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Nov 03, 2016 1st Factor (Image: Fragezeichen) 2nd Factor (Image: Fragezeichen) 3rd Factor (Image: Fragezeichen) |
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Nov 03, 2016 The required bursting force depends on: 1. Breaking resistance of the old pipeline 2. Displacement capability of the soil in the embedment 3. Amount of expansion (Image: Breaking resistance) (Image: Displacement capability) (Image: Amount of expansion) |
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(Image: Breaking resistance) The resistance to breaking of the old pipe is established by the:
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(Image: Displacement capability) The soil displacement capability is mostly established by its density. The main influencing factors include the:
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(Image: Amount of expansion) The amount of soil displacement (expansion) corresponds to the difference between the radius of the expansion and the internal radius of the old pipe. The overcut (i.e. radius of expansion minus external radius of the new pipe) should be as small as possible in order to minimize the movement of the old pipe fragments. (Image: Amount of expansion and overcut) |
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In determining the amount of soil displacement, the following questions must be answered while taking into account the existing soil conditions:
In order to prevent surface heaving or settling, a minimum depth of cover of 10 times the amount of expansion has proven to be effective. … |
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A buffer between parallel pipes of at least three times the amount of expansion (minimum 40 cm) has proven to be effective for cohesive soils [DWAM143-15:2005] (Image: Fragezeichen) Here is an example for the calculation of expansion amounts in cohesive soils: Diameter of the old pipeline: DN 10 in (250 mm) Calculation according to DWA-M 143-15: 3 x ( … |
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For non-cohesive and/or rocky soils, special considerations apply regarding the diameter and the material of neighbouring pipes. For brittle pipe materials and diameters smaller than DN 8 in (200 mm), the minimum spacing should be at least 5 times the amount of expansion. For nominal sizes larger than DN 8 in (200 mm), the spacing should not be less than 3.3 ft (1.0 m). (Image: Fragezeichen) Here is an example for the calculation of the expansion amount … |
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For non-cohesive and/or rocky soils, special considerations apply regarding the diameter and the material of the neighbouring pipes. For brittle pipe materials and diameters less than DN 8 in (200 mm), the minimum spacing should be at least 5 times the amount of expansion. For nominal sizes larger than DN 8 in (200 mm), the spacing should not be less than 3.3 ft (1.0 m). (Image: Fragezeichen) Example calculation: 5 x (13 in - 10 in) = 1.5 ft < min. … |
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(Image: Measured soil deformation as a result of an expansion [Zimme88]) Supporting findings come from the studies by Zimmermann and the LGA Nuremberg. These are the resulting relationships: Eb = (A – DN) x (4 to 6) with: Eb = Area of influence Example:
This results in a area of influence of: Eb = (575-400) x 4 = 27.5 in (0,7 m) Eb = (… |
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Nov 03, 2016 |
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Nov 03, 2016 The minimum distances to neighbouring utilities and structures depend on:
In case that minimum distances cannot be adhered to, special protective measures (such as open cut excavation at the crossing points) must be taken in order to prevent the transfer of loads. (Image: Underground utilities in … |
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Nov 03, 2016 Soil deformation is generally defined as the horizontal or vertical positional change of the soil surface or a point inside the soil. Vertical soil deformation in the direction of the ground surface is called heaving and in the opposite direction is referred to as subsidence, settling or settlement. |
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Nov 03, 2016 Subsidence is the vertical displacement of an entire soil layer (stratum), as a result of soil movement at a great depth. In this case, the size of the displacement can be determined, but not its timing [Schmi96]. Settling occurs in granular soils due to a sudden rearrangement of the grain particles caused by the addition of water. For loosely compacted soils, this settling can amount to up to 5 % of the layer thickness, and for densely compacted … |
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Nov 03, 2016 (Image: Soil deformation during pipe bursting as per [TTC2001]) |
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(Image: Target manhole - capstan winch) (Image: Tension sensor) (Image: Overload protection [Jürge05]) During the pulling-in process, the value of the allowable tensile forces on the new pipe must be strictly enforced. This is accomplished by continuous monitoring (measurement and documentation). Methods of tensile force monitoring:
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(Image: Target manhole - capstan winch) Pulling devices automatically limit the tensile force to the predetermined maximum value. Additional systems for the measurement and documentation of the tensile forces on the pulling device (cable winch) include electronic monitoring gauges and detailed printout reports. In some cases, these devices also have a PC interface for convenient data transfer. |
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In order to receive real time data from the pulling head, a data cable must be inserted ahead of the new pipe and connected to a computer. Otherwise, the data can only be collected after the completion of the pulling-in of the new pipe. (Image: Tension sensor) |
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As a reference, the following table shows the allowable tensile forces for PE 100 pipes for a load duration of 30 minutes (according to the German DVGW working sheet GW 323: Trenchless replacement of gas and water supply pipelines with pipe bursting; Requirements, quality assurance and inspections / not available in English at present). (Table: Allowable tensile forces for PE 100 pipes under a 30 min load) |
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The rupture strength of HDPE pipes is 2.5 times the allowable tensile strength [DVGWGW323]. The cross sectional area of a pipe section used as overload protection may only amount to 40 % of the cross sectional area of the new pipe being pulled in. (Image: Overload protection in form of a predetermined breaking point by reduction of the wall thickness) (Table: Example calculation of an overload protection for HDPE 100 used in pipe bursting) |
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Illustrated example of the steps involved in the manufacturing of the overload protection in the form of a predetermined breaking point. (Image: Step 1: New pipeline) (Image: Step 2: Wall thickness reduction) (Image: Step 3: Welding on of the overload protection) (Image: Step 4: Removing the weld seam) |
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A cross section reduction is obtained by reducing the effective circumference of the pipe or the effective cross-sectional area. (Image: Overload protection in form of a predetermined breaking point by reduction of the effective pipe circumference) (Table: Overload protection) |
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