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.
The stage construction of seven high embankments on soft clays on the north shore of the St. Lawrence Valley has provided an excellent opportunity to check the applicability of the concepts of limit and critical states to the analysis of the behaviour of clay foundations.The construction pore pressures have confirmed the development of a significant consolidation in the initial period of construction.The consequences of this consolidation on the behaviour of the clay, in particular in terms of available strength, and on the method of stability analysis have been found entirely consistent with the general model proposed by Leroueil, Tavenas, Mieussens and Peignaud.It is suggested that the so-called [Formula: see text] analysis based on the vane shear strength corrected according to Bjerrum gives the minimum factor of safety and may be too conservative during stage construction. Effective stress analyses are shown to be more representative of the true stability conditions, and they have been successfully used to accelerate the construction of the embankments.
A large number of laboratory tests, carried out to determine index and physical characteristics of Champlain marine clays, using conventional testing procedures and the Swedish fall cone tests, have led to reliable relationships between the cone penetration and certain characteristics.The purpose of this study has been to establish a rapid method of estimating some index and physical characteristics of this clay. The method described in this paper allows the estimation of clay properties, such as liquid limit, compression index, preconsolidation pressure, undisturbed and remolded shear strength, sensitivity, water content, void ratio, and unit weight, within as little as half an hour and using a single undisturbed specimen. When testing according to conventional procedures, the determination of these characteristics takes several days or even weeks.This paper presents the method of estimation and the procedure used to establish the relationships between the results obtained by conventional methods and those derived using the Swedish fall cone.
The Autoroute de la Rive Nord on the north shore of the St. Lawrence River traverses deep deposits of compressible soils in the Berthierville area. Where the four-lane autoroute spans a railroad spur line and Highway 41, the upper 60 ft (18 m) of subsoil consists of layers of silty sand, silty clay, sand and silt, stratified silty clay and sand, and overlies 182 ft (55 m) of marine clay. The distance between the railway and Highway 41 is 400 ft (120 m), and the overpasses are connected by a granular fill. This fill has a total height of 35 ft (10.7 m), and, for stability reasons, required stage construction and stabilizing berms. A 25 ft (7.6 m) temporary preloading fill was also placed on Highway 41 to increase the shear strength of an underlying upper clay layer as required for steep slope design at the overpass abutments.Laboratory testing indicated that the upper 60 ft (18 m) of the foundation soils are normally consolidated fluvial deposits and that large settlements of the embankments were to be expected. The lower marine clay is overconsolidated by 0.8 ton/ft2 (0.8 kg/cm2).Periodic observations taken since the beginning of construction in 1964 show that the autoroute embankment has settled 7.4 ft (2.26 m) and that settlement is continuing at a gradually decreasing rate. Deep settlement gauges and piezometers show that most of the settlements are due to the consolidation of the upper 60 ft (18 m) of soil. The lower marine clay is consolidating at a much lower rate and will cause settlements for many years.Analysis of field observations demonstrates that the measured settlements are attributed to the primary consolidation of the compressible strata resulting from the dissipation of pore pressure. In general, the measured settlements compare favorably with the predictions based on laboratory tests. Field and laboratory soil properties are also compared.This paper presents a detailed record of the laboratory investigation and field observations made in conjunction with the construction of the permanent autoroute embankment and the temporary preloading fill. Extensive field studies on negative skin friction on piles have been conducted at the same site, and the results have been reported elsewhere.
An apparatus was set up for load testing piles at constant rate of penetration (C.R.P. test). The testing equipment consists of a hydraulic jack fed by a high pressure electrical pump equipped with a flow regulator. Examples of pile test results are given.
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