Vibratory compaction of coarse-grained soils

Abstract

The variation of the coefficient of earth pressure in normally consolidated and overconsolidated soil and the effect of soil compaction on the change of the horizontal effective stress are discussed based on cone penetration test (CPT) data. A method is outlined for estimating the increase in the effective earth pressure based on sleeve friction measurements. Soil compaction increases not only soil density, but also horizontal effective stress. Since the cone stress is influenced by the vertical and horizontal effective stress, particularly at shallow depths, the cone stress needs to be adjusted for effective mean stress. A relation is presented for determining the soil compressibility from the adjusted cone stress. A case history is presented where a 10 m thick sand fill was compacted using vibratory compaction. Cone penetration tests indicated a significant increase in cone stress and sleeve friction and a decrease in compressibility (increase in modulus number) due to compaction. The friction ratio was unchanged. It was concluded that the earth pressure about doubled corresponding to an increase in the overconsolidation ratio of at least 5. The results of settlement calculations based on the Janbu method demonstrate the importance of considering the preconsolidation effect in the analyses.Résumé : La variation du coefficient de pression des terres dans un sol normalement et surconsolidé et l'effet du compactage de sol sur le changement de la contrainte horizontale sont discutés sur la base des données de CPT. On décrit une méthode pour estimer l'augmentation de la pression effective des terres basée sur les mesures du frottement du manchon. Le compactage augmente non seulement la densité du sol, mais aussi la contrainte effective horizontale. Puisque la contrainte sur le cône est influencée par les contraintes effectives verticale et horizontale, particulièrement aux faibles profondeurs, la résistance du cône doit être ajustée en fonction de la contrainte moyenne effective. On présente une relation pour déterminer la compressibilité du sol à partir de la résistance ajustée du cône. Une histoire de cas est présentée dans laquelle un remblai de sable de 10 m d'épaisseur a été soumis à un compactage par vibration. Les essais de pénétration au cône ont montré une augmentation significative de la résistance du cône et du frottement sur le manchon et une diminution de la compressibilité (augmentation du nombre modulaire) dues au compactage. Le rapport de frottement est inchangé. On a conclu que la pression des terres a environ doublé, ce qui correspond à une augmentation du rapport de surconsolidation d'au moins 5. Les résultats des calculs de tassement basés sur la méthode de Janbu démontrent l'importance de prendre en compte l'effet de la préconsolidation dans les analyses.

Liquefaction perspective of soil ageing

“…In line with this, Matsuo (2004) stated that aged alluvial sand is systematically more resistant to liquefaction than recently deposited manmade islands, even if normalised N 1 values are identical. Although Skempton (1986) suggested the increase of SPT-N over 100 years, Mesri et al (1990), Baxter & Mitchell (2004), Mitchell & Solymer (1984) and Massarsch & Fellenius (2002) stated that the increase of SPT-N or CPT (cone penetration test) resistance is completed within 1 year after land construction or significant compaction. This short-term increase of SPT-N value implies that the ageing of SPT-N cannot account for the observed improvement in liquefaction resistance that occurs over a timescale of hundreds or thousands of years.…”

On ageing of liquefaction resistance of sand

“…Because the present paper addresses the high vulnerability of liquefaction in very recent subsoil having the age of only decades or one hundred years, the engineering ageing is the topic to be discussed. Noteworthy is that SPT blow counts and other sounding resistance increase as well with time and, more interestingly, Baxter and Mitchell (2004) as well as Mitchell and Solymer (1984) and Massarsch and Fellenius (2002) reported that the increase occurs in a time scale of weeks or months only. In line with this, Fig.…”

Influence of stone column installation on settlement reduction

“…In vibrocompaction, the vibrator is used in granular soils, and the vibration compacts the surrounding soil. The soil densification is the most important effect of vibrocompaction, and has been mainly analysed using field measurements [6,7], as it is difficult to model the process numerically [8]. In contrast, stone columns are typically used in soft cohesive soils, as these cannot be compacted.…”