Soil Investigation

The element of a site investigation depend heavily on the project but generally should provide the following :

1. Information to determine the type of foundation required (shallow or deep)
2. Information to allow the geotechnical consultant to make a recommendation on the allowable load capacity of the foundation.
3. Sufficient data/laboratory tests to make settlement predictions.
4. Location of the groundwater table. For certain projects, groundwater table fluctuations may be required. These can require installation of piezometers and monitoring of the water level in them over a period of time.
5. Information so that the identification and solution of construction problems (sheeting and dewatering or rock excavation) can be made.
6. Identification of potential problems (settlements, existing damage, etc) concerning adjacent property.
7. Identification of environmental problems and their solution.

METHOD OF EXPLORATION.

A. DISTURB SAMPLES TAKEN

1. Auger Boring
Depth : Depends on equipment and time available, practical depths being up to about 35 m.
Applicability : All soils.

2. Rotary drilling, wash boring, percussion drilling.
Depth : Depends on equipment, most equipment can drill to depths of 70 m or more.
Applicability : All soils.

3. Test pits and open cuts.
Depth : As required, usually less than 6 m, use power equipment.

B. UNDISTURB SAMPLES TAKEN.

1. Auger drilling, rotary drilling, percussion drilling, wash boring.
Depth : depends on equipment, as for disturbed sample recovery
Applicability : thin-walled tube samples and various piston samplers are used to recover
samples from holes advanced by these methods. Commonly, samples of 50-
to-100 mm diameter can be recovered.

2. Test pits.
Depth : Same as for disturbed samples
Applicabilty : hand-trimmed samples. Careful trimming of sample should yield the least
sample disturbance of any method.


(taken from Joseph E. Bowles, Ch.3)

Clay Mineral & Soil Consistency

Clay Mineralogy

• Crystalline structure of clay minerals
• Important due to water movement and management considerations

Soil Consistence

• Field method to relate another soil property to clay mineralogy

Building Blocks of Clay

• Silica-tetrahedron-four sides, four oxygen molecules and one Silica (Si)
• Alumunium Octahedron-eight sides. six oxygen molecules and one Aluminum.

Definitions

• Silica tetrahedral sheet : a single-thickness plane of joined silica tetrahedra. The Silica tetrahedra are joined together by shared oxygen atoms.
• Aluminum octahedral sheet : a single-thickness plane of joined aluminum octahedra. The aluminum octahedra are joined together by shared oxygen atoms.
• Layer : combination of sheets, e.g.1:1 or 2 : 1

1 : 1 Clay Mineral :

• Like an open face sandwich
• A silica tetrahedral sheet (bread) joined to an aluminum octahedral sheet (filling). These sheets are joined by shared oxygen atoms.
• The most common 1:1 clay mineral is kaolinite.
• Layers are held together strongly by hydrogen bonding.
• Water will cause much expansion (swelling) beetween the layers.

Hydrogen Bonding

2 : 1 Clay Minerals :

• Like a sandwich with two slices of bread
• A silica tetrahedral sheet (bread) joined to an aluminum octahedral sheet (filling) joined to a silica tetrahedral sheet (bread). These sheets are joined by shared oxygen atoms.
• The 2:1 clays can be broken into 2 groups
  
• Non-expansive
• Expansive