Reading and Understanding From Soil Test Report
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Description
Subsurface investigations: Subsoil conditions are examined using test borings, provided by soil engineer (geotechnical).
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Number of borings and location location of borings depends depends on building building type and site conditions. conditions.
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Typically for uniform soil conditions borings are spaced 1001!0" apart, for more detailed #or$, Typically #here soil footings are closely spaced and soil conditions are not even borings are spaced !0" apart.
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%arger open #arehouse type spaces, #here fe#er columns are present (long span) re&uired less boring samples.
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Borings must extend to firm Strata (go through unsuitable foundation soil) and then extend at least 20 feet more into bearable soil. %ocation of borings samples are indicated on engineer plan.
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'orings are not ta$en directly under proposed columns.
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'orings indicate depth, soil classification (according to the unified soil system), and moisture content and sometimes ground #ater level is sho#n as #ell. (h ysical properties particle si*e, moisture content, density).
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Soil report recommendation should be based on testing of materials obtained from on site borings and to include
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1.
'earing capacity of soil.
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oundation design recommendations.
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aving design recommendations.
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/ompaction of soil.
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%ateral strength (active, passive, and coefficient of friction).
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ermeability.
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rost depth.
Surface investigations: •
2igh 3ater Table.
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resence of trouble soils eat, soft cla y, loose silt, or fine #ater bearing sands.
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4oc$ close to the surface (re&uire blasting for excavations).
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5umps or ills.
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6vidence of slides or subsidence.
Factors Affecting Selection of Foundation are: 1. Loads from Building:
The first factor considered is loads from building on the foundation. This load is a combination of dead load and imposed loads on the buildings. 7ther loads such as #ind loads, earth&ua$e loads, sno# loads etc. are also considered based on location.
The &uantity of loads depends on the type of structure, number of floors and material of construction. 8s the number of floors increases, the dead load and imposed loads also increase. /hoice of material for construction such as reinforced concrete or steel construction also has impacts on foundation. 4einforced concrete buildings exert more loads on the foundation compared to steel structures. 'ased on the safe bearing capacity of structure and &uantity of loads on foundation, type of foundation and its base area is calculated. 2. T!e of Soils:
Soil is a mixture of solid particles, moisture and air. Soil can be of many t ypes such as clayey soil or expansive soil, sandy soil or loose soils etc. The soil near surface is called as top soil and belo# a depth of -00mm is called as sub soil. 9enerally subsoil is used as base for foundation for small buildings.
2o#ever, soil investigation should be carried out to $no# the nature of soil, depth of #ater table, t ype of soil, depth of different layers of soil and to $no# the bearing capacity of soil at different levels for large structures. 3hen the load is transferred from the structure to soil through foundations, the soil tends to consolidate and settlement of foundation occurs. This consolidation process can be &uic$ in case of noncohesive soils such as sands and can even ta$e years for other soils. The complete settlement of foundation in sandy soil may occur even before the building construction has been completed. /layey soil can hold the #ater for longer time and thus settlement is very slo# and can ta$e years. Soil clayey holds large amount of #ater, and thus settlement of foundation is large in such soils. The settlement of foundation causes crac$s in building #alls, beams, slabs etc. and building can even fail in case of large settlement.
The soil investigation is necessary #hen the loads from the building are large and the bearing capacity cannot be estimated based on type of soil condition at site.
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The soil investigation should be carried out for follo"ing information: The nature and thic$ness of madeup ground:top soil above the subsoil
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The nature, thic$ness and stratum depth of subsoil
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8n assessment of allo#able bearing pressure
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9round#ater levels, chemicals in the ground, etc.
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6xisting structures or ha*ards in the ground.
#. T!e of Structure in $eighborhood:
The selection of foundation for building construction can also be done based on the t ype of foundation selected for the buildings in the neighboring buildings for the same types. Based on the success or failure of foundations for such buildings, decision can be ta$en for the selection of foundation. %. T!es of Foundations:
Types of foundation such as isolated foundations, combined footings, pile foundations and raft or mat foundations etc. based on the type of soils and loads from the buildings can be selected based on suitability and re&uirement.
T&'($)*+&S +S&, F- )/-)$ B&A)$ 'AA')T3 -F S-)L The follo#ing techni&ues can be used for improving bearing capacity of soil as per the site condition.
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;ncreasing depth of foundation
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5raining the soil
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/ompacting the soil
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/onfining the soil
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4eplacing the poor soil
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