Ground Improvement Case Histories (eBook)

Chemical, Electrokinetic, Thermal and Bioengineering

Jian Chu, Buddhima Indraratna, Cholachat Rujikiatkamjorn (Autoren)

eBook Download: PDF | EPUB

2015 | 1. Auflage
724 Seiten
Elsevier Science (Verlag)
978-0-08-100238-4 (ISBN)

Infos

Written by an international group of experts, Ground Improvement Case Histories: Chemical, Electrokinetic, Thermal and Bioengineering Methods provides over 700 pages of case-histories collected from all over the world. Each case-history provides an overview of the specific technology followed by applications, and in some cases, comprehensive back analysis through numerical modelling is discussed. The book includes methods for employing bacterial and biological treatment, and native vegetation for stabilizing problematic soils. Specific case-histories included in the book are: Effect of Drainage and Grouting for the World Longest Seikan Undersea Tunnel Construction, Cement/lime Mixing Ground Improvement for Road Construction on Soft Ground, Use of Jet Grouting in Deep Excavations, and Stabilization of Reactive Sulphide Mine Tailings using Water Cover Technology.

• Provides recent case histories using chemical and bio-engineering methods by world-renowned engineering experts
• Includes over 200 illustrations and 150 equations from relevant topics, including state-of-the-art chemical and bioengineering methods
• Presents comprehensive analysis methods using numerical modelling methods
• Case histories include the 'Effect of Drainage and Grouting on the World's Longest Seikan Undersea Tunnel Construction' and 'Cement/Lime Mixing Ground Improvement for Road Construction on Soft Ground'

Professor Indraratna is the author of more than 500 publications, including 6 books, about 200 journal papers and 50 invited keynote and plenary lectures. His contributions through research and development towards the understanding of soft soil improvement have been incorporated by numerous organizations into their engineering practices for the design of rail and road embankments.

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Written by an international group of experts, Ground Improvement Case Histories: Chemical, Electrokinetic, Thermal and Bioengineering Methods provides over 700 pages of case-histories collected from all over the world. Each case-history provides an overview of the specific technology followed by applications, and in some cases, comprehensive back analysis through numerical modelling is discussed. The book includes methods for employing bacterial and biological treatment, and native vegetation for stabilizing problematic soils. Specific case-histories included in the book are: Effect of Drainage and Grouting for the World Longest Seikan Undersea Tunnel Construction, Cement/lime Mixing Ground Improvement for Road Construction on Soft Ground, Use of Jet Grouting in Deep Excavations, and Stabilization of Reactive Sulphide Mine Tailings using Water Cover Technology. Provides recent case histories using chemical and bio-engineering methods by world-renowned engineering experts Includes over 200 illustrations and 150 equations from relevant topics, including state-of-the-art chemical and bioengineering methods Presents comprehensive analysis methods using numerical modelling methods Case histories include the "e;Effect of Drainage and Grouting on the World's Longest Seikan Undersea Tunnel Construction"e; and "e;Cement/Lime Mixing Ground Improvement for Road Construction on Soft Ground"e;

Textauszug

Chapter 2

Full-Scale Tests on Stiffened Deep Cement Mixing Piles Including Three-Dimensional Finite Element Simulation

Pitthaya Jamsawang1; Dennes T. Bergado2; Panich Voottipruex1    1 King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand
2 Asian Institute of Technology, Bangkok, Thailand

Abstract

The stiffened deep cement mixing (SDCM) pile employs a precast concrete pile inserted at the center of the DCM pile. A series of full-scale tests involving SDCM and DCM piles under axial compression, lateral, pullout, and embankment loads were performed. The ultimate bearing capacities of two DCM piles have significant differences, confirming the low quality that commonly occurs on DCM piles, resulting in their low bearing capacity. The length of the concrete core pile affected both the ultimate bearing capacity and settlement, whereas its sectional area had a negligible effect. The DCM piles failed by pile body failure. The SDCM pile with a length ratio of 0.85 failed by soil failure. Thus, the effective length ratio of the SDCM pile should be larger than 0.85. The average lateral ultimate bearing capacities of SDCM piles with area ratio of 0.11 and length ratios of 0.54 and 0.85 could be improved by 11 times compared to those of DCM piles. The average lateral ultimate bearing capacities of SDCM piles with area ratio of 0.17 and length ratios of 0.54 and 0.85 could be improved by 15 times compared to those of DCM piles. Thus, the sectional area of the concrete core pile affected both the lateral ultimate bearing capacity and displacement. The SDCM pile with area ratio and length ratio of 0.17 and 0.85, respectively, effectively reduced the settlement and lateral movement induced by the embankment loading compared to the DCM pile, with a settlement reduction of 40% less than that of the DCM pile. The lateral movement in SDCM piles was 60% less than that in the DCM pile. The lateral movement:settlement ratio can be reduced in SDCM piles, especially in the surrounding clay, by as much as 50%. Three-dimensional finite element simulation of the results of full-scale embankment showed that the length of concrete core pile significantly affected the settlement of the SDCM pile. The effective length of the concrete core pile should be greater than 6 m, corresponding to the length ratio of 0.85. Both the length and the sectional area of the concrete core pile affected the lateral movement of the SDCM pile under embankment loading.

