EI 02C097
01 Jul 97
Table 1-5 (Concluded)
Disadvantages (Concluded)
Construction techniques sometimes sensitive to subsurface conditions; susceptible to "necking" in squeezing ground; caving or loss of
ground in fissured or cohesionless soil.
Construction may be more difficult below groundwater level; concrete placement below slurry requires careful placement using tremie or
pumping artesian water pressure can require weighting additives to drilling fluids to maintain stability; extraction of casing is sensitive to
concrete workability, rebar cage placement must be done in a careful, controlled manner to avoid problems; underreams generally should
be avoided below groundwater unless "watertight" formation is utilized for construction of underreams.
End-bearing capacity on cohesionless soil often low from disturbance using conventional drilling techniques.
Enlarged bases cannot be formed in cohesionless soil.
Heave beneath base of shaft may aggravate soil movement beneath slab-on-grade.
Failures difficult and expensive to correct.
foundation designs, and the scope of in situ soil and foundation
(3) Local experience. The use of local design and
load tests. Required cost estimates and schedules to conduct the
construction experience can avoid potential problems with certain
soil investigation, load tests, and construction should be prepared
types of foundations and can provide data on successfully
and updated as the project progresses.
constructed foundations. Prior experience with and applications
of deep foundations in the same general area should be
b. Site conditions. Examination of the site includes history,
determined. Local building codes should be consulted, and
geology, visual inspection of the site and adjacent area, and local
successful experience with recent innovations should be
design and construction experience. Maps may provide data on
investigated.
wooded areas, ponds, streams, depressions, and evidence of
earlier construction that can influence soil moisture and
(4) Potential problems with driven piles. The site
groundwater level. Existence of former solid waste disposal sites
investigation should consider sensitivity of existing structures and
within the construction area should be checked. Some forms of
utilities to ground movement caused by ground vibration and
solid waste, i.e., old car bodies and boulders, make installation of
surface heave of driven piles. The condition of existing structures
deep foundations difficult or result in unacceptable lateral
prior to construction should be documented with sketches and
deviation of driven piles. Guidance on determining potential
photographs.
problems of deep foundations in expansive clay is given in TM 5-
c. Soil investigation. A detailed study of the subsurface soil
818-7, "Foundations in Expansive Soils." Special attention should
be payed to the following aspects of site investigation:
should be made as outlined in TM 5-818-1. The scope of this
investigation depends on the nature and complexity of the soil, and
(1) Visual study. A visual reconnaissance should check for
size, functional intent, and cost of the structure. Results of the soil
desiccation cracks and nature of the surface soil. Structural
investigation are used to select the appropriate soil parameters for
damage in nearby structures which may have resulted from
design as applied in Chapters 2 through 5. These parameters are
excessive settlement of compressible soil or heave of expansive
cohesionless soil, undrained shear strength Cu for cohesive soil,
soil should be recorded. The visual study should also determine
soil elastic modulus Es for undrained loading, soil dry unit weight,
ways to provide proper drainage of the site and allow the
performance of earthwork that may be required for construction.
and the groundwater table elevation. Refer to TM 5-818-1 for
guidance on evaluating these parameters.Consolidation and
(2) Accessibility. Accessibility to the site and equipment
potential heave characteristics may also be required for clay soils
mobility also influence selection of construction methods. Some of
and the needed parameters may be evaluated following procedures
these restrictions are on access, location of utility lines and paved
presented in TM 5-818-7. Other tests associated with soil
roads, location of obstructing structures and trees, and
investigation are:
topographic and trafficability features of the site.
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