Bridge Footing Design

Project Brief

Emm Brook

Project Background

The Emm Brook is a tributary of the River Loddon and is failing its ecological targets due to its industrial

legacy and urbanisation. The weir behind Morrisons supermarket in Woosehill Park, Woosehill,

Wokingham (NGR SU7982469269) has been identified as contributing to this.

Project Aim

The proposed solution is to provide fish passage past the weir by reconnecting the former route of

the river which runs through the public parkland to the east of the current modified channel.

To provide pedestrian and vehicle (up to 5 tonnes) access across the newly restored channel, two

bridges will need to be installed. This ‘Scope of Works’ covers the design of the bridge

footings/substructure only.

Site Details

Figure 1 & 2. Location of the project site (left) and the proposed route of bypass channel (right)

The proposed locations of the two bridges are indicated in Figure 3.

The northern bridge (NGR: SU 79937 69107) will replace an existing piped culvert crossing of the

former/bypass channel (Figures 4 & 5).

The southern bridge (NGR: SU 79891 68998) will cross the newly dug section at the start of the start

of the bypass channel (Figure 6).

Figure 3. Location of the proposed bridges along bypass channel. Numbered arrows indicate

orientation of photo’s shown below .

Figure 4 – Proposed location of northern bridge. Existing culverted crossing of Paleo channel running

into pond (left). Looking NE towards Brookside.

Figure 5 – Proposed location of northern bridge. Existing culverted crossing of paleo channel running

into pond (right). Looking SW towards main channel of Emm Brook.

Figure 6 – Proposed location of southern bridge. Yellow arrow indicating approximate location of

proposed bridge crossing new bypass channel.

Bridge Requirements The exact bridge specifications are yet to be finalised but the designs will be matched as close as possible to the existing bridges upstream shown in Figures 8 and 9 in the appendix. Bridge locations: Woosehill, Wokingham National Grid References: SU 79937 69107 & SU 79891 68998 Type: Pedestrian and Vehicle Weight: To be confirmed Vertical loading: 5Kn/m2 / 10KN + 5t Vehicle loading Lateral loading: To be confirmed following velocity calculations. No of bridges: 2 Design Width: 3m Bridge Length: 7-10m. No of spans: 1 Materials: Northern bridge will be Hardwood. southern bridge will have steel and hardwood components. Other specs: The southern bridge at the start of the bypass channel will be acting as a control structure to limit the amount of flow coming down the channel. This bridge will likely have higher specifications than the northern bridge further down the bypass channel. Peak velocity calculations are yet to be determined by the hydraulic modeller, and lateral loading calculations are therefore yet to be finalised by bridge designers.

Preliminary Site Assessment

1. Analysis of historic OS maps suggests there has been little change in the channel planform

through the restoration site since the late 19th Century. However, evidence from online aerial

imagery, OS mapping and field observations show the bypass channel to be the original route

of the brook.

2. An assessment of site geology has confirmed a band of alluvium (consisting of clay, sand, and

gravels) runs through the site in the general alignment of the brook. The wider project site is

underlain by London Clay with a drift geology of very slowly permeable clay soils. Trial pits

along the proposed bypass channel shows a hard gravel bed between 0.8 – 1.2m below top of

bank.

3. Two topographic surveys of the project site have been undertaken which include the

proposed bridge locations. This data is included in the tender pack as a dwg file.

4. Initial flood risk assessments for the proposed designs show the location of the southern

bridge to be inundated by flood flows over the 5 year return period and the entire project site

to be inundated by flows over the 100 year return period.

5. There are a number of underground utilities within the project site that cross the proposed

bypass channel. All known utilities are marked on the site plan within the appendix:

a. High Risk (Thames Water foul sewer 1) – This will span the bypass channel as a pipe

bridge/crossing c.5m downstream of the southern bridge.

b. Medium/Low Risk (Scottish and Southern High voltage electricity cable) - This runs

c.500m below the hard bed of the bypass channel c.25m downstream of the northern

bridge.

c. Low Risk (South East Water clean water) - This runs c.500m below the hard bed of

the bypass channel C.70m downstream of the northern bridge.

d. Low risk (Thames Water foul sewer 2) - This will span the bypass channel as a pipe

bridge/crossing c.115m downstream of the northern bridge.

e. Low Risk - This will span the bypass channel underneath a footbridge (not part of the

scope of this project) c.165m downstream of the northern bridge.

6. A number of trees (and therefore their roots) are present within the proposed bridge

locations. The trees around the northern bridge location (Figure 5) will need to be removed

to install the bridge. The likely presence of tree roots within the proposed location of the

southern bridge (Figure 6) may cause some issues and require further investigation.

Project Detail/Scope of Works

1. Assess and select a cost effective design for the foundations/substructure of two bridges as

described above.

2. Consideration to making the design of the footings to be environmentally friendly. For

instance, if it is possible to reduce the use of concrete by using ground screws.

3. Explore constraints on installing the footings/substructure for the bridges described above.

Propose solutions to those constraints identified. For instance, the potential for bank erosion

and the safe distances to set back the footings from the sloping bank.

4. Once a preferred solution has been identified and agreed with the South East Rivers Trust,

compile construction drawings and associated specifications to be used at tender.

5. Assume the role of Designer under CDM regs and compile a ‘Designers Risk Assessment’.

6. Compile a ‘Buildability Statement’.

Suggestions for Required Investigations

SERT would like to hear your suggestions of other work that is likely to be required in order to inform

the options to realise the Project Aim.

1. Geotechnical ground investigations in the locations where the footings/substructure would

be installed.

2. Additional topographical surveys of the bridge locations.

Appendix

Figure 7 – Looking in SE direction across existing pond with proposed location of northern bridge in

distance. Alder trees either side of culvert will be removed.

Figure 8 – 5t Vehicle Bridge further upstream of the project site which will be a similar design to new

bridges.

Figure 9 – 5t Vehicle Bridge further upstream of the project site which will be a similar design to new

bridges.

Figure 10 – Topographic survey screenshots at proposed northern bridge.

Figure 11 – Topographic survey screenshots at proposed southern bridge.

Figure 12 – Site plan of proposed works to new bypass channel.

Figure 13 – Utility plans for Thames Water foul sewers.