Engineering Geology Flashcards
UofG Elective 2024
What is GI
Ground Investigation
What is “Soil”?
Unconsolidated ground
What is a desk study used for?
Historical development
Constraints on development - potential contamination? Source, Pathway, Receptors. Geotechnical constraints? Pollution?
GI strategy
Recommend appropriate GI if needed
What is a site walkover used for?
Observations on nature of the ground
Obvious contamination?
Identify basic information that may not be available online
On-site constraints to development
Take photos
Invasive species?
Name 2 common Invasive Species in UK
Japanese Knotweed
Giant Hogweed
Why are invasive species bad?
Very expensive to remove
Grows and spread fast
Mortgage problems
Can attack foundations/buildings
What is the DS: Historical Development stage?
Look through historical maps for development
What has the site been used for?
Previous land uses?
Land use in surrounding area (~1km???)
Pollution/contamination from surrounding areas
What is the DS: Geology stage?
Solid/bedrock and drift/superficial deposits
Borehole records (GeoIndex)
Type, Depth, Mineworkings/Coal seams
Mine abandonment plans (Coal Authority) (if deeper than 30m coal seams are normally irrelevant)
Hydrogeology/Hydrology - Aquifer quality, surface water (GeoIndex)
What is the DS: Environmental Assessment
Using Historical and Geology Data:
Preliminary Environmental Assessment (land use)
Potential contaminants
- Source, Pathway, and Receptors (end users)
- Metals, HCs, Solvents, Pesticides, Asbestos
- Environmental Legislation
What is a Qualitative Risk Assessment (RA)?
The likelihood of Occurrence
The Severity of Consequences
Is an Investigation Required?
What are some examples of Sources?
- Metals
- Semi-metals and non-metals
- Oil and fuel HCs
- Polyaromatic HCs
- Solvents
- Phenols
- Pesticides
- Detergents
- Asbestos
- Ground gas
What are some examples of Receptors?
- Humans (residents, workers) and animals
- Plants in gardens, landscaped areas
- Buildings, property and services
- Controlled waters (surface and groundwaters)
What are some examples of Pathways?
- Humans and animals
- Inhalation of dust
- Ingestion of dust/soil by hand or from plants grown in soil
- Dermal contact with soil/water
- Plants
- Direct contact with soil/groundwater
- Uptake of contaminants
- Buildings
- Direct contact with soil/groundwater
- Service trenches act as migration pathways
- Controlled Waters
- Run-off entering water courses
- Contaminants from soil leaching into groundwater
- Movement of dissolved contaminants in soil pore water
- Movement of contaminants via ground to surface water
What is the process of pollution linkages and Qualitative RA
Determine whether linkages can be completed
How they may be broken (to stop them happening)?
Likelihood
Severity
Investigation required?
What is clean cover?
Suitable cover put in place to prevent attack/corrosion from environmental issues
What is the DS: Engineering Assessment stage?
Geotechnical constraints
Made Ground
-Variable engineering properties
- Uncompacted, randomly placed
- Large obstructions
- Not compact, not strong, has variable grain sizes (bad for construction)
Natural Soils
- Bearing capacity of soils to be determined
- Piled foundations may be required
Mineral Stability
- Presence of worked coal seams?
- Grouting? (injecting concrete in to void under ground) - affects placement of piles (if required)
Slope Stability
- Unstable slopes?
- Re-grading of slopes?
- Revision of development plans?
How do you deal with made ground?
The use of piles
Vibro-compaction
Bypass the made ground in some cases and bury foundation below it
What does the GI test?
Depth and nature of superficial deposits
Extent and nature of made ground
Nature of bedrock
Extent and condition of mineworkings
Groundwater regime
Extent and type of any contamination present
Presence of ground gas
What are types of GI testing?
