摘要:

Three-component, digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater Vancouver area, particularly on the Fraser River delta. The 1996M= 5.1 Duvall, Washington, earthquake (180 km southeast of Vancouver) triggered strong-motion seismographs at seven sites and the 1997M= 4.3 Georgia Strait earthquake (37 km west of Vancouver) triggered instruments at 13 sites in the greater Vancouver area. The latter data set is especially important because it contains the first three-component recordings made on bedrock in greater Vancouver. Both data sets represent weak ground motion, with peak horizontal accelerations of 0.5-1.5% gravity (g) for the Duvall earthquake, and 0.2-2.4%gfor the Georgia Strait earthquake. Using the method of spectral ratios, we estimate the site response for each of the strong-motion instrument soil sites. On the Fraser River delta amplification is observed over a relatively narrow frequency range of 1.5-4 Hz (0.25-0.67 s period), with peak amplification of 4-10 (relative to competent bedrock) for the thick soil delta centre sites, and about 7-11 for the delta edge sites. Relative to firm soil, the peak amplification ranges from 2 to 5 for the thick soil delta centre sites, and 2 to 6 for the delta edge sites. At higher frequencies, little or no amplification, and in many cases slight attenuation, is observed.Key words: seismic site response, Fraser delta, earthquakes.

ISSN:0008-3674    

DOI:10.1139/t98-096

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Construction data from a large braced excavation are evaluated in comparison to several methods of predicting the response of buildings to excavation-induced ground movements. The project included an excavation of up to about 20 m depth, over 650 m long, and 20 m wide made through generally competent glacial overburden. Excavation support was achieved using a braced soldier-pile and lagging wall system. A detailed instrumentation program was undertaken by the owner to monitor contractor compliance with ground and structure movement criteria. Data from 46 structures, with damage ranging from negligible to moderate categories, are presented, with four cases presented in detail. A modified approach to estimating potential damage categorization is provided and compared to case histories. Good agreement is demonstrated between actual and estimated damage categories.Key words: building damage, excavations, cracking, angular distortion, settlement.

ISSN:0008-3674    

DOI:10.1139/t98-100

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The two main transportation corridors of southwestern British Columbia are subject to a range of rock slope movements (rock falls, rock slides, and rock avalanches) that pose significant risks to road and rail traffic travelling through the region. Volumes of these landslides range from less than 1 m3to over 4.0 × 107m3. A database of rock falls and slides was compiled for rail and highway routes in each transportation corridor using maintenance records spanning four decades. The records number approximately 3500, of which about one half includes information on volume. Magnitude - cumulative frequency (MCF) relationships were derived for each corridor. A scaled sampling procedure was used in part to reduce the effects of censoring. Both corridors yield MCF curves with significant linear segments on log-log plots at magnitudes greater than 1 m3. The form of both railway and road plots for each corridor shows similarity over several orders of magnitude. The slope of the linear segments of the curves depends on geological conditions in the corridors. Temporal histograms of the data show a trend towards reduction of rock fall frequency as a result of rock slope stabilization measures, implemented during the 1980s and 1990s. A risk analysis methodology using the slope of the magnitude-frequency relationship is outlined. The major part of the risk to life in the case examined results from rock falls in the intermediate-magnitude range (1-10 m3).Key words: rock fall, rock slide, landslide hazard, risk, magnitude-frequency, British Columbia

ISSN:0008-3674    

DOI:10.1139/t98-106

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The effects of sampling disturbance on the laboratory-derived mechanical properties of brittle rock were measured on cored samples of Lac du Bonnet granite taken from three different in situ stress domains at the Underground Research Laboratory of Atomic Energy of Canada Limited. A variety of independent measurements and scanning electron microscope observations demonstrate that stress-induced sampling disturbance increased with increasing in situ stresses. The degree of damage was reflected in laboratory measurements of acoustic velocity and elastic stiffness. Examination of the stress-induced microfracturing characteristics during uniaxial compression of the samples revealed that the degree of sampling disturbance had only minor effects on the stress levels at which new cracks were generated (i.e., the crack initiation stress threshold). Crack-coalescence and crack-damage thresholds, on the other hand, significantly decreased with increased sampling disturbance. The presence of numerous stress-relief cracks in the samples retrieved from the highest in situ stress domains was seen to weaken the rock by providing an increased number of planes of weakness for active cracks to propagate along. A 36% strength decrease was seen in samples retrieved from the highest in situ stress domain (sigma1- sigma3approximate 40 MPa) as compared with those taken from the lowest in situ stress domain (sigma1- sigma3approximate 10 MPa).Key words: sample disturbance, brittle fracture, crack initiation, crack propagation, material properties, rock failure.

ISSN:0008-3674    

DOI:10.1139/t98-109

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Unsaturated soils are generally near the ground surface and are commonly overconsolidated due to environmental effects. The stress state variables for an unsaturated, in situ profile consist of the net total stress, (&sgr; -ua), and matric suction, (ua-uw), where &sgr; is the total stress (in three directions),uais the pore-air pressure, anduwis the pore-water pressure. These stress state variables control the behavior of the unsaturated soil. A total stress ratio, TSR, was used in this study as a measure of the stress history. The total stress ratio is defined as the ratio of the compaction pressure to the current confining pressure. Shear tests were conducted using a modified direct shear apparatus on a statically compacted unsaturated soil subjected to various total stress ratios with controlled matric suction. The shear strength parameters (i.e., φ', φb, andc') for an unsaturated soil were measured using the modified direct shear apparatus. The total stress ratio influences the shear strength parameter φbof a compacted soil. The shear strength parameter φbdecreases with matric suction regardless of the loading history. For a compacted soil with a total stress ratio of 1.0, φbwas higher than that for the soil tested at a total stress ratio greater than 1.0, regardless of increase in matric suction, and was shown to be influenced by loading history.Key words: unsaturated soil, shear strength, stress history, compacted soil, direct shear test, matric suction.

