Dynamic cone penetrometer

Dynamic cone penetrometer (DCP) is used to measure quickly the in situ bearing capacity or strength of the subgrade material as well as the weakly bound material. The strength is expressed in penetration rate or index and may be related to in situ CBR value. 

One advantage of the DCP over the static cone penetrometer is that coarser and stronger material can be tested (with CBR values up to 100%). Additionally, the layer s thickness and its strength can be identified down to a depth of, normally, 1 m or more. 

The device has a very basic construction and can be easily used. It uses a standard 8 kg rammer (4.6 kg optional for weaker materials) dropping through a height of 575 mm and a steel drive rod with a replaceable point or disposable 60° cone tip. During the test, the depth of penetration is recorded every time the load is applied and results are expressed in millimetres per blow, known as the DCP index or rate. 

To convert the DCP index to CBR values, correlation equations are used. According to ASTM D 6951 (2009), the correlation equations used are as follows  

The Highways Agency in the United Kingdom uses a different correlation equation developed by TRL (Highways Agency 2008), which is as follows  

---

Probing methods commonly used are dynamic (e.g. Mackintosh Probes, which is also commonly known as JKR dynamic cone penetrometer, shown in Figure 3.2) or static (e.g. Cone Penetration Tests). Probes comprise sharpen steel rods that are driven (by hammer blow) or pushed into the soil (by static load). Investigation depth is limited by thrust available for pushing the penetrometer into the ground or when dense/coarse gravel is encountered. Soil type, strength and compressibility can be assessed from available correlation charts developed for the respective methods. 

Nithiaraj, R., Ting, W.H. Balasubramaniam, A.S. 1996. Strength parameters ofresidual soils and apphcation to stability analysis of anchored slopes. Geotechnical Engineering, Dec 1996, SEAGS, Thailand. 27 (2). Ooi, T.A. Ting, W.H. 1975. The use of a light dynamic cone penetrometer in Malaysia. Proc. 4th SJi. Asian... 

In Malaysia, light weight dynamic penetrometer (a.k.a JKR dynamic cone penetrometer) is also widely used for preliminary assessment of subsoil conditions. Figure 4.9 shows an example of a design chart for allowable bearing capacity based on the penetrometer value. 

ASTM D 6951/D 6951M. 2009. Standard test method for use of the dynamic cone penetrometer in shallow pavement applications. West Conshohocken, PA ASTM International. 

The in situ determination of the strength of the compacted unbound layer is carried out by the Dynamic Cone Penetrometer (DCP) or by the plate bearing test. The DCP test is gaining grounds because of its simplicity in use. It must be reminded that the penetration index, determined by DCP, or k value, determined by the plate bearing test, can be correlated to the CBR value (see Sections 1.6.3 and 1.7). 

The CPT was originally known as the Dutch CPT. The test is a versatile sounding method that can be used to determine the stratigraphic identification, soil strength, deformation, and dynamic properties of sediments. In recent years, this has been expanded to include chemical data and hydraulic properties of the subsurface strata. The current cone penetrometer has its beginnings in the early 1930s in the Netherlands. Cone penetrometers... 

Laboratory tests can be classified into two groups (1) shipboard testing including Torvane, laboratory miniature vane shear (ASTM D4648), pocket penetrometer, and fall cone penetrometer and (2) shore-based tests, which includes the above as well as triaxial tests (ASTM D4767) direct simple shear, dynamic, and cyclic tests, consolidation tests (ASTM D4186, ASTM D2435) and the usual array of index property tests, and special tests appropriate... 

Dynamic Soil Properties In Situ Characterization Using Penetration Tests, Fig. 5 Electronic cone penetrometer... 

There are two categories of penetrometer tests, the dynamic and the static. Both methods measure the resistance to penetration of a conical point offered by the soil at any particular depth. Penetration of the cone creates a complex shear failure and thus provides an indirect measure of the in situ shear strength of the soil. 

---