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Aug 01, 2008
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Jul 31, 2008 This presentation is part of the series of presentations "Utility Tunnelling" and intends to give an extensive introduction to the topic of trenchless technologies. |
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The open cut method of pipeline installation is characterised by:
(Image: View into an inner-city building pit with linear shoring elements with boogie car/roller frame) |
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(Image: Example of subsoil risks) The planning stage requires information regarding the projected construction and the local boundary conditions. It appeared in practice that especially the following criteria are to be considered:
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Information on the subsoil and its characteristics (soil parameters) as well as on groundwater conditions is required for the:
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The subsoil conditions either have to be known or need to be investigated. Methods for geotechnical investigation are:
(Image: Direct explorations – Trial pit) (Image: Direct explorations – … |
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(Image: Subsoil exploration by means of dynamic probing) The number of, and spacing between, the individual subsoil explorations have to be chosen in accordance with the geological conditions and the engineering needs, and should normally be between 165 ft and 655 ft (50 m and 200 m). The depth of the explorations has to include all soil strata that might be influenced by the structure, and has to extend to at least 7 ft (2 m) below the trench base. |
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The extent of the assessment regarding the degree of aggressivity of different types of water, soil and gas is significantly influenced by the pipe material. Examples for the requirements for the evaluation of the corrosion probability of metallic material can be found in [ [DIN50929-3]]. Cement-bound material can be detrimentally affected by different types of water and soil, if these contain the following components:
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Planning and execution of utility trench construction should follow the rules and regulations shown in the table below.
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As a part of the execution planning, a detailed design of the sewer lines and structures is prepared, and includes the following components:
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(Image: Installation of gas- and water supply lines and sewer in a trench - Image 2) If there are several pipes (e.g. supply- and disposal piping) installed in one trench, the required material- and system-dependent minimum distances have to be kept. |
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The following information includes some of the details required by, and for, the successful execution of work:
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Where required, the limiting values for deviations from the determined lateral and vertical position of the pipe are to be specified. They depend primarily on the following factors:
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(Image: Attention!) It is important to note that the materials used in the construction process should not negatively affect the structural components or the groundwater and soil. |
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Apr 17, 2019 |
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Apr 17, 2019 There has to be a contractual settlement between the client and the contractor with respect to the following items on the agenda:
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Apr 17, 2019 (Image: Open cut method of construction – Built-up area in the zone of influence of the building pit) Prior to the start of the civil engineering works, the exact position of the structures (buildings, piping, cables etc.) within the construction area of the excavation is to be crosschecked by the contractor. The trench construction process should never result in deformations or settlements of the surrounding structures. It is important to ensure that … |
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Apr 17, 2019 Depending on the individual requirements, the open cut method of construction allows for different cross sections of utility trenches, ranging from the sloped trench to trenches with vertical faces [Stein88d]. Combinations, such as stepped trenches with vertical, sloped or partly sloped trench walls, can also be found. (Image: Cross sections of utility trenches for the installation of sewers by means of the open cut method of contruction in accordance … |
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(Image: Attention!) Excavations and trenches are to be sloped, lined or secured in any other way in order to ensure that they remain stable during all individual states of construction. All conditions and influences that could have a negative effect on the stability of the excavation walls or trench walls are to be taken into account, particularly the differences in the behavior of non-cohesive and cohesive types of soil. (Image: Unshored trench with … |
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Apr 17, 2019 OSHA defines cohesive soil as "clay (fine grained soil), or soil with a high clay content, which has a cohesive strength. Cohesive soil does not crumble, can be excavated with vertical sideslopes, and is plastic when moist. Cohesive soil is hard to break up when dry, and exhibits significant cohesion when submerged. Cohesive soils include clayey silt, sandy clay, silty clay, clay and organic clay." [[OSHA 29 CFR 1926 Subpart P App A]] Non-cohesive … |
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Apr 17, 2019 (Image: Attention!) (Image: Trench excavation úsing a crawler excavator) During the excavation process, it is necessary to inspect the in-situ soil in order to ensure that it’s properties match the assumptions that have been made in the structural calculations (e.g. by means of soil identification). In case of deviations, it is imperative to inform the construction supervisor or structural engineer. |
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Existing piping and cables need to be taken into consideration when working in urban locations. In case of doubt, it is recommended to excavate the area in question using hand tools or hydro or vacuum excavation in order to determine the exact position of other services, as their actual position very often deviates from the planning drawings. Located services need be properly secured through suspending, supporting, rerouting etc. measures as specified … |
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