|
Site information |
Client |
Westhill Company |
|
Site |
Broadway, Worcestershire, United Kingdom |
|
|
Current land use and description |
Currently used for livestock grazing and private residential area. |
|
|
Development |
Proposed pipeline installation |
|
|
Conceptual site model |
Topography |
Uneven surfaces withsteep slope. |
|
Geology |
BirdlipLimestone Formation, Bridport Formation, Whitby Mudstone Formation, Marlstone Rock Formation, Dyrham Formation and Charmouth Mudstone Formation. |
|
|
Hydrology |
There are springs, seepages and groundwater discharge |
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Hydrogeology |
BirdlipLimestone Formation- Moderate Aquifer BirdportSand formation. |
|
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Landsliding and stability |
Characterised by ancient to recent landslides. Widely unstable area with visible earth movement. |
|
|
Historical land uses |
Evidence of agricultural land use by the presence of ridge and farrow and various drainage channels. |
|
|
Site model and geomorphology |
Multiple rotational landslips in the Whitby Mudstone formation. Marlstone rock formation shows mudslide movement and deposits. Cambering in the Birdlip Limestone formation. |
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|
Recommendations |
Constraints |
Restriction of some potential accessible sites. Topography of the site. |
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Proposedpipeline routing |
Proposed pipeline route is approximately 1.09km. This is subdivided into 3 zones. |
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Limitations |
No geophysical, laboratory test were conducted. |
In March 2017, Motives Survey Services was commissioned byWesthill Construction Company to undertakea desk study and field survey report at Broadway, Worcestershire and produce a report to assist in their selection of a suitable pipeline route across the Cotswold escarpment.
The pipeline route is to be laid in the east of Broadway, at Farncombe House, to the west of the Cotswold escarpment, at Hill Farm where it will enter a further network. The pipeline will be laid across variable geology susceptible to landslide and slope instability, therefore Westhill Construction Company requires a reliable desk study and the design of an invasive ground investigation revealing constraints that may be encountered on site.
1.1 Objectives
The objectives of this investigation are:
- Undertake a desk study of available information to include analysis and interpretation of aerial photograph of the study area using Anaglyph.
- To assess potential ground hazards in the site
- Carry out a site walk over survey (Geomorphological mapping).
- Provide preliminary geotechnical information on the ground conditions in the site area.
- Develop a conceptual site model.
- Propose a potential pipeline route.
1.2 Site Information
Table 1.1
|
Report |
Brief description |
|
Site name |
Cotswold escarpment |
|
Site location |
Site is situated at Broadway, Worcestershire, United Kingdom (see Figure 1). |
|
Site topography |
Uneven surfaces with steep slopes |
|
Grid reference |
SP099372 |
Broadway village lies between 80m and 100m OD on the west facing scarp slope at the foot of Cotswold escarpment. The area is extensively used for farming and agriculture (Malcom et al, 2000). The site area is located on the escarpment slope facing east of Broadway village.Previous studies in site area have extensively delineated areas of slope instability, including ‘relict’ landslides, which may have been initiated under periglacial climatic conditions
1.3 Sources of Information used for this study
Sources of information used in preparation of this report are presented in Table 1.2 below.
