Client: LondonMetric Property PLC
Completion Date: September 2020
Architect: Corstorphine + Wright
Project Manager: Sharman Projects
Quantity Surveyor: Quantem Consulting
The single-storey 18,500ft² superstructure was designed around a braced steelwork frame with 23m Warren-type truss supporting the roof, with truss spacing of approx. 7m. A lightweight insulated sheeting supported on cold form purlins formed the roof while the façade was comprised of a proprietary cladding panel on cold form rails with internal mid-height 140 thick blockwork leaf.
With sustainability and environmental best practice being key priorities for the client, the building was designed to achieve a BREEAM rating of ‘Very Good’.
Despite the added complexities of the COVID-19 lockdown, social distancing measures and UK government guidelines were strictly adhered to, allowing work to continue and ensuring the successful delivery of the project.
In addition to the associated external works, a new bus stop adjacent to the site was provided as well as improvements to an existing bus stop. The local community and economy have also benefitted from the various jobs provided throughout the construction phase and since the full occupation of the site.
The level of complexity in this scheme included the following:
- Poor ground conditions
- Network rail constraints due to proximity to railway tracks
- Tree protection order (TPO) which required that excavation be kept to a minimum to ensure that the integrity and health of the identified trees was unaffected
- Existing and proposed ground levels which required a retaining wall solution
- A kingpost retaining wall solution was proposed which also limited the impact on tree roots and subsoil
- Diversion and modification of existing services and headwall
The site proposed levels and its relationship to the existing levels were considered using a cantilever retaining wall of kingpost type construction with hot rolled steel post at 1.8m c/c’s and pressure treated timber sleeper infill to timber durability class UC4 or precast panels where applicable.
The lateral stability to wind loads and notional horizontal loads were achieved via a combination of wind girder in the roof and vertical cross bracing on elevations as agreed with the architects.
A full site investigation was carried out to ascertain the subsoil conditions and record information obtained to help inform our engineering design.
Due to the variable strength characteristics and compressibility of the Made Ground and Alluvium beneath the site, the strata were not considered suitable to support traditional strip or pad foundations without ground improvement. Dynamic ground improvement methods were adopted as per advice provided by a ground improvement specialist, which then allowed mass concrete spread footings and ground bearing slabs to be formed.
Prior to the Planning Application being made, a CCTV survey of the existing drainage was carried out to ascertain the position and condition of the existing public foul drainage adjacent to and through the site.
The drainage design for the development sought to match the existing 1:1year Greenfield run-off rate for all storms up to and including the 1:100year. This was achieved through a reduction in flow by attenuating the surface water on site to allow it to be slowly released to the public sewer at the agreed reduced rate of 1.4l/s. The drainage was designed in line with the agreement between the Lead Local Flood Authority and evolve.
The requirements for a Sustainable urban Drainage System (SuDS) were also incorporated into the design, aiming to mimic natural drainage.
Below ground, the following drainage considerations were also made:
- Indirect connection to Wessex Water Foul and Surface Water Thames Water manholes
- Hydrobrake flow control unit
- Below ground attenuation tank
- Permavoid drainage channels with Biomat units for petrol interception
- Private gravity surface and foul water drainage
On the basis that the development has an assumed lifespan of 50 years, an additional allowance of 20% peak surface water discharge was included to allow for the predicted effects of climate change and increase in rain intensity.