________________ Whether in hard rock or in loose soils – maximum safety always comes first in tunnelling. Accurate preliminary exploration of the ground conditions is of immense importance. Despite intensive geological exploration, the construction ground along the tunnel route always holds surprises in store in terms of safety. The early detection of obstacles or difficult geological zones warns the machine operator, allowing him to take countermeasures in due time.
A look ahead with ISP and SSP
In hard rock, water- and air-filled cavities or abruptly changing weak zones in the rock represent a potential source of danger. These problems can be detected at an early stage by Herrenknecht‘s exploration system ISP (Integrated Seismic Prediction). A surface wave (Rayleigh wave) is transmitted along the tunnel wall which becomes a space wave at the tunnel face. When it encounters an obstacle, a “response” is generated via the reflected space wave. In this way, a water-/air-filled cleavage or a zone of decomposed rock can be detected, if the external dimensions (5 – 10 meters) are large enough.
In loose soils, the Herrenknecht exploration system SSP (Sonic Soft Ground Probing) helps to identify boulders, old sheet piles or shafts before they become an obstacle. The required transmitter and receiver are integrated into the cutting wheel. A signal is emitted during the tunnelling operations and it spreads out and is reflected by geological or artificial surfaces. The reflected signals are recorded and evaluated by several receivers. In this way, obstacles lying up to 40 meters ahead can be detected and displayed. The preliminary exploration process with ISP or SSP is carried out simultaneously to the advancing process without impairing tunnelling operations.
+ Early detection of potential obstacles in rock and loose soils
+ Preparation and alignment of tunnelling to geological fault zones
+ Optimal preparation of the mountain and the tunnelling strategy
Drilling devices for probe drilling
Probe drilling equipment with a range of up to 100 meters to the tunnel face work – depending on their design – with a top-hammer, a down-the-hole-hammer and rotary drillheads. To ensure that all drilling patterns are possible in the rock, the indexing systems, travel units, hydraulic power units and controls are developed by Herrenknecht in-house. Drainage and injection drilling rigs are used to stabilize heterogeneous soils. With the suitable equipment, they can be employed with a water pressure of up to 40 bar. A computer-supported system records and processes the surveying and drilling data collected during tunnelling in real time, and translates it into a geology report. This enables the machine operator to take the appropriate countermeasures in due time, for example, grout injection or ground freezing to stabilize the rock.
The Herrenknecht exploration systems enhance safet for personnel and machine, while at the same time making it possible to keep to schedule and budget and ensure rapid tunnelling operations.