摘要:

Compacted granular soils with small additions of bentonite have been used to build geotechnical structures such as impervious liners and cores of zoned earth dams. This paper presents a laboratory study showing how physical and mechanical characteristics of a silty sand are modified by a low percentage of bentonite. The effects of the addition of bentonite on the silty sand are reflected by an increase in the plasticity index, a reduction in maximum modified Proctor density, and a decrease in hydraulic conductivity. The most significant consequences on the mechanical properties are an increase of compressibility and secondary consolidation coefficients, and a reduction in shear strength. Different mixtures were either dynamically compacted at the optimum water content (compacted samples) or prepared after slurry consolidation from the minimum density (remoulded samples). Although the compacted and remoulded specimens show different isotropic compression lines, their critical-state lines in thev:p':qspace are identical, wherevis specific volume,p' is average effective stress, andqis deviator stress. Comparisons of the mechanical parameters with the existing literature database show that the compression coefficients of the remoulded mixtures are comparable to those of normally consolidated clayey soils of similar plasticity; nevertheless, those of the compacted mixtures are considerably lower. Also, the slopes of their critical-state lines in theq:p' plane are in good agreement with those predicted by empirical correlations for fine-grained soils.Key words: bentonite, silty sand, compaction, physical properties, compressibility, critical state.

ISSN:0008-3674    

DOI:10.1139/t98-066

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper first describes the numerical implementation of the coupled formulation for the theory of consolidation of unsaturated soils. The developed computer code is verified using the Mandel-Cryer problem and then is applied to the solution of coupled multidimensional consolidation problems. Using a parametric study, it is demonstrated that, in unsaturated soils, the Mandel-Cryer effect is suppressed and the consolidation process in unsaturated soils is affected significantly by the shape of the soil-water characteristic curve. Finally, the developed model is used to analyze the consolidation of an unsaturated-saturated soil column. Analysis results indicate that the classical "undrained" pore-water pressure response to an externally applied load only occurs in the saturated zone while the pore-water pressure response is subdued in the unsaturated zone. This paper also shows a method of deriving one of the two additional material parameters required for the analysis of unsaturated soils from laboratory test results.Key words: coupled consolidation, unsaturated soils, Mandel-Cryer effect, soil-water characteristic curve.

ISSN:0008-3674    

DOI:10.1139/t98-065

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A new in situ remediation method is described, "upflow washing," in which contaminants are flushed to the surface within an in situ fluidized zone produced by a jet inserted into a granular formation. The suitability of the method for LNAPL (light non-aqueous phase liquid) remediation is examined by experiments on diesel-contaminated soils within column and tank settings. The experiments indicate significant reductions in diesel levels (96-99.9%) may be achieved by fluidization with water and gas (gas-liquid upflow washing, GLUW) for a wide range of initial diesel concentrations (10 000 to 150 000 mg/kg) and for soil fines contents of 0 to at least 10%. Final diesel levels of <1000 mg/kg in a uniform fine sand and <200 mg/kg in clayey sands can be achieved. The efficiency is much higher than that of fixed bed flushing (simulated pump-and-treat), as the method overcomes the trapping of NAPL ganglia. Fludization with water alone (liquid upflow washing, LUW) is less effective than fixed bed flushing in the uniform sand, but approaches that of GLUW in clayey and silty sands. The results are explained by theoretical analysis of the removability of isolated NAPL droplets and mixed solid - NAPL particles from a fluidized bed due to buoyancy and elutriation, which may be represented using a "removability regime map" for the diesel-water-sand system.Key words: fluidization, in situ, remediation, NAPL, diesel.

