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3. Micro-tunnelling: methods ATV A 125 describes the currently practised methods of micro-tunnelling for unmanned pipe jacking. Non-controllable methods and controllable methods are distinguished. Because of the high requirements with respect to positional accuracy, under ATV A 125 Section 5 only controllable methods should be employed for thrust-boring sewers and drains. The figures shown below for maximum deviations in mm from the specified position (Table 11 in A 125) should not be exceeded. DN vertical horizontal 600 20 25 600 bis 1000 25 40 1000 bis 1400 30 100 1400 50 200 Max. deviation in mm from specified position for sewers and drains 3.1 Non-controllable methods In constructing lareral sewers non-controllable horizontal thrust borers, used mainly for nominal size DN 150 and limited jacking distances, are also employed. Given favourable local conditions and appropriate gradients, jacking distances below 20 metres are possible. The horizontal thrust borer advances a steel casing tube, the ground being simultaneously broken down mechanically at the face by the cutting head and the extracted soil conveyed by augers (Fig. 5). The horizontal thrust borer is installed and braced precisely with respect to level and direction in the starting shaft. When the target shaft has been reached and the augers retracted the steel casing tubes are pressed into the target shaft and there removed, allowing an adaptor holding product pipes of the same bore being inserted. It sometimes happens that the location for the target shaft on the plot to be connected is for various reasons not yet available. To avoid the necessity for intermediate shafts in or close to the pavement in front of the plot, socalled blind shafts have been developed. As soon as the horizontal thrust borer reaches the target for the advance, the augers with cutting head are retracted and the product pipes inserted into the steel casing tubes Micro-tunnelling Page 9 with stopped ends. Then, while the product pipes are retained, the steel casing tubes are retracted to the starting access shaft (Fig. 6). With careful matching the void formed between steel and product pipe can be kept so small that any setting is negligible; neither, because of their greater wall thickness, are any problems caused for the jacking pipes by the absence of lateral support. Sizeable voids should however be filled. The blind boring, providing the means of underground connection to existing collectors ≥ DN 300 or shafts, was developed some years ago by Bohrtec. Here, in addition to the horizontal thrust borer, a drill rod, diamond bit and special sealing element are needed. Once the thrust borer has reached the collector or shaft, augers and cutting head are retracted and the drill rod with diamond bit inserted. Drilling into the collector is monitored from inside by television camera. There the drill core too Starting shaft 1. Boring Fig. 5: Non-controllable horizontal thrust boring Steel casing tube Thrust borer Screw conveyor 2. After-pushing of product pipes Starting access hole 1. Boring Cutting head Product pipe (jacking pipe) Steel casing tube Steel casing tube Adaptor Drill head Thrust borer Screw conveyor Product pipe Steel casing tube 2. Insertion of product pipes Retaining assembly Stopper 3. Retraction of steel casing tubes Target shaft Fig. 6: Non-controllable horizontal thrust boring: making a blind hole
Fig. 7: Non-controllable horizontal thrust boring: blind hole with underground connection to a collector Page 10 Micro-tunnelling is removed. The lateral sewer made of DN 150 vitrified clay pipes is then drawn in. At the point of this rod is the special sealing element, which ensures proper connection of the product pipe to the collector. The steel casing tubes are then retracted and the void surrounding the product pipes filled with a special slag (Fig. 7). An alternative method of non-controlled thrust boring is underground drilling from a ≥ DN 1200 collector. A trolley can be brought to any drilling point in the collector and be set to the required angle of incline up to 90˚. Using adaptor and diamond bit, the collector is then bored through to the required external diameter. Subsequent drilling through the ground is performed with steel Starting shaft 1. Boring 2. Collaring casing tube and augers. When the thrust-bore target is reached, the augers are retrieved and the underground wall or inspection chamber drilled through with drill pipe and diamond bit. Finally the product pipe is inserted and the steel casing tube retracted while the product pipe is Fig. 8: Non-controllable horizontal thrust-boring: boring from a ≥ DN 1200 collector Steel casing tube Cutting head Thrust borer Screw conveyor 3. Insertion of product pipes with special sealing element 4. Retraction of steel casing tubes Collector Pipe Ø DN 1200 mm upwards retained. If there is adequate working space in the thrust-bore target, the product pipes can alternatively be pushed through afterwards and the steel casing tubes removed at the target (Fig. 8). 3.2 Controllable methods For constructing sewers and drains three thrust-boring methods in particular have come to predominate in practice: pilot pipe jacking and thrust boring using steel joint heads and mechanical or hydraulic soil transport (auger orslurry conveying). Pilot pipe jacking In this process a steel pilot pipe, hollow and therefore having an optical channel, in sections normally of 100 cm length and with an external diameter of about 10 cm is driven from a starting shaft to a target hole, compressing the soil. Directional accuracy is normally monitored by means of a theodolite with CCD camera located in the starting shaft and a diode panel fitted in the optical channel in the first pilot pipe. The position of the externally tapered first pilot drill pipe is continuously transmitted to a monitor in the starting shaft. If it deviates from the specified axis, the pilot drill rod is turned so that the angled head at the point of the string brings about a directional correction as it is further advanced. Accurate arrival of the pilot drill rod in the target shaft and its recovery there rod by rod are followed by an adaptor widening the cross-section to accommodate steel casing tubes with augers. The soil is conveyed to the starting shaft. When the steel tubes have reached the target shaft, the augers are retracted, an adaptor is inserted, the product pipes are pushed in behind and the steel casing tubes are recovered in the target shaft (Fig. 9). Fig 10 shows the final phase of pilot pipe jacking using DN 150 vitrified-clay pipes. This method has proved itself over years for installing house connections up to 20 (max. 30) metres long. In loosely bedded soils without embedded rock two-phase application, i.e. without steel casing tube, is also sometimes practised. Numerous improvements in detail, especially in the coupling for the pilot pipes, have enabled this technique to be used for about two years now also for underground laying of DN 200 and DN 250 sewers with the section lengths normal in sewage systems. Like all pilot pipe jacking, however, this technique requires displaceable soil without substantial embedded obstacles. The pilot drill pipe has recently also become available in watertight form, so that with a modified screw-conveying
Page 1 and 2: Cost-effective and environmentally
Page 4: Contents 1. Introduction . . . . .
Page 7 and 8: m 350.000 300.000 250.000 200.000 1
Page 9: Page 8 Micro-tunnelling Quite diffe
Page 13 and 14: Page 12 Micro-tunnelling Elements i
Page 15 and 16: Page 14 Micro-tunnelling pipe. Used
Page 17 and 18: Page 16 Micro-tunnelling The follow
Page 19 and 20: Fig. 20: Berlin method: by-shaft be
Page 21 and 22: [m] 8.000 7.000 6.000 5.000 4.000 3
Page 23 and 24: Page 22 Micro-tunnelling - 6 classe
Page 25 and 26: Page 24 Micro-tunnelling 7. Cost-ef
Page 27 and 28: Page 26 Micro-tunnelling 7.2 6000 5
Page 29 and 30: Page 28 Micro-tunnelling 7.4 7000 6
Page 31 and 32: Page 30 Micro-tunnelling 7.6 Social
Page 33: Page 32 Micro-tunnelling 6. For eve

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