HomeMy WebLinkAboutBLD1985-00424 i
Foundation Evaluation of Mobile Home Site
for
John Dineson Property
February 1985
General
On February 16 , 1985 , Norman A . Dixon of Clark Associates , A
Division of Northwestern Territories , Inc . , made a field
inspection of a mobile home site on the property of John
Dineson. This property is located just off Lindsey Hill Road,
about two and three quarters of a mile from the junction of
Lindsey Hill Road and East Quilcene Bay Road . At the time of
Mr . Dixon's visit , forms for a non-bearing perimeter wall , and
four sixty-six foot long concrete footings to support a double
wide mobile home had been constructed , and appeared to be ready
for the placement of concrete .
Non Uniformity of Foundation Soils
The native soils at the Dineson property site can be classified
as silty-gravelly sands , covered by only a few inches of humus
topsoil . As shown in the enclosed sketch , the northern two
thirds of the mobile home foundation has been developed in a
"cut" area of the native soil , and thus has an adequate
foundation due to the relatively high natural soil density and
moderately low soil moisture . In contrast , the southernmost
one third of the foundation has been developed in disturbed and
loose "fill" soil materials . Although these are geologically
similar soil types , the fill portion of the foundation is much
less dense , and therefore absorbs more water which further
increases its weakness . As a result , the foundation footings
now rest on two different soil types , in so far as supporting
capacity is concerned . This situation can ultimately give rise
to substantial differential settlement , with possible damage to
the mobile home , if some type of remedial action is not now
taken .
General Observations
If time were not a consideration , allowing the fill materials
to slowly consolidate over a period of one or two seasons would
likely improve the bearing capacity of the soils to the point
where they could be safely utilized for at least moderate
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foundation loading . However , the Dinesons wish to proceed with
construction as soon as possible . Accordingly , the type of
remedial treatment recommended will be somewhat more expensive ,
but capable of immediate implementation . One further important
consideration is the preservation, if possible , of all the
existing footing and wall forms during the course of remedial
treatment .
Recommendations
Each of the present footings are sixteen inches wide , and
contain two longitudinal Number 4 bars of reinforcing steel .
By temporarily removing the reinforcing bars , a number of
twelve inch auger holes can quickly be drilled through the fill
material utilizing a two man motorized auger . These holes , of
maximum depth of about four feet , should penetrate at least one
foot into original soil , and be drilled on five foot centers ,
but only in those portions of the footings on fill materials
( see sketch ) . Once drilled and cased , if necessary to prevent
caving , the holes should be filled with concrete , after
placement of four Number 4 vertical rebars in each hole . This
vertical steel reinforcement should be structurally attached to
the overlying footing before placement of footing concrete . It
is also recommended that each portion of the footings which
have been placed on fill material , be reinforced by four Number
4 bars of longitudinal reinforcement in lieu of the existing
two bars , which are adequate only for the non-fill portions of
the foundations .
In addition to providing protection against differential
settlement , the proposed reinforced piling will provide
additional hold down force to the mobile home , which has
several points of built in structural steel attachment to each
concrete footing . This additional hold down feature may at
some future date be an important consideration in view of the
fact that nearly one hundred knot winds were believed to have
traversed this area on the night that the Hood Canal floating
bridge was destroyed .
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p Norman A. Dixon
p 1• : �oF"'"sil,: %,�2 ° Engineering Geologist
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