Deep Excavations in Taipei Metro Construction
R. N. Hwang and Z. C. Moh
ABSTRACT: Discussed herein are the geological features of the Taipei Basin relevant to the construction of Taipei Metro and the deep excavations carried out with emphasis on back analyses of wall deflections. The excavation at the crossover next to G17 Station of the Green Line is adopted as an example to illustrate the applications of wall deflection paths and reference envelopes. The importance of calibrating inclinometer readings to account for the movements at the tips is confirmed by numerical analyses; and the assumption that movements at the joints between the struts at the first level and the diaphragm walls would be negligible in subsequent stages of excavation once these struts are preloaded is verified. Furthermore, it is proved that the concept of wall deflection path is very useful to quantify the influence of various factors, e.g., the depth and width of excavation, wall length, preloads of struts, and the thickness of soft deposits, on the performance of diaphragm walls.
KEYWORDS: Taipei Basin, Underground Construction, Deep Excavation, Dewatering, Wall Deflection Path, Reference Envelope
Development of Reinforced Concrete Segmental Lining Design for MRT Bored Tunnels in Singapore
D. Wen
ABSTRACT: Reinforced concrete segments are commonly used as tunnel linings for bored tunnels constructed by tunnel boring machines (TBM). They have been used from 1980s till today for the majority of the Singapore Mass Rapid Transit (MRT) bored tunnels constructed by TBM as permanent supports. This paper describes the development and evolution of the segmental lining design from the Phases I/II of the MRT construction in the 1980s to the current design for the MRT lines under construction. The topics include the general arrangement of the segmental linings, structural design requirements, durability requirements, fire resistance and selection of waterproofing materials of the linings. The design and construction of bored tunnels in close proximity is presented with the experience gained in the past projects. Fire tests conducted by the Land Transport Authority are also presented. The rational, experience and challenges of adopting steel fibre reinforced concrete segments in recent MRT projects are discussed in the paper. The paper also presents in detail the experience gained in Singapore MRT projects in selecting the gaskets for waterproofing of the joints between segments to achieve the durability requirements for the bored tunnels.
KEYWORDS: Bored tunnels, Segmental linings, Waterproofing gaskets
Geology and Its Impact on the Construction of Singapore MRT Circle Line
Jeyatharan Kumarasamy
ABSTRACT: The Circle Line (CCL) is a fully underground railway line in Singapore connecting the inner suburban areas of the city. It is 39.5 km long with 34 stations and built in six separate packages. Site investigations comprising boreholes, CPTs and geophysical surveys for the project were carried out in various phases to reveal ground conditions along the route and decide on the construction methods. Extensive field and laboratory testing were also carried out to establish geotechnical design parameters. This paper summarises geological conditions encountered along the CCL route and highlights the effect of geology on selected construction methods.
KEYWORDS: Site investigation, Construction methods
Constructing the Cut-and-Cover Tunnels and Bored Tunnels of the Singapore Downtown Line
K.H. Goh and Y. Zhang
ABSTRACT: The Downtown Line (DTL) is a major MRT line under construction after the completion of the Circle Line in Singapore. This paper will review the ground conditions for the DTL and how the ground condition has influenced the decision on the selection of the support systems adopted for the excavation for the stations which are constructed using cut-and-cover method, and also the selection of tunnel boring machines for the bored tunnelling works. The key features of the temporary support systems will be presented in the paper and their performance will be reviewed in terms of ground movements and ground water table drawdown and its impacts. Issues encountered during the excavation, in particular for DTL Stage 2 in the soils and rocks of the Bukit Timah Granite Formation will be presented in the paper and the effectiveness of various measures implemented will be discussed based on the experience and observations during the construction. The key features and parameters of the TBM used in the projects will also be presented.
