How my time passed by 1959- 2017

1. 28 Years at AIT in Bangkok

2. Now 16 years at Griffith University in Gold Coast

3. 9 years in University of Ceylon, Colombo & Peradeniya (include student days)

4. One Year in PWD, Sri Lanka

5. One year at NGI, Norway

6. One Year at NTU Singapore

Vol. 42 No. 3 September 2011

Building Damage Assessment for Deep Excavations in Singapore and the Influence of Building Stiffness

K.H. Goh and R.J. Mair

ABSTRACT: One of the biggest issues for underground construction in a densely built-up urban environment is the potentially adverse impact on buildings adjacent to deep excavations. In Singapore, a building damage assessment is usually carried out using a three-staged approach to assess the risk of damage caused by major underground construction projects. However, the tensile strains used for assessing the risk of building damage are often derived using deflection ratios and horizontal strains under ‘greenfield’ conditions. This ignores the effects of building stiffness and in many cases may be conservative. This paper presents some findings from a study on the response of buildings to deep excavations. Firstly, the paper discusses the settlement response of an actual building – the Singapore Art Museum – adjacent to a deep excavation. By comparing the monitored building settlement with the adjacent ground settlement markers, the influence of building stiffness in modifying the response to excavation-induced settlements is observed. Using the finite element method, a numerical study on the building response to movements induced by deep excavations found a consistent relationship between the building modification factor and a newly defined relative bending stiffness of the building. This relationship can be used as a design guidance to estimate the deflection ratio in a building from the greenfield condition. By comparing the case study results with the design guidance developed from finite element analysis, this paper presents some important characteristics of the influence of building stiffness on building damages for deep excavations.

KEYWORDS: Building Damage Assessment, Deep Excavations in Singapore, Building Stiffness

DOI: 10.14456/seagj.2011.10

Vol. 42 No. 3 September 2011

Concept and Design Methodology of Redundancy in Braced Excavation and Case Histories

G. Zheng, X.S. Cheng, Y. Diao, and H.X. Wang

ABSTRACT: The conventional design methodology of deep excavation retaining structure generally proceeds elements by elements, consequently, the retaining structures are/may be lack of redundancy. This could lead to catastrophic collapse of retaining system. It is necessary to introduce the concept of redundancy into the design of retaining structure and develop the design methodology based on redundancy. In this paper, redundancy of deep excavation retaining structure is classified into five aspects. Necessity and importance of each aspect are explained. A method to evaluate and quantify the retaining structure redundancy is presented through the analysis of an example. Two typical case histories are studied to reveal the redundancy problems that may exist. Finally, a series of measures are proposed to increase the redundancy of deep excavation retaining structure.

KEYWORDS: Concept and Design Methodology, Redundancy, Braced Excavations

DOI: 10.14456/seagj.2011.11

Vol. 42 No. 3 September 2011

Three-Dimensional Deformation Behavior of an Over-sized Excavation in Shanghai Clay

ABSTRACT: In this paper, a case study regarding the excavation of the largest excavation in Shanghai soft clays (Zhongsheng Shopping Mall) is investigated through field studies and numerical modelling. To reduce the excavation induced deformation and construction time, a combination of excavation support schemes, the central part by bottom-up method and the peripheral part by top-down method, is used in this construction project. Extensive field performance data, including wall deflections and ground surface settlements, were collected. Construction sequences are summarized and correlated with the measured data. Three-dimensional effective stress elasto-plastic finite element analysis is conducted to examine the wall deflections and ground surface movements. A comprehensive comparison with the field observations has demonstrated the capacity of numerical models for the predictions of wall deflections and ground surface settlements. Numerical studies indicate that both the wall deflection and ground surface settlement are affected by the excavation corner as well as the length and the shape of the wall. Parametric studies of two construction sequences reveal that the deformations of the wall and soil are larger due to the circumstance that some supports are not installed in time during excavation. Zone excavation exerts a slight effect on the wall deflection for the wall panels near the centers of the excavated zones, but causes less wall deflection for the wall panels near the corners of the excavated zones.

Keywords: Over-sized excavation, combined method, deformation, three-dimensional, finite element analysis

DOI: 10.14456/seagj.2011.11

Vol. 42 No. 3 September 2011

Numerical Study on the Movement of Existing Tunnel Due to Deep Excavation in Shanghai

J. J. Chen, J. H. Wang, G. W. Xiang, S. L. Wen, and Y. Du

ABSTRACT: Adjacent excavation can have significant impact on the stress and deformation of existing tunnels. Several construction techniques have been proposed to reduce the movement of a metro tunnel due to two adjacent excavations in Shanghai. To evaluate the effectiveness of these different methods, the interactive impact of the two adjacent excavations on the crossing tunnel is studied numerically in this paper. The 2D FEM numerical analysis uses the Cam-clay model to simulate the behaviour of soft clay and considers the nonlinear performance of the soil-wall interface and the excavation sequences. The analysis investigates the influence of various factors, including the excavation procedure, installation of resistance piles, and relationship between the tunnel and the retaining wall of excavation. The results show that the crossing tunnel heaves during excavations because the distance between the two adjacent excavations is very small and the diaphragm walls for the original tunnel are used as the retaining structure of the new excavations. This predicted trend is verified by field measurements. The parametric study shows that dividing the whole dividing the whole excavation into several pit excavations and installing resistance piles tied to the tunnel can decrease the vertical displacement of the tunnel effectively.

