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signed for a maximum penetration ratę. They are therefore relatiyely unsensitive to variations In the hardness of rock or the relative density of soil.

The contact between the soil and rock can be de-termlned accurately on locatlons where the rock is overlain by loose soil. The method can also be used to check that rock is not present within the depth of excavations for water or sewer lines. It is also possible, under favourable conditions, to detect with soil-rock sounding in the rock crack or fault zones or other zones with poor rock.Such zones are indicated by high penetration rates, by the tendency of the drlll to get caught or by the loss of drilling fluid. Also the content of boulders in soil can be estimated through soi 1-rock soundings. A reliable determination requires, however, a relatively large number of borę hol es. Then the method becomes uneconomic and timecon-suming.

On locations where a dense cohesionless materiał overlays rock, or where the rock surface is very decomposed, it can be difficult to determlne the boundary between rock and soil. It is also dif-ficult to separate rock from till, when the penetration ratę in the rock is relatively high.

The work group for soil-rock sounding within the Committee on Penetration Testing of the Swedish Geotechnical Society suggests one or several of the following methods as a complement to soil-rock sounding to facilitate the interpretation of the test results.

1.    Study of cuttings

2.    Acoustical methods

3.    Permeability measurements in the borę hole (water pressure tests)

4.    TV-inspection of borę holes

5.    Coring

6.    Borę hole seismic methods.

The work group also recomnends that soil-rock sounding should be supplemented by geological inyestigations.

Morfeldt et al(1973) has suirwarized some parame-ters which should be investigated in connection with rock inyestigations. They are principally the same as for soil-rock soundings, but the aim may be slightly different. The inyestigations should give Information about type and strength properties of the rock (e.g. compressiye strength), its particie size and minerał composition, cracks, compression zones and permeability. Durlng drilling it is possible to measure drilling ratę, depth of borę hole, air or fluid pressure, feed pressure, rotation ratę and torque and to observe the cuttings. Before or after the drilling the influence of the operator, circulating fluid, drilling machinę (size, type and condition), dimension, type and wear of drill bit, losses in splices and thickness of soil cover are estimated.

Some of the parameters mentioned above are inclu-ded in the proposed standard for soil-rock soundings. This proposal by the soil-rock sounding group is based on an inquiry among mainly boring contractors. The proposed standard can 1n certain parts be used imnediately. Some modifications of the machines will, however, be required before 1976 to comply with the proposed standard.

Machines for soil-rock soundings are classified according to the proposed standard as light, medium and heayy (Fig.22). Which type should be cnośefi is deplńdent on soil type, thickness of soil coyer and the purpose and required quality of the inyestigation. The maximum drilling depth in soil is for light and medium machines about 8 m and 15 m, respectiyely. When the depth ex-ceeds this value heayy equipment should be used.

Fig. 22

Proposed classes for soil-rock sounding equipments

a)    Light (reference equipment: Atlas Copco drill wagon Promec with drilling machinę BBC 24).

b)    Medium (reference equipment: Atlas Copco drill wagon BVB 23 with drilling machinę BBC 100).

c)    Heayy (reference equ1pment: Atlas Copco drill wagon ROC 601 with drilling machinę BBE 57).

d)    Drill bit with four cutting edges.

It has been proposed to adopt as standard 1n 1974 (1) separate percussion and rotation system for heayy machines, (2) chassis for medium and heayy machines, (3) outside and 1ns1de diameter the drill string of 25 mm/8mm (light), 32 mm/12 mm (medium) and 38 mm/15 mm (heayy),respectiyely,

(4) nominał diameter and diameter at rejection of drill bit equal to 41 rran/38 mm (light),51 mm/

47 mm (medium)and 64 mm/59 mm (heavy), respectiyely and (5) air pressure indicator. The drill bit should normall be proyided with four cutting edges (Fig. 22d).

In addltion it will be necassary to conslder the following points, some of which may be included in a futurę standard. (1) Pressure 1n circulating fluid, (2) flow yelocity of the circulating fluid, (3) rotation ratę, (4) torque, (5) axial force in the drill rods, (6) hoses, (7) length of drill rods and (8) need of silencers and dust separators to improye the working conditions.

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