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
upper limit of 80% of ultimate tensile strength of steel bars.
(iii) To check if there is any slippage or creep occurrence.
(iv) To check the elastic and plastic deformations of test nails. This is
observed during the repeated loading and unloading cycles of soil
nails.
Note: Pull-out tests are carried out by applying specified forces in an attempt to pull out
the constructed soil nails.
4. What is the purpose of loading and unloading cycles in pull-out
tests of soil nails? (SN3)
In carrying out pull-out tests for soil nails, it normally requires the loading
and unloading of soil nails of several cycles up to 80% of ultimate tensile
strength of soil nails. The principal function of soil nail tests is to verify the
design assumptions on the bond strength between soil and grout which is
likely to exceed the design values based on past experience. In addition,
the ultimate bond strength between soil and grout can be determined and
this information is helpful as a reference for future design.
Then someone may query the purpose of conducting load/unloading cycles
of soil nails as it does not provide information on the above two main
purposes of soil nails. In fact, loading and unloading soil nails can provide
other important information on their elastic and plastic deformation
behaviour. However, as stress levels in soil nails are normally low, the
knowledge on elastic and plastic performance may not be of significant
value. On the other hand, the creep and slippage performance of soils nails
can also be obtained which may be useful for some soils.
Fig. Typical pull-out test result
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