SAMPLING

1.     Disturbed samples
These should be collected as drilling or digs proceed, where possible attempting to preserve the in situ water content; disturbed samples are mainly required for soil identification and for classification and quality test; or tin, or plastic bags

  

 

Split spoon sampler



 2.  Undisturbed samples
In which the structure and water content is preserved, as far as possible, to truly represent site conditions; undisturbed samples are required for test of shear strength, consolidation and permeability; these are usually obtained by a suitable coring method

3. ROCK CORING

When a rock layer is encountered during a drilling operation, rock coring may be necessary. To core rocks, a core barrel is attached to a drilling rod. A coring bit is attached to the bottom of the barrel (Figure  ). The cutting elements may be diamond, tungsten, carbide and so on. The coring is advanced by rotary drilling. Water is circulated through the drilling rod during coring, and the cutting is washed out.



GROUND EXPLORATION

 1. MACKINTOSH PROBE

The Mackintosh Probe Test is a simple and economic testing method to gather preliminary data on sub surface conditions. Such data maybe adequate for the designs of foundations for lightly loaded structures as this provides a very economic method of determining the thickness of soft deposits such as peat.

  



MACKONTOSH PROBE APPARATUS



2. HAND AUGER              

Used in soft to stiff cohesive soils or sandy soils above water table. Maximum depth is about 5m. Is particularly valuable in connection with ground-water determination

   

HAND AUGER

 

HAND AUGER

   

3. STANDARD PENETRATION TEST

Suitable for almost all soil types except very soft clay & coarse gravel. Disturb samples (35 mm diameter) are procured from the test for field. Identification/description of soil types and subsequent lab classification and index properties test. Is usually carried out at a change of strata or 1.5 m interval .

4. VANE SHEAR TEST

Very suitable for very soft to stiff clay to obtain Undrained Shear Strength of these soils. A four –blade is drive into the soil at the end of a rod and the   vane then  rotated at a constant rate between 6 and 12 deg./min until the cylinder of soil contained by the blades shear. The maximum torque required for this is recorded.

 

VANE SHEAR TEST

 

  



6 STAGES INVOLVED IN SITE INVESTIGATION

1. DESK STUDY

This is essentially the collection of a wide variety of information relating to the site. eg : maps, drawings,local authority information; geological maps, memoirs, records; details of utilities.

2.SITE RECONNAISSANCE

An early examination of the site by appropriate experts is most desirable eg. Geologist, land surveyor, soils engineer, hydrologist etc. Information should be collected on the overall site layout, topography, basic geology; details of access, entry and height restrictions. Local conditions should be examined, such as climate, stream flows, groundwater conditions, site utilisation related to weather and time of year. Where possible photographic records should be kept.

3.  SITE EXPLORATION & SAMPLING

Investigation of detailed geology and sub-surface soil conditions using surface surveys, trial pits, headings, boreholes, sounding, geophysical methods, as appropriate; survey of groundwater conditions over a signification period of time (Maybe even after completion of works); examination of existing and adjacent structures or cavities, buried pipes, services, etc.; provision of samples for further examination and laboratory testing.

4. FIELD TEST / INSITU TEST

Test carried out on the site either prior to or during the construction process; ground test such as shear-vane, standard penetration, cone penetration, plate bearing, pressure meter; structure loading test, such as test on piles, proof loading; displacement observation.

 5.  LABORATORY TESTING

Tests on disturbed and undisturbed samples submitted from the site team; test on soils (as specified) for classification, quality, permeability, shear strength, compressibility,etc.; test on rock cores and samples for strength and durability; test on constructional materials, such as California Bearing Ratio; test on groundwater, chemical and petro graphic analyses.

LABORATORY TESTING

6. REPORT WRITING

Details of geological study, including structures, stratigraphy andmapping; results of borings, etc., including log, references for samples and stratigraphy interpretations as requested; comments and recommendations relating to the design and construction of the proposed works; recommendations relating to further investigating ortesting, and to ongoing or post-completion monitoring.