|
PLACEMENT
AND PIPEJACKING PROCESS FOR METAL JOINTS |
1.-GENERALITIES
As part of the construction and pipe-jacking of the 2.44, 2.13 and 1.83 m diameter collector piping, it will be necessary to place a temporary cofferdam and scaffolding system to allow the excavation to be done while preventing any water filtration into the ditch during the construction process.
To that end, the use of a scaffolding system has been proposed, that consists of a metal cofferdam supported by a group of joists located placed throughout the rest of the lateral excavation walls.
This specification provides the general guidelines and necessary recommendations that should be followed exclusively for the driving and placement of the metal cofferdam.
The driving of cofferdam metal plates will be carried out with mechanical equipment powerful enough to drive plate’s outer wall into the pipe.
The following steps are the stages into which the construction process has been subdivided, and it is also applicable to the construction of the access port, making note of some restrictions which will be outlined later.
PERIOD I.-REMOVAL OF EXCISTING INSTALLATIONS AND STRUCTURES
PERIOD II.- GUIDE INSTALLATION
PERIOD III- COFFERDAM PLATE DRIVING
PERIOD IV.- COFFERDAM PLATE REMOVAL
2.-CONSTRUCTION PROCEDURE
The following is a detailed procedure to be followed during cofferdam plate driving, plate placement, and plate removal activities.s.
STAGE 1. - REMOVAL OF EXCISTING INSTALLATIONS AND STRUCTURES
Before beginning any work involving the placement and driving of metal plates, it is necessary to remove all types of existing structures and installations such as roots, or tree stumps that might exist in the driving zone. Once the preliminary tracing and leveling work is done, it will be necessary to precisely locate the spot on the field where the cofferdam plates will be driven.
STAGE II. - GUIDE INSTALLATION
Once the previous stage is completed, a guide will be placed over a surface 2.50 m above the natural terrain, which will be used to maintain the base of the metal plates steady during driving, as well as to prevent lateral deviations in any of the plates to be driven. The position and orientation given to each metal plate will have to be placed perfectly on site.
Once the plate positions are set are set, a ditch with an approximate depth of 2.50 m will be dug with a 235 Cat backhoe loader.
Next, a metal frame (made of joists and 12” x 8” IPR profile stamped steel previously soldered with 1/8” E-7018 solder) is placed inside the excavation site and leveled according to the projects leveling benches. The soldering will only require visual inspection by the project’s resident engineer since it is only provisional piling work.The ditch will then be partially covered with the excavation material, so that the guide frame will be fixed in place, and the 1.26 m thick and 12.2 m long steel plates can be driven in pairs, making sure they are properly leveled and plumed.
STAGE 111. - COFFERDAM PLATE DRIVING
The plates will be made from profiles type AZ13 structural, in 1.26 m wide and 12.2m long pairs.
The cofferdam plate driving process has been divided into to phases which will be carried out simultaneously with some restrictions outlined later. The phases are as follows.
PHASE 1. -COFFERDAM PLATE LINEUP
The cofferdam plates will be lined up over the natural terrain surface, and they will consist of a group of 4 metallic plates maximum, which will be numbered and coupled, making sure to properly grease up the joints as they are joined; and with the use of a crane with a sufficiently long arm, they will be hoisted and placed in the previously installed guide.
PHASE 11. - PANNEL DRIVING
Once phase 1 is completed, mechanical equipment with sufficient power will be used to drive the cofferdam plates. Once a plate is placed on the guide with its bottom end of the lying within the space defined by the guide, the driving of the cofferdam plate will proceed while minding the following guidelines:
- The placement of the first plate should be done in one of the extremes of the metallic sheet piling that is being placed.
- In order to place a second panel, the previous one must have been driven all the way flush with the surroundings.
- Every piece of the cofferdam should be correctly joined to the previous piece, except for the access port corners.
Once each of the steel plates has been driven, the head level is obtained, and this level must be verified to conform to the project’s specifications once all the cofferdam plates have been driven.The plates will be embedded to 0.5 times the maximum depth of excavation.
Their length will be 12.2m.The cofferdam metal plate driving should be done in such a way that correct placement of the plates is guaranteed, so that the project’s objective can be met.
Furthermore, the driving process should not cause any damage to neighboring structures and installations.
STAGE V. - COFFERDAM PANEL EXTRACTION
The extraction of the cofferdam metal plates should be done once the pipe-jacking work has been completed.
The extraction of the plates will depend on the quality of the driving work done previously. A well driven cofferdam will be much easier to extract than one who’s elements are twisted, separated, or misaligned.
3.- IMPORTANT NOTES
1. -A greasing compound must be used on the joining surface of all cofferdam plates in order to reduce friction.
2. -The vertical orientation of all cofferdam plates should be closely observed and verified during the driving process. Any deviation tendencies that may be displayed must be immediately corrected.
3. - In order to obtain good alignment and vertical control of all cofferdam plates during placement, the use of a crane is recommended to minimize the risk of experiencing driving difficulties and alignment deviation problems.
4. - During the hoisting and driving processes involving cofferdam panels, the vertical orientation and alignment of their walls should be verified with an art plumb.