ISSN:0008-3674    

DOI:10.1139/t98-067

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

As part of an ongoing research program to develop local seismic engineering ground motion parameters for implementation in the Jordanian Seismic Building Code, a practical contribution is made to determine the local site coefficient (S) for the Port City of Aqaba, southern Jordan. Employing probabilistic peak ground acceleration estimates using FRISK, the overall dynamic site response design spectrum is obtained through the calculated response spectrum based on selected soil-rock column profiles applying SHAKE91. The parabolic shape of theScoefficient design spectrum is given by the following relationships:S= 1.06 forTb/Ts<= 0.56S= -0.81 + 4.68(Tb/Ts) -2.38(Tb/Ts)2for 0.56 < (Tb/Ts)<=1.43S= 1.00 forTb/Ts>1.43whereTbandTsare the structural and site response design periods (in seconds), respectively.Key words: dynamic, site, response, Aqaba, spectrum, design.

ISSN:0008-3674    

DOI:10.1139/t98-064

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The removal of naphthalene from soils using a surfactant-enhanced flushing process was studied. Column tests were conducted on sand-kaolinite specimens (0, 5, and 20% kaolinite content) with water and sodium dodecylsulfate (SDS) surfactant used as permeants. Upon the introduction of surfactant, the hydraulic conductivity (k) of the various test specimens containing kaolinite decreased by up to two orders of magnitude but then recovered gradually to its initial value upon further flushing. Although more than 90% of the naphthalene contaminant was removed from the test soils, excessively long periods of flushing were needed due to the clogging phenomenon. Upon varying the concentration of the liquid constituents (SDS, naphthalene, and NaCl), the micellar solutions were observed to convert into phases including liquid crystals and gel. The viscosity of these phases was measured to range from 10 to 1000 cP. Several hydraulic conductivity tests conducted with SDS amended with NaCl indicated the alleviation of the reduction inkwhen sufficient NaCl concentration was used.Key words: surfactant, hydraulic conductivity, kaolinite, sand, naphthalene, SDS, contaminant, remediation, viscosity.

ISSN:0008-3674    

DOI:10.1139/t98-054

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Much of the southwestern part of Ontario between Lake Huron and Lake Erie has a thin freshwater aquifer overlain by an aquitard of Late Pleistocene clayey glaciolacustrine deposits and underlain by a thick Devonian shale aquitard. In a large area east of the St. Clair River, where the Quaternary aquitard is 30-50 m thick, groundwater of Pleistocene origin (identified by18O and2H signature) occurs in the aquifer and in the bottom part of the Quaternary aquitard. Numerous piezometer nests in the aquitard show a downward hydraulic gradient with depth. In some areas, the aquitard has downward gradients only in the upper part and upward gradient in the lower part, indicating a transient condition. The piezometer nests in the clayey aquitard also show an increase in Cl-concentration with depth. Long-term piezometer monitoring at two sites show a major shift in the aquitard hydraulic gradient since 1983 and a large rise in head in the underlying aquifer. Analyses of initial aquifer water levels, reported in well drilling records, indicate a large decline in the potentiometric surface of the aquifer between the 1940's and the 1970's followed by a recent rise in the surface in part of the region. This pattern is consistent with well drilling and water use records indicating that 7000 wells were installed in the aquifer in the three decades since 1940 and that groundwater use has greatly diminished in the past 10-15 years due to rural pipeline distribution of lake and river water. The hydraulic gradient in the aquitard is slowly adjusting to the rise in the aquifer potentiometric surface. One-dimensional solute transport modelling provides close matches to the vertical profiles of Cl-migrating upward from the aquifer since deglaciation, 15 000 - 18 000 years before present, by diffusion with little or no advection. The lack of advection indicates a near-neutral long-term hydraulic gradient. As the withdrawal rate of water from the aquifer continues to decline, it is expected that the hydraulic head in the aquitard in much of the area westward of the recharge area will continue to adjust for many decades.Key words: clay, aquitard, aquifer, water use, hydraulic gradient.

