Lime treatment as a mix-in-place technique has been widely and successfully used around the world to improve weak soils. Novel techniques using lime are now being developed. One such technique is the use of lime piles to stabilize shallow slopes. Recent research has investigated the reaction mechanisms associated with lime pile stabilization. This paper describes excavation work undertaken at two sites where previously lime piles had been installed to prevent further movement of a failing slope. Laboratory tests undertaken on the retrieved material are also presented and discussed in terms of whether/how the reaction mechanisms have improved the stability of the slope. Results suggested several ground improvement mechanisms, some of which could only be relied upon in the short term. Since installation of the lime piles at both sites no further movements have been recorded, suggesting that this method of stabilization has been successful. Le traitement du mélange in-situ par la chaux a été largement utilisée à travers le monde, dans le but d'améliorer les caractéristiques des sols mous. Des nouvelles techniques utilisant la chaux sont maintenant bien développées. L'une d'entre elles est l'utilisation des pieux à chaux afin de stabilizer les talus peu profonds. Les recherches récentes ont examiné les mécanismes de réaction associées à la stabilité du pieux à chaux. Cet article décrit les travaux d'excavation qui ont été realisés sur deux sites où les pieux à chaux etaient déjà installés, afin de réduire les mouvements du talus en question. Des essais en laboratoire ont été réalisés sur ces matériaux récuperés dont les résultats sont preséntés, et analysés en fonction de l'évaluation de ces mécanismes de réaction vis à vis de la stabilité du talus. A l'issue de ces résultats, plusieurs mécanismes d'amélioration des terrains ont été proposés, quelques-uns d'entre eux sont valable uniquement à courtterme. Aucun mouvement n'a été enregistré suite à l'installation de ces pieux à chaux sur les deux sites, cette methode de stabilization s'est donc révélée fiable.

Two refined clay minerals, English China Clay (predominantly kaolinite) and Wyoming Bentonite (predominantly sodium montmorillonite), were used to develop a method for assessing the time-dependent physicochemical behavior of lime-treated clay subgrade. The two clays, representing the extremes of structural negative charge development, were treated with two lime contents. Changes in the physicochemistry of the samples were monitored after three curing periods by performing batch leaching tests and by monitoring changes in undrained shear strength and Atterberg limits. The effects of changing the batch test operating parameters and increasing the curing period were assessed by measuring changes in solution pH and conductivity and by analyzing eight elements in solution. The solidification mechanisms caused by lime addition were found to be different for the two minerals. Pozzolanic reactions involving English China Clay and Wyoming Bentonite occurred because of the dissolution of aluminum and silicon from the respective mineral. Development of the batch leaching test showed that changing the operational parameters had no effect on the observed trends associated with the time-dependent modification and solidification reactions. In addition, it was shown that successful solidification could be monitored using simple conductivity measurements without the need for extensive and complex elemental analysis.

The USA field experiences in the 1960s with lime treatment of marginal materials for pavement layers resulted in the introduction of a ‘mellowing’ period of between 24 and 72 hours, after mixing and prior to final compaction. This period facilitates reaction between the soil and the lime so that pulverization criteria and compact-ability can be achieved. As a result of these early experiences, the ‘mellowing’ period has become an integral part of specifications for lime-treatment processes used globally but it has been based on limited scientific justification. Under the Department of Transport (DoT) Specification for Highway Works (1991 and 1993 amendments) a ‘mellowing’ period of between 24 and 72 hours is mandatory. This period of mellowing is also recommended in volume 4 of the Design Manual for Roads and Bridges HA/74/95. 1 Part 1 of this paper, 2 also presented in Transport, discussed results of a research programme that investigated the effect of mellowing on the modification process of four British soils (Mercia Mudstone, Oxford Clay, Lower Lias and London Clay) treated with quicklime. This second paper presents the findings of the second phase of this research, which investigated the effect of mellowing on the stabilization process of the same four soils discussed in Part 1. Both papers suggest a need to improve the design methods for lime treatment of clays in the international procedures. 3

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