Content
Slide 34
Subsidence Site Investigations
Investigations are carried out to check:
The Foundation
Soil make up and condition
This is done by digging trial pits to expose the foundation and taking the measurements of the foundation and material and Auger under the foundation and taking samples of the soil and any roots.
Soil samples are then sent to the Laboratory to have required tests carried out.
Typical lab tests
Atterburg Limits – The plasticity of the soil
Moisture Content – The level of soil desiccation
Oedometer – Performed by applying different loads to a soil sample and measuring the deformation response.
Soil Suction - The affinity of soil to retain water and can provide information on soil parameters that are influenced by the soil water
Tree Roots –Identifying the type of tree
Swell Strain - Evaluation of swell behavior of expansive Clays
Slide 35
Drain Survey – CCTV survey of the drainage system within the zone of influence to check if any damage that could cause leaks that could be influencing the soil including water testing
On Site Investigation and Testing
Slide 36
Trial Hole and Borehole
- A Trial Hole is the excavation to get the foundation details.
- A Borehole is the Auger hole used to recover soil and root samples.
Trial Hole
Borehole
Trial Hole
Borehole
Slide 37
Water testing of drain
Slide 38
Watermain Test
- To check if a supply pipe is leaking, turn off the internal stop tap so that no water reaches the taps or inside pipes.
- Check the meter.
- If it is still spinning, then there is a leak between the external and internal stop tap.
If the results of the Th/Bh show the ground to be more, moist than it should be and it is not a drain, check where the water supply pipe runs and if in the area of concern check the water supply pipe. If water is running into Trial hole and there is no meter, turn external stop tap off and see if that slows the water down.
Slide 39
Shear Vane
Vane shear test is used to determine the undrained shear strength of soils especially soft clays. This test can be done in laboratory or in the field directly on the ground. The result of the test is put on the Borehole Log.
Slide 40
Shear Vane
Trainer note: Vane shear test is used to determine the undrained shear strength of soils especially soft clays. This test can be done in laboratory or in the field directly on the ground. The result of the test is put on the Borehole Log.
Dial Gauge Pocket Penetrometer and/or Hand Shear Vane measurements of shear strength at regular (0.25 m) depth intervals, including a graph of the results plotted against depth.
Slide 41
Pocket Penetrometer
A penetrometer is a tool used to test the compaction level and tilth of your soil. Penetrometers measure the resistance of the soil in Pounds Per Square Inch (PSI) giving an indication of how compacted your soils are as an indication of the soil quality.
It is a small handheld gauge which contains a telescoping rod which can be pushed into the soil. The distance the rod goes into the soil corresponds to a compressive strength on the dial.
Slide 42
Mackintosh Probe
- Mackintosh probe is a lightweight portable penetrometer that is designed to be a tool to investigate the soil bearing capacity.
- It is standard practice to count the number of blows for every 75mm
Slide 43
Hand Auger
A hand auger is a tool used to obtaining soil and root samples
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Site Investigation Instruction Sheet
Policy Holders name and Risk address details
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Site Investigation Instruction Sheet
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Site Investigation Instruction Sheet
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Site Investigation Instruction Sheet
Slide 48
Site Investigation Instruction Sheet
Site Plan
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Subsidence Investigation
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Soil Description
There are many types of tests. You can check how many tests have been done by counting the results
Slide 53
Soil Suction and Plasticity Charts
Slide 54
Plasticity Chart For Soil Mechanics
Slide 55
The main soil types are designated by capital letters:
G Gravel M Silt, M-soil
S Sand C Clay
F Fine soil, Fines Pt Peat
The classification 'F' is intended for use when there is difficulty in determining whether a soil is a silt or a clay.
Originally all soils that plotted below the A-line of the plasticity charts were classified as silts. The term 'M-soil' has been introduced to classify soils that plot below the A-line but have particle size distributions not wholly in the range of silt sizes.
Behind the letter designating the main soil type additional letters are added to further describe the soil and to denote its grading and plasticity. These letters are:
W Well graded L Low plasticity (wL<35%) P Poorly graded I Intermediate (35<wL<70) Pu Uniform H High plasticity (50 < wL < 70)
O Organic E Extremely high (wL>90%)
The letter O is applied at the end of the group symbol for a soil, no matter what type, if the soil has a significant amount of organic matter within it. Examples of the use of the symbols are set out below.
Main Soil Type
Slide 56
Many properties of clays and silts (the cohesive soils) such as their compressibility* can be correlated with the liquid limit and the plasticity index. This correlation has been expressed in Casagrande's plasticity chart for fine-grained soils. It is based on the following observations:
As the liquid limit of soils increases, the plasticity and compressibility of soils also increase;
The values LL = 30 percent and LL = 50 percent differentiate between the various degrees of plasticity of inorganic soils;
At equal LL values, the dry strength of inorganic soils increases generally with an increasing plasticity index.
The plasticity chart for fine-grained soils is divided into six sections by the oblique line A drawn so that the PI = 0.73 (LL - 20) and two vertical lines drawn at LL = 30 percent and LL = 50 percent.
Each section of the chart characterizes a group of soils with well-defined mechanical characteristics. The three sections above line A are inorganic clays of low, medium or high plasticity. The three sections below line A are inorganic silts of varying compressibility, organic silts and organic clays. These form the basis of a useful soil classification system.
Note: soils with a plasticity index lower than 10 percent and a liquid limit lower than 20 percent are cohesionless soils. These appear in a separate section of the plasticity chart and the above considerations do not apply.
The plasticity chart for fine-grained soils
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Plasticity Chart For Soil Mechanics
Slide 58
The Atterberg limits are a basic measure of the critical water contents of a fine-grained soil: its shrinkage limit, plastic limit, and liquid limit. ... Thus, the boundary between each state can be defined based on a change in the soil's behavior.
The consistency of a soil sample changes with the amount of water present. Such changes in soil consistency may be accurately measured in the laboratory following standard procedures which determine the Atterberg Limits. These limits may then be used for judging the suitability of the soil
The liquid limit (LL)
The percentage moisture content at which a soil changes with decreasing wetness from the liquid to the plastic consistency or with increasing wetness from the plastic to the liquid consistency.
The plastic limit (PL)
The percentage moisture content at which a soil changes with decreasing wetness from the plastic to the semi- solid consistency or with increasing wetness from the semi-solid to the plastic consistency.
Atterberg Test
Slide 81
There are many types of test however the basic ones are below. You can check how many tests have been done by counting the results. Below shows 7 moisture and 5 Atterberg
Slide 83
The soil sample lab test file requires naming ready to send. Example of file name: Catalyst Claims Soil Report – Smith -101010 – JJ6 1SQ
Costing of what tests have been carried out requires noting for costings on the report. The soil testing sheet from the contractor requires checking for what samples have been taken and checking with what SE requested then checking with what the lab tested.
Soil description in lab report
