What's been done so far?
Work to Date
August 2004
Project Development Manager appointed by Council to develop and deliver the scheme.
October 04 - Jan 05
Design Competition held. 5 architects selected from 31 who responded to OJEU advert entered into a competition.
March 05
Marks Barfield Architects and Mott Macdonald appointed to design and engineer scheme.
April 05
Project Ryde web site set up. First public exhibition held in Ryde.
July 05
Second public exhibition held in Ryde.
August 05
Park and ride completed at Ryde St Johns Road.
September 05
Concept Design completed (RIBA Stage D). Design submitted for planning.
November 05
Planning Permission and conservation consent granted.
February 06
Value Engineering and Risk workshops undertaken.
April 06
Stage E Development brief completed.
June 06
Business case submitted to Government Office.
September 06
Detailed Design complete.
October 06
Geophysical and Geotechnical surveys undertaken.
November 06
Tender sent out to contractors following OJEU procedure.
January 07
Tenders returned and evaluated
February 07
Contractor selected
Ryde Transport Interchange – Ground Investigation
Client
Isle of Wight Council
Foundation & Geotechnical Engineers
Mott MacDonald
Ground Investigation Contractor
Norwest Holst Soil Engineering Division
Main Works Proposed
A new transport interchange is to be constructed in place of the existing facilities which are considered poor and inefficient for both facility users and pedestrians. The proposed interchange facility is primarily located on the south side of the railway line at the existing train and bus terminals. The proposed development comprises the following:
- A number of interlocking structures including a two storey interchange facility and ancillary buildings constructed off piled foundations.
- Road realignment, parking areas, bus stops and pedestrian walkways.
- Pedestrian footbridge over the railway linking the existing Hovercraft Terminal with the interchange facility constructed off piled foundations.
Works carried out to Date
Desk Study
The study was to obtain readily available information on the site history and underlying ground conditions in order to provide preliminary information relating to foundation construction and provide a focus for the ground investigation works.
Geophysical Survey
The Desk Study identified that one of the key risks to the Ryde Interchange development was the risk of encountering buried obstructions. As a result a geophysical survey of the site was carried out in advance of the ground investigation works, in order to identify the location of buried structures.
There are two areas where historical (buried) structures and sea walls are thought to be present beneath the footprint of the proposed transport interchange:
-
Former Royal Pier Hotel
- It is known that the Royal Pier Hotel was demolished within the western area of the site opposite houses 1 to 9 on the Esplanade. It is possible that basements, tanks, walls or foundations may still be present beneath the site.
- Esplanade Sea Wall
It is known that a sea wall was constructed along the seaward boundary of the Esplanade during Victorian times with the area landward of the sea wall in filled. The location of the sea wall transects the site.
Therefore, it is possible that the historical sea wall may still be present beneath the site. The sea wall is recorded as being 2.7m wide at the base and 6m in height.
Drawing No. 217393/FNG/004 shows the postulated location of the former Pier Hotel and esplanade sea wall.
217393/FNG/004
Scope of Works
The Fieldwork for the ground investigation will comprise cable tool boring, window sampling, dynamic probing and shallow hand dug trial/ observation pits. Soil sampling will be carried out and in-situ testing undertaken. Drawing No. 217393/FNG/004 indicates the proposed location of the ground investigation exploratory holes. Table 1 details the proposed ground investigation exploratory holes, the proposed depth of holes and instrumentation to be installed.
The objectives of the ground investigation are as follows
- Carry out laboratory and in situ testing to obtain the geotechnical parameters required to undertake the foundation design for the structures.
- Establish the nature, variability and thickness of Made Ground and superficial deposits.
- Establish the nature and distribution of Limestone beds within the underlying Osborne Beds.
- The installation of groundwater monitoring equipment in order to improve the understanding of the groundwater regime and its tidal variability.
- Carry out chemical testing to assess the aggressiveness of the ground and groundwater.
- Carry out contamination testing to assess the nature and distribution of any contaminants within the ground or groundwater.
- Obtain information on the presence of obstructions associated with former sea walls, demolished structures (e.g. Pier Hotel) and land reclamation processes undertaken. See Drawing No. 217393/FNG/004.
The locations of exploratory holes are, constrained by the nature of the site and the need to maintain its operational status during the ground investigation works, and dug trial pits are proposed to both gain a visual appreciation of the near surface fill / superficial materials and also to investigate the presence of buried obstructions.
A geophysical survey has been carried out in advance of the ground investigation works, with the aim of locating buried structures. The location of the hand dug trial pits have been targeted towards proving the findings of the geophysical survey. Should additional holes be required or positions moved during the course of the ground investigation, then on site agreement and approval with the relevant land-owners/agencies will again be sought. The geophysical survey indicated the presence of the former sea wall specifically in the area east of the bus station. The alignment and position appears to match that indicated from historic ordnance survey plans of the site.
Works Operations
The main investigation phase will commence on Monday 9 October 2006 and should be completed on Friday 27 October 2006.
The time required to complete each exploratory hole will primarily dependant on access being available to the location and ground conditions encountered.
Working hours are to be restricted to 0800 to 1800 Monday to Friday.