KEYWORDS: Deep excavations, Tunneling, Singapore geology, Downtown Line construction, Management of construction and commercial risks, TBMs in DTL
Bored Tunnelling Directly below Buildings in Singapore Downtown Line
K.H. Goh, S. S. Ng and K.S. Ho
ABSTRACT: Other than basement construction of building complexes for parking and other functions, many cities in the world are also embarking on major construction projects to put roads, metro infrastructure, municipal services and utilities, under the ground. One of the specific challenges faced is the construction of bored tunnels directly below buildings. This paper reports the experiences of bored tunnelling directly below several buildings in the recently implemented Downtown Line project. These case studies would include details such as the structural system and foundation details of the buildings, ground condition, geometry and clearance between the building foundation and the tunnelling works, as well as instrumentation monitoring results of ground and building settlement during tunnelling. It is hoped that these cases could be used as references in the design of future bored tunnelling works, to give greater confidence that tunnelling directly below buildings can be carried out without affecting the buildings so long as appropriate tunnelling controls are taken to mitigate ground deformation issues.
KEYWORDS: Tunnelling, Buildings
Application of Gravity Survey in Urbanized City Environment
Charles Im, John Davies, Frank Collar and Seng Tiok Poh
ABSTRACT: Subsurface information and geotechnical data are required during the planning, development and design stages of all construction projects particularly where major components are supported on or in the earth and underlying rock. An understanding of the basic site geology is also necessary for the proper planning of the ground investigation works. Consequently, the geological features that will affect the design and construction of the project must be investigated and evaluated as much as possible within the allowable project timeframe to ensure successful implementation of the project. This paper presents an overview of the authors’ experiences in using Gravity Survey, as a reconnaissance ground investigation method to identify areas of enhanced ground risks, in the complex variable and unpredictable Kuala Lumpur Karstic Limestone formation during the underground reference design stage of the Klang Valley Mass Rapid Transit Line 2 (SSP Line) in Kuala Lumpur, Malaysia. This paper also presents some lessons learnt of the past in the region, and what were the specific measures that had been strictly implemented on this occasion to ensure quality results can be derived from the Gravity Survey within the urbanized city environment and meet the objectives of the survey.
KEYWORDS: Ground Investigation, Urbanized City Environment, Geophysical Survey, Gravity Survey, Karstic Limestone
Water Sealing by Wire Brush with Grease for Pneumatic Caisson Method at Great Depth Underground
M. Kawasaki, K. Yoshizaki and M. Sugimoto
ABSTRACT: Pneumatic caisson method can be widely applied to various ground and has high reliability, while its applicable depth is limited due to the work under high atmospheric pressure. To overcome the problem, the pneumatic caisson method employing an unmanned excavation method with helium mixed gas has been developed, which enables the work under pressure up to 0.7 MPa. However, the new technology of the pneumatic caisson method will be required to construct a vertical shaft for urban tunnels at great depth underground space. Therefore, applying water-sealing technique at shield tail to friction cut space around pneumatic caisson wall, a method to reduce atmospheric pressure in a working chamber at the ground with low permeability has been proposed. This research carried out the element tests to examine the water-sealing performance of the proposed method, and discussed the influence of some properties on water-sealing performance and its mechanism. As a result, it was confirmed that the proposed method can keep the grease pressure of 1 MPa for one hour.
KEYWORDS: Pneumatic caisson method, Great depth underground, Water sealing, Wire brush, Grease
Geotechnical Challenges of Kolkata Metro Construction
N. Som
ABSTRACT: The paper gives an account of the Kolkata Metro construction which included the first underground railway for mass rapid transit system of an Indian city. Construction was started in 1975 and the first line of the metro covering a length of 17 km was opened in 1984. Thereafter construction had been taken up in phases. Currently Kolkata metro construction includes an ambitious package of 140 km of underground, at grade and viaduct stretches. Construction has to be done in very difficult condition through congested urban areas which includes a tunnel below the Ganga river. Resource crunch and construction through heavily built-up urban land extended the period of construction but modern design techniques and field instrumentation have helped to ensure high quality work in densely populated urban centre.
