266371444

APPENDIX B

RECOMMENDED STANDARD FOR DYNAMIC PROBING 1. SCOPE

The expression probing is used to indicate that a continuous record is obtained from the test in contrast to, for example, the SPT test. The aim of dynamie probing is to measure the effort reąuired to force a point through the soil and so obtain resistance values which correspond to the mechanical properties of the soil. Two procedures are recommended (A and B). Fundamentally the same eąuipment can be used for both DPA and DPB as for the SPT (cf Table I).

cohesionless soils when static penetration testing is difficult to perform or the dynamie properties of the soil are of special interest (e.g. in connection with driven piles). Dynamie probing can be used to detect soft layers in cohesionless soils and to locate strong layers as, for example, with end bearing piles. The soil type and the cobble and boulder content can be evaluated under favourable conditions. The test is normally not suitable for cohesive soils or very loose cohesionless soils. It is normally not possible to evaluate the mechanical properties of a soil at great depths with dynamie probing type B (DPB) when friction along the extension rods is significant.

Dynamie probing type A (DPA) should be re-garded as a reference test. The friction between the soil and the extension rod is negligible.

Dynamie probing type B (DPB) morę economical than method

is simpler and A. DPB has morę the character of a reconnaissance test than DPA sińce the friction between the soil and the extension rod is only partially eon-trolled.

1.1 General principles and nomenclature

A hammer of mass M and a height of fali H is used to drive a pointed probe. The hammer strikes an anvil which is rigidly attached to extension rods. The penetration resist-ance is defined as the number of blows reąuired to drive the penetrometer a dis-tance of 0.2 m. The resistance is within the reference rangę when the number of blows reąuired to drive the probe 0.2 m is between 5 and 100. The energy of a blow is the mass of the hammer times the acceleration of gravity and times the height of the fali (M.g.H).

The number of blows reąuired for 0.2 m of penetration within the reference rangę is

1.2    Classification

Two different methods are recommended, type A and type B, to fit different geological conditions. The driving eąuipment is the same for the two methods.

Dynamie probing A (DPA): drilling mud or casing is used to eliminate friction along the extension rods.

Dynamie probing B (DPB) is performed without drilling mud or casing. The friction along the rods can be estimated by measuring the torąue reąuired to rotate the extension rods.

Data for both DPA and DPB are summarised in Table I.

Other types of eąuipment may be reąuired for special purposes, such as light dynamie probing or heavy dynamie probing (see notę 1 para. 6 ) •

2. APPARATUS

2.1

Hammer

defined as the N,-value ively).

(N. and N dA

dB

respect-

Results from different types of dynamie prób ing may be presented as resistance values <qdA f W ^{or r}d (r_dA , r_dB) in Pa, kPa or MPa ^x‘_f such as :

The mass of the hammer shall be 63*5 kg +0.5 kg. The ratio of the length to the diam-eter of the hammer shall be between 1 and 2. The hammer shall be provided with an axial hole with a diameter which is 3-^ mm larger than the diameter of the guide rod. The shape of the bottom surface of the hammer shall be in accordance with Fig. 1.

MgH

^rd - Ai“

^d

M

MgH

M + M

Ae

where :

r_d and q_d are resistance values M is the mass of the hammer M' is the total mass of the extension rods, the anvil and the guiding rods H is the height of fali e is the average penetration per blow A is the cross-sectional area of the point g is the acceleration of gravity

The primary use of dynamie probing is in

2.2 Anvil and guide rod

The anvil shall be rigidly fixed to the ex-tension rods. The mass of the anvil shall be between 10 and 15 kg and the diameter not less than 100 mm and not morę than half the diameter of the hammer. The axis of anvil, guide rod and extension rod shall be straight with a maximum deviation of 5 mm per metre. The top surface of the anvil shall be as shown in Fig. 1. The combined mass of the anvil and guide rod must not exceed 30 kg.

x)

Pa (Pascal) = 1 N/m

110