Geological exploration is the first step of a complex value creation chain, which results in the production of high-end products in brick factories. For the search and exploration of clay deposits years of experience are needed. This concerns not only the choice of location, but also the type and number of outcrops/drill holes. To reach an optimal price/quality value the extraction technique has to be individually chosen.
For the exploration of brick clays a drill hole pattern in a grid of 100 m x 100 m has proved to be successful. If the results of the drillings can be correlated well, the grid can be widened to 200 m x 200 m. Although if the underground is heterogenous it is recommended to choose a smaller grid pattern of 50 m x 50 m. Only if the geology is still not known after this procedure, a grid of 25 m to 25 m should be chosen.
In Mesozoic solid rocks like shales the strike and dip angle of the layers has to be considered. In principle the following applies: Drill holes in strike direction include the same stratigraphic sequences and result in similar drill profiles. Drill holes perpendicular to the strike direction perforate different stratigraphic sequences and therefore show the maximal width of the raw material deposit.
Systematic prospection including outcrop description in the region of the planned exploration area. Oriented laboratory experiments to register the raw material characteristics. Registration and evaluation of competing uses.
Inspection and evaluation of geological background maps. Procurement of performance and cable plans. Preparation of an optimized drilling plan with type, number, location and depth of each drill hole (drill holes and if necessary excavator grooves).
Geological supervision of the drilling work and drill core documentation after DIN 4022 with individual adjustment of the drilling plan depending on primary results.
Qualified sampling of drill cores with the quality classes 1-5 after DIN 4021 and transportation of samples to the ceramic laboratory. Alternatively transfer of drill cores. Handling of formalities for international orders.
Raw material testing includes the ceramic body parameters and mineralogical/chemical testing in the laboratory. Chemical analysis, mineral phase analysis, simultaneous thermal analysis, amount of mixing water, plasticity, shrinkage, water absorption, body density, interfering components.
Georeferenced presentation in site plans, drilling profiles, cross-sections and ISO-plans. Evaluation of results regarding the specific eligibility for brick factories including quantity proof.
Drilling methods and drill diameters primarily comply with the type and quality of the required raw material samples. Generally drilling methods in which the bore hole cuttings are extracted as intact as possible are preferred. The boreholes are normally lined according to the drilling progress, so that no bore hole detritus gets into the cuttings.
In order to prevent settlement and environmental damage, the boreholes should be carefully filled by complete borehole linings/casings. In case of encountering confined groundwater the hydraulic barrier effects of the original interlaminar bonding have to be restored by filling up the borehole with technical swellable clay. Other criteria, which are decisive for the drilling method, regard the stability and consistency of the underground.
Drill holes with a bore hole diameter of 32-80 mm are classified as small drillings, which are drilled with an engine driven or electronically driven manual drill. A slitted sensor is hit into the underground meter by meter. Sounding drill holes can only be drilled into geological formations of the classes 1-4 after DIN 18.300, if the consistency is pasty to maximal stiff. For the brick producer this means: clay cannot be explored, because of its high cohesion forces. Loams and sands, however, can be drilled, which often represent the overburden of clay deposits. The achievable final depths depend on the penetration resistance in the subsoil. They amount to about 6-12 m.
The essential advantage of sounding drill holes is the possibility to obtain completely intact and depth equal samples of the quality class 2-3 from soft layers. Other advantages are minor crop damage, good access of the drill points and low cost and time effort. Close-mesh sounding drill holes are recommended especially in combination with core drillings, if loam-like layers of low consistency and thickness shall be explored.
Drilling methods with shell can be employed in unconsolidated sediments above the groundwater level. A cylindrical drilling scoop loosens the substrate with cutting edges or spiral tips. The casing pipe picks up the disturbed drilling material. It is perforated for better emptying. It is driven by a drill rod in a rotating and pressing manner. The sample quality corresponds to quality classes 3-4 and is therefore sufficient for a first raw material assessment. The structure is disturbed. However, important layer boundaries are visible.
Dry rotary auger drilling is a cost-effective method for the exploration of cohesive loose rocks for example loam or plastic clay. It can be used for the Geological Classes 1-5 after DIN 18.300. The final depths usually reach 30-40 m.
The drilling auger cuts the soil with a cutting edge at the end of the spiral. A rotating drill pipe is the driving force to push the material out.
The sample material is compressed due to drilling according to the Quality Classes 3-4 after DIN 4021. The internal structure is destroyed but layer boundaries are well visible. Quality and amount of specimen are sufficient for a proper evaluation of the raw material. Modern plants are able to take special samples of the Quality Class 1 after DIN 4021.
The Rotary Drilling Method with auger or shell can be employed in geological formations of Classes 1-7 (all unconsolidated and solid rocks). It is an established method in the mineral oil and natural gas industry and allows final depths of several thousands of metres. In the case of direct jetting drilling the rock is detached by the rotary movement of the drilling tool (e.g. step bit, roller bit) from the bottom of the borehole and conveyed to the ground surface. The rinsing medium is pumped with piston or centrifugal pumps from a rinsing tank or rinsing bath through a pressure tube and the rotary head in the drilling rod assembly, or string of drill pipe, by the drilling tool to the borehole bottom. The rinsing medium together with the rock drillings enter the cavity formed between the drilling rod assembly (i.e. stand) and the borehole wall and is conveyed to the surface via the annular space.
The extracted drilling material settles in rinsing tanks or rinsing baths. The rinsing liquid, after removal of the solids, is then once more put into circulation via a suction tube. As with the use of such rinsing drilling methods specimen of Quality Class 5 according to DIN 4021 can be obtained which are only to a limited extend of appropriate depth, disturbed and above all incomplete, the use of this drilling method for brickmaking clay prospection is not recommended. In order to record important geological stratification boundaries, supplementary geophysical borehole measurements have to be carried out.
