摘要:

Using the integrated form of Mindlin's equations that relate the stress and displacement field anywhere within a three-dimensional space in an isotropic and elastic soil medium, a boundary-element-based numerical model is presented for analyzing soil–structure interaction problems involving excavations around embedded structures. The solution procedure involves combining the stiffness matrix of the wall and soil system and computing the displacements from a knowledge of the stress changes due to excavation. An interative approach is adopted to apply the correcting forces at locations that reach active or passive states, thus resulting in correct displacements for plastic conditions that cannot be accounted for by the Mindlin's elastic solutions. The model is shown to provide matching results against a finite-element model under plane-strain conditions. Application of the proposed model within the context of a practical project has demonstrated its role both as a predictive tool and as a theoretical model for performing sensitivity analysis and establishing practical guidelines to control magnitude and mode of wall deflections, which are important design considerations in excavations close to movement-sensitive structures.Key words: numerical modelling, elasticity, three-dimensional effects, soil–structure interaction, retaining wall, excavation.

ISSN:0008-3674    

DOI:10.1139/t92-060

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Data have been reviewed from sites in Europe and North and South America as well as published data from South Africa. The review has concentrated on dissipation data from piezocone tests (CPTU) to compare predicted coefficient of consolidation and permeability values using published interpretation techniques with available reference values. The results of this review have shown that the theoretical solutions provide reasonable estimates of thein situcoefficient of consolidation. Results were evaluated for pore-pressure data from different locations on the piezocone, and the least scatter in results was obtained with the pore-pressure element location immediately above the cone tip. A new correlation has been proposed to estimatein situhorizontal coefficient of permeability (kh) from piezocone dissipation data.Key words:in situ, coefficient consolidation, cone penetration test, permeability.

ISSN:0008-3674    

DOI:10.1139/t92-061

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

According to the International Reference Test procedure for the standard penetration test (SPT), in situations where comparisons of SPT results are important, calibrations should be made to evaluate the efficiency of the equipment in terms of energy transfer. However, equipment to measure the energy transfer of the hammer anvil system is not commonly available. Ten years ago a system was developed and made commercially available. However, this system is no longer available. An SPT energy calibration system is described that has been developed based on a microcomputer. The load cell to measure the compressive stress wave beneath the SPT anvil consists of a 0.5-m length of strain-gauged AW rod. Specialized software has been developed to record the force–time record for each hammer blow on a portable microcomputer. Examples of energy measurements are presented and discussed.Key words: standard penetration test,in situ, microcomputer, energy.

ISSN:0008-3674    

DOI:10.1139/t92-062

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A modified version of the spectral analysis of surface waves (SASW) equipment and analysis procedure has been developed to determinein situshear-wave velocity variation with depth from the ground surface. A microcomputer has been programmed to acquire waveform data and perform the relevant spectral analyses that were previously done by signal analyzers. Experimental dispersion for Rayleigh waves is now obtainable at a site and inverted with a fast algorithm for dispersion computation. Matching experimental and theoretical dispersion curves has been automated in an optimization routine that does not require intermittent operator intervention or experience in dispersion computation. Shear-wave velocity profiles measured by this procedure are compared with results from independent seismic cone penetration tests for selected sites in western Canada.Key words: surface wave, dispersion, inversion, optimization, shear-wave velocity.

ISSN:0008-3674    

DOI:10.1139/t92-063

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

In recent years a new type of pile test employing a short-duration load was developed that became known as pile statnamic test. The paper describes a method of dynamic analysis specifically formulated for this test. The aim of the analysis is twofold: to calculate the pile load displacements in such a way that a satisfactory match with the data measured during the test is obtained; and using the model parameters established from this comparison to predict the bearing capacity of the pile. The mathematical model is one-dimensional and accounts for slip as well as energy dissipation in the far field. Unlike the empirical parameters of the Smith model for pile driving analysis, the parameters of the proposed model are, for the most part, directly related to standard geotechnical parameters. The case studies conducted thus far and described in the paper indicate that the proposed mathematical model works very well and that the statnamic test may become a useful tool for pile capacity prediction.Key words: piles, pile driving, dynamic response, dynamic tests, bearing capacity.

ISSN:0008-3674    

DOI:10.1139/t92-064

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A probabilistic approach to the analysis of the bearing capacity of jack-up spud can foundations is described. The procedure includes three steps: (i) a priori deterministic and probabilistic calculation of bearing capacity interaction diagram for the soil foundation under each leg of the jack up, (ii) updating of the interaction diagram from the measured vertical preloading values, and (iii) one-leg component and multileg system reliability analyses of the structure under environmental loads. The probabilistic formulation is based on the first- and second-order reliability approximations. An example calculation of a jack-up spud can structure on a layered clay profile is made to illustrate the procedure.Key words: jack up, bearing capacity, probabilistic analysis, system reliability.