ISSN:0008-3674    

DOI:10.1139/t98-057

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

There are two general types of settlement profiles induced by excavation, the spandrel type and the concave type. Based on a regression analysis of the field observations of settlement curves with predominantly cohesive subsurface conditions, an empirical method for predicting the spandrel and concave settlement profiles is proposed. The proposed method is verified through several case histories. For comparison, the results obtained from other empirical methods are also presented. The proposed method provides a fairly good prediction of ground surface settlement and yields better prediction of angular distortion than other empirical methods for the concave- and spandrel-type settlement profiles. Furthermore, the relationship of cantilever area and deep inward area of wall deflection is established which can be used as the first approximation to predict the type of settlement profile.Key words: prediction, excavation, settlement profile, spandrel, concave.

ISSN:0008-3674    

DOI:10.1139/t98-056

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The numerical simulation of the breakwater construction at Sergipe Harbour, Brazil, is described and the results compared with instrumentation data. The numerical simulation was carried out in plane-strain conditions using the modified Cam-Clay model and the Biot consolidation theory. Field observations and the numerical simulation show that the horizontal displacements under the breakwater toe increase with time. This happens during the loading and consolidation stages. It is argued that the process does not necessarily derive only from undrained creep, since the model used does not simulate this phenomenon. The shear strains, measured by an inclinometer, increase more rapidly near the free-draining surfaces, in a process similar to the dissipation of excess pore pressure.Key words: clay, embankment, numerical analysis, shear strain, consolidation.

ISSN:0008-3674    

DOI:10.1139/t98-063

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper discusses the application of piezoceramic bender elements for measurement of damping ratio in the frequency domain in a triaxial cell under isotropic confinement. The emitter was excited with a constant voltage and varied frequency sine signal while the phase difference and amplitude in the receiver were measured. The resonant frequency and dynamic characteristics of cell components were analyzed to study the influence of possible additional modes when the modal analysis of a soil sample is performed. Damping ratio and shear wave velocity were determined in a sample of dry silica sand at different confinements from the first resonant mode of the sample. A relationship was found between measured travel time and resonant frequency that satisfies the solution for the general wave equation. The measured damping ratio compares very well with approximated empirical models. It is concluded that the methodology assumed in this work performs satisfactory when the dynamic response of the cell components is properly identified.Key words: wave velocity, shear modulus, material damping, bender elements, frequency analysis, silica sand.

ISSN:0008-3674    

DOI:10.1139/t98-058

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Clay-rich glacial till and Cretaceous clay are common throughout the Interior Plains of North America. Quantifying groundwater flow through these aquitards has implications for solute transport in aquitards and protection of underlying aquifers. Groundwater flow through a two-tiered aquitard system was investigated using laboratory and field methods at a test site in Saskatchewan, Canada. The aquitard system consists of 80 m of uniform, plastic clay-rich Battleford till (deposited 12-18 ka BP) disconformably overlying 77 m of late Cretaceous plastic marine clay (Snakebite Member, deposited 70-72 Ma BP). The upper 3-4 m of till is oxidized and fractured whereas the remainder is unoxidized. For the scales investigated, results suggested that hydraulic conductivity,K, is independent of scale for relatively thick till and clay bedrock deposits. Analysis of slug tests in the unoxidized till and laboratory tests on cores of unoxidized till yielded geometric meanKvalues of 5.4 × 10-11and 2.7 × 10-11m/s, respectively. LaboratoryKtests of clay samples yielded a geometric meanKof 4.3 × 10-12m/s. BulkKof the clay was estimated to be 2.3 × 10-12m/s assuming steady-state flow through the till and clay. The present-day groundwater velocity through the aquitard system was estimated to be between 0.5 and 0.8 m/10 ka downward based on the measuredKvalues, measured hydraulic gradients, and measured porosities. Results suggested that pore water in much of the till was introduced during or shortly after glaciation.Key words: hydrogeology, aquitards, Cretaceous clay, Battleford till, hydrogeologic properties, geotechnical propert

ISSN:0008-3674    

DOI:10.1139/t98-060

出版商:NRC Research Press    

年代:1998

数据来源: NRC