Keywords

Bearing Capacity

Composite

Deep Mixing

Field Load Test

Full Scale Test

Ground Improvement

Stiffener

2.1 Introduction

Deep cement mixing (DCM) pile is widely used to improve the engineering properties of thick deposits of soft ground. DCM piles can effectively reduce settlements of full-scale embankments (Bergado et al., 1999; Lai et al., 2006). However, they have variable strength and stiffness, specifically flexural strength (Petchgate et al., 2003, 2004), leading to low bearing capacity and large settlements (Wu et al., 2005). Consequently, DCM piles are not suitable for medium to high design loads (Dong et al., 2004). Liu et al. (2007) introduced geogrid-reinforced and cast-in-place concrete pile for supported embankment over soft clay. Dong et al. stated that concrete or cast-in-situ pile is deemed uneconomical as a friction pile for this purpose because much of the strength of pile materials has not been utilized when the low-capacity ground fails. The DCM pile can be subjected to both vertical and horizontal forces induced by the embankment loads.

Thus, the stiffened deep cement mixing (SDCM) pile is more suitable than DCM pile because SDCM pile has higher strength and stiffness and can sustain higher bending moment and resist higher lateral loads. SDCM pile employs a precast reinforced concrete pile inserted at the center of DCM pile. The concrete core, which is a precast concrete pile, takes most of the load and gradually transmits it to the surrounding soil–cement through the interface between the concrete core pile and the DCM pile. This chapter presents a series of full-scale tests consisting of SDCM piles and DCM piles in soft Bangkok clay under axial compression load, lateral load, and pullout interface. Moreover, a 5-m-high embankment on stiffened deep cement mixing pile was constructed on soft Bangkok clay improved with both SDCM and DCM piles in order to compare their performances under working stress level.

2.2 Full-scale load tests on SDCM and DCM piles

Full-scale pile load test studies of soft clay foundation improved by SDCM piles and DCM piles installed by jet mixing method were performed. A series of the full-scale tests consisted of SDCM piles and DCM piles under axial compression load and lateral and pullout interface between concrete and deep cement mixing under axial tensile load. Tests of the SDCM piles and DCM piles under axial compression load and lateral load were conducted to study their load-bearing capacities and the effect of section area and length of concrete core on bearing capacities, whereas the pullout interface tests were conducted to study interface resistance between concrete and deep cement mixing.

2.2.1 Test site and subsurface investigation

The test site was located at the northern part of the Asian Institute of Technology (AIT) campus in Klong Luang, Pathumthani, Thailand. The soil profile and soil properties of the subsoil in the uppermost three layers at the AIT campus are presented in Fig. 2.1. The uppermost 10 m can be divided into four layers. The weathered crust forms the uppermost layer consisting of weathered clay, with the uppermost 2.0 m underlain by a soft clay layer down to approximately 6-m depth. The medium stiff clay layer was found at 8- to 10-m depth. Below this layer is the stiff clay layer. The undrained shear strength obtained from field vane test of the soft clay was 16 or 17 kPa. Underlying the soft clay layer is the medium stiff clay layer, with a strength of more than 30 kPa.

Figure 2.1 Subsoil profile and relevant parameters.

2.2.2 Concrete core pile

The prestressed concrete pile was proposed to bear compression and lateral loads. The prestressed concrete pile was selected as the stiff core because it has high strength and stiffness, and it is also cheaper than steel pile. The selected prestressed concrete piles were square shaped with dimension of 0.18 and 0.22 m in cross section and 4.0 m and 6.0 m in length, as shown in Fig. 2.2.

Figure 2.2 Details of prestressed concrete piles.

2.2.3 Installation of deep mixing piles by jet grouting

A total of 27 deep mixing piles were installed down to the bottom of the soft clay layer, as shown in Fig. 2.3, with 2.0-m spacing in a square pattern by jet mixing method employing a jet pressure of 22 MPa. The water:cement ratio (W:C) of the cement slurry and the cement content employed for the construction of deep mixing piles were 1.5 and 150 kg (m3of soil), respectively. Each deep mixing pile had a diameter of 0.6 m and length of 7.0 m. Twenty of the deep mixing piles were utilized as SDCM piles. Each SDCM pile was constructed by insertion of prestressed concrete pile immediately after deep cement mixing had completed. The prestressed concrete pile was sunk by its weight without any pushing force because of very low fiction between prestressed concrete pile and cement–admixed clay due to the high water content produced by jet mixing. The construction of SDCM pile is shown in Fig. 2.4. All deep mixing piles were allowed to cure in situ for 80 days after completion of installation; three deep mixing piles installed to represent all deep mixing piles were cored by drilling machine to obtain unconfined compressive strength and modulus of elasticity of undisturbed samples in laboratory, and a full-scale pile load test program was performed.

Figure 2.3 Pile test layout.

Figure 2.4 Construction of SDCM pile.

2.2.4 Axial compression load tests

Figure 2.5 shows the schematic setup for applying axial compression loads to the test pile using a hydraulic jack acting against a platform. The platform was composed of steel sheets and concrete boxes with a total weight of 500 kN supported by upper cross H beams. The reaction beam or test beam was support by lower cross H beams supported by a concrete box that distributed the total weight of the platform to the surrounding soil. The vertical load was applied to the test pile through a 600-kN capacity hydraulic jack. A 500-kN capacity proving ring was inserted between the jack and the reaction beam to measure the applied load. The ball bearing was inserted between the proving and the reaction beam to ensure the vertical direction of the applied loads from the hydraulic jack. The vertical settlement of the test pile under the applied load was measured using two dial gages, which were connected to two reference beams placed on both sides of the jack. The axial compression tests were performed in accordance with ASTM D1143 (1994a). The load was applied in increments of 10 kN. Each load increment was maintained for 5 min. The load was applied until continuous vertical displacements occurred at a slight or no increase in...

Produkt-Details

• Erscheint lt. Verlag: 28.5.2015
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Technik ► Bauwesen
• ISBN-10: 0-08-100238-6 / 0081002386
• ISBN-13: 978-0-08-100238-4 / 9780081002384