Brief Description Of Structure.docx

Brief Description of Structure The River Ash Culvert is a single 6.4m span simply supported culvert. The inlet of the culvert can be found between A308 London Road Eastbound Off-slip and A30 Staines Bypass Northbound On-slip; and the outlet can be found on the A308 Staines Bypass Westbound Off-slip. The exact path of the culvert is unclear; however, it is believed that the culvert runs underneath the Crooked Billet Roundabout. The culvert is approximately 265m long in total and has a clear span of 6.4m. The Culvert comprises of 4 distinct sections constructed at different times adjacent to one another to form the current structure. The sections are as follows: 1.

Billet Bridge: Before the construction of the Crooked Billet Roundabout the road crossing of the River Ash was located in the middle of the current roundabout. The structure consists of a reinforced concrete slab, simply supported on concrete abutments. The date of construction is unknown.

2.

Original Culvert (forming two sections): When the Crooked Billet Roundabout was constructed in 1960, Billet Bridge was extended both eastwards and westwards by a culvert, which is labelled “Original Culvert” in multiple reports. The deck consists of precast prestressed inverted T beams with in-situ concrete infill. The deck is simply supported on concrete side walls. Where changes in direction occur, the deck consists of an insitu reinforced concrete slab. The structure was constructed in 1960.

3.

Culvert Extension: After the construction of Crooked Billet Roundabout, the road layout was changed again and the culvert was extended further eastwards to its current layout. The structural form of the extension matches that of the Original Culvert. The date of construction is unknown.

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METHODOLOGY Based on the objectives and scope of the consultancy services, an appropriate methodology has been developed in order to address the various requirements of the project. Since the scope of the services to be provided covers both independent and inter-dependent activities, it has been proposed to adopt a Task Approach to ensure that the entire scope of services is completed comprehensively and with reasonable accuracy.

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Investigations for Bridges and Structures

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Inventory and Condition Survey for Bridges and Culverts Inventory and condition survey of culverts, bridges and other structures shall be done to ascertain the need for reconstruction / widening and rehabilitation of these structures. The condition assessment of bridges will be carried out by Senior Bridge/Structural Engineer in accordance with guidelines given in IRC-SP:35-1990. The data shall include construction details, type of foundation, substructure and superstructure, details of span, waterway, design loading and functioning of the structure in the past, both from hydraulic and structural considerations.

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Hydraulic and Hydrological Investigations These studies will be carried out in accordance with IRC Special Publication No.13 (Guidelines for the design of small bridges and culverts) and IRC:5-1998 (Standard Specifications & Code of Practice for road, bridge section 1 - General features of design). These investigations will be carried out for all existing drainage structures along the road sections under the study. Its quality will be ensured by:    

Collection of data by an experienced engineer Its correct interpretation based on experience, site inspection and behaviour of other structures across such streams in the near vicinity by such experienced engineers. For HFL, reliance will be placed on past records, local enquiries and flood marks on structures in the vicinity. For road sections getting overtopped during heavy rains will be placed on local enquiries.

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Geo-technical investigations will be carried out for determining engineering characteristics of subgrade soil, the sub-soil underlying the foundations of the proposed bridges and other structures, etc. as per IRC 78-2000 and underneath the road pavement. Appropriate field tests will be conducted and boreholes drilled at selected locations as indicated in the TOR. The minimum scope of geo-technical investigations for bridge structures is: