Soil and Rock Sampling

1. Soil and Rock Sampling

2. Environmental Site Characterization • Number of samples taken depends on the size of the site • Hollow stem auger normally used for environmental work • Usually sample every 5ft in depth or at every change in formation

3. Sample Examination • Samples are examined in field for physical characteristics • Grain size, color, degree of sorting, and moisture content • Visually present contamination • Usually screened in field using • FID (flame ionization detector) • PID (photoionization detector) • for volatile organic compound (VOCs)

4. Sample Examination Cont’d • A selected number of samples are sent to the lab • Usually one per soil boring • Shipped in jars to off-site lab for chemical analyses • Waiting period of 6 to 10 weeks

5. Sample Examination Cont’d • Drill cuttings • Stored in drums • Potentially contaminated • Approx. 1 drum for every 17ft of drilling in a hole drilled with a 4.25 ID hollow stem auger • Analyzed to determine proper disposal

6. Detection Probability • A soil or core sample may only be representative of a limited area surrounding the hole • Fractures, bedding planes, solution cavities, bedrock channels, sand lenses, and permeable zones can be missed be borehole programs

7. Types of Samples

8. Bulk Samples • Shovelful or handful of drill cuttings from borehole • Provides generalized picture of formations cut by drilling • Formations are mixed together in this type of sample • Least accurate of four types

9. Representative Samples • Generally taken in some sort of drive or push tube • Represent a specific depth interval in a borehole • Chemical constituents present but not necessarily undisturbed

10. Undisturbed Samples • Physical and chemical disturbances minimized • All parts of formation sampled without altering presampling relationship • Required for hydraulic conductivity testing

11. Composite Samples • Combination of discrete samples from different intervals in the same borehole, mixed to represent the entire borehole • Combination could be from same formation in different boreholes • Represents similar formation materials across site

12. Types of Soil Samplers

13. Solid Barrel Sampler • Consists of steel tube attached to a connector head at top and drive shoe at bottom • 12-60in long, 1-6in wide • Sampler made of steel or stainless steel with brass, stainless steel or plastic liner • Liner material determined by specific application

14. Split-Barrel Samplers • Tubular section is split longitudinally into two semi-cylindrical halves • Made from high strength or stainless steel • Driven in 2ft increments • Most commonly used sampler in geo-tech and environmental work • Samples are often physically disturbed, but are suitable for soil chem testing

15. Thin-Wall Tube Samplers • Consists of a connector head and a length of thin-wall steel brass or stainless steel tube • Usually 30in tube for 24in sample • Sharpened at cutting end and crimped to 1% of its inside diameter to allow free movement of the sample into the tube • Primarily used in cohesive, soft, or clayey formations where a relatively undisturbed sample is required

16. Continuous Tube Sampler • Used exclusively with a hollow-stem auger • 5ft long split-barrel sampling tube, cutting shoe at bottom, head at top • The head connects in a way that allows the sampling tube to remain stationary while the auger turns • Works well in clays and other cohesive soils and in granular material above the water table • Material inflow may occur when the water table is encountered • This makes it very difficult to recover samples

17. Rotary Samplers • Pitcher or Denison sampler, or the Geo-barrel • Requires circulation fluids • Useful for Geo-tech work, not environmental • Retrieves disturbed and undisturbed samples

18. Piston Samplers • Consists of a thin-wall tube, a piston, and mechanisms for regulating movement between the tube and the piston • Specifically for use in soft formations • Some physical disturbance of samples • The sampler is flush with the end of the fixed piston, lowered into hole on drill rod • Hydraulic fluids force the tube into the soil while the fixed piston remains stationary • Sampler then pulled back by hydraulic fluids

19. Methods of Sampling • Environmental samples are generally taken from the bottom of the borehole • Bulk samples are generally taken from the cuttings

20. Driving • Most common method for obtaining split barrel samples • Uses 140lb safety hammer • Hammer sits at ground level • Back-hammering or hydraulic fluid used to lift the sampler • Back-hammering may result in loss of sample

21. Driving Cont’d • The number of hammer blows made to drive the sampler is recorded for every 6in • This provides useful information about the type of material being penetrated • If the sampler reaches 50 blows in 6in interval, refusal is met • Excessive hammering may result in drill rod failure

22. Pushing • Uses a hydraulic feed system on a drill rig to press the sampler into the soil • The drill rod string should be connected to the drill so hydraulic retract can be used to withdraw samples from the borehole • Normally used for thin-wall tube samplers • Occasionally used for split-barrel or solid-barrel samplers in soft soils

23. Rotation While Pushing • Denison or Pitcher samplers or continuous tube samplers • Sampling barrel is suspended from a bearing inside the barrel so the sampler remains stationary while the auger drills into the formation • Sampler barrel is connected to the drill rods or a wire line system for retrieval from the bottom of the borehole