Graven Hill to Ambrosden Replacement Water Pipeline and Tank, Bicester, Oxfordshire

Transcription

1 Graven Hill to Ambrosden Replacement Water Pipeline and Tank, Bicester, Oxfordshire An Archaeological Watching Brief For Trant Construction Ltd by Stephen Hammond and Pamela Jenkins Thames Valley Archaeological Services Ltd Site Code BPO 03/108 June 2004

2 Summary Site name: Replacement water main and tank, Bicester, Oxfordshire Grid reference: SP SP Site activity: Watching Brief Date and duration of project: 8th December th June 2004 Project manager: Steve Ford Site supervisor: Stephen Hammond Site code: BPO 03/108 Summary of results: Two features; one ditch and one ditch terminus or pit were revealed within the replacement pipe trench in Area A. No finds were recovered therefore both features are undated. Monuments identified: None Location and reference of archive: The archive is presently held at Thames Valley Archaeological Services, Reading and will be deposited with Oxfordshire Museum Service in due course with accession code OXCMS: This report may be copied for bona fide research or planning purposes without the explicit permission of the copyright holder Report edited/checked by: Steve Ford Steve Preston i

3 Graven Hill to Anbrosden Replacement Water Pipeline and Tank, Bicester, Oxfordshire An Archaeological Watching Brief Introduction by Stephen Hammond and Pamela Jenkins Report 03/108 This report documents the results of an archaeological watching brief carried out on the route of a pipeline from the top of Graven Hill to a pumping station on the south west side of Ambrosden, Oxfordshire (SP to SP ) (Fig. 1). The work was commissioned by Mr M C Habgood of Trant Construction Limited, Rushington House, Rushington, Southampton, SO40 9LT after Cherwell District Council were consulted (02/02144/GD) in respect of replacing the existing water tank and laying a new water pipe from the new tank to the pre-existing pumping station. The route of the pipeline was considered to have archaeological implications and an archaeological watching brief was requested to take place during the groundworks. This is in accordance with the Department of the Environment s Planning Policy Guidance, Archaeology and Planning (PPG ), and the District s policies on archaeology. The field investigation was carried out to a specification approved by Mr Hugh Coddington, Deputy County Archaeological Officer to Oxfordshire County Council. The fieldwork was undertaken by Stephen Hammond, Andy Taylor and Pamela Jenkins between the 8th December 2003 and 15th June 2004 and the site code is BPO 03/118. The archive is presently held at Thames Valley Archaeological Services, Reading and will be deposited with Oxfordshire Museum Service in due course, with accession code OXCMS: Location, topography and geology The site is located between the top of Graven Hill and a pumping station on the south-west side of Ambrosden. Graven Hill lies at a height of approximately 115m above Ordnance Datum within an existing Ministry of Defence establishment to the south-east of Bicester. The replacement pipeline runs from the top of Graven Hill south-eastwards down to approximately 62m AOD before rising slightly to 70m and then returning to 65m as it approaches Ambrosden. The underlying geology, according to maps (BGS 1994; 2002) and as observed, between Graven Hill and Ambrosden Pumping station varies from Oxford Clay Formation Weymouth Member (pale grey mudstone) at the top of Graven Hill changing to Stewartby Member (mudstone, pale to medium grey) and then Peterborough Member (mudstone, dark brownish grey, fissile) at the bottom of Graven Hill, then Kellaways Formation Kellaways Clay Member (mudstone, dark grey) and finally Cornbrash (rubbly limestone) 1

4 on the approach to Merton Road in Ambrosden. The geology maps also indicate significant made ground and disturbance across the whole area. Archaeological background The archaeological potential of the site has been pointed out by Mr Coddington s design brief for the project (Coddington 2002). An earthwork (lynchet), from the interior of which came a piece of Iron Age pottery, encircles part of Graven Hill and has been identified as possibly being of either post-medieval or Iron Age date. This has given rise to consideration of the possible presence of an Iron Age Hill fort on Graven Hill. The name Graven Hill suggests a hill with a ditch (from the OE word for ditch [*grafan], although it could also derive from graf meaning copse or wood). The site of Ambrosden Hall, built in 1673, lies close to the pipeline route although it is no longer evident above ground. In more general terms, the site lies in an area noted for Roman and other activity (Briggs et al. 1986). An east-west Roman road which lies to the north (Akeman Street) meets the road from Dorchester to Towcester just to the east. Merton Road in Ambrosden appears to be on the line of this second Roman road Just to the west of Graven Hill lies the Roman town of Alchester. Objectives and methodology The purpose of the watching brief was to excavate and record any archaeological deposits affected by the new construction work. This was to involve the examination of areas stripped of topsoil/overburden for the replacement tank, topsoil stripping for any easement required and excavation of the trench for the pipe itself. Particular attention was to be paid to the location where the pipeline route traverses the earthwork on Graven Hill. Spoilheaps were monitored for finds. Results The groundworks comprised several ground disturbing components namely the digging of a pipe trench, digging of thrust pits, removal of the existing tanks and excavation for the new tanks and, with minor archaeological relevance, thrust-bored piping. For the purposes of this report, the pipeline has been divided into eight sections (A H) (Fig. 2). At the top of Graven Hill (Area H) topsoil stripping of an area 26.50m x 15.0m onto the natural clay and subsequent excavation for the new water tanks was carried out to a depth of 0.50m at its south-west point 2

