摘要:

Several methods are available to interpret slug tests; however, when applied to the same test data, they usually yield very different results. The methods are classified into three categories depending on their assumptions about the solid matrix deformability during the test. This paper deals with overdamped tests for elastic solids that deform instantaneously. It provides a unified interpretation of transmissivityTand storativitySbased on the velocity graph for variable-head tests in monitoring wells or cased boreholes. IfShas little influence, the velocity graph is a straight line. IfShas some influence, the graph should give a smooth curve. However, smooth curves are exceptions in practice, thereby leading to a reexamination of the influence ofSduring a slug test. Three independent approaches are used. (1) A mathematical review shows that the overdamped solution, as adapted from a heat conduction problem, did not correctly treat storativity terms and the type of problem: it corresponds to a special pulse test, not a slug test. (2) A physical investigation of deformability shows that the influence ofSdoes not exceed 1% of the initial slug for most compressible materials. Thus, it is almost impossible to detect its influence in test results. (3) Numerical analyses confirm thatShas a negligible influence: test results provide straight lines, not curves. The numerical analysis of the special pulse test provides exactly the classical solution, and the correct values ofTandSafter eliminating the confusion about storativity terms. It is concluded that (1)Shas a negligible influence in slug tests, (2) the existing classical solution givingTandSmust be abandoned, and (3) the velocity-graph equation and its integral equation (Hvorslev or Bouwer and Rice) which correctly describe the process must be used.Key words: slug test, hydraulic conductivity, storativity, numerical modeling.

ISSN:0008-3674    

DOI:10.1139/t98-041

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

To evaluate operational problems in evaporite deposit utilization associated with brine, halite, sylvinite, and carnallitic ore were creep tested under unconfined conditions, both with and without added brine. Axial deformation and dissolution chemistry where observed throughout the tests. In both the sylvinite and carnallitic ore tests, selective dissolution of sylvite and carnallite minerals was associated with the precipitation of halite. The nature of this process was dependent on temperature and initial brine and ore composition. Generally, the presence of brine caused a decrease in the resistance to creep deformation. It is suggested that observed weakening in evaporites under dilatant conditions and in the presence of brine is due primarily to the enhancement of fracture mechanics processes through selective dissolution from stressed areas in the rock, such as fracture-process zones and asperities acting as barriers to slip. Correlation of results with a variety of practical environments, including brine inflow problems, waste salt backfilling practices, and underground storage facilities, was possible. Since there is always inherent brine in salt rock deposits, the results also add to the existing body of knowledge regarding advanced evaporite rock mechanics in general.Key words: evaporite, potash, salt, brine, creep, mining.

ISSN:0008-3674    

DOI:10.1139/t98-050

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Conventional and truly undrained behaviour of granular soils is compared by direct experimental measurements. The truly undrained behaviour was determined by compensation for membrane penetration induced volume changes, using a feedback controlled water injection system. A more reliable, nondestructive, specimen-specific method is presented to measure the magnitude of membrane penetration, for use in the injection routine. This new method, unlike the existing methods, does not make any assumptions regarding either the constitutive behaviour or isotropy of sands. It is shown that the truly undrained pore pressures predicted by correcting those observed in conventional undrained tests are too large, implying incorrect linkage between membrane penetration induced volume change and volumetric constitutive behaviour of the granular material. The sand which responds in a strain-hardening manner in conventional undrained loading may, in fact, be strain softening (liquefiable) when truly undrained, a matter of serious practical concern.Key words: sand, truly undrained behaviour, liquefaction, membrane penetration.

ISSN:0008-3674    

DOI:10.1139/t98-048

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This case study presents the design, operation, and results of a soil improvement project using the vacuum preloading method on 480 000 m2of reclaimed land in Xingang Port, Tianjing, China. The areas treated with vacuum ranged from 5000 to 30 000 m2. The effects of soil improvement are demonstrated through the average consolidation settlement of 2.0 m and increases in undrained shear strengths by a factor of two to four or more. The study shows that the vacuum method is an effective tool for the consolidation of very soft, highly compressive clayey soils over a large area. The technique is especially feasible in cases where there is a lack of surcharge loading fills, extremely low shear strength, soft ground adjacent to critical slopes, and access to a power supply.Key words: vacuum preloading consolidation, soil improvement, soft clays, land reclamation, prefabricated vertical drains.

ISSN:0008-3674    

DOI:10.1139/t98-039

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The Confederation Bridge is a 12.9 km long multi-span bridge spanning the Northumberland Strait to connect the provinces of Prince Edward Island and New Brunswick on the east coast of Canada. It is the longest continuous marine span bridge over ice-covered water in the world. The bridge is a design, build, operate, and transfer facility with the Government of Canada being the ultimate owner. Construction started in October 1993, and the bridge officially opened, on schedule, to traffic on June 1, 1997. The combination of deep water, high lateral and eccentric loads, complex geology and variable strength bedrock, and short construction window due to ice and bad weather introduced many foundation engineering challenges. This paper summarizes and discusses the geotechnical aspects of foundation design and construction monitoring services for the bridge. The geological setting and geotechnical conditions, the loading conditions and design criteria, specialized geotechnical analyses, foundation design, and construction quality assurance - quality control issues are described and discussed.Key words: Confederation Bridge, Northumberland Strait, foundation design, quality assurance, ring footing, drilled shafts.

