A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Moreover, when the soils inside the zone of failure are improved, block
failure based on Coulomb is still feasible. By installation of soil nails, it
helps to defer the original failure planes of slopes to a greater depth inside
the slope, which it is normally of high stability condition with less ingress of
surface rainwater.
8. Why are steeply inclined soil nails not commonly used in
stabilizing slopes? (SN1)
Based on stress-strain relations, when the angle of soil nails below the
horizontal (angle b in the figure below) is small, the soil nails intersect the
normal to the potential slope failure surface at a relatively large angle.
Tensile stresses can be readily developed in the soils nails. However, if the
angle of soil nails below the horizontal is large, the soil nails intersect the
normal to the potential slope failure surface at a small angle and little or no
tensile stress would be mobilized in the soil nails. In this case, it is
ineffective in utilizing its tensile strength to prevent slope failure. In the
worst scenario, the soils nail would under the state of compression for even
steeper soil nails.
Fig. Different inclination of soil nails
9. Can grout be utilized in providing tensile resistance of soil nails?
(SN4)
The passive nature of soils nails requires a small movement for the nails to
take up loading. During this process, it is understood that the grout annulus
around the nail would crack to allow for these small displacements.
319