Some factors affecting deep excavation in clay over gassy bedrock
Ahmed B Mabrouk and R Kerry Rowe
ABSTRACT: A study of excavations within normally to slightly over consolidated deposits over a gas source is presented with reference to the potential for gas venting from a bedrock aquifer. The effects of key design factors on excavation integrity and potential of inducing hydrofractures are examined. Based on the calculated gas distribution, the study introduces the gassy effect to the deepest 6 m of the clayey layer by: a) increasing pore fluid compressibility, b) reducing Young’s modulus of soil skeleton. The study illustrates the importance of considering hydrofracturing potential and gassy behaviour when assessing the stability of excavations in deposits overlying a gas source.
Effects of Consolidation and Specimen Disturbance on Strengths of Taipei Clays
Richard N Hwang, Za-Chieh Moh and I-Chou Hu
ABSTRACT: Presented herein are the results of a study supplementing the one carried out in the early 90’s for investigating the characteristics of Taipei clays for the design and construction of the Taipei Metro. It has been found that the lowering of piezometric level in the Chingmei Formation in the 70’s has drastically increased the shear strengths of the clays which can be estimated by using the SHANSEP equations, as a result of consolidation. Furthermore, the shear strengths obtained in the routine unconsolidated undrained shearing tests are far too low due to specimen disturbance.
Lime Stabilisation of Organic Clay and the Effects of Humic Acid Content
NZ Mohd Yunus, D Wanatowski and LR Stace
ABSTRACT: The effectiveness of lime as a chemical additive for the stabilisation of organic clay is considered uncertain, especially in the long term. The presence of humic acid is believed to be the main detrimental constituent of organic matter that renders lime stabilisation inefficient. In this paper, the amount of humic acid that may render lime stabilisation inefficient was carefully investigated. Artificial organic clay, prepared by mixing commercial kaolin and various amounts of humic acid (0.5%, 1.5% and 3.0%) was treated with hydrated lime. The strength properties of lime-treated organic clays were examined by unconfined compressive strength (UCS) and drained and undrained triaxial compression tests. Curing periods of 7, 28 and 90 days were chosen as key points to monitor the evolution and the effect of the stabilisation process on lime-treated specimens. Overall, the development of physical and engineering properties of lime-treated organic clay was most affected when the humic acid content in clay exceeded 1.5%.
Estimating Wetting-induced Settlement of Compacted Soils using Oedometer Test
EC Leong, S Widiastuti and H Rahardjo
ABSTRACT: Compacted soils undergo volume changes when wetted. Oedometer tests have been commonly used to estimate the settlement of unsaturated soils when wetted. Several variations of the oedometer test are available. The double-oedometer test has been more popular as it requires only two nominally identical specimens for the test to produce the unsaturated and saturated compression curves. The wetting induced settlement of a compacted soil at any load can be estimated by the difference in ordinate between the unsaturated and saturated compression curves. In this paper, it is shown that the unsaturated and saturated compression curves are linked by the initial degree of saturation and soil type. The compression curve of an unsaturated compacted soil can be derived from the compression curve of an inundated compacted soil, making it possible to estimate the wetting-induced settlement of compacted soils using a single oedometer test on an inundated specimen.
Compaction Curve with Consideration of Time and Temperature Effects for Mudstones
A Puttiwongrak, H Honda, T Matsuoka and Y Yamada
ABSTRACT: A compilation of compaction curves shows that the curves vary widely (porosity-burial depth), especially at the depth shallower 2000 m. There is no unique physical or mathematic expression of mudstone compaction. In this study, we have considered the burial depths (shallower 2000m), where the process of mechanical compaction dominate, and point out on time and temperature effects influencing variations of mudstone compaction curves. We revised and reconstructed the existing, widely referred, mudstone compaction curves using a correction of clay mineral dehydration and thermal correction based on time and temperature effects, respectively. The results show that the mudstone compaction curves seem to improve matching with one another. These corrections are possible toward establishment of a standard compaction curve of mudstones.
Small strain behavior of sand under various stress paths considering anisotropic initial stress state
Lai Yong, Shi Jian-yong, Yu Xiao-jun and Cao Qiu-rong
ABSTRACT: The stress-strain characteristics in small strain region for a Chinese sand were investigated under different stress paths. The strain contour circle method was used to simulate the small strain characteristics of the sand under various stress paths. The test results showed that the inherent stress-strain characteristics of the sand depend on the anisotropic initial stress state. The contraction and dilation behaviors of the tested sand under various K0 initial stress conditions are different from that under isotropic initial stress state conditions. The test results of the sand agreed with the Wong-Mitchell’s research results very well. The strain contour circle method can approximately simulate small stress-strain characteristics of the sand for various stress paths by using the proportion function λ and expansion function l. The calculation results from the new method agree with the test results for Bothkennar clay.
