Introduction From an engineering viewpoint, the ground beneath a site can conveniently be divided into the categories, based upon generalizations of its expected behaviour in construction works. Soil used to be rock, which was tuned into soil by weathering, chemical and mechanical forces. Nature recycles the soil to rock, that this takes millions of years.
HORIZONS Surface horizon is usually referred to as the O layer. It consists of loose organic matter such as fallen leaves and other biomass. Below is the A horizon, containing a mixture organic mineral materials and organics.
HORIZONS Next is E horizons, layer from which clays, iron and aluminum oxides have been lost by leaching process Below horizons E is B, which most of the iron, clays, and other leached materials have accumulated. After that is C horizons consisting of partially weather bedrock And last is R horizons of hard bedrock
SOILThree main size groups : Sand (0.05 to 2.00 mm) Silt (0.002 to 0.05 mm) Clay ( less than 0.002 mm
COLOR Soils come in a wide range of colors. Shades of brown, red, orange, yellow, gray and even blue or green. A dark color usually indicates the presence of organic matter.
TEXTURE A soil texture depends on its content of the three main mineral components of the soil, sand ,silt and clay. Very fine textured soils may be poorly drained. Medium texture and a relatively even proportion of all particle sizes are most versatile
AGGREGATION Individual soil particles tend to be bound together into lager units referred to as aggregates or soil peds. Aggregation occurs as a result of complex chemical forces acting an small soil components in soil act as glue binding particles together.
POROSITY Part of the soil that is not solid is made up pores of various sizes and shapes Porosity greatly affects water movement and gas exchange.
ION CONTENT Particularly the clay, hold groupings of atoms known as ions. These ions carry a negative charge. Like magnets, these negative ions (anions) attract positive ions (cations)
pH Another important chemical measured is soil pH. Refers to the soil acidity or alkalinity. A greater concentration of hydrogen results in a lower pH, meaning greater acidity
Soil InvestigationSpecifically related to the subsoilbeneath the site under investigationand could be part of or separate fromthe site investigationA well designed soil investigation canoften lead to project cost savings inthe long term by allowing contractorsto foresee potential problems.
Purpose 1. Determine the suitability of the site for the proposed project. 2. Determine an adequate and economic foundation design. 3. Determine the difficulties which may arise during the construction process and period. 4. Determine the occurrence and/or cause of all changes in subsoil conditions.
Soil Samples 1) Disturbed Soil Samples Soil samples obtained from boreholes and trial pits. The method of extraction disturbs the natural structure for visual grading, establishing the moisture content and some lab tests. Disturbed soil samples should be stored in labelled air tight jars.
Soil Samples 2) Undisturbed Soil Samples Soil samples obtained using coring tools which preserve the natural structure and properties of the subsoil. The extracted undisturbed soil samples are labelled and laid in wooden boxes for dispatch to a lab for test. This method of obtaining soil samples is suitable for rock and clay sub-soils but difficulties can be experienced in trying to obtain undisturbed soil samples in other types of subsoil.
Soil Investigation Methods Method chosen will depend on several factors: 1. Size of contract; 2. Type of proposed foundation; 3. Type of sample required; 4. Type of subsoils which may be encountered.
Soil Investigation Methods As a general guide the most suitable methods in terms of investigation depth are: 1. Foundations up to 3.000d – trial pits; 2. Foundations up to 30.000d – borings; 3. Foundations over 30.000d – deep boring and in-situ examination from tunnels and/or deep pits.
Types Of Investigation Generally the following soil investigation techniques are employed for the majority of projects: Trial Pitting Dynamic Probe Testing Cable Percussive Boreholes Rotary Drilled Boreholes
Trial Pitting 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.
Trial Pitting All trial pit investigations are supervised by experienced engineers with a thorough understanding of geology and soil mechanics.
Cable Percussive Boreholes Suitable for most projects, cable percussive boreholes are a common method of site investigation. Using a land rover towed rig or a specialist cut down rig suited to restricted access locations most sites can be investigated
Cable Percussive Boreholes In-situ testing techniques including Standard Penetration Testing, Permeability Testing, Borehole Vane Testing and Packer Testing can all be carried out in the boreholes in order to provide information for geotechnical design
Cable Percussive Boreholes Disturbed and undisturbed samples are retrieved from the boreholes for inspection and logging by engineers and subsequent testing in a laboratories.
Operation of cable percussion rig for working inareas of restricted access or with restrictedheadroom
Rotary Drilled Boreholes Rotary drilling techniques are employed where boreholes are required into very dense gravel or bedrock. Samples of bedrock are recovered in seamless plastic tubes for subsequent logging by a suitably qualified engineer and for laboratory testing
Rotary Drilled Boreholes Most of rotary coring work relies on the use of drilling rigs which can also obtain continuous samples of soils using dynamic sampling equipment. The rigs are suitable for limited access works.
Rotary Drilling Techniques On AJackup Platform
OTHER EXAMPLES….. Drilling in restricted areas…