2.4.1 Rock and Soil Samplers

There are many different types of samplers used to retrieve soil and rock specimens from the boring. For example, three types of soil samplers are shown in Fig. 2.10, the California sampler, Shelby tube, and SPT sampler. One of the most important first steps in sampling is to clean-out the bottom of the borehole in order to remove the loose soil or rock debris that may have fallen to the bottom of the borehole. For hard rock, coring is used to extract specimens (see Table 2.4). The coring process consists of rotating a hollow steel tube, known as a core barrel, which is equipped with a boring bit. The drilled rock core is collected in the core barrel as the drilling progresses. Once the rock core has been cut and the core barrel is full, the drill rods are pulled from the borehole and the rock core is extracted from the core barrel. A rotary drill rig, such as shown in Fig. 2.6, is often used for the rock coring operation. For further details on rock core drill and sampling, see ASTM D 2113-99 (2004), “Standard Practice for Rock Core Drilling and Sampling of Rock for Site Investigation.” For soil, the most common method is to force a sampler into the soil by either hammering, jacking, or pushing the sampler into the soil located at the bottom of the borehole. Soil samplers are typically divided into two types.

Thin-Walled Soil Sampler. The most common type of soil sampler used in the United States is the Shelby tube, which is a thin-walled sampling tube consisting of stainless steel or brass tubing. In order to slice through the soil, the Shelby tube has a sharp and drawn-in cutting edge. In terms of dimensions, typical diameters are from 2 to 3 in. (5 to 7.6 cm) and lengths vary from 2 to 3 ft (0.6 to 0.9 m). The typical arrangement of drill rod, sampler head, and thin-wall tube sampler is shown in Fig. 2.11. The sampler head contains a ball check valve and vents for escape of air and water during the sampling process. The drill rig equipment can be used to either hammer, jack, or push the sampler into the soil. The preferred method is to slowly push the sampler into the soil by using hydraulicjacks or the weight of the drilling equipment. Thin-walled soil samplers are used to obtain undisturbed

soil samples, which will be discussed in the next section. For further details on thin-walled

sampling, see ASTM D 1587-00 (2004), “Standard Practice for Thin-Walled Tube ampling of Soils for Geotechnical Purposes.”

Thick-Walled Soil Sampler. Thin-walled samplers may not be strong enough to sample gravelly soils, very hard soils, or cemented soils. In such cases, a thick-walled soil sampler will be required. Such samplers are often driven into place by using a drop hammer. The typical arrangement of drill rod, sampler head, and barrel when driving a thick-walled sampler is shown in Fig. 2.11. Many localities have developed thick-walled samplers that have proven successful for local conditions. For example, in southern California, a common type of sampler is the California sampler, which is a split-spoon type sampler that contains removable internal rings, 1.0 in. (2.54 cm) in height. Figure 2.10 shows the California sampler in an open condition, with the individual rings exposed. The California sampler has a 3.0 in. (7.6 cm) outside diameter and a 2.50 in. (6.35 cm) inside diameter. This sturdy sampler, which is considered to be a thick-walled sampler, has proven successful in sampling hard and desiccated soil and soft sedimentary rock common in southern alifornia. Another type of thick-walled sampler is the SPT sampler, which will be discussed in Sec. 2.4.3. For further details on thick-walled sampling, see ASTM D 3550-01 (2004), “Standard Practice for Thick Wall, Ring-Lined, Split Barrel, Drive Sampling of Soils.”