Soil Investigation
Soil Investigation
It is necessary for a structural designer to know the physical properties and the arrangement of the underlying soils for selecting and prepare the design of foundation safer, economically. In order to determine the physical properties several field and laboratory tests are done to get the required information. This process is termed as soil investigation.
The soil investigation study are as follows,
1. Objectives or Purpose of soil investigation
2. Preliminary Investigations
3. Methods of site exploration
4. Depth and spacing of trial pits and borings
5. Choice of a method
6. Recording of data - Interpretation of results
1. Objectives or Purpose of soil investigation:
The main objectives of soil investigation are,
* To study the nature of soil its strata variation, and the depth,
* Obtaining the soil samples for determining its properties which will be useful in designing and selecting the right type of foundation,
* The change in ground water table and its impact on existing soil strata,
* To collect the approx. values of compressibility of soil strata,
* The extent of depth of rocks.
2. Preliminary Soil Investigation:
The following preliminary soil investigation are taken at the site. The data can be obtained from the people living in the locality, or from engineers or from the records of test pits or bore holes. Also, it can be obtained from the character of the existing buildings.
Some of the preliminary soil investigation are summarized below,
* The condition of soil at various depths,
* Depth of the underlying rocks,
* Depth of water table at its variations,
* Topographical features like slope of ground, valley, hill station should also taken in to account.
3. Methods of site exploration:
Some of the most common methods used for soil investigation are,
* Probing
- Auger boring
- Shell and auger boring
- Wash boring
- Percussion boring
- Rotary boring
* Geo-physical method of soil exploration.
4. Depth and spacing of trial pits and bore holes:
The depth and spacing of trial pits and bore holes are discussed here in brief.
5. Choice of a method:
The choice of a method mainly depend on these factors,
* Nature of the ground: The borings are suitable for deep exploration especially in clay soils. Test pits can be adopted for shallow exploration. In sandy soils, special boring equipments should be used to take samples below water table. In case of rocks, core borings are used in hard rocks and pits can be dugged in case of soft rocks. However in borings, we cannot able to study the joints and fissures of rocks. But in test pits, we can able to examine it.
* Topography: The topography of ground also affects the choice of exploration. The steep inclined soil strata can be examined by headings, the horizontal strata can be examined by trial pits or bore holes.
* Cost of exploration: The cost factor is up to us. We can chose the best method depend upon the data required by us.
6. Recording of Data - Interpretation of Results:
A complete data sheet called boring log of each bore hole is needed. The details obtained should be entered at the site itself because any corrections found later cannot be easily accounted for and thereby the whole process is to be repeated.
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