5 increasing in depth to 1.30m towards the north-east. Excavation of a thrust pit 1m x 1.5m x1m at the north-west corner of tank 1, the inlet and outlet chambers (approx. 2m x 2m x 1.50m) and their associated pipe trenches (1.50m deep and 0.60m wide) was also observed particularly where they lay beyond the stripped area (Fig. 2). The stratigraphy observed was 0.20m of dark grey brown, very rooty, silty clay topsoil above yellow/blue/grey clay natural. The pipe trench leading from the direct drilled pipe in Area G into the inlet chamber in Area H was dug to a depth of 3m. It was 2.20m wide at the top, stepping in to 0.60m wide at 1m. The same stratigraphy as described above was observed. Removal of the old water tank did not reveal any archaeology though as conditions for observation were poor. No archaeology was observed and no finds recovered. In Areas B, C, E, F and G a total of 12 thrust pits were excavated measuring c 2.0m square and 2.0m deep revealing a consistent 0.25m of topsoil overlying clay natural. In Area B a stripped area 10m wide between thrust pits 1 and 3 was observed. The natural clay was exposed only within the first 21m at the southernmost end. This was very disturbed by machinery and no archaeology was visible. However, four prehistoric struck flint tools were recovered within Area B from the exposed topsoil. No further monitoring of these areas was necessary as the laying of the new pipe was carried out through direct drilling. Areas G included the line of the known earthwork (at SP ); however no archaeology was observed. In Area D a pipe trench 2.0m deep and 0.70m wide was excavated to reveal 0.25m of topsoil above yellow/blue/grey clay natural. No archaeology was revealed and no finds recovered. In Area A an easement 13m wide was stripped of only c. 0.05m of turf and therefore did not reveal any natural horizons or archaeologically relevant levels, although a prehistoric flint was recovered. Removal and replacement of the existing asbestos pipe was therefore monitored within this area from the Ambrosden pumping station northwards uphill for 280m into thrust pit 1 in Area B. The replacement pipe trench averaged 2.0m deep and the new pipe was laid above approximately 0.20m of small gravel chippings and covered with a further layer of the same to a depth of c. 1.50m. During the replacement of the asbestos pipe in Area A, the presence of a further redundant steel water pipe meant that the laying of the new pipe had to respect the former as this was not scheduled to be removed and may have caused some deviation from the provided plans. Trench excavation was carried out by a JCB-type machine with a toothed ditching bucket 0.60m wide. The stratigraphy observed within the southernmost section of the replacement pipe trench revealed 0.60m 1.30m of modern made ground and backfill containing modern brick and tile and plastic etc., relating to the above-mentioned and various other water pipes within this area. At 70m from the south-east end of the pipe trench a limestone culvert aligned north south was encountered at a depth of 3

6 1m below 0.30m of made ground, and 0.70m into a limestone and clayey subsoil (55). It was not possible to establish the relationship between the subsoil and the culvert due to truncation at this point by the steel water pipe trench. Several stones were accidentally removed by machine and showed the inner side walls of the drain to consist of approximately dry courses of limestone slabs c. 30mm thick and 50mm long. The capping stones varied between 0.20m and 0.40m long with a breadth and depth of c. 0.25m within a limestone mortar. The drain was recapped with a sheet of metal and sealed with a layer of concrete. No further breach of the culvert occurred. Trench backfill relating to the steel pipe encountered at 70m was dark greyish brown with modern brick and tile and glass and was observed up to approximately 120m. At this point the made ground changed in nature and now consisted mostly of medium sized fragments and larger blocks of creamy yellow limestone in a pale brownish yellow clayey sand with post-medieval brick and tile (50) (Fig. 3 resembling demolition material to a depth of m above greyish clay natural. At 133m a further clay water pipe was encountered below the made ground (50) at a depth of 1.80m truncating the clay natural. It was not clear whether the trench for this was cut from the surface and the nature of the ground meant that it was unsafe to enter the trench to investigate further. At 146m a layer 0.40m thick of loose soft dark reddish brown sandy clay containing charcoal flecks and very small flecks of brick and tile (51) was observed at a depth of 1.50m below the made ground (50) and was still visible in the bottom of the trench at a depth of 2.0m. It was too dangerous to enter the trench so a sample was taken with the machine bucket. No finds were recovered. Further north at 170m it was seen to thin to only 0.15m thick above a natural pale creamy yellow limestone and clayey sand and related to a ditch (1) observed in both sections at c.170m (Fig. 3). Ditch (1) was 1.30m wide and 0.45m deep below 0.85m of made ground (50). It was filled with a friable dark greyish brown clayey sand (52) containing small flecks of charcoal and brick and tile. Unfortunately it was again not safe to carry out further investigation, and although it was cleaned up in section from the edge of the trench with a shovel, no finds were recovered and the relationship between this feature and layer (51) could not be easily established. This ditch was, however, also seen to cut a natural layer of limestone as described above which in turn overlay grey clay natural. At 175m a further feature (2), 1.80m wide and 0.50m deep was revealed below 0.50m of made ground (50) in the west facing section only. Truncation by the asbestos pipe trench meant that nothing remained in plan and it can only be suggested that this feature could be a ditch terminus or a pit. Its only fill (53) was similar in nature to 52 and it was also seen to cut layers of natural limestone and clay as described for (1) above. 4

