the production efforts of future units by applying the principles to the prefabrication and driving of prestressed concrete piles. The individual time to cast each of the concrete piles was recorded and used to compute the cumulative average time (CATN) to fabricate the concrete piles. The data were used to compute the learning rate (?) and the theoretical time to complete the first unit (Kc). From this information, predictions were made as to the amount of effort to fabricate future piles. The results showed that the pile fabrication crew improved its learning throughout the pile fabrication effort, but this improvement was quite small. The learning curve theory was found to apply well to large numbers of repeated items, and that the predictions made with learning curves are reasonably accurate.     

Twin Tunnel Interaction: Surface and Subsurface Effects

This article presents the results from 13 plane strain, coupled consolidation, non‐linear finite element analyses of twin tunnel construction. There are two sets of analyses, the first models two tunnels running parallel side‐by‐side, and the second one above the other (piggyback). The spacing between the tunnels is varied so as to ascertain the zones of influence, and the time between the construction of the two tunnels is varied to establish the influence of prolonged consolidation or swelling. The results present the expected modification to the settlement profile above the second of two close tunnel excavations, and the expected distortion induced in an existing tunnel lining when an adjacent tunnel is excavated. Field data, where available, are presented to support the magnitudes of the interactions being predicted numerically. It is concluded that the relative position (above, below, or to the side) and the physical spacing of the tunnels has a significant effect on the surface settlement profile due to the second tunnel, and on the response of the first tunnel lining to excavation of the second tunnel. The length of rest period has a negligible effect on these interaction effects.     

Numerical Approximations of Design Points in Reliability Analysis under Parametric Changes

Traditional approaches for repeatedly updating reliability estimates, as needed in reliability-based optimal designs or real-time system control, require the iterative application of a reliability method. This paper explores a new strategy for repeatedly estimating reliability under frequent parameter variations. The central idea is to update the design point in the parameter domain, rather than in the traditional random variable domain, by evaluating several parametric sensitivity measures which are systems of nonlinear first-order ordinary differential equations relating the design point to parameter changes. Four numerical algorithms for evaluating the sensitivity measures are developed using the Euler and the improved Euler algorithms. Two solution procedures are applied. One procedure solves for the updated design point directly, while the other solves for both the unit normal vector at the design point and the reliability index separately, and evaluates the product of these to determine the updated design point. The numerical techniques are thoroughly compared with the classical Hasofer and Lind-Rackwitz and Fiessler (HL-RF) algorithm in five numerical examples regarding efficiency and accuracy. It is found that they are efficient and robust under given conditions.     

Empirical Analysis of Construction Enterprise Information Systems: Assessing System Integration, Critical Factors, and Benefits

Attaining higher levels of system integration is seen as the primary goal of construction enterprise information systems (CEIS). Increased system integration resulting from CEIS implementation is expected to lead to numerous benefits. These benefits encompass information technology infrastructure and strategic, operational, organizational, and managerial aspects of the firm. By adopting CEIS, firms seek tangible and intangible benefits, such as cost reduction, improved productivity, enhanced efficiency, and business growth. Through the use of statistical analysis, this study quantifies the critical success factors that impact CEIS integration and the ensuing benefits. Furthermore, it analyzes the effects of system integration on CEIS induced benefits. It also investigates the impact of CEIS strategy on CEIS induced benefits and identifies the relationship between CEIS strategy and system integration. Finally, it assesses the effects of CEIS induced benefits on user satisfaction and provides a CEIS implementation guide map for construction firms.     

Validation and Application of Empirical Liquefaction Models

Empirical liquefaction models (ELMs) are the standard approach for predicting the occurrence of soil liquefaction. These models are typically based on in situ index tests, such as the standard penetration test (SPT) and cone penetration test (CPT), and are broadly classified as deterministic and probabilistic models. No objective and quantitative comparison of these models have been published. Similarly, no rigorous procedure has been published for choosing the threshold required for probabilistic models. This paper provides (1) a quantitative comparison of the predictive performance of ELMs; (2) a reproducible method for choosing the threshold that is needed to apply the probabilistic ELMs; and (3) an alternative deterministic and probabilistic ELM based on the machine learning algorithm, known as support vector machine (SVM). Deterministic and probabilistic ELMs have been developed for SPT and CPT data. For deterministic ELMs, we compare the “simplified procedure,” the Bayesian updating method, and the SVM models for both SPT and CPT data. For probabilistic ELMs, we compare the Bayesian updating method with the SVM models. We compare these different approaches within a quantitative validation framework. This framework includes validation metrics developed within the statistics and artificial intelligence fields that are not common in the geotechnical literature. We incorporate estimated costs associated with risk as well as with risk mitigation. We conclude that (1) the best performing ELM depends on the associated costs; (2) the unique costs associated with an individual project directly determine the optimal threshold for the probabilistic ELMs; and (3) the more recent ELMs only marginally improve prediction accuracy; thus, efforts should focus on improving data collection.     

