摘要:

The adjoint sensitivity method is applied to a pack ice motion model based on the solution of the two-dimensional momentum equations for a floating ice cover. The equations were solved using the Galerkin method of weighted residuals. Adjoint sensitivity theory is used to efficiently calculate the rate of change of a model performance measure with respect to any model parameter. The sensitivities are shown to be functions of the solution of the ice-motion model, called the primary problem, and the solution of an adjoint problem obtained from the primary problem through suitable transformation. Adjoint sensitivity theory is applied to both the continuum and discretized forms of the primary problem to generate corresponding adjoint and sensitivity equations. Single solutions of the primary equation and the adjoint form are sufficient to calculate total sensitivity with respect to any model parameter as well as showing the spatial variation of sensitivity contributions for a distributed parameter. Adjoint sensitivity theory may be more computationally efficient than sampling-based techniques. The application of the finite element forms of the primary problem and adjoint sensitivity calculations are demonstrated.Key words: ice mechanics, ice parameters, sensitivity theory, finite elements, adjoint method.

ISSN:0008-3674    

DOI:10.1139/t92-100

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The time-averaged motion of shore-fast ice near a small Arctic island is analysed through the solution of the momentum equation for the ice cover using the Galerkin finite element method coupled with an adjoint sensitivity formulation. A linear-viscous rheology is used. Shore boundaries were modeled by prescribing ice velocity components such that the ice velocity vectors at shore boundaries were directed towards the ice cover, normal to the shoreline. A sensitivity analysis using the adjoint methodology showed that the velocity of the ice near the island is strongly influenced by the magnitude of the prescribed boundary velocities. The surface shear stresses from wind and ocean currents and the ice viscosities over part of the modeled domain also have a significant influence. The influence of Coriolis acceleration and the mass of the ice are not significant.Key words: ice mechanics, momentum, viscous rheology, finite elements.

ISSN:0008-3674    

DOI:10.1139/t92-101

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

For the design of underground structures in rocks, the states of initial stresses in the rock mass are required. For structures located at great depths, the hydraulic fracturing test for stress measurements is the only practical method. For vertical fractures, existing solutions for calculation of stresses from test results are satisfactory. For horizontal or mixed-mode fractures, appropriate solutions are required. Closed-form solutions for horizontal and mixed-mode fractures including strength anisotrophy are presented. The method enables the determination of which fracture (horizontal or vertical) occurs first at the first breakdown pressure during the test, so appropriate stress calculation may be carried out. Results of hydraulic fracturing tests in three case histories have been reanalyzed using the method developed. It is shown that for horizontal fractures the ranges of stress values computed are considerably reduced compared with existing solutions. The reinterpreted horizontal stresses in a case record are consistent with results of field observations in underground excavations. Experimental requirements for the measurements of rock parameters relevant to the specific stress paths in hydraulic fracturing tests are discussed.Key words: hydraulic fracturing, stress measurements, mixed-mode fractures, underground structures, rock strength.

ISSN:0008-3674    

DOI:10.1139/t92-102

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

An interpretation method has been developed to incorporate nonlinear soil behavior to interpret undrained pressuremeter test results. The method makes use of both the loading and unloading portions of the pressuremeter test. The proposed interpretation method accepts that some level of soil disturbance may exist during the early loading portion of the pressuremeter test. This is accomplished by putting greater emphasis on the unloading portion and the final part of the loading portion of the test. The method is evaluated using self-boring pressuremeter results from Fucino, Italy.Key words: pressuremeter, interpretation, undrained, unloading.

ISSN:0008-3674    

DOI:10.1139/t92-103

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A simple, numerically based procedure for the estimation of the so-called gap parameter is described. The gap parameter represents the vertical displacement above the crown of the tunnel and is a measure of ground loss owing to tunnelling in soft ground. This parameter is a function of the three-dimensional elastoplastic deformation at the tunnel face, the tunnelling machine shield and lining geometry, and workmanship. This parameter can then be used to predict the resulting ground deformations using either two-dimensional finite element methods or empirical correlations.Key words: tunnelling, settlement, subsidence, clays, soft ground, analysis, design.

