6.3.2.3 Sampling by flight auger drilling

6.3.2.3.1 In sampling by flight auger drilling, an auger consisting of a spiral flight, wound round a solid centre stem and fitted with a cutter head, is drilled into the ground. Two sampling methods can be used:

  • continuous sampling method;
  • non-continuous sampling method.
Table 2 – Sampling by drilling in soils
Column 1 2 3 4 5 6 7 8 9 10 11 Column
Line Drilling method Equipment Guideline for application and limitations d Achievable sampling categories e Achievable quality class e Remarks Line
Soil cutting technique b Use of flushing medium Extraction of sample by Designation Tool Guideline values of borehole diameter range mm Unsuitable for d Preferred method for d
1 Rotary drilling No Drilling tool Rotary dry core drilling c Single-tube corebarrel 100 to 200 coarse gravel, cobbles, boulders clay, silt, fine sand, silt B (A) 4 (2-3) Good interior, outside dried out 1
Hollow stem auger 100 to 300 clay, silt, sand, organic soils B (A) 3 (1-2) —
2 Yes Drilling tool Rotary core drilling Single-tube corebarrel 100 to 200 non-cohesive soils clay, clayey and cemented composite soils, boulders B (A) 4 (2-3) — 2
Double-tube corebarrel a B (A) 3 (1-2)
Triple-tube corebarrel a A 1
3 Yes Drilling tool Rotary core drilling Double/triple-tube corebarrel with extended inner tube 100 to 200 gravel, cobbles, boulders clay, silt A 2 (1) — 3
4 No Drilling tool Auger drilling Drill rods with shell or flight auger; hollow stem auger 100 to 2 000 boulders larger than De/3 all soils above water surface, all cohesive soils below water surface B 4 (3) — 4
5 Yes Reverse flow of flushing medium Reverse circulation drilling Drill rods with hollow chisel 150 to 1 300 — all soils C (B) 5 (4) — 5
6 No Drilling tool Auger drilling with light equipment Shell auger or spiral flight auger 40 to 80 coarse gravel with a particle size larger than De/3, dense soils, cohesion-less soils beneath groundwater surface clay to medium gravel above water surface; cohesive soils below water surface C f 5 Only to be used for small depths 6
7 Hammer driving No Drilling tool Percussive core drilling Percussion clay cutter with cutting edge inside; also with sleeve (or hollow stem auger) b 80 to 200 soils with a particle size larger than De/3 laminated soil, e.g. varve clay, silt and soils with a particle size up to De/3 cohesive soil: A 2 (1) Plotting of driving chart on the basis of number of impacts 7
non-cohesive soil: B (A) 3 (2)
8 No Drilling tool Percussive drilling Percussive clay cutter with cutting edge outside b 150 to 300 soils with a particle size larger than De/3 gravel and soils with a particle size up to De/3 B 4 8
9 No Drilling tool Small diameter hammer driving Hammer driving linkage with tube sampler 30 to 80 soils with a particle size larger than De/2 soils with a particle size up to De/5 C f 5 Only to be used for small depths 9
10 Rotary hammer driving Yes Drilling tool Rotary percussive drilling Single- or double-tube corebarrel 100 to 200 composite and pure sands with a particle size larger than 2,0 mm, gravel, firm and stiff clays clay, silt, fine sand cohesive soil: A 2 (1) — 10
non-cohesive soil: B 4 (3)
11 Vibration drilling with an optional slow rotation No (only for lowering casing) Drilling tool Resonance drilling Thick wall sampler or single tube corebarrel with optional plastic lining tube 80 to 200 — — cohesive soil: B 4 — 11
non-cohesive soil: C 5
12 Percussion No Drilling tool Cable percussion drilling Cable with percussion shell auger 150 to 500 gravel above water surface, silt, sand and gravel below water surface clay and silt above water surface, clay below water surface C (B) 4 (3) — 12
13 No Drilling tool Cable percussion drilling Cable with valve auger 100 to 1 000 recovery above water surface gravel and sand in water C (B) 5 (4) Can also be used in cohesive soils if water is added 13
14 Pneumatic/ continuous thrust No Drilling tool Small diameter pneumatic/ continuous thrust drilling Pneumatic/ continuous thrust linkage, with tube sampler 30 to 80 dense and coarse-grained soils clay, silt, fine sand C f 5 Only to be used for small depths 14
15 Grabbing No Drilling tool Grab drilling Cable with grab 400 to 1 500 firm, cohesive soils, boulders of size larger than De/2 gravel, boulders of size less than De/2, cobbles above water surface: B 4 — 15
below water surface: C 5
a Conventional or wireline corebarrel.
b Using the hammer driving technique, the drilling tool will be driven by a special driving tool. Using the percussion technique, the drilling tool will be driven by its repetitive lifting and falling.
c Rotary dry core drilling is commonly used if the observation of the groundwater surface is the most important aim of the ground investigation.		 d De is the internal diameter of the sampling tool.
e The sampling categories and quality classes given in parentheses can only be achieved in particularly favourable ground conditions, which shall be explained in such cases.
f Sampling category B is sometimes possible in light cohesive soils.
NOTE Straight flush drilling is not covered because the sample quality class that can be achieved is generally worse than class 5.

6.3.2.3.2 With the continuous sampling method, the flights act as a screw conveyor and continuously bring the cuttings to the surface. Additional sections of auger can be added until the required depth is reached. At the mouth of the borehole, the obtained samples are remoulded.

6.3.2.3.3 With the non-continuous sampling method, the flight auger is screwed into the soil with the penetration rate suitable for the auger rotational speed and the pitch of the flight auger. The sampling length into the soil shall not exceed the maximum length of the flight auger. During the screwing of the flight auger, the vertical displacement of the soil between the flights shall be minimised. After the screwing, the drilling tool shall be completely removed from the borehole without rotation of the auger and the samples shall be taken from the material adhering to the auger flights.

6.3.2.3.4 With the non-continuous sampling method, flight auger drilling shall be only used if the borehole is stable or if stabilized with an auxiliary casing.

6.3.2.3.5 Sampling by flight auger drilling is suitable for cohesive soils and soils above the groundwater surface.

ISO 22475-1 Sampling by drilling and excavation and groundwater measurements. Part 1: Technical principles of execution