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Why are aqueous lubricants considered inappropriate for cohesive soils in pipe jacking?

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Lubrication performs effectively in pipe jacking by maintaining a layer of lubricant between the outside surface of jacking pipes and the adjacent soil. However, once the ground has collapsed onto the jacking pipe, the effect of lubrication would be greatly reduced. Hence, it is important to maintain sufficient pressure to avoid these occurrences.

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Bentonite slurries are commonly used in silty, sandy and granular soils but it is not recommended to use in clayey soils because it may cause swelling in clays by absorption of water and this results in increased contact between the jacking pipe and soils. Hence, non-aqueous lubricants should be considered for cohesive soils.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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