Futher Applications and Drilling Procedures
A profound understanding of the manufacturing and drilling processes is required in order to develop optimised machinery and tools for special foundation industry. At KLEMM Bohrtechnik, this know-how flows directly into the products.
Production Process for grouted Anchors
To install and fix a grouted anchor the following stages are essential:
Drilling of the bore hole by way of one of the drilling processes dictated by the conditions (type of ground, groundwater, adjacent buildings ...).
Withdrawal of the drill rods after or during the filling and grouting with mortar and sinking in the anchoring tendon.
Subsequent grouting of the anchor. At an increased suspension pressure the grout body is ripped open. The resulting cracks and gaps are post-grouted with cement suspension, possibly several times.
Acceptance testing and fixing of the anchors. The steel tendon is tensioned by a hollow piston jack beginning with a high pressure test load, and in stepped load cycles, tensioned and released to fixing force several times. At each stage the time-dependent settling behaviour (creep) of the grout body in the ground and the elastic behaviour of the free tendon length are verified.
If the creep of the component reaches a steady state and the required free elongation length of the anchor are satisfactory then the tension member is finally fastened and wedged in place, using the anchor head. A test protocol is prepared for every anchor. Any projecting strand ends are removed and the anchor head is closed with a cap. This is the final stage in the production process of an anchor.
Drilling Procedures for grouted Anchors
There are various methods of producing a drilled hole. At the time of the invention of the grouted anchor it was mainly percussion drilling with lost drill bits, for non-cohesive soils hammer rods with an external diametre of 76 mm were very widely used. In cohesive soils came rotary drilling method with stage drill bits or tricones. Very soon drilling with a wider diametre was required. Quickly higher anchor forces and additional post grouting pipes mounted on the tension member made greater drilling diametres necessary. The expansion of the traffic routes called for even more stabilisation of slopes with extremely long permanent anchors – and this too placed more demands on the drilling depths. These could go from 40 m to 60 m, and in exceptional cases up to 100 m. This exceeded the depths achievable at the time with percussion of about 20 m, and with a compressed air driven rotary percussion to around 30 m. Pure flushing bore methods – as generally used in water well drilling – couldn’t tackle this due to the associated fine soil washout and risk of subsidence.
Back then a new process and drilling tools were developed by KLEMM Bohrtechnik, for example for overburden drilling with a hydraulic drifter. The term overburden drilling comes from the fact that the outer casing and drilling rods first move together through loose soil that covers the bedrock horizon. As soon as solid rock is met the outer casing is left in place and drilling is continued with just the drilling rods. Today the expression overburden drilling is used for almost all drilling where loose rock is found near the surface.
The limits of classic overburden drilling are determined by the presence of intercalating loose and firm rock formations because the casing advanced by rotation only cannot get through rock shelves and in addition loose rock layers below the shelf normally collapse.
01 Rotary drilling with a single rod
02 Rotary drilling with auger rods
03 Rotary percussion drilling with a hydraulic drifter and a single rod
04 Overburden drilling with hydraulic hammer and double bit
05 Overburden drilling rotary / rotary with double head drilling equipment
06 Overburden drilling rotary / rotary percussion with double head drilling equipment and down-hole-hammer