摘要:

This paper presents a qualitative and quantitative study of the microstructure of a compacted silt, carried out using a scanning electron microscope and mercury intrusion pore size distribution measurements. Samples have been statically compacted at three water contents: on the dry side of the standard Proctor optimum water content, at the optimum, and on the wet side. The wet sample has a matrix type structure, with a clayey fraction filling the voids and adhering to the silt-sized grains, whereas the other samples display a structure characterized by a skeleton made of silt grain aggregates linked together by clayey bidges. The distribution of water and air within the microstructure of the compacted soil is described for each of the three compaction states.Key words:compacted soil, microstructure, scanning electron microscope, pore size distribution, mercury intrusion, clay hydration.

ISSN:0008-3674    

DOI:10.1139/t96-030

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The viscoplastic constitutive theory of Perzyna, and Olszak and Perzyna has been modified and used to model one-dimensional compression of cohesive, normally consolidated soils. Predictions of the model have been compared with the results of a few nonstandard oedometric tests. The model simplifies the one-dimensional creep theory of Yin and Graham by eliminating the traditional concept of plastic strain. Both stress- and strain-controlled tests are discussed. The reference timet0used in the literature for the description of creep subsequent to a load step has been shown to be a function of the overconsolidation ratio.Key words:compression, consolidation, constitutive modelling, creep, viscosity, relaxation.

ISSN:0008-3674    

DOI:10.1139/t96-031

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The rate of deterioration of gravel base course materials may influence the durability of flexible pavements. In particular, selected gradation curves usually satisfy filter criteria thus avoiding migration of fines from one layer (subgrade, base, and subbase) into adjacent one. This paper shows that even if filter criteria are met between successive layers, some 0–20 mm materals do not satisfy the fines mobility criteria that presently are not considered in gradation criteria. This means that fines (<80 &mgr;m) can move within the pores of the layer. Three gradations of two 0–20 mm crushed stones were tested in the laboratory. Experiemrnts were designed to avoid degradation (breakage of particles), in order to study segregation only. One of the tested materials (No. 2) satisfies the gradation criteria but does not satisfy the fines mobility criteria. The experimental results confirmed that material No. 2 is subject to marked segregation during dry placement and compaction. When palced moist, it has a negligible initial segregation, but cyclic loading produces segregation. This internal instability was predictable from fines mobility (suffossion) criteria. It produces layers with different fines contents, which would reduce vertical drainage, increase pore pressures produced by traffic loading, and increase both capillary retention and frost damage.Key words:road, gravel base course, segregation, suffossion, seepage, gradatio

ISSN:0008-3674    

DOI:10.1139/t96-032

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

This paper describes a mathematical model for predicting the hydraulic conductivity of partially frozen soils on the basis of limited input data such as grain size distribution and bulk density or porosity. A new model is based on an analogy for the hydraulic conductivity of frozen and unfrozen soils and models for the estimation of hydraulic properties of soils and unfrozen water content. Campbell's model was used for prediction of soil-water characteristics from limited data, while unfrozen water content was obtained from two models (by P.J. Williams and D.M. Anderson) applied to two different temperature ranges. The new model can be used for the rapid estimation of the hydraulic conductivity of practically any freezing soil having log-normal grain size distribution and for computer simulation of moisture migration in soils below the freezing point. An acceptable conformity between the model prediction and measured data for pure sand has been achieved. The computer program developed requires the following input data: grain size distribution, bulk density or porosity, and soil temperature.Key words:frozen soils, hydraulic conductivity, bulk density, grain size distribution, unfrozen water content.

ISSN:0008-3674    

DOI:10.1139/t96-033

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The soil restraint on pipelines due to oblique relative movement betwen the pipeline and dry loose sand was investigated. Model pipes 1.22 m long with diameters of 38.1, 76.2, 152.4, and 228.6 mm are obliquely moved from vertical to horizontal direction in the drag box to study the soil restraint of the oblique pipes with various relative velocities. All test results indicate that the dimensionless ultimate soil restraints have a power law relationship with the pipe velocity. The velocity exponent increases slightly with the oblique angle and embedded depth of the pipe. Furthermore, the soil restraint also increases with both the pipes oblique angle and embedded depth. Most of the increase in the soil restraint is associated with the oblique angles in the interval between 45 and 90°. The limit equilibrium model succesfully predicted the soil restraint of the pipe. Normailized force–displacement relationships of soil–pipe interaction could be represented by two-constant hyperbolic equation. The findings show that the first constant value,a, increases, whereas the second value,b, decreases with the oblique angle, respectively.Key words:pipelines, soil restraint, oblique motion, san

ISSN:0008-3674    

DOI:10.1139/t96-034

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

An in situ testing programme was carried out in 1992 aimed at obtaining design parameters for the construction of the Brasília Underground line, Brazil. The top layer of soil consisted of an unsaturated and collapsible soft porous clay layer 5–30 m thick followed by residual soils from slate and interlayered metasiltsones and quartzites. A series of Marchetti dilatometer (DMT) logging tests results were comapred with Ménard pressuremeter (PMT) and horizontal plate loading (PLH) tests, as well as laboratory tests on block samples. In situ stresses, strength, and deformation parameters were obtained for the porous clay. The DMT yielded very good results: excellent repeatability, low cost, and results that agree with other in situ tests and laboratory data.Key words:porous clay, in situ testing, dilatometer, pressuremete

ISSN:0008-3674    

DOI:10.1139/t96-035

出版商:NRC Research Press    

年代:1996

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t96-036

出版商:NRC Research Press    

年代:1996

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t96-037

出版商:NRC Research Press    

年代:1996

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t96-038

出版商:NRC Research Press    

年代:1996

数据来源: NRC

ISSN:0008-3674    

DOI:10.1139/t96-039

出版商:NRC Research Press    

年代:1996

数据来源: NRC