M2 CONCEPTS Flashcards
- Process of investigating the properties of the ground beneath the earth’s surface.
- Typically conducted before any construction project commences.
- Map the subsurface in order to give geotechnical recommendations
Subsurface Exploration Program
Different Methods of Mapping the Subsurface
- Non-destructive Methods
- Destructive Methods
Different Methods of Mapping the Subsurface
- Involves methods that do not require disturbing the ground
- Utilizes electrical resistivity, magnetic susceptibility, radar waves
- Measures physical properties of the subsurface (e.g., strength, density, moisture content)
Non-destructive Methods
Different Methods of Mapping the Subsurface
- Involves intrusive methods to obtain soil and rock samples
- Typically requires drilling, excavating, and taking large soil samples
- Obtains accurate and reliable information on soil and rock properties
Destructive Methods
Different Non-Destructive Methods
Advantages
* Quick
* Provides high-resolution images of subsurface stratigraphy
* Can be used to identify buried structures
* Portable
Disadvantages
* Depth limited to 20-30m depending on the soil type and frequency of the radar
* Challenges in the interpretation of data
* More expensive than other subsurface techniques
* Cannot inspect or sample soils
Ground Penetrating Radar or GPR
Different Non-Destructive Methods
Advantages
* Can penetrate deeper into ground than some other geophysical methods
* Can be performed in soil, rock, and ice
* Provides quantitative information on soil and rock (density and elastic modulus)
* Can be used to map large areas
Disadvantages
* More expensive to perform than other geophysical methods
* Noise and disturbance
* Limited resolution
* Challenges in the interpretation of data
Seismic Survey – Reflection and Refraction
Different Non-Destructive Methods
Advantages
* Rapid data collection
* Can be used in soil, rock, and ice
* Provides high resolution images of subsurface and subsurface structures
Disadvantages
* Limited to a few meters of depth
* Signal interferences
* Limited accuracy
* Challenges in data interpretation
Electromagnetic Survey
Different Destructive Methods
Advantages
* Cost effective
* Provide detailed information of stratigraphy
* Large quantities of disturbed soils are available for testing
* Large blocks of samples cam ne carved out from the pits
* Field tests can be conducted at the bottom of the pit
Disadvantages
* Depth limited to 6m in stiff clays
* Deep pits are uneconomical
* Excavation below groundwater and into rock is difficult and costly
* Too many pits may scar the site and require backfilling
* Time consuming
Test Pit
Different Destructive Methods
Advantages
* Cost effective
* Not dependent on the terrain
* Portable
* Low headroom is required
* Used in encased holes
* Groundwater location can easily be identified
Disadvantages
* Depth limited to about 3m
* Labor intensive
* Undisturbed samples can be taken only for soft clay deposits
* Cannot be used in rock, stiff clays, and dry sand
Hand Auger
Different Destructive Methods
Advantages
* Quick
* Used in encased boreholes
* “Undisturbed” samples can be obtained easily
* Groundwater location can be identified
Disadvantages
* Depth limited to 15m
* Site must be accessible to motorized vehicles
Power Auger
Different Destructive Methods
Advantages
* Can be used in difficult terrain
* Low equipment cost
* Used in encased holes
Disadvantages
* Depth limited to 30m
* Slow drilling through stiff clays and gravels
* Difficulty in obtaining the accurate location of groundwater
* Undisturbed soil sample cannot be obtained
Wash Boring
Different Destructive Methods
Advantages
* Quick
* Drill through any type of soil and rock
* Deeper drilling reach
* Undisturbed soil samples can be easily recovered
Disadvantages
* Expensive equipment
* Terrain must be accessible to a motorized vehicle
* Difficulty in obtaining the location of the groundwater level
* Additional time required for setup and cleanup
Rotary Drills
TRUE OR FALSE
Borings should be located near heavily loaded parts
TRUE
FILL IN THE BLANK/S
Borings should be located not more than a radius of [measurement] from the center of the load
5 meters
Minimum distance between boring locations
For Vertical Structures
Minimum required number of borholes for 50 < A <= 500 m^2
2
For Vertical Structures
Minimum required number of borholes for A >= 500 m^2
2 + (A/1000)
For Vertical Structures
General minimum depth of boreholes
at least 5 meters into hard strata
For Vertiical Structures
Minimum depth of boreholes to be used with buildings having basements
Depth of Basement + Twice the least dimension of structure footprint (H + 2B)
For Horizontal Structures
Minimum number of boreholes for Retaining Walls
at least 1 for each retaining wall
For compressible soils
Minimum Depth of borehole
1 to 3 times the width of the proposed foundation
For very stiff clays and dense coarse-grained soils
Minimum Depth of borehole
should penetrate 5 to 6 meters
May be used during drilling operations to determine the in-situ undrained shear strength (cu) of clay soils – particularly of soft soils
Vane Shear Test
For Vane Shear Test
Standard rate of torque applied at the top of the rod to rotate the vanes
0.1 deg/sec (6 deg/min)
Maximum Torque applied to cause failure is measured
Geotechnical In-Situ Tests
- Originally known as Dutch cone penetration test and is also called static penetration test
- It is a versatile-sounding method that can be used to determine the materials in a soil profile and estimate their engineering properties
Cone Penetration Test