Moisture content
Grading analysis
Atterberg limits
pH/sulphates
Undrained triaxial shear strength
Unconfined compressive strength
Chemical testing
- Soil
- Leachate
- Groundwater
Gas Monitoring (CH4, CO2, O2, H2S, LEL…)
What are the GI practices
Preparation
Trial pits
Soils drilling
In-situ tests and sampling
Rotary drilling
Installations
Reinstatement
What is the Preparation Stage in GI
Check for buried services
Inspection pins
Overhead obstructions
What are trial pits
Dug by back-hoe excavator
Up to 4-5m
Unsupported pits >1.2m depth (no entry unless supported)
Create visual log of strata as being dug
Take disturbed samples
What should be recorded while trial pitting
Thickness and description of each stratum
Depth of each change of stratum
Depth and position of each sample
Depth and position of each test
Dates of excavation and logging
Equipment details
Groundwater conditions
Record of ease of excavation
Record of pit stability
Weather conditions
Details of any installations
Methods of backfilling
Sketch plan
Photographs
How are trial pits reinstated
Filled and compacted by excavator
Topsoil and turf carefully replaced
Remedial work
If left open = covered and fenced off
What is Cable Percussion Drilling (CP) (aka shell and auger or Light Percussion)
Slow, but simple and cheap
Collapsible ‘A’ frame, with pulley
Diesel engine connected to winch drum
Winch lifts tool, suspended on cable
Release clutch, tool drops
Sunk by repeated dropping
What is Clay Cutter (CP)
- Heavy steel tube
- Elliptical slot
- Weight added by sinker bar
- After several blows, brought to surface
- Clay removed with press-out tool
What is Shell (CP)
- Granular materials
- Surged in water at bottom of hole
- Disturbs material = goes in suspension
- Enters shell on downstroke
- Non-return (clack) valve closes on upstroke
- Retains soil
What is Chisel (CP)
- For breaking through obstructions (cobbles and boulders)
- Slow and expensive
How do Undisturbed CP samples work?
U100 open-tube sampler
100mm diameter
Plastic liner
What do Undisturbed CP samples show
Changes in stratum
Regular intervals
Used of geotech tests
What are included in CP Logs
Daily drillers logs (basic)
Record samples numbers and types
Record in-situ tests
Continue to set depth or rockhead
Geologist uses samples back in lab
Logged to BS
Types of Sampling
Undisturbed (U)
- Taken for lab tests
Disturbed (D)
- Sealed plastic tubs
- Suitable for moisture content, index tests
Bulk disturbed (B)
- Unsealed plastic bags
- Classification tests
How do you sample a borehole
U100 or SPT
- 0.5m, 1m, every metre to 5m, then every 1.5m
Small D
- Topsoil and each change in soil type/consistency
- Halfway between U100/SPT samples
B
- Each soil type
Chemical Jar (CJ)
- Depends on budget
How do you sample Trial Pits
B samples every 1m (at least 1 per soil type)
Soil D samples
- Topsoil
- Each change in soil type
- Midway between BD samples
Chemical Jar samples
What is In-situ testing
Standard Penetration Test (SPT)
- Determination of soil resistance
- “Split spoon sampler” or “split barrel”
Dropping a hammer of 67.5kg onto an anvil/drive head from 750mm
- Number of blows to penetrate 450mm into soil
How do you describe soils?
Decide principal soil type (i.e. “gravel”)
Describe secondary and minor fractions
Describe other features (i.e. bedding, colour, particle shape)
What does SPT measure
Consistency of soil
What are the Mass Characteristics when describing soils?
Density/Consistency
Discontinuities
Bedding
What are the Material characteristics when describing soils?
Colour
Composite soil types (i.e. grading, composition, shape, size)
Principal soil types (in capitals, based on grading and plasticity shape)
How do you describe the stratum name
Formation
Age
Type
Classification
How do you distinguish silt from clay?
Dry Strength
- CLAY will not crumble when rolled into moist thread/ribbon, SILT will
Dilatancy
- Wet sample and pat for 5-10s
- If water rises to surface (it shines) = SILT
What is Rotary Drilling?
Cuts through solid rock to extract core
“Follows on” from soil drilling
What is Rotary “Open holing”?
Through soils
Highly disturbed
No sampling
What equipment is used for rotary drilling?
Drill rod
Diamond/tungsten carbide drilling bit
Soil/Rock cuttings removed by circulating fluid (water, air, mist, foam)
Are the cores from Rotary drills good quality?
The core is variable in quality and amount
Due to drilling, discontinuities
Geology means could be weaker, therefore, break
Who reports and describes these cores?
Typically the contractor
How are rock descriptions carried out for core?
Material Characteristics
- Strength, structure, colour, texture, grain size, rock name (IN CAPITALS)
General Information
- Additional info and minor constituents, geological info
Mass characteristics
- State of weathering, fracture state, discontinuities
How is rock strength measured (estimation)?
Field index test - hit with hammer (strong if can withhold), indented with fingernail (extremely weak)
Back up later with geotechnical test
How is rock structure described?
