Settlement Performance of Two Embankments on Deep Compressible Soils

Abstract

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.

Behaviour of friction piles in soft sensitive clays

“…The design and performance of the approach embankments to these structures have been reported by Samson and Garneau (1973) and Tavenas et al (1978). The cases considered in this paper are the bridges at Rivibre MaskinongC and Rivikre du Loup (locations A and B in Fig.…”

Bearing capacity of pile preloaded by downdrag

“…It was raised to a surcharge heiqht of 10.7 to 11.3 m in November 1965, and finally paved in June 1967 (Samson, 1968;Samson and Garneau, 1973 (Fig. 3): They occurred at the neutral point, which coincided with the base of the fine sand and silt formation…”

“…The groundwater table is normally less than 1.5 m below the ground surface. The engineering properties of these soils have been described in detail (Bozozuk and Labrecque, 1968;Samson and Garneau, 1973).…”

Settlement record of tower silos built on Champlain clays

“…One such case is documented by Samson and Garneau (1973). They present a case study of a 10.7 m high fill over soft clays in the Berthierville area.…”