Medium DCP

The medium DCP (DPM) has a hammer mass that is too large to be comfortably operated by hand for efficient use but too small for use with a drill rig and a conventional SPT hammer. Several configurations of this test have been reported as summarized in Table 3.5. Figure 3.8 shows a schematic of a portable DCP rig mounted on a trailer.

Figure 3.6 LDCP used by the author.

Figure 3.7 Typical results obtained at four sites using LDCP.

Table 3.5 Summary of Different Medium DCP Equipment.

Triggs & Liang (1988) presented results using a small commercially available penetration rig with a 30 kg (66 lbs) hammer that can be transported in components and assembled at a site by a two-person crew. The equipment is manufactured in Italy and can be used for both static and dynamic penetration. In the dynamic mode, the hammer is operated by a small gasoline engine and an automatic lift/drop mechanism. The cone may be either fixed to the rods or may be expendable.

In the UK, a medium DCP (DPM15) with a cone diameter of 43.7mm (1.72 in.) (giving a cone area of 15 cm²) is sometimes used (Butcher et al. 1995). Because of the larger area of the cone, the DPMI5 has a specific work per blow twice that of the DPL.

Heavy DCP

A heavy DCP (DPH) with a hammer mass of 50 kg (110 lbs) was described by Card & Roche

(1989) and Scarff (1989). The equipment was developed in the UK and is mounted on a small self-contained trailer pulled by a vehicle to the site. Table 3.6 gives a summary of some different heavy DCP equipment used.

In most cases, the hammer is raised by a chain drive mechanism operated by a small gasoline engine and released automatically to give a drop height of 50cm (19.7in.) with a driving rate typically between 25 and 30 blows/min. This is similar in design to the mechanism used with some automatic SPT hammers. The rods are guided between rollers at the base of the

Figure 3.8 Trailer-mounted automatic medium DCP.

Table 3.6 Summary of heavy DCP equipment

mast and at the drive head to resist bending. This equipment also conforms to the German Standard DIN 4094 Part I (Card & Roche 1989) and has been used in Eastern Europe (e.g., Paunescu & Gruia 1982).

Super Heavy DCP

For routine site investigation work in which a drill rig will be on site, the use of the super heavy DCP (DPSH) appears to be the most practical and useful configuration of the test. The most common technique for conducting super heavy DCPs is to use the 63.5 kg (140 lbs)

Table 3.7 Reported use of hammers larger than 63.5 kg (140 lbs) to conduct super heavy DCPs

SPT hammer although other hammer masses have also been used. AW rods are used for driving, and normally a cone with a 60° apex and a diameter of 63.5 mm (2.5 in) is used, although in some cases, a 76.2 mm cone (3.0 in.) may also be used. The number of hammer blows to advance the cone 150 mm (6 in.) is typically recorded, and the results are reported as N_c blows/30cm (1 ft).

Borros produces a small portable rig that provides equipment in the “SPT” configuration,

i.e., 63.5 kg (140 lbs) hammer, 76cm (30 in.) drop height, for driving a 50.5 mm (2 in.) diameter cone with an apex angle of 90°. The driving is automatic, being operated by a small gasoline engine, and is conducted at a rate of about 20 blows/min. The number of blows required to drive the cone a distance of 10cm (3.9in.) is recorded.

In some cases, it may be desirable to use a hammer with a mass larger than 63.5 kg (140 lbs), especially in very dense or gravelly materials. For example, Hanna et al. (1986) used a 470kg (1034 lbs) hammer with a 92 mm (3.6 in.) diameter cone to evaluate ground improvement in sands and sandy gravel. Table 3.7 presents a summary of reported use of some heavy hammers for conducting super heavy DCPs.