摘要:

This paper describes two new apparatuses recently developed at the Università di Napoli Federico II (Italy) in order to test soils under unsaturated conditions. The related experimental procedures and the first results obtained on a dynamically compacted silty sand are also discussed. The devices mentioned are a Bishop and Wesley stress-path cell and a Wissa oedometer, modified to control matric suction and to measure all the stress-strain variables relevant to unsaturated soil mechanics. Specific experimental procedures were established to perform tests under general conditions and were carefully verified during several tests. Using the triaxial cell, isotropic and anisotropic compression stages were carried out under constant suction levels of 0, 100, 200, and 300 kPa. Furthermore, two deviator stages were performed following different stress paths and water drainage conditions. Using the oedometer, an additional suction level (400 kPa) was investigated during compression tests driven up to 5 MPa of vertical net stress (sigmav-ua). This research is a part of a major project in progress at the Dipartimento di Ingegneria Geotecnica of Naples; it is aimed at the experimental analysis of the behaviour of several dynamically compacted soils and at the numerical modelling of boundary problems related to earth structures.Key words: unsaturated soils, equipment layout, silty sand, matric suction

ISSN:0008-3674    

DOI:10.1139/t98-093

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

We analyze analytically and numerically the stress distribution along the plug-rock interface and within an axially loaded plug emplaced in a borehole in rock. Experiments show that the interface strength increases with decreasing plug radius and with increasing plug length. Axial strength decreases as a power law of plug radius. An increase in the modulus ratio (ratio of plug modulus to rock modulus) increases the interface strength, until it levels off at a ratio of about 5.0. For short plugs, the tensile stresses may reach a magnitude significant to be of concern for long-term stability of the plug and of the host rock. Out studies suggest designing friction plugs with a length to radius ratio of at least 8.0. In practice, especially for short-term performance, e.g., emergency flood control or temporary diversions, a ratio of 8.0 may not be necessary or justified. For permanent abandonment plugs, it is essential to reduce the tensile stresses in the plug and in the host rock to a level that will minimize the risk of long-term deterioration. We recommend in situ experiments on larger diameter plugs to assess the validity of the proposed size effect extrapolation obtained in this study. Key words: borehole plugging (sealing), shaft seal design, plug-rock interface strength, axial strength, bond strength, cementgrout.

ISSN:0008-3674    

DOI:10.1139/t98-078

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

We analyze analytically and numerically the stress distribution along the plug-rock interface and within an axially loaded plug emplaced in a borehole in rock. Experiments show that the interface strength increases with decreasing plug radius and with increasing plug length. Axial strength decreases as a power law of plug radius. An increase in the modulus ratio (ratio of plug modulus to rock modulus) increases the interface strength, until it levels off at a ratio of about 5.0. For short plugs, the tensile stresses may reach a magnitude significant to be of concern for long-term stability of the plug and of the host rock. Our studies suggest designing friction plugs with a length to radius ratio of at least 8.0. In practice, especially for short-term performance, e.g., emergency flood control or temporary diversions, a ratio of 8.0 may not be necessary or justified. For permanent abandonment plugs, it is essential to reduce the tensile stresses in the plug and in the host rock to a level that will minimize the risk of long-term deterioration. We recommend in situ experiments on larger diameter plugs to assess the validity of the proposed size effect extrapolation obtained in this study.Key words: borehole plugging (sealing), shaft seal design, plug-rock interface strength, axial strength, bond strength, cement grout.

ISSN:0008-3674    

DOI:10.1139/t98-089

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The performance of clayey liners and covers is assessed by several methods including borehole variable-head permeability (k) tests. Different interpretations of the end-of-casing and Lefranc tests are discussed. In Quebec, most tests have been interpreted using the velocity-graph method. Its equations are presented and differences are illustrated by examples. Numerical simulations confirm the validity of the velocity-graph method. It eliminates a frequent error in thekvalue resulting from a poor evaluation of the piezometric level for the test. Using an incorrect interpretation method may yield akvalue up to 50 times lower than the actual value. Smearing the clayey surface in the injection zone may be a source of uncertainty in thekvalue. A numerical analysis shows that a 1 or 2 cm smeared zone may change the testkvalue by over one order of magnitude. It is also shown that it is illusory to try to extract the anisotropy in hydraulic conductivity of the compacted clay.Key words: clay liners, clay covers, permeability, in situ test, interpretation.

ISSN:0008-3674    

DOI:10.1139/t98-091

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Eighteen lateral loading tests were conducted on large-scale steel piles to establish the lateral behaviour of tapered piles in cohesionless soil. Three piles 1.52 m in length with different taper angles but the same average embedded diameter of 168 mm were installed in sand enclosed in a steel chamber 1.5 m in diameter and 1.445 m in depth. The soil chamber was lined with an air bladder so that sand inside the chamber could be pressurized to vary the confining pressure. The piles were instrumented with electrical resistance strain gauges and the horizontal pile movements at grade and the loading point were measured with displacement transducers. The bending-moment functions along the pile were calculated from the strain measurements by curve fitting the measured strain data. The soil resistance (p) and pile displacement (y) relationships were developed in the form ofp-ycurves by differentiating and integrating these bending-moment functions. It was found that tapered piles carried up to 77% more lateral loads than straight-sided-wall piles with the same average diameter. The maximum bending moment occurred in all piles at almost the same depth of one third of the embedded length of the pile. Hence, the cross section of tapered piles at the location of maximum bending moment was larger than that of straight-sided-wall piles, resulting in lower stresses in the pile. It was concluded that the tapered piles represent a more efficient distribution of the pile material and display better performance under lateral loading conditions.Key words: tapered piles, lateral response,p-ycurves, modulus of subgrade reaction.