7 Access to this feature was made possible by a step at the end of the trench but no finds were recovered from the section. Further north, at the top of the slope at 183m, the stratigraphy revealed was 0.10m of machine-disturbed ground overlying 0.20m of undisturbed fine and loose yellowish brown clayey limestone sand subsoil (54). This overlay solid natural limestone which shattered into fragments when dug through with the machine to obtain the necessary depth of 1.80m. Between 200m and 205m the subsoil (54) lensed out to only 0.10m thick above a layer of solid limestone approximately 1.20m thick. At the bottom of the trench the natural clay was visible. At 200m the limestone geology was naturally exposed and visible at the surface and no archaeology was present. Finds Struck flint by Steve Ford Four prehistoric struck flints were recovered. A single flake was found on the stripped part of Area A and two flakes and a scraper from the topsoil on Area B. They are all likely to be of Neolithic or Bronze Age date. Conclusion The enclosure encircling Graven Hill was not encountered, but a significant amount of pipework replacement was carried out by direct drilling and little opportunity was available to inspect the ground. A couple of features, a ditch and pit or ditch terminus were encountered in the field immediately north of the Ambrosden pumping station but the absence of finds prevents dating. This area (Area A) has been substantially disturbed as a result of previous pipelaying activities and it seems likely, when considering the topography of the surrounding landscape, that a significant depth of the original subsoils and natural has been truncated. At the top of Graven Hill there was no evidence in terms of either archaeological features or finds to suggest the use of this seemingly ideal vantage point as a hill fort. The size of the area affected by the two new water tanks accounts only for a very small proportion of the hilltop and need not necessarily coincide with any area of archaeological activity identifiable under the constraints of a watching brief. Due to both the minimal impact of the replacement tanks and water pipes and the nature of much of the pipelaying methods, this project has failed to provide any evidence either for or against the existence of a hillfort on Graven Hill. References BGS, 2002, British Geological Survey, 1:50000, Sheet 219, Solid & Drift Edition, Keyworth BGS, 1994, British Geological Survey, 1:50000, Sheet 237, Solid & Drift Edition, Keyworth 5

8 Briggs, G, Cook, J, and Rowley, T (eds), 1986, The Archaeology of the Oxford Region, Oxford Univ Dept External Stud Coddington, H, 2002, Land at Graven Hill, MOD Bicester, Ambrosden, replacement water main and tanks: design brief ofr archaeological watching brief, Oxfordshire County Archaeological Services Mills, A D, 1998, Oxford Dictionary of English Place Names, Oxford PPG 16, 1990, Archaeology and Planning, Dept of the Environment Planning Policy Guidance 16, HMSO 6

9 SITE SITE SP Graven Hill to Ambrosden Replacement Water Pipeline and Tank, Bicester, Oxfordshire, 2004 BPO03/108 Figure 1. Location of site within Bicester and Oxfordshire. Reproduced from Ordnance Survey Pathfinders 1092 SP41/51, 1069 SP42/52, 1093 SP61/71 and 1070 SP62/72 at 1:25000 Ordnance Survey Licence

10 21000 Graven Hill H 15 G 14 F E D 5 C 4 F2 F1 B Thrust pit Pipe trench observed Pipe trench observed 2 1 Ambrosden A SP58500 Graven Hill to Ambrosden Replacement Water Pipeline and Tank, Bicester, Oxfordshire, BPO03/108 Figure 2. Location of site, showing Areas examined, thrust pits and features (F1, F2) Scale. 1:10000

11 Graven Hill to Ambrosden Replacement Water Pipeline and Tank, Bicester, Oxfordshire 2004 NW 170m SE 150m Limestone and clay (natural geology) (made ground) Base of trench 51(buried soil) 0 10m Figure 3. Sections of features 1 and 2 in Segment A. BPO03/108