site_investigation notes for be civil 6th sem

Site investigation notes

1. Site Investigation/Subsurface Exploration

2. Soil Exploration A detailed enquiry or systematic of the subsurface profile up to a depth based on the structure to be founded on the ground .

3. Purpose of the soil explorations Evaluate general suitability of site for proposed project Enable an adequate and economical design Make provision for difficulties that may arise during and after construction due to ground conditions. Determine potential problems and Avoid Surprises

4. Information required from soil explorations Select type and depth of foundation Evaluate load bearing capacity of foundation Estimate probable settlement Determine potential foundation problems Predicting lateral earth pressure for retaining structures Establishing construction methods for changing subsoil conditions Determine location of water table Areal extent and thickness of each layer Depth to bedrock Engineering properties of soil

5. Stages of Sub-surface Investigation Reconnaissance Preliminary Exploration Detailed Exploration

6. Reconnaissance Includes a visit to the site and to study maps and other relevant records Information obtained in reconnaissance General topography of the site Existence of drainage ditches and dumps of debris and sanitary fills Evidence of landslide and creep of slopes Stratification of soils as observed from deep cuts near the site

7. Reconnaissance The location of high flood marks (on nearby building and bridges) Depth of groundwater watertable (as observed in well) Types of vegetation existing at the site Drainage pattern existing at site

8. Preliminary Exploration To determine the depth, thickness and composite of each soil layer at site To determine the depth of bed rock and ground water table Soil sample is collected from boring and shallow test pits Simple laboratory tests are conducted (moisture content ,density etc )

9. Detailed Exploration To determine the engineering properties of the soil at different strata Includes extensive boring ,sampling and testing of sample in laboratory Field tests are conducted to determine the properties of soils in different strata (vane shear test, plate load test and permeability test)

10. Methods of S oil Exploration/Site Investigation Open excavation Boring Subsurface sounding Geographical methods

11. Open excavation Open excavation is made to inspects the subsoil strata Two methods Pits and Trenches Drifts and shafts

12. Boring Soil samples can be lifted from deeper depths by deilling bore holes by using mechanical devices called samplers The process consists of Drilling a hole and visually examining the cutting coming out from the different depths Lifting the soil samplers from different depths by using samplers

13. Methods of Boring Auger Boring Rotary Boring Wash Boring Percussion Boring

14. They are useful for subsurface investigations where the depth of exploration is small Eg : highway,railways The main disvantage is that the soil samples are highly disturbed.

15. The soil sample is highly disturbed The change in soil strata while boring is indicated by the change in colour of the soil-water suspension Disadvantages It is slow in stiff soils and coarse soils It cannot be used efficiently in hard soils, rocks and soils containing boulders It is not suitable for taking good quality undisturbed samples above ground water table

16. This method is not well adopted for use in materials containing a large percentage of particles of gravel size and larger

17. Percussion drilling It is used for making holes in rocks,boulders and other hard strata (all types of soils) A heavy chisel is alternately lifted and dropped in a vertical hole,the material gets pulverized The water is added which forms slurry with the pulverized material which is removed by a sand pumps at intervals Main disadvantages is that soil is heavily disturbed.

18. Soil Sampling Soil sampling is the process of obtaining samples of soil from the desired depth at the desired location in a natural soil deposit in order to assess the engineering properties of the soil. There are two types of soil samples Disturbed sample Undisturbed sample