KEYWORDS: Numerical Study, Movement, Existing Tunnel, Deep Excavation, Shanghai

DOI: 10.14456/seagj.2011.12

Vol. 42 No. 3 September 2011

Observed Performance of Diaphragm Wall Construction

C.Y. Ou and L.L. Yang

ABSTRACT: This study presents the behavior of ground movement induced by the construction of diaphragm wall based on the results of full-scale field tests or panel tests in the construction of the Taipei mass rapid transit system. Two typical test results are presented to understand the general characteristics of ground movement induced by the construction of one wall panel and multiple wall panels. Moreover, the panel test results from the other contracts are also summarized. Results show that the ground settlements after the completion of the whole diaphragm wall construction were much larger than those measured from panel tests because ground movement during the “normal” construction was heavily affected by construction factors. Use of panel test results to evaluate ground settlements might result in a misleading conclusion. Use of the envelope, as established in this study, was a rational way to evaluate ground settlements at the present stage. Besides, the maximum ground settlement of panel tests occurred was about 0.05~0.07 times the trench depth (D) percent and the primary settlement influence zone fell within a normal distance of 0.6D from the panel. The maximum ground settlement after the completion of the whole diaphragm wall construction was about 0.13D(%). The ground settlement beyond 1.5D ~ 2D was found to be insignificant.

KEYWORDS: Observed Performance, Diaphragm Wall Construction

DOI: 10.14456/seagj.2011.13

Vol. 42 No. 3 September 2011

Performance of Construction with New Pneumatic Caisson Method in Shanghai Soft Ground

F.L. Peng and H.L. Wang

ABSTRACT: In the new pneumatic caisson method (NPC), soil excavation and removal is completed remotely by workers on the ground. In 2007, this method was successfully applied in a tunnel shaft in Shanghai. Combined with the construction example, field monitoring and measuring has been conducted. Typical monitored results, such as the working pressure, lateral earth pressure, reaction pressure, and ground movements, were presented and analyzed. In addition, a numerical approach considering the soil disturbance during construction was proposed to predict the soil movements induced by the NPC construction. It was successfully implemented in the three-dimensional finite element method (FEM) codes. Calculated soil movements were examined and verified by the field measurements. In the meantime, these results were compared with the ones obtained from the two-dimensional approach proposed by the authors in the previous study. Results showed that, they agreed well with each other, and in general the three-dimensional analysis results approached the actual situation more closely.

KEYWORDS: Performance of Construction, New Pneumatic Caisson Method, Shanghai Soft Ground

DOI: 10.14456/seagj.2011.14

Vol. 42 No. 3 September 2011

Technologies of Micro-disturbance Construction of Pipe-Jacking

W. Q. Ding, B. Li, S. L. Yuan and J. K. Ge

ABSTRACT: As a mature subsurface excavation method, pipe-jacking has already been widely used in many fields of city construction. The fact that the construction environment becomes more and more complicated requires micro-disturbance pipe-jacking. Combining the successful micro-disturbance construction of the pipe-jacking part of Shanghai Expo Power Cable Tunnel, some methods such as the preparations before construction, disturbance controlling during different construction phases and many specific construction technologies are summarized. During pipe jacking, a lot of measures like keeping the stabilization of the excavation surface, controlling the pipe jacking speed, adopting new sludge lubricating sleeve technologies, achieving precise attitude control and conducting timely slurry replacement. It is hoped that this will be helpful to the later micro-disturbance pipe-jacking.

KEYWORDS: Micro-Disturbance Construction, Pipe-Jacking

DOI: 10.14456/seagj.2011.15

Vol. 42 No. 3 September 2011

Design and Construction of InJe Tunnel, the Longest Road Tunnel of Korea

S. M. Cho, S. D. Lee, and Y. J. Kwon

ABSTRACT: Inje Tunnel, an 11 km-long twin-tunnel will be the longest road tunnel of Korea. Two parallel tunnels including two vertical shafts and one inclined shaft are under construction. Details of the tunnel design including geotechnical characteristics, cross-section of the excavation, reinforcement, drainage, ventilation operation, safety facility corresponding with a tunnel fire, and portal planning are introduced. Various analyses that systematically make comprehensive utilization of available data obtained from geotechnical investigations were applied for the optimal evaluation of ground conditions. The typical NATM excavation scheme by a combination of drilling, blasting and reinforcement has been undertaken. Steel-fiber mixed shotcrete, steel rib with Lattice girder, and rock bolt were designed for the reinforcement. Ventilation plan using the inclined shaft and vertical shafts are summarized considering traffic conditions and emergency situations. Current construction procedures are also briefly described.

KEYWORDS: Design and Construction, InJe Tunnel, the Longest Road Tunnel, Korea

DOI: 10.14456/seagj.2011.16