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Burroughs Stewart Associates
1.1 Site Investigation 1.2 Drain Survey 1.3 Building Defects Survey
2.1 Low Level Superstructures 2.2 Higher Level Superstructures – Pitched Roof Area 2.3 Substructures 2.4 Internal Alterations
3.1 Existing (Combined) 3.2 New Stormwater Drains 3.3 New Foul Drains 3.4 Current Proposals – Derby Road 3.5 General
4.1 Existing 4.2 New Paving Throughout 4.3 Retention of Existing Pavement 4.4 Specification of Materials
This showed good competent soils at foundation level and no difficult foundation problems or special foundation types required.
The soils near surface level gave very low CBR (California Bearing Ratio) results and formation preparation (rolling) and a designed road make-up are required.
This showed drain conditions varying from adequate to urgent repairs required. The scheme should therefore address the issues highlighted in the drain survey.
This survey was limited to investigation of horizontal cracking due to corroded eaves brackets, timber condition at the junction of new structure to existing timber system buildings and delamination of the outer masonry leaf over the existing basement boiler room. The causes of these defects have been identified in those areas where the new structures abut the original.
These areas will be generally constructed with traditional masonry walls supporting timber flat roofs. Where curved elevations occur lightweight steel posts will be introduced to stiffen the elevation and provide support for steel roof beams which will in turn carry the timber flat roofs. The exception to the above is the north east gable of Block F which is of framed construction. The structural solution, however, will be similar with a grid of light weight steel columns and roof beams supporting a flat timber roof.
This occurs in the new assembly hall, which will be constructed using a grid carrying laminated timber/stainless steel trusses. The roof will consist of a timber diaphragm supporting the insulation and roof sheeting. This diaphragm will carry lateral loads to a steel frame in each gable of the hall, while longitudinal stability will be provided by steel flat bracing hidden in the collar joints of the main 215mm thick walls.
The site investigation shows competent soils at convenient levels and the foundations will be either standard strip footings or small mass concrete pad footings under columns as appropriate.
These alterations consist mainly of the introduction or removal of light non-load bearing partitions. The removal of partitions will generally have no structural implications and effects will be purely cosmetic. In the odd instance a partition may be providing lateral restraint to an external elevation (although currently no such situation exists) and the introduction of a light steel section spanning between floor and roof will replace this function.
Where partitions are to be introduced the options available are dense blockwork, studwork or lightweight blockwork. Dense blockwork would pose handling problems and would be limited to 100mm in width on health and safety grounds. Studwork while acceptable structurally may pose sound transmission problems.
Thermal insulation blocks pose a variety of problems, the major one of which is fixings. This, however, is generally due to the very low block strengths which are normally used. If a stronger block such as Thermalite Hi-Strength 7 is used this
problem is largely over come and wall thicknesses of 100mm to 150mm can be achieved. As the weight of a 150mm thick block is 11.2kg the health and safety issues are overcome and material handling is eased.
The latter specification is therefore recommended with the introduction of light anti-crack bed joint reinforcement for longer panels. The low loads generated by these partitions will allow them to be built off the existing floor slabs.
In a few cases load bearing walls are to be removed or openings created in them. As these walls generally support a light flat timber roof the propping of existing ceiling and the insertion of steel beams will constitute only minor construction items.
The existing drainage consists generally of three main combined lines running from the north east corner of the site towards the south west corner of the site. These lines are collected at manhole No. 1 towards the south west corner of the site and from there discharge in a south westerly direction through a 150mm diameter vitrified clay drain. Unless otherwise stated all existing drains are of vitrified clay and manholes are constructed of brick.
Of the three main combined lines the one running parallel to the north-west boundary is in a state of collapse and should be replaced as soon as practical. As the conditions of the manholes are basically satisfactory the preferred solution would be to replace the pipework between the manholes.
The middle line of combined sewer is not in good condition with at least one break, one crack and many displaced joints. However, this line is presently fulfilling its current function and as the proposed increase in flow from this portion of the alterations is less than 20% of the pipe capacity the line can be utilised.
The most southerly of the existing lines is not in good condition with several breaks, some root penetration and displaced joints. It is, however, fulfilling its current function and as the drainage regime upstream will require extensive alteration for the new hall etc., the lower drainage run can be utilised as required.
As the smaller isolated areas of new build largely consist of covering impervious areas (hard standing) with new roofed areas the effect on flows to the existing pipework will be negligible and the existing combined drains may be utilised.
The drains in the area of the main entrance and new hall will require replacing and the layout will, to a large extent, be dictated by the requirements of the new stormwater drains serving the roads, parking and hardstanding.
Excluding existing areas of roads and hardstanding, which are undrained or are poorly drained, there are approximately 2000 square metres of new roads, footpaths and parking to be serviced. To this must be added the main building extension and present inadequately drained areas, which total approximately 1150 square metres. Thus the total additional impervious area to be drained is 3150 square metres.
The design criteria to be utilised would normally be a two-year return period, 100 percent run off and a pipe roughness of 0.6mm. For the area in question the total time of concentration will be approximately 5 minutes and this will result in an additional piped flow of 44 litres per second.
To summarise the above, the stormwater from the small independent areas to be developed around the existing buildings may be discharged to the existing combined system. The roads down the south-east boundary of the site and the roads and parking along the front boundary of the site will require to be served by an independent stormwater system. The head of this system can be utilised to pick up the stormwater flow from the hall and extended administration area. The discharge from the system would be in the south west corner to the new split system currently proposed for Derby Road. It is necessary to separate the surface water from the foul flow regardless of whether the existing road areas are retained or not.
The foul drains would be similar to the storm drains in that small independent areas developed around the existing building can be discharged to the existing combined system. The new hall and the extended administration area should be discharged westward parallel to the existing drain run, then pick up the flows from the special needs unit and discharge to the south west to the new split main in Derby Road.
There is at present a scheme designed to replace and divide the Peel drainage system into foul and stormwater lines. The scheme starts at the harbour and runs up Derby Road past the school. Phase I of the scheme from the harbour to Albany Road is due to commence this year with the timing of Phase II as yet undecided. If Phase II has been completed by the time the school reticulations are ready then two direct connections for foul and stormwater drainage will be required. If Phase II is not available temporary foul and stormwater connections can be made to the present combined system through a single manhole.
The scheme described above allows for the new extensions to be provided with storm and foul drainage systems and, where practicable, for these systems to be split. It makes no specific allowance for duplicating existing drains and manholes or for repairing or improving existing drains. However, where new drains can be utilised to pick up and separate existing flows this has been done.
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