LIMITS OF SURFACE SETTLEMENT
The method of jacking adopted by the Contractor shall be such that the initial surface settlement measured directly above the front face of the shield during the jacking operations do not exceed 25 mm and the maximum surface settlement after the tail voids are grouted shall not exceed 50 mm. Subsequently, the ground shall be reinstated to the original level.
However, for the sections of pipeline crossing under all roads along the route of the pipeline and paved area, the Contractor shall be required to incorporate in his jacking method measures to arrest the expected settlements so as to safeguard the integrity of the road surfaces at all times. The Contractor shall ensure that the traffic flows along all roads are not affected in any way by his work.
Not withstanding the above, the Contractor shall comply with the latest Code of Practice for Railway Protection (where applicable) by LTA and all other LTA regulations and requirements.
The jacked pipe shall be controlled such that;
The vertical deviation from the design grade is not greater than 25mm and
The horizontal deviation from the design alignment is not greater than 50mm.
An as-built survey shall confirm the line and level of the centre of the pipe. These surveys shall be carried out at a frequency to be agreed with the S.O.
Should the excavation be off line or grade, the return to the design line and/or grade shall be at a rate of not more than 10mm per 4m (1:400) or that shown in the pipeline drawings。
The S.O. shall be notified immediately if the alignment reaches 18mm off level and 40mm off line.
In the event that the vertical or horizontal tolerances are exceeded or in the opinion of the S.O. are likely to be exceeded the Contractor shall cease advancement of the jacked pipe and submit to the S.O. for acceptance a Recovery Plan that demonstrates clearly a methodology and procedures for return to the design alignment
Under no circumstances shall the pipe jack continue once either the vertical or horizontal tolerance has been exceeded until the S.O. has accepted the Contractor's Recovery Plan.
After factory testing and before despatch, every pipe shall be marked in accordance with the Standard used. In addition, each pipe shall be stamped with a number corresponding with the order of manufacture. Test certificates from the manufacturers or other relevant authority shall be submitted to the S.O. with a copy retained by the Contractor on site and made available upon request from the S.O.
All workmanship and materials used in the manufacture shall be subject to the acceptance of the S.O. who shall be from time to time be permitted to inspect materials at source and the manufacturing processes in the factory.
Pipes shall have roundness such that the difference between the minimum and maximum external diameter does not exceed 1% of the specified nominal external diameter or 6mm, whichever is the lesser.
Pipes shall have an outer circumference that is within -+1% of the nominal circumference or within +_12mm, whichever is the lesser.
SHAFrS, ACCESS MANHOLES AND CHAMBERS AND OTHER SURFACE OPENINGS
Temporary Trench Support of Surface Openings
32.1.1 Wherever the sub-soil conditions are expected to be of a soft and unstable character, the normal methods of timbering shall probably prove insufficient to avoid subsidence of the adjoining road surfaces, concrete drains and canal and other services.
32.1.2 In such circumstances the Contractor shall be required to use steel trench sheeting or steel sheet piling or some other retaining wall system adequately supported by timber struts, wailings, etc.
Steel sheet piles shall conform to the provision of B.S. 4360 and shall be driven where required and approved or directed by the S.O.
32.1.4 Where used the Contractor shall be required to design the layout of the temporary support system and the overall dimensions of the excavation to suit the available working space and geometry in order to provide and to give sufficient working space for the proper construction of the work.
32.1.5 The Contractor shall be expected to supply, pitch, drive and subsequently remove trench sheeting or piling in accordance with other items of the Specification and the terms "timber" or timbering" shall also apply to steel trench sheeting or steel sheet piling throughout.
32.1.6 All temporary trench support must be designed by the Professional Engineer engaged by the Contractor. The Professional Engineer must make an effort to visit the site on a regular basis to ensure and certify the adequacy of the construction of the works designed by him. He shall submit a certificate of supervision to S.O's acceptance for each shaft/trench constructed.
The excavations for manholes/chambers may be used as working shafts. Where a working shaft is used for the construction of a manhole/chamber, the Contractor shall allow for this in his rates for construction of the manhole/chamber. Additional working shafts may be sunk with the approval of the S.O. but shall not be paid for.
32.2.2 The Contractor shall submit for approval to the S.O. dimensioned drawings and calculations of the timbering or trench sheeting details for the working shafts. Each working shaft shall have a separate ladder bay for access, which shall be isolated from the part of the shaft used for hoisting materials.
Shaft Break-Outs and Break-Ins
32.3.1 Ground improvement such as jet-grouting or other acceptable means shall be provided at shaft breakouts and break-ins as required to prevent instability of the ground as the pipeline excavation or pipejacking work exits or enters a shaft and elsewhere as required. The Contractor shall allow for such ground improvement works in his tender and no claims for extension of time and loss and expense with respect to such work shall be entertained.