摘要:

To investigate the possible error introduced by the assumption of a linear Mohr–Coulomb criterion on the stress distribution near a circular opening, a numerical approach is used to calculate both the damage-zone radius and the stresses near a circular opening. A general solution procedure for the stress calculation under a uniform far-field loading is presented and a closed-form solution for the near-opening stresses is given for a cohesionless medium. Based on the numerical results calculated, it is concluded that the linear assumption is acceptable for a strong rock with an unconfined compressive strength that is of similar magnitude to the far-field stress. However, the tangential stress calculated with this linear assumption may be overestimated, but the damage zone may be underestimated in weaker rock or soil such as an oil sand formation.Key words: Mohr–Coulomb criterion, circular opening, nonlinearity, oil sands, Gauss–Legendre method.

ISSN:0008-3674    

DOI:10.1139/t94-011

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This paper presents the effect of lateral cyclic loading on the pullout capacity of model and helical piles in clayey soil. The tests were conducted on short rigid model piles in the laboratory in three phases, namely lateral static load tests, lateral cyclic load tests, and vertical pullout tests. From the test results it was found that the lateral cyclic loading affects the pullout capacity of piles substantially. Reduction in pullout capacity mainly depends upon the lateral deflection of the pile during cyclic loading and the embedment ratio of the pile. This reduction in the pullout capacity of model piles is presented in terms of nondimensional parameters, viz., degradation factor, lateral deflection ratio, and embedment ratio of pile. However, in the case of helical piles under similar conditions, it was found that the lateral cyclic loading has very little influence on the pullout capacity. The reasons for the better performance of helical piles over ordinary piles are explained.Key words: clay, degradation factor, helical pile, lateral cyclic loading, lateral deflection, Joading level, pile, pullout capacity.

ISSN:0008-3674    

DOI:10.1139/t94-012

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Effective techniques are currently available to obtain undisturbed samples of cohesive soils. However, little advance has been made in the procurement of undisturbed samples of cohesionless soils such as sands, silty sands, and clayey sands. In the area of earthquake design and liquefaction, researchers and practitioners are becoming increasingly aware of the importance of obtaining high-quality undisturbed samples of cohesionless soils. In situ ground-freezing techniques can be used to obtain undisturbed samples of cohesionless soils. However, there is still concern regarding the possibility of disturbance during the freezing and thawing of the samples. Shear wave velocity is a direct measurement of the stiffness of the soil skeleton at small strains (<10−4%). Hence, shear wave velocity can be a sensitive measurement to detect changes in void ratio and soil structure due to freezing and thawing. A laboratory study has been performed to evaluate the use of shear wave velocity measurements to detect sample disturbance due to freezing and thawing of cohesionless soils. Samples prepared with different amounts and type of fines were frozen using uniaxial freezing techniques and subsequently thawed. Shear wave velocity measurements were made before and after freezing and thawing of the reconstituted samples. The measured shear wave velocities were unchanged for samples that did not heave (undisturbed) during the freeze–thaw cycle. Samples that heaved (disturbed) showed an associated change in shear wave velocity. Hence, measurements of shear wave velocities in situ and in the laboratory have the potential to identify sample disturbance in granular soils.Key words: in situ, sampling, freezing, disturbance, shear wave velocity.

ISSN:0008-3674    

DOI:10.1139/t94-013

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Estimation of the total primary settlement is critical in determining when the required compression has been achieved and a surcharge loading can be removed. Conventionally, the total primary settlement is predicted using laboratory-determined compressibility data. However, the rectangular hyperbolic-fitting method allows estimation of the total primary settlement during the process of consolidation. In this paper, the hyperbolic-fitting method is extended to the case of consolidation with combined vertical and radial flow, which occurs when vertical drains are used to speed consolidation. Solutions are presented for the slope of the first linear segments between the 50 and 90% settlement points of the theoretical hyperbolic plots (time/settlement versus time). The proposed hyperbolic-fitting method was tested using data from the case history of the Changi Airport field test in Singapore, where Geodrains and sand drains were used for soil improvement following land reclamation and prior to airfield pavement construction. The predictions of the proposed method agree well with the measured and estimated soil settlements from compressibility calculations. The method can complement existing methods to provide a practical means of monitoring the progress of consolidation in field applications using drains and surcharge, and to determine the appropriate time for surcharge removal, if required.Key words: consolidation, vertical drains, settlements, hyperbolic method.

ISSN:0008-3674    

DOI:10.1139/t94-014

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A given sand is presumed to have a unique steady-state line. The proximity of an initial state to the steady-state line is considered to be a measure of liquefaction potential. This line of reasoning and application in practice is based on data obtained predominantly from triaxial tests in compression-mode loading. In such tests, relative orientations of bedding plane and principal stress directions remain fixed while stress states along actual failure surfaces may range from active to passive. This study examines the uniqueness of the steady state relative to the mode of loading, form of consolidation, and initial anisotropy as induced by bedding orientation. A sample-preparation method was developed to form triaxial samples with different bedding orientations. Steady states of a uniform sand reached under compressional and extensional modes of triaxial undrained loading of samples with different bedding orientation are compared. Effects of isotropic and anisotropic consolidation are examined. The results indicate the steady-state line obtained for compression-mode loading is different from and does not apply for extension-mode loading. Use of a compression side steady-state line for extension-mode failure states would result in overestimation of steady-state strengths and unconservative stability evaluations.Key words: anisotropy, compression, extension, liquefaction, sand, steady state, triaxial.

ISSN:0008-3674    

DOI:10.1139/t94-015

出版商:NRC Research Press    

年代:1994

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t94-016

出版商:NRC Research Press    

年代:1994

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t94-017

出版商:NRC Research Press    

年代:1994

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t94-018

出版商:NRC Research Press    

年代:1994

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t94-019

出版商:NRC Research Press    

年代:1994

数据来源: NRC