ISSN:0008-3674    

DOI:10.1139/t98-094

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A critical examination of the procedures commonly used to estimate earthquake-induced sliding displacements of earth structures is essential due to their widespread use and application to new types of systems such as solid-waste landfills. Rigid sliding block analyses are performed, along with decoupled and fully coupled deformable sliding block analyses using a distributed mass model with a mode shape appropriate for an earth structure. Results from using several earthquake ground motions and a sinusoidal input indicate that a decoupled analysis does not always provide a conservative estimate of sliding displacement. Conservative decoupled displacements are calculated for lower values of yield acceleration (i.e.,ky/kmax< 0.6) when the fundamental period of the sliding mass is less than twice the mean period of the input ground motion. For systems with larger values ofky/kmaxor large fundamental periods, a decoupled analysis may predict smaller displacements than a fully coupled analysis. However, in these cases, the displacements calculated from both analyses are generally small (i.e., less than a few centimetres). A decoupled analysis generally provides an estimate of the coupled sliding displacement within a factor of three, which is conservative, except for particular cases where caution is warranted. A rigid sliding block analysis can be significantly unconservative, and it should not be used.Key words: computation, decoupled, displacements, embankments, seismic performance, seismic response, soil dynamics, solid-waste landfills.

ISSN:0008-3674    

DOI:10.1139/t98-076

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Publications associated with sands are often limited to clean (i.e., little fines content), uniform, uncemented silica or quartz sand. On the other hand, the importance of mineral content, particle shapes, as well as gradation to the behavior of sand has long been recognized. Although systematic studies of sands other than clean quartz sand have been limited, there is increasing attention being paid to sands with an appreciable fines content. Because of a major construction project, extensive field and laboratory experiments were performed on a silty fine sand from Mai-Liao, which is located on the central west coast of Taiwan. Results show that Mai-Liao Sand (MLS), a silty sand, can be significantly more compressible than clean quartz sand under static load. The particles of MLS have moderate strength, and significant crushing can be induced by triaxial shearing. As a result, MLS has low dilatancy and a relatively small range of peak friction angles. Cone penetration tests in MLS were conducted in a calibration chamber. Analyses of the data indicate that interpreting cone tip resistance in MLS using methods developed based on clean quartz sand without considering the differences of compressibility can be unrealistic. This paper documents results of the experimental studies on MLS.Key words: silty fine sand, strength, dilatancy, compressibility, crushing, in situ test.

ISSN:0008-3674    

DOI:10.1139/t98-090

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The cone penetration test (CPT) is viewed by a majority in the geotechnical engineering profession as a preferred in situ testing tool, while the self-boring pressuremeter test (SBPMT) is sometimes viewed to be of questionable reliability. A comparative statistical study of SBPMT data and CPT cone tip resistance is undertaken in this research to examine whether the test data do actually support the perceived notion. Data from seven sand and silt sites in western Canada and one location in the United States have been examined. The sensitivity of the SBPMT to the variability in the state of packing is quantified and compared with the corresponding values for the cone tip resistance. The results indicate that the sensitivity of cone tip resistance and the SBPMT data to the variability in the in situ state of packing is comparable. Comparison of estimates of procedural uncertainties in the SBPMT and the CPT also leads to a similar conclusion. These observations do not support the notion of a general lack of reliability of the self-boring pressuremeter at sand-silt sites.Key words: reliability, sand, self-boring pressuremeter, piezocone, inherent variability, procedural uncertainty.

ISSN:0008-3674    

DOI:10.1139/t98-075

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In the Kaministiquia River valley near Thunder Bay, Ontario, shallow ground movements are common on the grassy slopes, whereas the forested slopes generally appear stable. These slope failures may be the result of a rise in the groundwater table due to forest clearing and a subsequent reduction in evapotranspiration. Slope movements on one of the grassy slope in the valley have been monitored and examined since 1989. An explanation as to the cause of these slope failures is presented in this paper.Key words:shallow ground movements, fractured clay, deforestation, evapotranspiration.

ISSN:0008-3674    

DOI:10.1139/t98-077

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The Norman Wells oil pipeline has been operating successfully since 1985. The pipe was designed to operate as an ambient-temperature pipeline and accommodate up to 0.8 m of thaw settlement in inorganic terrain. The pipeline has settled close to this amount in some areas, without excessive straining of the pipe. An average thaw strain for the soil back-calculated from the thaw depth and resulting thaw settlement at several sites gives average values of 16-20%. At one location (kilometre post 5.2), the pipeline has experienced uplift of 1.1 m or more. The mechanism for pipe movement is likely a combination of high axial stresses and some small initial frost heave, which triggered uplift buckling of the pipe. Low-density thawed soils contributed to this behavior. An internal profiling device (Geopig) has been run through the pipe in recent years. Analysis of the profiles indicates excellent agreement with manual surveys at the site. The pipe is experiencing about 0.3% bending strain in the uplift zone, and about 0.4% strain in a settling area immediately to the north. Pipe strain analysis using a structural model indicates that about 0.2 m of frost heave would be required to initiate uplift buckling over a critical heave length of 22-25 m.

ISSN:0008-3674    

DOI:10.1139/t98-092

出版商:NRC Research Press    

年代:1999

数据来源: NRC