Eulerian-Lagrangian Numerical Scheme for Simulating Advection, Dispersion, and Transient Storage in Streams and a Comparison of Numerical Methods

Past applications of one-dimensional advection, dispersion, and transient storage zone models have almost exclusively relied on a central differencing, Eulerian numerical approximation to the nonconservative form of the fundamental equation. However, there are scenarios where this approach generates unacceptable error. A new numerical scheme for this type of modeling is presented here that is based on tracking Lagrangian control volumes across a fixed (Eulerian) grid. Numerical tests are used to provide a direct comparison of the new scheme versus nonconservative Eulerian numerical methods, in terms of both accuracy and mass conservation. Key characteristics of systems for which the Lagrangian scheme performs better than the Eulerian scheme include: nonuniform flow fields, steep gradient plume fronts, and pulse and steady point source loadings in advection-dominated systems. A new analytical derivation is presented that provides insight into the loss of mass conservation in the nonconservative Eulerian scheme. This derivation shows that loss of mass conservation in the vicinity of spatial flow changes is directly proportional to the lateral inflow rate and the change in stream concentration due to the inflow. While the nonconservative Eulerian scheme has clearly worked well for past published applications, it is important for users to be aware of the scheme’s limitations.     

Numerical Implementation of Anisotropic Continuum Model for Rock Masses

In this technical note, rock mass has been regarded as an equivalent anisotropic continuum. Constitutive relationships for the rock masses have been derived. The approach aims to capture the overall behavior of the rock mass based on the constitutive characteristics of intact rock and rock joints including their orientation, spacing, roughness (waviness), number of joint sets, block size, and normal and shear stiffness, etc. This model has been applied to analyze a tunnel using a software package developed for the purpose, with satisfactory results.     

Deformation and Failure of the Tymfristos Tunnel, Greece

The Tymfristos tunnel, a 1,365?m long road tunnel with an 11?m section diameter, was excavated through the highly tectonized, low strength Flysch formation of central Greece. About 1 year after the completion of the excavation in 1995, convergence of up to 20% followed by failure of the support system was recorded. A 501?m long segment, in which the failure occurred, was reexcavated based on a more detailed study of the ground conditions; however, this second phase was also followed by an up to 6% convergence. The detailed geodetic study of the three-dimensional kinematics of the support shell in relation time, ring closure delays, and support measures reveals an unusual time-history of convergence occasionally continuing even after the ring closure and a nonuniform distortion of the lining. Furthermore, uncontrolled deformation of certain “weak” sections propagated bidirectionally to adjacent, previously stabilized sections producing a “chain effect,” responsible for destabilization and resumed convergence of long ( ～ 90?m) segments.     

Management of Radon in Tunnel Drilling

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report in 1982, radiation from radon contributes about 50% of all natural radiation sources to the public. The situation is worse in Hong Kong where large area is granitic containing larger amount of uranium when compared to the global mean. Radon level can therefore be on the high side during tunneling especially where poor ventilation is envisaged. This article includes realistic field study of radon in tunnel under construction. A maximum concentration of over 30,000?Bq/m3 was recorded (1 Becquerels per cubic meter is equivalent to 0.027?pico?Curies/L). Radon concentration in tunnel environment is found to be related to groundwater ingress, ventilation provision and geology. A review of the current statutory control in Hong Kong is done as well as its comparison with other countries’ practices. In fact, the situation can be improved through education, adopting control legislation and more specifically, having a suggested radon management plan in every tunnel drilling project.     

Ground Subsidence due to a Shallow Tunnel in Dense Sandy Gravel

Finite-element procedures have been applied to predict ground subsidence caused by tunneling; however, the calculated results are strongly dependent on the adequacy of the model used. The construction of a shallow tunnel in the typical gravel of Santiago (Chile) is herein back-analyzed using a finite-element method based on a modified version of the hyperbolic model. Observed ground subsidence as a function of distance to the face and to the tunnel axis is examined and related to the construction procedure. Although the ratio of overburden cover to excavation width was 0.52, the maximum settlement measured was only 9 mm. It was found that, as a result of the excavation process, a certain thickness of soil behind the excavation line experienced a significant alteration. The hyperbolic parameters of the disturbed soils were determined by fitting the calculated subsidence to the observed results. From the good agreement obtained, it is concluded that the model used represents reasonably well the construction stages of the tunnel and the stress–strain behavior of the materials involved.     