Bedding
Foliation
Flow-banding
How is rock mass characteristics described?
Description of weathering profile
Description of discontinuities (or sets)
Evaluation of fracture state
What are Discontinuities (DC)?
Joints (DC with no visible displacement)
Faults (with displacement)
Bedding fractures
Cleavage fractures
Induced fractures (non-geological)
Incipient fracture (may be cement or something (not open fracture))
How do you describe the fracture state of core?
Total Core Recovery (TCR) - % of core recovered, to length of core run
Solid Core Recovery (SCR) - % of solid core recovered to length of core run
Rock Quality Designation (RQD) - % of solid core pieces longer than 100mm to length of core run
Fracture index (FI) - Number of fractures per metre
Fracture Spacing (If, mm) - space between fracture (reported as minimum, means, maximum)
What are groundwater installations?
Ingress measured during sinking of borehole
Time for rise and fall (recharge?)
Monitoring = standpipe piezometer
What are gas installations?
Standpipe installed
Gas valve at surface or borehole
How is reinstatement of boreholes done?
Hole backfilled - cement-bentonite grout, gravel
Sealed with a top cap
What does Laboratory testing tell us?
Geotechnical:
Classification, shear strength (total and effective), compressive strength, permeability, durability, chemical and elector-chemical, consolidation
Environmental:
Sulphate, pH, metals, solvents, HCs
What is included in an Interpretive Report (IR)?
Summary of BHs and Trial pits
Summary of materials
- Chemical properties
- Geotechnical properties
Engineering assessment
- Foundation design
- Mineral stability
- Slope stability
- Concrete
Environmental assessment
- Revised conceptual model
- Revised qualitative risk assessment
- Failure = Tier 2 Quantitative risk assessment
- Remedial measures
What is included in the IR: Environmental Assessment?
Chemical Data
- Assessment criteria
- Different criteria for different usage
- Soil (non-residential no plant uptake to residential with plant uptake)
What is leachate pollution
Where the contaminant leaches from source into surrounding area
Often most problematic
Difficult to break linkage
Failure = further assessment
Pollutant can be diluted
What is the dilution factor calculation?
Qc = (Qu/Qc)
Qu = water flow in surface water receptor (m^3/day)
Qc = contaminated groundwater flow from hte site (m^3/day)
Calculates site specific assessment criteria
Pass or fail
What are the main types of Remediation?
Dig and dump
- Removal of soil to landfill (but tax, transport costs and traffic)
Containment in situ
- Barriers around soil (impermeable)
Treatment
- Pump and treat (Intercept contamination, treat at surface re-inject)
- Permeable reactive barriers (removes or destroys contaminants)
- Soil vapour (Vacuum) extraction (vacuum applied to soil through BHs, induces airflow through unsaturated soil and removes contaminants)
- Soil washing (dissolving and/or separating suspending contaminants into wash water, chemicals used to improve)
- Solidification/Stabilisation
- Phytoremediation (use plant types to remove/transfer/stabilise)
- Bioremediation (natural micro-organisms degrade contaminants
- Invasive species treatment (spraying, disposal of plants to facility, deep burial on site)
What are the three types of shallow foundations?
Strip, Pile (pad/column), Raft (mats)
What are strip foundations?
Narrow (>1m), concrete footing that typical supports the walls
What are pad foundations?
Support columns, various types (stepped, plain, and sloping upper face reinforced concrete, and mass concrete for steel column)
What are raft foundations?
Spreads load, used for soft/loose soils, reinforced steel grid with pumped concrete
What are the two main types of pile foundations?
End bearing - terminate in hard stratum
Friction - capacity from end bearing and skin friction
What are the three main piling methods?
Displacement piles - soil displaced, concrete and steel used, typically driven
Driven piles - Drive a steel tube into the ground, forms a void, filled with concrete, tubes removed
Non-displacement piles - soil removed, filled with concrete, pre-cast piles, useful in made ground
What is bearing capacity?
Capacity of soil to support loads applied to ground
Ultimate bearing capacity - the max. pressure without failure
Allowable bearing capacity - FOS = 2-3
These is a “bulb of pressure” - pressure does not act straight down, it spreads out with depth
What are the two types of settlement - explain what they are?
Total
- Uniform settlement of the entire structure
- Weight of structure and imposed loads
Differential
- Loads on structure are unevenly distributes
- Variation in soil properties
- Construction related variations