ISSN:0008-3674    

DOI:10.1139/t98-038

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Stages 1 (1967) and 2 (1982) of the Gloucester test embankment are studied using a fully coupled finite-element model. The rate-sensitive characteristics of the foundation soil are modelled using an elastoviscoplastic constitutive equation based on the elliptical cap yield surface and Perzyna's overstress theory of viscoplasticity. The aspect ratio of the yield surface for the Gloucester foundation soil is estimated using conventional laboratory shear and consolidation test results. Calculated and measured behaviour during consolidated isotropically undrained triaxial tests and long-term Rowe cell consolidation tests are compared and the ability of the model to describe the measured behaviour of stages 1 and 2 of the Gloucester test embankment is studied. This paper explores the implications of modelling the residual or restructured properties of the Gloucester foundation soil and demonstrates the ability of a single elastoviscoplastic yield-surface model to describe the undrained and drained response of the Gloucester foundation soil during laboratory and field loading conditions.Key words: elliptical cap, rate sensitive, elastoviscoplasticity, embankment settlements, pore pressures, field performance.

ISSN:0008-3674    

DOI:10.1139/t98-037

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

It is important to verify if a monitoring well was correctly sealed into the ground to avoid preferential flow between aquifer layers (hydraulic short circuit). Previous papers have shown how to check this by variable-head permeability tests interpreted with the velocity-graph method. This paper presents a new method to make this check with the recovery curve of an aquifer test. The theory of this new method is presented. When there is a hydraulic short circuit, the drawdowns and recoveries due to a pumping test in a confined aquifer do not yield unique values of transmissivity and storativity as they should theoretically. An example is provided, that of monitoring well E1 of the Pelican River aquifer test. The pumping phase was interpreted using the methods of Theis and Cooper-Jacob. The recovery phase was interpreted by two methods: (i) the usual graph ofsprime versus log (t/tprime) gave transmissivityTand either the Jacob method or the U.S. Department of the Interior Ground Water Manual gave storativityS; and (ii) the method of (sp-sprime) versus logtprime gave bothTandS. As a result, four values ofTandSwere obtained. They differed by 9% forTand by 186% forS. According to the proposed method there was a hydraulic short circuit close to the monitoring well: it gave an initial water level that differed from the real piezometric level by 40 cm. Drawdown and recovery values were corrected for reinterpretation. The new log-log and semilog graphs yielded identicalTandSvalues, thus validating the diagnosis of a hydraulic short circuit and illustrating the detection method.Key words: monitoring well, pumping, recovery, quality control, transmissivity, storativity.

ISSN:0008-3674    

DOI:10.1139/t98-046

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper presents the result of plate-load tests conducted on a gravelly cobble deposit in Taichung Basin, Taiwan. The geologic formation of the gravelly cobble deposit makes it very difficult to obtain large undisturbed samples for laboratory testing. These field tests provide an opportunity to examine the applicability of existing theories on bearing capacity and subgrade reaction in this geologic formation. The modulus of subgrade reaction is of particular importance in the local practice of designing high-rise buildings on mat foundations. The results of the plate-load tests on this soil deposit are analyzed and discussed.Key words: plate-load test, gravelly cobble deposit, modulus of subgrade reaction, bearing capacity.

ISSN:0008-3674    

DOI:10.1139/t98-044

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The role of degree of saturation on the coefficient of diffusion of contaminants in the aqueous phase is presented and theoretical models for predicting the coefficient of diffusion at any degree of saturation are described. Three predictive models were developed based on three different diffusion modes: diffusion in parallel and series arrangements and combination of both. Diffusion tests were conducted on a sand at various water contents ranging from saturation to the residual degree of saturation using potassium and chloride ions as tracers to verify the applicability of the models. Results from the diffusion tests showed a decrease in effective diffusion coefficient of potassium with a decrease in degree of saturation. The functional relationship between the normalized diffusion coefficient for potassium and the degree of saturation is slightly nonlinear. The results for chloride also showed a decreasing trend, although the data were quite scattered and further verification is needed. Model verification based on the results for potassium showed that among the three models proposed, the model which combines the diffusion pathways in parallel and series arrangements provides the best fit to the experimental data.Key words: unsaturated, contaminant transport, aqueous diffusion, degree of saturation.

ISSN:0008-3674    

DOI:10.1139/t98-045

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The ability of the soil cover system at the Equity Silver Mine to limit oxygen and water fluxes to underlying waste rock was evaluated using a detailed instrumentation program. Field instrumentation was installed to monitor temperature, gaseous oxygen, and gaseous carbon dioxide in the waste rock piles. Lysimeters were constructed at the base of the soil cover system to monitor infiltration across the soil cover. Sensors to measure matric suction, soil temperature, and water content were installed. An automated weather station was also installed to monitor climate conditions at the mine site. The field data indicates that the lower compacted layer maintained a high degree of saturation (i.e., 90% or higher) during 3 years of data collection (August 1992 to August 1995). This is a positive result, since the lower compacted layer was designed as an oxygen limiting barrier. The average measured infiltration from lysimeters placed at the base of the soil cover system was 5% of precipitation (from October 1992 to August 1993). The measured matric suction data indicates that the hydraulic gradient within the soil cover system is predominantly upward except for relatively short periods of heavy rainfall and snow melt in late fall and early spring.Key words: waste rock, soil cover, instrumentation, monitoring, unsaturated soil, soil-water characteristic curve.

ISSN:0008-3674    

DOI:10.1139/t98-051

出版商:NRC Research Press    

年代:1998

数据来源: NRC