The works will be undertaken by three work crews, contracted by Norwest Holst Soil Engineering Division. These being:
- 1 No. Cable Percussion (CP) Drilling Team (2 man crew)
- 1 No. Hand Excavation (HE) Team – New Roads and Street works Accredited (2/3 man crew)
- 1 No Window Sample & Dynamic Probing (WS & DP) Team (2/3 man crew)
Below is an outline of the investigation techniques to be employed during the investigation:
Cable Percussive Drilling
Cable percussion (cable tool) drilling is the oldest and simplest, drilling method. It has been used in China for over 3000 years.
The method uses tools suspended on a wire rope, which are lifted and dropped to break up and remove material from the bottom of a hole. Clay cutters and stubbers allow rapid drilling in clays and in sands with some clay content, employing the 'long drop' technique to cut and remove solid plugs of material. A mechanical free-fall winch controls all the in-hole operations, and is the heart of the system. Below is a picture of a typical cable percussion rig
Cable Percussive Drilling
Hand Excavated Trial/ Observation Pits
Trial/ observation pits excavated using hand tools and hand breaking equipment if necessary to break through hard surfaces. The excavation will take place from ground level. The plan area of the pit will be approximately 1.0m by 1.0m and will not exceed 1.20m depth.
Window Sampling
The equipment comprises a selection of sampling tubes each consisting of a steel tube with a hardened cutting shoe, with 400mm long ‘windows’ running axially every 0.5m. The sample tube is driven into the ground using petrol or diesel powered hydraulic unit driving a jackhammer and then withdrawn using either a hand or hydraulically operated jack. The resultant soil sample is then logged and sub-sampled through the ‘windows’. The Window sample hole is usually commenced in 80mm diameter, with subsequent sample tubes reducing in size through 60mm, 50mm and 38mm diameter.
In general the following equipment is used to drive the tubes into the ground:-
A detailed log is produced showing the nature and depths of the various strata, groundwater ingress, installation details and any obstructions or visible contamination encountered.
Probing
Dynamic Probing
This is a simple test consisting of driving a rod with an oversize point at its base into the ground with a uniform hammer blow. The blow count is recorded for every 100mm of driving (N100) and the results presented as a plot of blow count against depth. Probing can be used before, as part of or after a main investigation to supplement the data obtained.
The standard equipment is a petrol powered unit using a 50kg hammer dropping through 0.5m onto 1.0m long 32mm diameter rods fitted with a 15cm2 area cone.
The hammer operation is automated and driving is carried out as a continuous operation from ground level without a borehole. The test therefore not only provides a continuous record for the full depth penetration. Results can be tabulated and plotted.
Dynamic Probing provides an excellent method for locating boundaries between strata of differing density and driving resistance as well as comparative assessments of a single stratum across a site.
Dynamic Probing
A provisional programme of works on the site will broadly be as follows:
Provisinal Programme
Works Support Services
The main investigation phase will require the establishment of a site compound/ stores area for the duration of the works. The compound will be set up at the eastern end of the Bus Station just beyond Bus Stop H. See Drawing No. 217393/FNG/004.
217393/FNG/004
The compound will include the following:
- Site Office/ Stores
- Welfare unit including toilet, washing facilities and staff mess.
The area of the compound will be delineated with temporary 'Heras' fencing.
Work Areas
The work areas for each individual exploratory hole will be maintained in a number of ways to ensure safety and security both for the work crews and the users of the site. See Drawing No. 217393/FNG/004. No above ground obstacles/ furniture including vegetation are expected to be removed in order to facilitate the work at the exploratory hole locations with the exception of BH1.
Cable Percussion Boreholes BH1, BH2, BH4, BH5 & BH6
The work area for the cable percussive exploratory holes BH1 to BH7 will be delineated with temporary wire mesh ‘Heras’ fencing and will occupy an area of approximately 5.0m by 10.0m in plan.
Removal of the public benches will be required in the vicinity of BH1 prior to the set up of the Cable Percussion Rig.
Cable Percussion Borehole BH3
The work area for the cable percussive exploratory hole BH3 will be delineated with temporary wire mesh 'Heras' fencing and will follow existing visual and physical barriers associated with the bus stand in this area. Therefore, the area occupied will be approximately 9.0m by 15m in plan.
Cable Percussion Borehole BH7
Cable percussive exploratory hole BH7 will be undertaken within the site compound area which will already be delineated with wire mesh 'Heras' fencing.
Window Sample Boreholes & Dynamic Probes BH6, BH7 & BH8
The work area for these exploratory holes will be delineated with temporary plastic road/ pedestrian barriers and will occupy an area of approximately 1.0m by 2.0m in plan.
Hand Excavated Trial Pits TP1 to TP5
The work area for these exploratory holes will be delineated with temporary plastic road/ pedestrian barriers and will occupy an area of approximately 1.0m by 2.0m in plan.
TABLE 1: List of Exploratory Holes
Exploratory Holes
Notes:
TP Hand Dug Trial Pit
CP Cable percussion
WS & DP’s to be undertaken at suitable locations to profile the site. DP to be undertaken at BH6 and BH7 locations in order to correlate with BH8.