摘要:

For a better understanding of the mechanical behaviour of reinforced soils, the paper presents a study of triaxial compression tests on soils reinforced by identical, equally spaced, plane ties. Soil–reinforcement interactions are considered by using a method similar to the one that resulted in the introduction of the cohesion effect concept in reinforced earth retaining walls. The material's limit-equilibrium equation is established for any tie orientation. These ties give to a reinforced soil a strength higher than the unreinforced soil strength. The difference may be considered as a cohesion term, which usually depends on the strength, concentration, and inclination of the ties, as well as on the radial stress level. The cohesion term given by triaxial tests is different from the cohesion effect term already introduced in reinforced earth walls, as there is no cohesion effect in a triaxial test. The paper also presents a study of adhesion conditions. By examining stress distribution in the soil between the ties, it is established that beyond a given inclination, no traction can be developed in the ties.

ISSN:0008-3674    

DOI:10.1139/t80-019

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

This paper examines the influence of the cutting shoe size of a pressuremeter apparatus in the light of soil behaviour after some unloading and loading. An oversized cutting shoe creates a gap between the borehole and the pressuremeter probe, causing a stress release with a probable consequence of overestimating the shear strength of the soil. An undersized cutting shoe imposes a certain load to the surrounding soil prior to the pressuremeter test, thus introducing errors in measuring the stress–strain relationship of the soil.To gain a quantitative idea of such an influence, Cambridge self-boring pressuremeter tests were carried out on Leda clay at two sites in the Ottawa region. It was found that in the case of an oversized cutting shoe, both the modulus and shear strength were overestimated by about 30 and 80% respectively. In the case of an undersized cutting shoe, the shear resistance was reduced at small strains. In both cases, however, the stress–strain relationship beyond a moderate strain (5%) showed little dependence on the cutting shoe size.

ISSN:0008-3674    

DOI:10.1139/t80-020

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

During construction of a 2.16 m diameter tunnel in a soft to firm clay deposit in Thunder Bay, Ontario, an initial array of instrumentation to provide data indicating overall performance and a second array to provide detailed spatial deformation and pore-water pressure distribution were installed. The tunnel lining consisted of unbolted rings composed of four trapezoidal, unreinforced concrete sections assembled within the tailpiece of the tunnel boring machine.This paper presents and discusses detailed observations of soil deformation, pore-water pressure changes, and total pressure on the lining obtained from the second array of instrumentation. The soil stratigraphy was similar to that at the first array and the data obtained are compared with the earlier data. Monitoring of the instruments is continuing and data from the first year of observations are presented.

ISSN:0008-3674    

DOI:10.1139/t80-021

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

In deep excavations below the water table, the transient and steady state drawdown conditions are often of interest. Particularly in moderately pervious soils, the stability of the slopes, the excavation methods, and equipment are affected by the groundwater response in the excavation. The extent of the drawdown in the area beyond the excavation must also be determined.For a site under construction by Ontario Hydro, a test excavation to determine the drawdown response in the irregularly stratified soils is described. Analyses of the data by the finite element method and by the theory of aquifer tests are presented. The effect of recharge on the steady state and transient drawdown is discussed.For the main excavation, approximate methods to determine the rate of drawdown, the quantity of seepage, and the steady state drawdown position with recharge from infiltration or deep seepage are outlined.

ISSN:0008-3674    

DOI:10.1139/t80-022

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

During the construction of heavy structures, such as bridges and overpasses, on soft clays on the north shore of the St. Lawrence Valley, a detailed load test program on friction piles was performed to establish the characteristics of the most suitable type of pile and to study its long-term behaviour. Three types of piles, timber, steel pipe with closed end, and precast concrete Herkules H-420 piles, were tested. Four timber piles driven in a group and submitted to a 712 kN load served to study the long-term settlement of a small group of piles. Three deep settlement gauges were installed in the centre of this group for measuring settlements in clay at various depths.This test program was completed by the instrumentation of two bridge piers in order to verify the behaviour of larger groups of piles.The paper presents the results of the test piles, the long-term behaviour (4 years) of the bridge pier foundations resting on friction piles in soft clay, and the interpretation of the results.This study shows that the pore pressures induced by pile driving are related to the pre-consolidation of the clay and that they are much larger for tapered piles. It is demonstrated that the effective stress analysis method proposed in 1976 by Meyerhof determines adequately the ultimate pile bearing capacity, but that the effect of the timber pile taper doubles the skin friction.The settlement analysis of pile groups shows that settlements are due to the reconsolidation of the clay and shear creep deformations in the clay close to the pile wall.