In order to obtain continuous, undisturbed, complete raw material specimen at appropriate depth rom geological formations of Classes 1-5 according to DIN 18300 (argillaceous clays, weathering clays and other loose rocks), ramming or punning core drills are successfully employed today. First a 168 mm stand pipe is positioned and the ramming core barrel is equipped with a PVC in-liner. Afterwards the core barrel is driven into the substrate with a pile hammer. The number of driving strokes is recorded to obtain information about the solidness of the subsoil. The distance core-drilled with PVC in-liner is usually one metre long. Once the ramming core barrel is completely driven into the substrate, according to the design of the pile hammer, the rammed core barrel is overdrilled with a string of casing (tubing dia. 168 mm) and the borehole wall thus secured. To make the extraction of the ramming core barrel easier and to protect the drilling core, water is used as rinse aid for overdrilling.
The rammer core barrel is then detached from the bottom of the borehole and secured with the help of a cable grad device via a cable winch. A core lifter clip at the bottom of the core barrel prevents the drilling core from falling out. After the drilling core in the PVC-in-liner has been removed from the core barrel, it is air-sealed and stored in core boxes.
A core diameter of 101 mm has established itself, because relatively large amounts of sample can be obtained. Depending on the solidness of the underground drill depths of more than 100 m are possible. The possibility to combine this method with the cable core drilling method is a great advantage of this method. In practice this means: after passing through the loose rock layers the ramming core drill can be deepened with the cable core drilling method. This is especially useful for the exploration of weathering profiles.
In solid rocks of the Classes 6-7 drilling cores are extracted with a rotary flushing drill technology. For the exploration of solid clay shales (playa clay sequences, clay stones, slate clays, phyllite slates) the rotary cable core drilling method with double core barrel is the best option. Especially because sediment structures and tectonic bedding conditions (inclined stratification, cleft structure, joint mineralization) can be well observed. The crucial advantage of double core drilling is the rotation of the outer barrel while the inner barrel is fixed. The drill core therefore is under permanent mechanical stress. The usual drill diameter is 146 mm with a core diameter of 101 mm.
The rinsing water in this drilling method flows via piston pumps from a rinsing bath or a rinsing tank through the rod assembly, so that the rinse flows by between the outside and the inside barrels and an undesirable influence on the drilling core is largely avoided. Only in the area of the drill bit, where the rinsing liquid comes out of the interlayer between inner and outer barrel, a 10 cm long piece of the core is in contact with rinsing liquid for a short time. The benefits of rinsing are cooling of the drill bit, separating drilling cuttings from the borehole bottom and stabilizing the borehole wall.
The standard length of the cored section is 1.5 or 3.0 m seldom 6.0 or 9.0 m. Once the core process is terminated the internal barrel with core yield can be recovered via a cable winch, while the drilling string with the drill bit remain in the borehole. After loosening the core catcher and careful extraction of the core the internal barrel can be put back into the borehole via cable winch. The essential condition for the extraction of ideally complete cores is a core maintained in good order. Loose rock fragments are not trapped by the core catcher spring and core losses occur.
The core quality and the core yield now naturally also depend on the right choice of drill bit used. In claystones generally hard, pin-type bits and carborite-faced bits of different types are to be recommended. If formations are to be deep-drilled where cores are difficult to obtain, the use is recommended with this dilling method also of a PVC in-liner, to give additional protection for the core from the mechanical influence of drilling rinsing. With the Cable Core Drilling Method, apart from the standpipe, core drillings without pipe lining of up to several hundred metres are possible. The so far deepest vertical Cable Core Drill reached a final depth of 3,500 m.
Formations of Classes 1-5 according to DIN 18 300 can be prospected without difficulty to depths of approx. 5 m below ground, using a hydraulic excavator set with backhoes. It is required that the layers to be explored are above ground water level. The essential advantages of this method consist of outstanding three-dimensional exploration and the possibility of on-site inspection under consideration of precautionary measures.
This way sedimentary structures can be described not only in depth but also in horizontal distribution and formation for example inclined stratification and type and intensity of joint structures. Low time effort and costs are also an advantage. In a short amount of time many outcrops can be obtained and geologically described.
Limiting factors are low exploration depth and the extend of crop damage.
Nonwithstanding the above excavation sites have to be closed carefully and in compliance with horizontal stratification. Prospect sites with excavator are recommended for a dense outcrop grid especially for the exploration of clayey overburden.
Geophysical measurements of the surface are based on the tracking of interfaces with different physical underground properties such as propagation of seismic waves or the electrical resistivity. The underground should be ideally built up by only two layers which should preferably differ significantly in seismic wave velocity and electrical resistivity.
Advantages of this method are widespread investigation and comparably low financial expenditure. Limitations result from the mandatory correlation of test results with results from direct outcrop methods usually core drillings. Geophysical measurements can be recommended to obtain a denser outcrop grid if the findings of direct outcrops are positive. While main raw material types like sand and clay can be differentiated, different types of clay cannot. No samples can be extracted with this method.
Exploration of deposits are associated with high cost and risk. The work results therefore should be well documented. All outcrops and sampling locations should be georeferenced and displayed in documentation maps for this purpose. To provide the officially mandatory proof of deposit, bore logs and bore profiles have to be confirmed by laboratory experiments. It has to be proven that the explored deposit is available in sufficient quality and quantity.
The duration of excavation proceedings differs in depending on the country and region. The proceedings tend to be more and more time-consuming and complex. In the European Union a preparation time of 10 years of more is to be expected. These long waiting periods are often underestimated by brick factories. With clay deposit remaining maturities of 15 years the search for new deposits should already be initiated.