KEYWORDS: Urban infrastructure, Cut and cover construction, East west metro, TBM Shield tunneling, Field measurements and instrumentation, Quality control
Use of Pressure Relief Wells to Optimise Ground Improvement Layer Thickness in Deep Excavations
Gerardo Agustin Pittaro
ABSTRACT: Deep excavations in soft ground often need stabilization with ground improvement (GI). One of the methods to improve the ground is to use Jet Grouting Piles (JGP) or Deep Soil Mixing (DSM). JGP and DSM are achieved by mixing the soil with cement and water, generating a structure that performs well under compression forces but not under tension forces. These ground improvement blocks provide larger passive resistance thereby reducing wall displacements. Due to the above mentioned behaviour of ground improvement, one of the necessary requirements for successful a design is that no tension forces are allowed in any zone of the ground improvement block. This paper discussed how pressure relief wells inside the excavation are used in order to decrease the tension strains in the ground improvement block and demonstrated it through a series of 2D numerical analyses.
KEYWORDS: Deep Excavation, Ground Improvement, DSM, JGP, Pressure Relief Wells, Numerical Analysis
Bukit Timah Granite Formation Engineering Properties and Construction Challenges
C. Veeresh and K.H. Goh
ABSTRACT: The Bukit Timah Granite Formation is one of the oldest geological formations in Singapore and is found mostly in the central and northern parts of Singapore. A major section of Singapore’s underground metro construction passes through the Bukit Timah formation soils, and extensive field and laboratory testing has been carried out on the rock samples. Uniaxial Compressive Strength (UCS) tests have been carried out on hundreds of samples, test results have shown wide variation in the strength and the maximum strength is found to be much higher compared to the previously published data by Zhao et al 1995. This paper presents a review of UCS strength of the Bukit Timah Formation, Point Load index tests and correlations which were developed for site specific locations. This paper also reviews the abrasivity of Bukit Timah Granite and factors affecting it. Influence of UCS and other factors on the drilling, coring and excavation rates in Bukit Timah Granite are also presented.
KEYWORDS: Bukit Timah Formation, Uniaxial Compressive Strength, Point Load Index Tests, Excavation rates
41 Years of Mass Transit Underground Railways
L.J. Endicott
ABSTRACT: In 1975 many cities in South East Asia were becoming congested and few had underground railways. Now several cities have underground railway systems comprising several lines and many stations, some extend above ground. Currently underground railways are being built or are being extended in many cities in South East Asia. Construction projects are often large including several sections of tunnels and stations in one contract. This paper reflects on the early days of pioneering and on some of the changes that have taken place in the planning, design, and construction of underground Mass Transit Systems during the last 41 years.
KEYWORDS: Underground, Railway, Tunnels, Excavations, Planning, Design, Construction.
Simulation of H&V Shield Behavior at Sharp Curve by Kinematic Shield Model
T. N. Huynh, H.V. Pham, M. Sugimoto, Y. Tanaka, H. Ohta and K. Yasui
ABSTRACT: Due to the restrictions of underground space use, the horizontal and vertical variation shield method (H&V shield) was innovated, of which the cross section is changed from horizontal multi-circular shape to vertical one or vice versa. However, this method has never been applied in practice. Therefore, this study aims to examine the H&V shield control method, using the developed kinematic shield model for the H&V shield. As a result, the following were found: 1) the calculated shield behavior has an overall good agreement with the planned one; 2) the ground displacement is a predominant factor affecting shield behavior; and 3) the proposed model can simulate the H&V shield behavior reasonably.
KEYWORDS: H&V shield, Articulation angle, Copy cutter range and length, Kinematic shield model
Comparison of the Effect of Fine Content and Density towards the Shear Strength Parameters
Badee Alshameri, Aziman Madun and Ismail Bakar
ABSTRACT: The improvement of soil strength is very important in the engineering design for the civil and geotechnical projects. However, this improvement can be achieved by improving the shear strength parameters of soil (i.e. shear strength, friction angle and cohesion) by using different techniques (e.g. densify the soil and change the soil composition). This paper will compare between the effects of density and fine content towards the shear strength parameters. Numerous soil samples (i.e. 99 samples) from six soil mixtures of sand-kaolin mixtures were compacted and subjected to direct shear box test to evaluate the effect of density and fine content. The results showed some discordant effects between the density and fine content. While the cohesion increased by the increment of the fine content, it decreased by the increment of the density. However, both of shear strength and friction angle increased to the highest value with the increment of the fine content and density then by further increment in the fine content and density, the shear strength and friction decreased where this behaviour can be explained through the inter-granular void ratio issue. On the other side, even the results showed interface between the effect of density and fine content, but the fine content has more significant effect in the shear strength parameters and also in the soil density value itself.