ISSN:0008-3674    

DOI:10.1139/t92-065

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A large number of geologic environments are composed of different layers of contrasting grain sizes. An accurate description of the locations of these stratigraphic units is necessary for defining flow-field boundaries. In groundwater contamination problems, preferential pathways are controlled by the hydraulic properties of these units. This work presents and applies a Bayesian Kriging technique to a subsurface characterization problem. Expertise guesses with given uncertainties are included in the estimation procedure. This technique assures that observation data (hard data) prevail in areas close to observation points, whereas in areas without observations the guesses (soft data) have greater influence. Maps of the estimates and the associated uncertainties are shown to be key tools in reflecting the quantity and quality of the available data. The Simple and Universal Kriging become subsets of this procedure.Key words: Kriging, subsurface characterization, conditional simulation, geostatistics.

ISSN:0008-3674    

DOI:10.1139/t92-066

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A novel technique of electrical strengthening of soil by dielectrophoresis was developed. The process employs an alternating current at high voltage, generating a converging electric field towards the electrode by which a net resultant movement of water in the clay mass is produced towards the direction of stronger electric field intensity. Laboratory tests were developed to investigate the mechanism of this process and to explore the possibility of its application in electrical strengthening of soft sensitive clays. The preliminary results of this study showed that the process is effective, and the shear strength of the treated clay (Wallaceburg clay) increased drastically by several times with a reduction of moisture content of approximately 25% at an applied electric potential of 20 kV for 28 days. When compared with electro-osmosis, similar results are obtained in dielectrophoresis, such as the increase in preconsolidation pressure, decrease in sensitivity, and improvement of stress–strain behaviour. It is also shown that the improvement of soil properties can be greatly enhanced by increasing the applied voltage and electrode depth.Key words: dielectrophoresis, alternating current, converging electric field, high-voltage electrode, dielectric constant, electro-osmosis, soft sensitive clay, shear strength, consolidation.

ISSN:0008-3674    

DOI:10.1139/t92-067

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

An overall long-term stability of unsupported shallow tunnels in overconsolidated clays which is directly related to the stand-up time is investigated. A new approach that combines finite element methods and the limit equilibrium theory is used to overcome limitations of current design practice. A more realistic initial stress field, unloading due to excavation, and variation of strength and modulus with depth are used. The pore-pressure change is analysed using a finite element model that incorporates an uncoupled consolidation theory. These pore pressures along with the previously obtained stress field are utilized to predict the variation of stability with time for given soil parameters such as strength and coefficient of earth pressure at rest. The results obtained employing a simple mechanism are presented using non-dimensional quantities. These results relate time, stability of the tunnel, and soil strength. The analysis showed that, under certain circumstances, the initial undrained stability may be of no practical value and may only be used as a starting point for more practical long-term stability. This procedure explains the stand-up time phenomenon in tunnels and may also be used in design as a direct tool for its evaluation.Key words: overconsolidated clay, long-term stability, stand-up time, shallow tunnels, finite elements, limit equilibrium.

ISSN:0008-3674    

DOI:10.1139/t92-068

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A major rockslide and debris flow occurred on Mount Cayley, British Columbia, in June 1984. Approximately 3.2 million cubic metres of volcanics travelled 2.0 km down Avalanche Creek at velocities up to 35 m/s to dam the confluence of Avalanche and Turbid creeks. The breaking of the landslide dam caused an extremely fast debris flow. The velocity of the debris flow and associated wind gusts, up to 34 m/s, caused superelevations, hurled rocks and wood through the air, uprooted trees, and spattered mud 16 m up trees. The debris flow removed the logging road bridge and road approaches at the mouth of Turbid Creek, blocked the Squamish River during surges, and introduced huge quantities of sediment to the Squamish River. The uniaxial compressive strength of wet tuff collected from the head scarp of the rock slide is 1.0–1.5 MPa, about two thirds of the strength of dry specimens, the friction angle on wet tuff bedding surfaces is 30°, and the slake durability index is 26%. Weak tuffs form the rupture surface of the 1984 rockslide on Mount Cayley, and their slaking contributed fines to the debris flow. The tuff, steep, narrow creeks intersecting at high angles, high precipitation, and snow and ice accumulation in creeks combine to make the western slopes of Mount Cayley extremely hazardous.Key words: rockslide, debris flow, volcano, landslide dam, Coast Mountains.

ISSN:0008-3674    

DOI:10.1139/t92-069

出版商:NRC Research Press    

年代:1992

数据来源: NRC