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
Level Two (Advanced FAQs)
Part I: Soil Nails
1. What is the basic mechanism of soil nails in improving soil stability?
(SN1)
Soil nails improve slope stability by:
(i) Partial increase in the the normal force and shear resistance along
potential slip surface in frictional soils.
(ii) Direct reduction of driving force along potential slip surface for
cohesive and frictional soils.
(iii) Soil nail head and facing provides containment effect to limit the
deformation near slope surface.
Soil nail head serves to provide reaction in mobilizing tensile force in soil
nail. Moreover, it provides confinement to soils in active zone behind soil
nail head and avoids the occurrence of local failure between adjacent soil
nails.
2. Is soil nail head an essential feature of soil nails? (SN2)
Soil nail head is an essential feature of soil nails which help prevent active
zone failure. Active zone failure involves shallow failure in the outer part of
slope within active zone and it fails by separating and sliding down the
slopes and sols nails remain in place.
Soils nail heads also enhances the mobilization of tensile resistance of soil
nails and increases the factor of safety of slopes.
3. What are the main reasons for conducting pull-out tests for soil
nails? (SN3)
There are mainly four reasons for this test:
(i) To check and verify the bond strength between soil and grout adopted
during the design of soil nails. This is the main objective of conducting
soil nail pull-out test.
(ii) To determine the bond strength between soil and grout for future
design purpose. However, if this target is to be achieved, the test nails
should be loaded to determine the ultimate soil/grout bond with a
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