Soil Investigation is carried out for designing a right type of foundation safely and economically, a designer must possess sufficient information about the physical properties and the arrangement of underlying materials. The field and laboratory investigations required to get this essential information is known as soil exploration. The study of complete soil investigations can be grouped under the following heads,
- Objectives or purposes,
- Preliminary investigations,
- Methods of site exploration,
- Depth and spacing of trial pits and borings,
- Choice of a method,
- Recording of data.
- Soil tests be conducted on samples that are truly representative of the soil at the site.
- Soil sampling, testing and test interpretation must be conducted under the guidance of specially trained an experienced personnel.
- Proper soil testing has proved to be a reliable basis for the design of foundations and has permitted the purpose of this Digest to describe engineering soil tests commonly used in site investigations and to indicate their potential use and limitations.
- Based on the premise that the behaviour of soil masses under imposed conditions can be predicted if certain soil properties can be measured.
- The results of soil tests must be interpreted in the light of past experience, climate, and the geology of the site.
- Most important requirements is that design of many notable structures on difficult sites.
TYPES OF SOIL TEST
- IN-SITU TESTING
- TRIAL PITTING
- DYNAMICS PROBE TEST
In-situ testing techniques including Standard Penetration Testing, Permeability Testing, Borehole Vane Testing, Pressure meter Testing and Packer Testing can all be carried out in the boreholes in order to provide information for geotechnical design. Disturbed and undisturbed samples are retrieved from the boreholes for inspection and logging by engineers and subsequent testing in our laboratories.
Trial pitting can be carried out by a variety of methods from hand dug pits to machine excavated trenches. Trial pitting is generally carried out to a maximum depth of 4.5m with standard excavation plant and, depending on soil conditions, is generally suitable for most low rise developments. All trial pit investigations are supervised by experienced engineers with a thorough understanding of geology and soil mechanics.
DYNAMICS PROBE TEST
Cone Penetration Test
To carried out the cone penetration test is pushed into a soil deposit while various measured parameters are recorded. The test is similar to the Dutch Deep sounding (or piezocone test) with the addition of a cone penetration element in the probe to measure water pressure. The test is also known as pore pressure sounding or CPTU.
Mackintosh/JKR Probe Test
This is a dynamic penetrometer test used to check the consistency of the subsoil. Mackintosh Probe which has 30° cone penetrometer while JKR Probes has 60° cone penetrometer. This is a light dynamic test and the cone is driven directly into the soil by driving a hammer 5 kg. Weight dropping through a free height of 280mm. The probe is unable to penetrate into medium strength soil and gravelly ground.
A borehole is used to determine the nature of the ground (usually below 6m depth) in a qualitative manner and then recover undisturbed samples for quantitative examination. Where this is not possible, for in gravelly soils below the water table, in-situ testing methods are used. Obviously the information gained from a borehole is an extremely limited picture of the subsurface structure. It is there fore essential to compare the results obtained with those that could have been expected from the desk study. the greater number of boreholes the more certain it is possible to be of the correlation and thus to trust in the results.
A large (4m x 4m x 7m high) percussion rig that drives a cutting or collecting instrument (dependent on ground conditions) into the ground, to collect soil that is then removed and sampled. This can be a slow technique however the advantage is that the hole can be cased to prevent collapse in loose soil layers, allowing easy installation of groundwater sampling pipework. It is highly adaptable to, and designed for, geotechnical testing.
LABORATORY TEST FOR SOIL
The Atterberg limits define the boundaries of several states of consistency for plastic soils. The boundaries are defined by the amount of water a soil needs to be at one of those boundaries. The boundaries are called the plastic limit and the liquid limit, and the difference between them is called the plasticity index. The shrinkage limit is also a part of the Atterberg limits.
This test provides the water content of the soil, normally expressed as a percentage of the weight of water to the dry weight of the soil.