ISSN:0008-3674    

DOI:10.1139/t80-023

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

High excess pore-water pressures were measured within a confined stratum of loose silt underlying an excavation slope during pile-driving operations at the slope toe.The range of observed pore-water pressure increase with distance is generally in excess of previously published data. This is attributed to a combination of factors including superposition of increments of excess pore-water pressures generated during driving of individual piles within a group, redistribution of excess pore-water pressures with time, the effect of soil displacement in a confined loose silt layer, and the greater disturbance associated with driving batter piles as opposed to vertical piles. A further contributing factor was considered to be the increase in pore-water pressures due to small straining within the silt layer.Because of uncertainty regarding the accuracy of pore-water pressure predictions and the presence of deformation-sensitive services at the slope crest, the observational approach was adopted during construction.Based on the results of stability analyses using observed pore-water pressures in the field, the construction procedures were modified to maintain an adequate factor of safety and to minimize slope deformation. It was recognized that the method of analysis may have been conservative because changes in total stresses along potential failure surfaces were not taken into account.

ISSN:0008-3674    

DOI:10.1139/t80-024

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The present design practice for embankments on clay foundations is reviewed and its shortcomings are evidenced.A detailed analysis of field observations shows that the actual foundation behaviour differs significantly from the postulated sequence of undrained construction reponse and drained long-term consolidation. In particular a significant consolidation occurs during the very first stages of embankment construction.Design methods are reviewed and modified if necessary to account for this phenomenon. The new design approach, while largely empirical, is simpler and more reliable than existing methods.

ISSN:0008-3674    

DOI:10.1139/t80-025

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

A review of the recent research literature concerning the geology, mineralogy, and physicochemistry of soft soils in Canada is presented. Soft clays are considered from three viewpoints: (1) their three-dimensional distribution and chronological evolution, (2) the sedimentological processes critical in their formation, and (3) geochemistry and mineralogy as they directly influence geotechnical behaviour, especially soft soil sensitivity.Canada's soft soils are products of sedimentation in proglacial and postglacial lake basins that existed between 18 000 and 6000 years BP. They consist of both freshwater and marine clays, which usually behave quite differently, due to peptization or dispersion of the marine clays following postglacial crustal rebound that elevated all clay deposits. The evolution of the major lakes and seas is briefly reviewed in a Canada-wide context.The sedimentology review shows clearly that varved clays are normally features of bottom, heavy-density turbidity current origin, probably in very cold, ice-contact glacial lakes. Warmer postglacial lakes were probably characterized by low-density overflows, and thinly laminated clay deposits developed rather than varved clay sequences. Marine clay deposits also developed from low-density freshwater overflows followed by flocculation, organic agglomeration, and sedimentation. Modern examples are given to illustrate the three major sedimentological processes.Mineralogy and physicochemistry are reviewed in terms of their practical relevance to soft soil sensitivity. Factors influencing both the undisturbed strength and the remoulded strength are reviewed with special reference to recent Canadian research. Included are discussions of cementing agents, specific surface, amorphous and smectite contents, and zeta potential controls as they influence depositional flocculation and postdepositional peptization.

ISSN:0008-3674    

DOI:10.1139/t80-026

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

This note describes a velocity sensor for monitoring directly the particle velocity of driven piles during the impact. A typical velocity pulse obtained by the sensor mounted on a model pile is shown and commented upon.The sensor coupled to a peak voltage indicator forms a very simple and inexpensive system for measuring the peak pile velocity. A procedure is outlined for using the measured value of the peak pile velocity for improving the quality of the input data for the wave equation analysis.

ISSN:0008-3674    

DOI:10.1139/t80-027

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The effect of the test pit size and the backfill density on the dynamic response of footings is studied. Results of steady-state torsional field vibration tests with and without backfill on a footing kept in an excavated pit of varying lateral dimensions are presented and discussed. The influence of backfill density on the response is also investigated. It is observed that the dynamic response is practically unaffected if the lateral dimensions of the test pit are equal to or more than 2.25 times the corresponding dimensions of the footing. The resonant amplitude of rotation decreases and the resonant frequency of vibration increases with increasing backfill density.

ISSN:0008-3674    

DOI:10.1139/t80-028

出版商:NRC Research Press    

年代:1980

数据来源: NRC