KEYWORDS: Shear strength parameters; Sand-kaolin mixture; Fine content, Density; Inter-granular void ratio
Shaft Resistances of Jacked Open-ended PHC Pipe Piles
Xiao-long Zhou, Hai-lei Kou, Chang-hong Li
ABSTRACT: The shaft resistance of open-ended pipe piles during installation and static loading test plays an important role in the design of pile foundation. One open-ended Pre-stressed High-strength Concrete (PHC) instrumented with sensors was jacked to investigate the performance of shaft resistance during installation and loading test. Test results indicated that the shaft resistances gradually transferred along depth during installation, and the magnitude is closely related to soil properties. The shaft resistance at the same depth decrease with jacked cycles. After five jacked cycles, the shaft resistances in sand silt at 6 m depth decreased about 58.8%. The decrement of silty clay at 10 m depth was about 12.1% after three jacked cycles. In the loading test, the shaft resistance of test pile were gradually mobilized from up to down.
KEYWORDS: Open-ended PHC piles; Shaft resistance; Installation; Static loading test
Estimation of Shrink / Swell Potential and Variability of Clays by Small-Scale Suction Tests
P. R. Stott and E. Theron
ABSTRACT: The relationship between suction and water content gives crucial information about a soil. Small projects like economic housing do not warrant the time and cost of determining the full soil water suction curve. A considerable range of soil suctions can easily be achieved within a reasonably short time by using small samples, simple suction control and a high precision balance. It appears that in this way it may be possible to estimate heave potential and variability of soil properties at reasonable cost in an acceptable time. Variability assessment appears to be of great value and may offer significant potential for improving the reliability of foundation design on shrink/swell soils.
KEYWORDS: Soil suction, Expansive clay, Shrink/swell, Heave potential, Soil variability
Pullout Tests on Strips with Anchorage Elements under Low Stresses
M. R. Selamat, M. H. Roslan, and M. A. M. Ismail
ABSTRACT: The lack of pullout capacity in reinforcement strips has often compromised the finishing quality of the mechanically stabilized earth (MSE) structures. In this research, three strips were each attached with 6 anchorage elements of 1cm, 2cm, and 3cm deep respectively in order to enhance the pullout capacities, while another strip was plain. Each strip was subjected to pullout tests under low normal stresses ranging from 1.61kPa to 13.20kPa to simulate shallow emplacement in the field. Under the low normal stress of 1.61kPa, the pullout capacities of strips with anchorage elements were enhanced up to 366% of the plain strip capacity while under the higher normal stress of 13.2kPa, the pullout capacity enhancements were only up to 163% of the plain strip capacity. The results indicate the merit of attaching anchorage elements to strips under shallow overburden in a MSE structure and the significant increase in pullout capacity achievable by such strips.
KEYWORDS: Reinforcement strip, Anchorage element, Pullout capacity, Shallow overburden
Numerical Simulation Analysis and In-situ Monitoring of Long, Narrow and Deep Foundation Pit
Changhong Li, Xiaolong Zhou, Long Zhang, Xiaoming Wei and Wanling Li
ABSTRACT: According to the characteristics of long, narrow and deep foundation pit, the displacement distribution of X-axis with different length-width ratios of 1:1, 2:1 and 3:1 were emphatically analyzed, and then the displacement distribution of Y-axis at the slope bottom and the displacement distribution of Z-axis at the foundation bottom were studied. Then, the different displacement distribution law of pile-anchor support and soil nailing wall support were analysed in different excavation processes considering in-situ supporting schemes, and the different supporting effects of the two supporting structures were presented on the stability of foundation pit slope. By comparing the monitoring values at the 32 in-situ positions, the numerical simulation result was basically identical with the monitored data, on average 3mm higher than the measured value. By using MIDAS software, the excavation and supporting process of the foundation pit could be simulated, and it can provide guidance for the construction of long and narrow deep foundation pit and adjust the monitoring period appropriately.
KEYWORDS: Long, narrow and deep foundation pit; Stability analysis; Numerical simulation; In-situ monitoring
