C.2 Probe placement techniques without soil displacement (p. II)

C.2.4 Continuous flight auger drilling (CFA)

A flight auger consists of a short helical length of steel welded to a slender solid stem with a cutting head connected either to drill rods or to additional auger sections over the length of the drilling string. The cutting head must be slightly greater in diameter than the auger flight to prevent smearing the cavity wall. The auger shall be rotated during withdrawal.

NOTE This method is not listed in ISO 22475-1 (see C.2.1)

When a hollow stem flight auger is used for simultaneous drilling and casing of the initial hole the auger end shall be kept closed. Great care shall be taken when this closer is withdrawn that the test zone is not damaged by the suction caused.

C.2.5 Rotary core drilling (CD)

Core drilling uses a core barrel sampler and rotary drilling.

Equipment and tool should be selected in a way that the mud circulation does not erode the pressuremeter test pockets. Application of ISO 22475-1 is limited (see C.2.1 and C.2.2)

This technique permits a detailed description of lithology and thickness of the various soil layers. In addition, the core sample can be tested but the priority shall be given to pocket wall quality.

C.2.6 Rotary percussive drilling (RP and RPM)

C.2.6.1 General

In the case of soils in which this technique is acceptable (see Table C.2 for guidance), rotary percussive drilling consisting in advancing the pressuremeter sounding by dropping and raising a drilling bit by pneumatic or hydraulic pressure may be used. The disintegrating action of the drilling bit is increased by rotation.

C.2.6.2 Rotary percussive dry drilling (RP)

The removal of cuttings is by air flush. When using this technique one shall bear in mind the water content, the clay content and the hardness of the ground. This technique may mostly be used for testing at shallow depths due to the limitation of available air pressure.

C.2.6.3 Rotary percussive drilling using drilling fluids (RPM)

In this technique the pocket should be advanced by a rapid reciprocating and rotating hammering action. Fluid circulation should remove the cuttings so formed.

C.2.7 Pushed, driven or vibrodriven tubes (PT, TWT, DT and VDT)

C.2.7.1 General

For certain ground conditions (see Table C.2 for guidance), a tube with a circular cross section may be pushed, driven or vibrodriven into the ground. The tube shall be fitted with an inward bevel cutting edge to minimize pre-stressing of the test cavity wall before testing.

NOTE The samplers described in the following are not in accordance with ISO 22475-1 but they can be classified as sampling methods corresponding to sampling category C of ISO 22475-1.

C.2.7.2 Pushed tubes (PT and TWT)

In soft to medium stiff clayey soils and in silty soils above water table, pushed tubes may be used to create the test pocket. If the pocket cannot be obtained in one single push, another method of preparing the test pocket shall be chosen. Full core recovery is required so as to avoid disturbance of the pocket wall and the underlying layers to be tested.

The tube shall be withdrawn slowly to limit inward yielding of the pocket wall due to suction. In sludge and soft clay, thin wall tubes shall be used.

C.2.7.3 Driven tubes (DT) or vibro-driven tubes (VDT)

For stiffer soils (see Table C.2 for guidance) thick wall tubes shall be used. They may be driven by ramming or by a vibrating hammer.

C.2.8 Slotted tube with inside disintegrating tool and mud circulation (STDTM)

In certain ground conditions (see Table C.2 for guidance), the STDTM technique may be used. It consists in creating the pocket using an open slotted tube which is an integral part of the casing close to its lower end. One of the two following methods may be chosen.

  • The casing is driven minimizing soil displacement by using a cutting shoe with an inside bevel. The soil inside the casing is removed by an appropriate drilling bit.
  • The casing is lowered using a rapid reciprocating hammering action. The drilling proceeds simultaneously with the advancement of a casing. The cutting tool associated with fluid injection is either slightly protruding from the casing shoe or flush with it.

Before each series of pressuremeter tests, the drilling string shall be pulled up. Then the probe shall be centred in the slotted section.

C.3 Probe placing by driven slotted tube (DST)

In buoyant granular material, if it appears impossible to prevent the test pocket wall caving in, the probe may be pushed or driven into the soil directly or inside its slotted tube with either a driving point or a cutting shoe.

Between the probe and either the point or the cutting shoe, an extension tube at the diameter of the probe or the slotted tube shall be included, so as to prevent compaction effect at the level of the probe.

In certain cases, drilling a pilot hole much smaller in diameter than the pressuremeter probe may be necessary to help probe placing. Once this smaller size open hole is completed, the pocket is trimmed to the proper diameter by pushing or (vibro) driving the probe.

Table C.2 — Guidelines for pressuremeter probe placement technique
Soil Type Boring technique
Probe placing without soil displacement Probe
1 < dt /dc ≤ 1,08 dt /dc ≈ 0
Rotary drilling Rotary percussion Tube pushing,
driving or vibrodriving
Sludge and soft clay
— ■   — ■

Soft to firm clayey soils
Stiff clayey soils
Silty soils:
— above water table
— below water table
Loose sandy soils:
— above water table
— below water table
— ■
— ■
Medium dense and dense sandy soils
Gravels, cobbles
—■○ —■ —■
Cohesive non-homogeneous soils (e.g. boulder clay)
Loose non-homogeneous soils, other soils not specified above (e.g. tills, some alluvial deposits, man made soils, treated or untreated fills)
Weathered rock, weak rock
Not suited
  Not covered by this standard
OHD Open hole drilling.
HA OHD performed with a hand auger
HAM OHD performed with a hand auger and mud
CFA Continuous flight auger
CD Core drilling
RP Rotary percussion
RPM Rotary percussion with mud
STDTM Slotted tube with inside disintegrating tool and mud circulation
PT Pushed tube
TWT Thin wall tube, pushed
DT Driven tube
VDT Vibrodriven tube
DST Driven slotted tube
Depending on the actual site conditions and on the evaluation of the operator
* Rotation speed should not exceed 1 s-1 and tool diameter not be more than 1,15 dc
Slurry circulation: pressure should not exceed 500 kPa and the flow rate 15 l/min. The flow can be temporarily interrupted if necessary.
+ Pilot hole with possible preboring techniques: DST, RP and RPM
Needs special care: add a guard tube at the toe of the slotted tube; carry out the tests while going down: keep slurry level in casing higher than water table level

ISO 22476-4:2012 Field testing — Part 4: Ménard pressuremeter test