Criteria for Selection and Design of Residential Slabs-on-Ground (1968) / Chapter Skim
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Part C: Soils
Part C: Soils
Pages 136-144
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From page 136... ...
Some justification for this attitude is that many soils can, in fact, be used as a base for slab construction with little or no modification; others, however, must be handled with extreme caution, and many will require competent engineering analysis. The importance attached to soil in the design of residential slabs needs to be understood.
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From page 137... ...
Site preparation is discussed, and a scale of suggested compaction densities based on climatic rating and soil plasticity index is provided.
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From page 138... ...
The procedures outlined in the Unified Soil Classification System are sufficient for the field identification of most soils; for complete classification, there must be information regarding natural moisture content, density, and consistency. If there is still any question as to soil type, more extensive and exacting tests should be conducted by a soils laboratory.
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From page 139... ...
There is a wide variation in the physical properties of soils even for almost identical grain-size curves, and neither grain size nor plasticity index alone can be fully relied upon to define expansive or compressible soils. Yet, the potential for volume change in a soil due to fluctuations in the moisture content is usually associated with the clay fraction and is indicated by PI.
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From page 140... ...
Since the loads associated with residential construction are not sufficient to control expansion by loading, extreme care must be exercised in placing slabs on highly plastic soils. (Although there is not yet full substantiation for this view, it is believed that removal of the highly plastic soils and replacement with a coarse granular mat may equalize settlement; it is further believed that this practice would result in maintenance of more stable moisture content in the soil beneath, reducing the possibility of expansion and the consequent generation of excessive pressures.)
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From page 141... ...
Its use could not normally be justified for investigation of a site for a one- or two-family residence, where the test holes usually need to be only 15 feet deep, but for larger residential developments it would be justified. The resistance to penetration varies somewhat with the grain size of We cohesionless material and depends upon whether the soil lies above or below the water table.
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From page 142... ...
The number of blows causing the splitbarrel sampler to penetrate to a depth of one foot is recorded; the sampler ::'nd driving apparatus must be in accordance with specifications. TABLE VII Consistency of Undisturbed Clay Soils Undisturbed qu Consistency (ts01 Rule-of-thumb Test Very soft 0.25 Core~eight = twice diameter)
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From page 143... ...
By their very nature, these soils possess excellent bearing capacity, since they are not subject to volume change. The only consideration required is that of ensuring that the natural confinement of the soil is not disturbed by trenching or grading operations.
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