Report (2) Nelco Inc. 00 C7-2—? CTI #99 -G1138
Geotechnical Investigation
June 30, 1999
Borings B -2 and B -4 indicated similar conditions: saturated, loose to very loose sand and silty
sand (est. 2% to 35% silt based on B -3 tests) between 14 and 22 feet below the ground surface.
Based upon the old topographic data and its relationship to the existing watercourses, these
conditions are interpreted to be present beneath a significant portion of the southeast and
northeast corners of the structure. Since footings will be founded some 15 feet above the zone
of liquefaction, bearing failure is not a hazard in our opinion. However, based upon the old
topography, the proposed fill height above the flood plain, and our subsurface interpretation,
lateral spreading of the pad in opposing directions is a hazard based on our empirical (historical
event based) analysis. It is important to note that the analysis does not take into account the
tensile strength of the structure. Further, liquefaction and resulting lateral spreading is not
anticipated to occur during small or moderate magnitude earthquakes (M of 3 to 5.8), or more
distant events. Magnitude of lateral spreading, should liquefaction be triggered, is most
dependant on the number of significant cycles that occur following the sudden strength loss that
occurs after several initial cycles •
/I Results of this lateral spreading analysis indicate the following:
• Lateral spreading of the fill pad on the order of 1 to 2 feet may occur during a design
IN level event.
• The direction of spreading is anticipated to be an outward direction at the West end of
the structure and northward near the NE corner of the structure.
• Vertical movement is anticipated to be significantly less (approximately 10 % -15% of
the lateral component beneath the structure).
Lateral spreading affects structures by over stressing the structures tensile properties at
sympathetic planes of weakness, or where large blocks of soil impart concentrated differential -
lateral forces resulting from slab friction imparted by the soil blocks. There are a number of
methods used for reducing lateral spreading risk, but few are economically feasible for a
structure of this size. Our proposed methodology for mitigating or decreasing risk of differential
lateral and vertical movement is discussed in detail in the following section.
CONCLUSIONS AND RECOMMENDATIONS
General - The major issues facing the site development are:
• variable fill consistencies (7.5 to 10 feet thick) in the zone of footing influence,
• the presence of any undetected concentrated organic or debris spoil within the fill,
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Nalco Inc. CTI #99 -G1138
Geotechnical Investigation
June 30, 1999
the mitigation area above elevation 139 is cut, the subgrade should be observed just prior to,
and during, ripping of the soil mat subgrade. Following ripping and moisture conditioning
(aeration), the subgrade should be heavily compacted to the Engineers satisfaction.
Compaction testing for verification will be unreliable, in our opinion, due to available fill variability.
However, CTI may elect to perform testing to evaluate moisture conditions or to assist with
monitoring should more uniform fills be utilized.
The subgrade soils on the site are generally fine - grained and, in our opinion, are moisture
sensitive. Hence, the earthwork should be scheduled for the dryer summer and fall months if at
all possible. Otherwise, special techniques and additional expenditures will be required during
construction to render soils compactable.
Excavation - In our opinion, proposed site excavations can be accomplished with conventional
excavation equipment such as scrappers or backhoes. Excavation for soil mat installation
should be performed in one or two phases; if excavated in two phases, reinforcement is to be
overlapped 4 feet at the joint (easily done by rolling the 4 feet on a used spool for retrieval when
the adjacent cut is made).
Because of safety considerations and the nature of temporary excavations, the Contractor
should be made responsible for maintaining safe temporary cut slopes and supports for utility
trenches, etc. We recommend that the Contractor incorporate all pertinent safety codes during
construction.
Structural Fill —, any soil, including the on -site soil that is free of organic or other deleterious
matter will be suitable for fills or structural backfill provided it is placed during dry warm weather
and it is moisture conditioned, if necessary, (to raise or lower the water content) before it is
placed to achieve optimal moisture content for compaction. If grading work is accomplished
during the wet time of the year, then a clean (not more than 7 percent passing the No. 200
sieve, based on a wet sieve analysis) granular, reasonably well graded soil is recommended.
Fills should be placed in thin lifts and compacted to a dry density of at least 98 percent of the
standard Proctor maximum dry density (ASTM D 698) within building areas and within a 2 -foot
depth of any pavement section, or to the satisfaction of the Engineer if soils are variable. All fills
outside of these limits can be compacted to 95 percent of the maximum dry density. The
thickness of the lifts will need to be determined in the field, but generally for self propelled
compactors, the lifts should not exceed about 9 to 12 inches as measured in a loose condition.
For small hand compactors, the lifts may need to be reduced to about 4 inches.
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Nelco Inc. ,.•4
CTI #99 -G1138
Geotechnical Investigation
June 30, 1999
Slopes - All permanent cut and fill slopes should be graded to 1 vertical on 2 horizontal or flatter.
Flatter slopes may be necessary for ground cover and maintenance operations.
Foundation Design
Based on the field exploration program and our understanding of the proposed project, it is our
opinion that the proposed structure can be satisfactorily supported on thickened edge type
spread footings founded on the reinforced soil mat as described previously in this report.
Footings as described above may be designed for an allowable bearing pressure of 2250 psf,
and may be increased to 3200 psf for seismic loading. The bearing pressure is based on an
allowable static settlement of 1 inch, maximum column loads of 50 kips, and maximum
continuous footing loads of 4 kips /If. The site coefficient may be assumed to be SE and the
Zone 3 factor of Z =0.3 is acceptable. A minimum base sliding coefficient of friction of 0.40 may
also be used. All perimeter footings should be founded at least 24 inches below exterior grade.
Settlement - For footings designed as described in the preceding paragraphs, we estimate a
maximum settlement of 1 inch or less. Differential settlement will be in the order of 50 percent to
75 percent of the maximum, considering a distance of 30 feet. Our settlement estimate
assumes that no disturbance to the foundation soils would be permitted during excavation and
construction.
Foundation Preparation - Each footing excavation should be evaluated by a qualified
Geotechnical Engineer to confirm suitable bearing conditions and to determine that all loose
materials, organics, unsuitable fill and softened subgrade, if present, have been removed. To
minimize the potential fo'r disturbance during excavations, we recommend that all excavations be
made with a smooth bGcket (no teeth) backhoe; and that a few inches of soil remain over the
geotextile, and be nominally compacted following excavation with a small vibratory plate
compactor. If the lift becomes saturated is should be removed by hand, and replaced with
granular material.
Floor Slab — A modulus of subgrade reaction of 250 psi /I may be assumed for slab design. All
floor slabs on grade, should be founded on a minimum 6 -inch layer of free - draining well - graded
sand and gravel or crushed rock with a maximum particle size less than 1.5 inches and
containing not more than 5 percent passing the No. 200 sieve (based on a wet sieve analysis).
The base aggregate should be compacted to a dry density of at least 98 percent of the standard
Proctor maximum dry density (ASTM D 698).
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