Ram core sounding

Ram core sounder in use

A ram core sounding (RKS) is a simple method for exploring the soil structure and for taking soil samples from unconsolidated rock , which is used in geology , in construction and for the exploration of contaminated sites .

Bulk

The procedure was previously standardized in Germany by DIN 4021 and from 2007 by DIN EN ISO 22475-1.

The process generally known as ram core sounding is a small-scale drilling (guide values for external drilling diameter 30 to 80 mm) in accordance with DIN 4021: 1990-10, Tab. 3, line 2, which belongs to the small-drilling process. The use of small holes is limited. In the case of extraction pipe lengths over 1 m, the determination of the height of the layer boundaries becomes uncertain and there is a risk that soft layers will be displaced by overlying solid layers due to the formation of plugs.

According to DIN EN ISO 22475-1, Tab. 2, line 9 (p. 23), small ram bores are generally classified for category C sampling, in which only samples of quality class 5 can be obtained (which allows statements about the sequence of layers), in In some slightly cohesive soils, extraction category B (determination of layer boundaries, grain composition, consistency boundaries) is classified in a footnote. Basically, the small drilling method in Section 6.3.6 (p. 26) states that these are only suitable for use in sand and fine-grained soils and that one should ensure that the size and mass of the samples obtained are suitable for the planned laboratory tests .

For higher requirements, a method according to DIN EN ISO 22475-1 must be used, which can be assigned to extraction category A or B. These devices require a higher outlay on machinery. An example would be the rotary dry drilling method, rotary core drilling method or ram core drilling method.

Probing device

The ram core sounding is carried out with a hollow steel probe that is slotted on one side, a firing pin screwed onto it and an impact device. In many cases an electric or motor-driven hammer drill is used as the impact device, in other cases the impact weight of a chain-driven drill device is used. The probe is pulled out with a hydraulic device or in simple cases with a manual double lever ( pulling the probe). A special clamping sleeve prevents the drill rod from slipping off.

The probe has a ring-shaped cutting edge at the lower end and is used in various diameters. Commonly used are 36, 50, 70 and 80, rarely 100 mm, depending on the drilling target and penetration depth. The length of the probe is a meter or two. Distance rods can be screwed between the probe and the impact head in order to reach greater depths.

Alternating clay-sandstone storage (up to 6 m depth) near Bad Salzuflen

Execution of a ram core sounding

After selecting the starting point, a one-meter probe is rammed vertically into the ground until only the impact head protrudes from the ground and the hollow probe is filled to the top. After pulling out the first probe insert, drilling is normally continued with a two-meter probe, which has to be pulled out again after every two meters of penetration, because the hollow body is then filled with soil. In the area of contaminated site exploration, probing with one-meter probes is planned in order to compress the soil material as little as possible. As a rule, ramming core soundings are carried out to a depth of six to ten meters, in some cases they can be significantly deeper under favorable conditions.

The drawn probes are stored horizontally. The soil structure can now be documented in a layer directory through the slot in the probe. It can also take samples for geological, geotechnical or chemical investigations. The conveyed drill cuttings are then completely removed from the probe and, depending on the purpose of the probing, either completely discarded or filled into sample vessels to form a mixed sample. After the soil has been removed and any cleaning that may be required, the probe can be used again.

After reaching the intended depth, the borehole is backfilled or expanded to become a measuring point. This is used to measure the groundwater level ( groundwater measuring point ) and to take samples of the groundwater or to take soil air samples (soil air measuring point ). Backfilling is usually carried out with the material previously removed, minus any samples. The termination to the top of the ground is to be selected depending on the type of this. If the surface is a floor, the borehole can also be closed at the top with drilling material; for concrete, rapid cement is usually chosen, and for black pavement cold asphalt is chosen as the finishing layer. It is important that the surface can still be used (e.g. driven on) and that there is no increased risk of accidents through the borehole.

Norms

DIN EN ISO 22475-1: Geotechnical exploration and investigation - sampling methods and groundwater measurements, Part 1, Technical principles of execution (ISO 22475-1: 2006). German version EN ISO 22475-1: 2006
DIN EN 1997-2: Eurocode 7: Design, calculation and dimensioning in geotechnical engineering: Part 2: Exploration and investigation of the subsoil. German version: EN 1997-2: 2007 + AC: 2010

Web links

Small bores according to DIN 4021 - a question of knowledge? Siebenborn, G .: Small bores according to DIN 4021 - a (ge) knowledge question ?, bbr 5/05, S .: 37-41 (2005)

Individual evidence

↑ DIN 4021: 1990-10 subsoil; Digestion through prospecting and drilling as well as taking samples . In: NORM . Beuth, October 1990.
↑ Gerd Siebenborn: Small bores according to DIN 4021 - a (ge) knowledge question? Ed .: bbr 5/05, p .: 37-41. 2005.

[1] DIN 4021: 1990-10 subsoil; Digestion through prospecting and drilling as well as taking samples . In: NORM . Beuth, October 1990.

[2] Gerd Siebenborn: Small bores according to DIN 4021 - a (ge) knowledge question? Ed .: bbr 5/05, p .: 37-41. 2005.