Study of Joint Effect on Pipe in Pipe Jacking Method
L G Le, M Takise, M Sugimoto and K Nakamura
ABSTRACT: Recently, pipe jacking method has become popular in micro tunnelling because of its benefits for economy and environment. However, jacked pipes have complex performance during installation process, particularly when the pipes are driven through a curved alignment. In such a case, the joints between the pipes significantly affect the behaviour of the pipes and the alignment deviation. To investigate the influence of joints on pipes, full scale tests and numerical modelling were carried out to simulate pipe jacking of two consecutive pipes in both straight and curved alignments. It was found that stress concentration occurs along pipe length at the range where cushion materials are set for both alignments and at the concave side of curve for the curved alignment. In addition, it was confirmed that the stack pipe model gives a reasonable result to simulate the experiments for the pipe jacking method.
Finite Element Analysis of Ground Behaviour due to Box-jacking Tunnel Work
K Komiya and T Nakayama
ABSTRACT: A box-jacking tunnel method is a new mechanized tunnelling method which has been developed to construct large scale tunnels undercrossing the existing traffics in urban areas. During the box jacking operation, a box-module is driven forward by applying mechanical forces and excavating the soil in front of the box-module with boring machine. The step-by-step insertion of the box-module forms a lining frame of the tunnel in the ground and after completion of the lining frame, the tunnel is complete by excavation of soil within the internal section of the frame. In this study, the step-by-step advancement and excavation processes of the box-module are modelled using the finite element method with the finite element remeshing technique. Three dimensional finite element analyses are conducted to simulate the construction process of a box jacking tunnelling work and the numerical results are compared with the field measurements.
Tunneling Induced Deformation of a Historic Building in Shanghai
Shi-ping Gea, Dong-wu Xied, Wen-qi Dinga, Ya-fei Qiao and Jin-chun Chai
ABSTRACT: Tunnelling induced deformations of a historic building, Chongsi Building, in Shanghai, China, are reported. The construction site located in Xuhui District, along the Metro line 11, and at the site the thickness of soft soil layer, soft clay and clayey silt, is about 30 m. The tunnelling method used is the earth pressure balance (EPB) shield tunnelling. The building with masonry structure was built about a century ago, and there were already considerable deformations. Considering this situation, the criteria for total and incremental deformations have been proposed; especially the twist criteria have been newly established and applied to the project. Controlling both the total and incremental deformations is called Dual-control criteria (DCC). The measured maximum settlement, differential settlement, and twist during tunnelling construction were 13.29 mm, 0.67 mm/m, and 3.23×10-5 rad/m respectively. Based on the monitoring results, the deformations of the historic building during and after tunnel construction were very small and, causing no serious damage to the building, and it is considered that the construction control is successful.
KEYWORDS: tunnelling, historic building, underground crossing, deformation criteria
In-situ monitoring of internal displacements by FBG sensors and slope stability analysis under rainfall infiltration
Dongsheng Xu, Fei Tong, Huahu Pei, and Jianhua Yin
ABSTRACT: The Wenchuan earthquake in Sichuan Province of China has caused tremendous loss of life and property. The severe earthquake along with the heavy rainfall has induced landslide and debris flows so that the slope stability is a significant concern in this earthquake region. A newly developed inclinometer based on the Fiber Bragg Grating (FBG) sensing technique has been installed in a slope in Sichuan Province for long-term monitoring of internal displacements. A series of FBG sensing bars are installed at different depths of two different boreholes in the slope; meanwhile, all optical fibers of the sensing bars are connected and extended to a monitoring station around 1000m away from the slope site through a main armored cable of optical fibers. Monitoring works are carried out in the monitoring station from 20 June to 25 September 2010. Thus, internal displacements of the slope are analyzed together with the rainfall data which are also collected by a rainfall gauge. The results demonstrate that rainfall infiltration has a strong influence on the internal displacements, while the influence reduces dramatically when the depth exceeds 5.2m. Through a numerical model for the effect analysis of rainfall intensity and duration, the slope stability decreases significantly when the rainfall intensity higher (or equal) than 0.5mm/h and rainfall duration longer than 100h.
Mechanistic-Empirical Pavement Design: A Brief Overview
A T Papagiannakis
ABSTRACT: This paper provides an overview of the state of the art of mechanistic-empirical pavement design, as established by NCHRP Study 1-37A in the United States. It describes the method used to characterize traffic loading and materials, as well as the methods used to analyse flexible and rigid pavement response and calculate damage. This methodology is referred as the Mechanistic-Empirical Pavement Design Guise (MEPDG) and was recently implemented into the commercially available software referred to as the AASHTOWare Pavement Mechanistic Empirical Design.