Nondestructive Analysis of a Concrete Tunnel Model Using a Newly Proposed Combined Stress Wave Propagation Method

This paper summarizes the measured properties of a three-layer model concrete tunnel lining using a newly proposed combined stress wave propagation (CSWP) method. The spectral analysis of surface waves (SASW) and impact echo (IE) methods were used in combination to determine the in-place dynamic properties of the tunnel lining and to locate embedded voids. Simultaneously, the free-free resonant column (FFRC) method was independently used to determine the dynamic properties of the materials used to construct the concrete tunnel lining. Finally, a direct P-wave (DPW) measurement was used to compare and verify measurements recorded using the CSWP method. Results indicate that the combination of the SASW and IE methods, along with FFRC measurements, provides a more efficient procedure that leads to the accurate determination of the P-wave and shear wave velocities, depths of layers, and locations of embedded voids without the need to make any assumptions of material properties. Thus, more physical properties can be found using this proposed procedure than by using the techniques independently, and the procedure is more efficient than performing each task separately.     

Numerical Analysis of Peristaltic Transport of a Tangent Hyperbolic Fluid in an Endoscope

This paper presents a tangent hyperbolic fluid in a cylindrical coordinate system. The governing equations are simplified using long-wavelength and low Reynolds number approximations. The solutions of the problem in simplified form are calculated with three methods: (1)?perturbation method, (2)?homotopy analysis method, and (3)?shooting method. Comparison of the three solutions shows very good agreement among them. Pressure rise and frictional force are calculated with the help of numerical integration. Graphical results for pressure rise and frictional forces are presented to show the physical behavior of the Weissenberg number We, amplitude ratio ?, tangent hyperbolic power law index n, and radius ratio ?.     

Face Stability Analysis of Circular Tunnels Driven by a Pressurized Shield

The aim of this paper is to determine the face collapse pressure of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of limit analysis theory. It is based on a translational three-dimensional multiblock failure mechanism. The present failure mechanism has a significant advantage with respect to the existing limit analysis mechanisms developed in the case of a frictional soil: it takes into account the entire circular tunnel face and not only an inscribed ellipse to this circular area. This was made possible by the use of a spatial discretization technique. Hence, the three-dimensional failure surface was generated “point by point” instead of simple use of existing standard geometric shapes such as cones or cylinders. The numerical results have shown that a multiblock mechanism composed of three blocks is a good compromise between computation time and results accuracy. The present method significantly improves the best available solutions of the collapse pressure given by other kinematical approaches. Design charts are given in the case of a frictional and cohesive soil for practical use in geotechnical engineering.     

Buckling of Circular Mindlin Plates with an Internal Ring Support and Elastically Restrained Edge

This paper is concerned with the elastic buckling problem of circular Mindlin plates with a concentric internal ring support and elastically restrained edge. In solving this problem analytically, the circular plate is first divided into an annular segment and a core circular segment at the location of the internal ring support. Based on the Mindlin plate theory, the governing differential equations for the annular and circular segments are then solved exactly and the solutions brought together by using the interfacial conditions. New exact critical buckling loads of circular Mindlin plate with an internal ring support and elastically restrained edge are presented for the first time. The optimal radius of the internal ring support for maximum buckling load is also found. An approximate relationship between the buckling loads of such circular plates based on the classical thin plate theory and the Mindlin plate theory is also explored.     

Performance of a Stiff Support System in Soft Clay

The performance of an excavation support system for a subway station renovation project in Chicago and its effects on an adjacent, shallow-foundation supported building are presented. The 13-m-deep excavation was made through soft to medium stiff clays and was supported by a 900-mm-thick secant pile wall, one level of cross-lot bracing, and two levels of tiebacks. Design considerations are discussed and construction procedures are summarized. Field performance data were collected, including lateral soil movements at five locations, building settlements along the exterior wall and interior columns, support system loads, and observations of building damage. As planned in the design, minor damage occurred to nonload bearing portions of the building. Of the 38 mm of maximum lateral movement adjacent to the building, 9 mm occurred during wall installation, 16 mm developed as the soil was excavated, and 13 mm occurred during tunnel demolition and station renovation as a result of soil creep and reduction of wall stiffness. Settlements extended beyond the secant pile wall a distance approximately equal to the depth of the secant pile wall. The effect of excavation was to cause larger settlements within the affected zone, but not to expand the width of the settlement trough. When distortions exceeded approximately 1/960, damage began to manifest itself in the nonload bearing portions of the building.     

Numerical Modeling of Local Scour below a Piggyback Pipeline in Currents

Local scour below a piggyback pipeline in steady currents is investigated numerically. A piggyback pipeline comprises two pipelines that are arranged in the so-called piggyback configuration with the small pipeline being located directly above the large pipeline. The Reynolds-averaged Navier–Stokes equations and the transport equation for suspended sediment concentration are solved using a finite element method. The bed scour profile is determined through solving sediment mass conservation equation. The numerical model is validated against experimental data available in literature on scour below a single pipeline. Computations are carried out for the diameter ratio [the small pipe diameter (d) to the larger one (D)] of 0.2 and the gap (G, between the two pipelines) to the large diameter ratio G/D ranging from 0.0 to 0.5. It is found that the flow and the scour profiles are influenced significantly by the gap ratio.