ISSN:0008-3674    

DOI:10.1139/t98-098

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

An experimental study was conducted to investigate the effect of the variable-aperture system of an oil sand fracture on its hydraulic and mechanical response to an increasing confining pressure. The oil sand fracture was induced in core samples along the axis of the sample using the Brazilian tensile test. A computer-assisted tomography (CT) scanning analysis was performed to determine the initial fracture geometry and monitor the closure process. The fracture was shown to be a variable-aperture system, with surface roughness and tortuosity playing an increasing role as the fracture closed under pressure. Flow tests revealed a nonlinear behaviour, deviating from the cubic law, and indicated the roughness effects of a natural oil sand fracture are significant. The mechanical response was similar to that of the hydraulic behaviour, indicating the strong relationship between the two. The nature of the uncemented oil sand was shown to strongly affect the strength of the fracture contacts and, therefore, the general closure process.Key words: oil sand, fracture roughness, fracture aperture, computer-assisted tomograhy, hydraulic conductivity.

ISSN:0008-3674    

DOI:10.1139/t98-099

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The fundamental factors controlling the expansive nature of Omani soils are their characteristics with respect to geology, mineralogy, engineering, and microstructure. The first three factors have been extensively studied, however, the fourth has not yet been fully investigated and no work has been published on this aspect. Therefore, this paper deals with the microstructure characteristics of these soils. The scanning electron microscope was employed in this investigation. Three samples selected from different sites where expansive soils problems were known (Al-Khod, Al-Murtafa'a, and Duqm) were investigated. Two specimens from each sample, representing the vertical and horizontal planes, were tested. In addition, two samples that were subjected to swelling were tested to investigate the microfabric changes caused by swelling. The fabric of the Omani expansive soils studied generally consists of dense clay matrices, although clay-granular matrices are occasionally observed. In addition, no connectors have been observed and only few aggregations have been seen. Pore spaces are mainly of the intra-assemblage and intra-elemental types. Significant microfabric changes were induced by swelling.Key words: microstructure, microfabric, SEM, expansive soils, Oman, clay minerals.

ISSN:0008-3674    

DOI:10.1139/t98-111

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In order to assess the quality and depth of ground densification due to compaction, standard and (or) cone penetration tests are often performed before and after compaction. Both methods are intrusive and one-location tests and require a substantial amount of time to evaluate a large area, and evaluation quality is quite dependent on the operation technique and soil type. In this paper, the quality and extent of ground densification by compaction were evaluated using the results from in situ spectral analysis of surface waves (SASW) tests and laboratory resonant column (RC) tests. The SASW test was used to determine the shear wave velocity profiles before and after compaction, and the RC test was adopted to determine the correlation between the normalized shear wave velocity and density of the site, which is almost independent of confinement. Testing and data-reduction procedures of both tests were discussed, and a simplified procedure for evaluating ground densification was proposed by effectively combining in situ shear wave velocity profiles determined by SASW tests with the correlation between normalized shear wave velocity and density determined by RC tests. Finally, the feasibility of the proposed method was verified by performing field studies at the Inchon International Airport project. Field densities determined by the proposed method matched well with those determined by sand cone tests.Key words: density evaluation, densification, compaction, shear wave velocity, spectral analysis of surface waves test, resonant column test.

ISSN:0008-3674    

DOI:10.1139/t98-103

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Site characterization activities involving a variety of different tools and techniques are a key component of any environmental rehabilitation program. Depending on the specific characteristics and requirements of the project, a range of tools can be used to characterize the surface and subsurface conditions. The results will be subject to specific limitations which will apply to a particular tool in terms of the depth investigated and the resolution of the measurements obtained as a result of the sensor capacity and background noise conditions. This paper presents a methodology that can be used to evaluate the relative merits of alternative sampling plans for a site and assist in identifying the optimal sampling plan taking into account the amount and type of prior information. This methodology allows new test results to be incorporated in real time as "prior information" as the site investigation proceeds. The methodology is implemented using a geographic information system (GIS) and a knowledge base system (KBS). Factors considered in the methodology include the effective measured area, the likely target characteristics, surface and subsurface noise conditions, and the level of confidence that exists about the possible source location as a result of prior studies at the site. The results of a sensitivity study are presented. An example is used to demonstrate the capability of the prototype system to assess different test configurations.Key Words: characterization, GIS, KBS, planning, quality.

ISSN:0008-3674    

DOI:10.1139/t99-002

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Laboratory experiments on granular avalanching of dry sands and gravels reveal a consistent pattern of runout distance varying with fall height, fall slope, and volume of material for volumes ranging from 0.1 to 1000 L. Data from the South Ashburton rock avalanche deposit show that its runout behaviour differs only slightly from that of the laboratory avalanches, extending the range of this behaviour to granular avalanches with volumes of about 100 000 m3. By contrast, data from much larger rock avalanches (> 107m3) depart significantly from the trends of the laboratory data; some factor not present in the laboratory, such as rock fragmentation or the presence of an erodible substrate, must influence the behaviour of these larger events. Travel angles as low as 13° in the laboratory tests result from grain flow mechanisms with normal friction coefficients; they are not associated only with large-volume events and do not necessarily indicate unusual material mobility at any scale

ISSN:0008-3674    

DOI:10.1139/t98-108

出版商:NRC Research Press    

年代:1999

数据来源: NRC