ISSN:0008-3674    

DOI:10.1139/t92-104

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A numerical and a simplified empirical design procedure (based on the concept of the gap parameter) for predicting settlement above tunnels constructed in soft ground are evaluated with reference to 14 case histories. These records encompass very stiff to soft clays. A comparison of observed and calculated behaviour indicates that the proposed numerical and empirical approaches are capable of providing a reasonable estimate of the gap and the surface settlement provided that the soil parameters are reliably determined. It is suggested that the simplified procedure may be used for preliminary design. The gap parameter can also be used in conjunction with more sophisticated numerical methods to predict the variation in settlement with position and depth at critical sections of the tunnelling project.Key words: tunnelling, settlement, subsidence, clays, soft-ground analysis, design, case history, finite element.

ISSN:0008-3674    

DOI:10.1139/t92-105

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

This paper presents results from a series of model tests of single vertical piles subjected to lateral monotonic pile head loading. Model tests were carried out in sand under a simulated field stress condition using the hydraulic gradient similitude technique. Studies were focused on examining various factors that affect the soil-pile interaction in terms ofP–ycurves. It was found that theP–ycurves are highly nonlinear and stress-level dependent but are insensitive to the pile head loading conditions. TheP–ycurves at depths below one pile diameter were found to be normalized by the maximum soil Young's modulusEmaxand the pile diameter. Comparison was made between the experimentalP–ycurves and those recommended by the American Petroleum Institute (API). It was found that the experimentalP–ycurves were significantly different from the APIP–ycurves. New procedures for constructingP–ycurves are proposed and verified by numerical analyses of the observed model pile response. The results indicate that the APIP–ycurves based on a hyperbolic tangent function tend to overestimate the pile head stiffness, especially for fixed-head piles due to their stiffer shape in the small to medium pile deflection range. The proposed parabolicP–ycurves can better resemble experimentalP–ycurves and consequently give a better prediction of pile response for both free- and fixed-head conditions. Finally, the proposed procedures were applied to analyze a full-scale pile load test, and good agreement was found between the predictions using the proposed parabolicP–ycurves and the field test data.Key words: lateral loads, piles, model tests, sands.

ISSN:0008-3674    

DOI:10.1139/t92-106

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The mechanism of progressive failure is well understood as one which involves nonuniform straining of a strain-weakening material. Traditional limit equilibrium analysis cannot be used alone to obtain a rational solution for progressive failure problems because the deformation of the structure must be taken into account in the analysis. The failure of the Carsington Dam during construction in 1984 has been attributed to progressive failure of the underlying yellow clay and the dam core materials. The dam was monitored extensively prior to failure, and an elaborate geotechnical investigation was undertaken after failure. The limit equilibrium analysis indicated that the factors of safety were over 1.4 using peak strength of intact clay material or 1.2 based on reduced strength accounting for preshearing of the yellow clay layer. Factors of safety were found to be less than unity if residual strengths were used. The actual factor of safety at failure was, of course, equal to one. By using the finite element analysis with strain-weakening models, the extent and degree of weakening along the potential slip surface were calculated. The calculated shear strength was then used in the limit equilibrium analysis, and the factor of safety was found to be 1.05, which is very close to the actual value of 1.0. More importantly, the mechanism of failure and the initiation and propagation of the shear zones were captured in the finite element analysis. It was also found that accounting explicitly for pore-water pressure effects using the effective stress approach in the finite element and limit equilibrium analyses provides more realistic simulations of the failure process of the structure than analyses based on total stresses.Key words: progressive failure, strain softening, finite element analysis, dams.

ISSN:0008-3674    

DOI:10.1139/t92-107

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

This paper presents a methodology to predict liquefaction of uncemented and cemented sands under multidirectional cyclic loading conditions using solely conventional unidirectional cyclic test data. The method is found to be reasonably accurate based on the reported multidirectional cyclic test results using a true triaxial apparatus.Key words: sand, cementation, triaxial, experimental, theoretical, liquefaction.

ISSN:0008-3674    

DOI:10.1139/t92-108

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

This technical note presents the results of a theoretical analysis of smooth elliptic vanes. Uniform and triangular shear stress distributions are used to obtain geometric vane factors. A preliminary field investigation has been carried out by means of two elliptic vanes.Key words: vanes, elliptic shapes, uniform, triangular, shear stress distribution, field investigation.

ISSN:0008-3674    

DOI:10.1139/t92-109

出版商:NRC Research Press    

年代:1992

数据来源: NRC