TM 5-818-1 / AFM 88-3, Chap. 7
injection stabilization (chap 16) may be used to underpin
building can actually undergo before being damaged.
structures by forming a zone of hardened soil to support
The values given in tables 5-2 and 5-3 may be used as
the foundation.
guidelines.
b. In carrying out an underpinning operation,
important points to observe include the following:
11-5. Excavation protection.
During foundation
(1) Pits opened under the building must be
construction, it is important that excavation subsoils be
as small as possible, and survey monitoring of the
protected against deterioration as a result of exposure to
building must be carried out in the areas of each pit to
the elements and heavy equipment. Difficulties can
determine if damaging movements are occurring.
occur as a result of slaking, swelling, and piping of the
(2) Care must be taken to prevent
excavation soils. Also, special classes of soils can
significant lifting of local areas of the building during
collapse upon wetting (chap 3). Methods for protecting
jacking.
an excavation are described in detail in table 11-1 along
(3) Concrete in piers must be allowed to
with procedures for identifying problem soils. If these
set before any loading is applied.
measures are not carried out, soils likely will be subject
(4) Chemically stabilized sands must not
to a loss of integrity and subsequent foundation
be subject to creep under constant load.
performance will be impaired.
c. The decision to underpin is a difficult one
because it is hard to estimate how much settlement a
U. S. Army Corps of Engineers
Figure 11-4. Methods of underpinning.
11-5
TM 5-818-1 / AFM 88-3, Chap. 7
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