Table 1.2: Information Sources
|
Information sources |
Description |
Sources reference |
|
Environment Agency |
Surface Water Map. To identify flood warning areas on site |
The Environment Agency, Flood Risk Map. Copyright and Database right 2017. |
|
Environment Agency |
Ground Water Vulnerability map. To determine vulnerable aquifers on the site |
The Environment Agency, Ground Water Vulnerability Map. Copyright and Database right 2017. |
|
Edina Digimap |
Base map for geomorphological mapping |
Edina Digimap 2017, Copyright and Database right 2017. |
|
Edina Digimap |
Hydrogeology map showing aquifer productivity on the site. |
Data extracted from Edina Digimap 2017, Copyright and Database right 2017. |
|
Edina Digimap |
Ordinance Survey Map for the site. Showing site location. |
Edina Digimap 2017, Copyright and Database right 2017. |
|
Edina Digimap |
Geological Survey Map Showing the geology of site. |
Edina Digimap 2017, Copyright and Data base right 2017. |
|
Edina Digimap |
Historical Map, showing the past history of the site |
Edina Digimap 2017, Copyright and Data base right 2017. |
|
ILWIS |
Lidar maps for terrain evaluation using aerial photography |
Environmental Agency map, Copyright and Data base right 2017. |
2.1 Geology
The bedrock geology of the site area is summarized in Table 2.1. This comprises of a sequence Lower Jurassic marine clays, sands and limestone including the Charmouth Mudstone Formation, Dyrham Formation, Marlstone Formation and Whitby Mudstone Formation (Barron et al., 2002). These rocks are overlain by limestones of the middle Jurassic inferior Oolite Group, which cap the escarpment above Broadway. The strata are gently dipping although cambering and faulting have produced local variations (Malcom et al, 2000). These formations are under the Lias Group. The Lias Group is characterised by mudstones interlayered with limestones and it is very fossiliferous. The main clay bearing formations are theCharmouth Mudstone and Whitby Mudstone Formations (Ambrose 2001). A geology map of this area is presented in AppendixB.
Table 2.1: Geology (afterBaron et al, 2002)
|
Formation |
Previous terms |
Description |
|
Birdlip Limestone Formation (Inferior Oolite Group) |
Lower Inferior Oolite |
Oolitic and sandy ferruginous LIMESTONE |
|
Birdport Sand Formation |
Cotswold Sands |
Fine to medium grained SANDSTONE |
|
Whitby Mudstone Formation |
Upper Lias Clay |
Comprises of dark grey CLAY with some oolitic LIMESTONE |
|
Marlstone Rock Formation |
Middle Lias Marlstone Rock |
Comprises of strong brown closely jointed Oolitic and fossiliferous LIMESTONE |
|
Dyrham Formation |
Middle Lias |
Comprises of moderately weak orange brown SANDSTONE and SILTSTONE with subordinate bands of SILT and CLAY. |
|
Charmouth Mudstone Formation |
Lower Lias Clay |
Comprises of dark grey CLAY with occasional bands of argillaceous limestone. Grades at depth into weak mudstone. |
2.2 Hydrology and Hydrogeology
2.2.1 Hydrology and Flooding
The environment agency map has rated the risk of flooding in the site area to be extremely low and there is no form of flooding risk from rivers, streams or springs in this area. This is vividly shown in appendix E.
2.2.2 Hydrogeology
The groundwater vulnerability map of environmental agency classified aquifers as:
- Major Aquifer High
- Major Aquifer Intermediate
- Major Aquifer Low
- Minor Aquifer High
- Minor Aquifer Intermediate
- Minor Aquifer Low.
The site area is classified by the environment agency to be of Minor Aquifer High and Minor Aquifer Intermediate. The Aquifer productivity zones are classified as:
|
Aquifer |
Productivity |
|
Birdlip Limestone Formation |
Moderate |
|
Bridport Sand Formation |
Low |
2.3 Aerial Photographic Interpretation
Anaglyph was used to interpret the aerial photographs and to gather information for this report. The basic features interpreted with the use of the aerial photographs are in accordance with researched literature from past work on Broadway study area. Interpretation from both aerial photographs and field survey was used in completing the engineering geomorphological base map. Ground features interpreted from the aerial photographs are:
- Landslide form and Cambering
- Slope changes
- Ground mass movement
- Ridge and furrow
2.4 Historical Land Uses
Extensive study of the historic Ordnance survey map was conducted to identify any geophysical and geotechnical properties considerations for the proposed pipeline route of site area. Historical map is presented in Appendix C. Maps and other sources of information has shown that Broadway land uses was mainly for Agricultural purposes and Quarries. Written documentation has been the primary source of evidence for understanding the farming during the Anglo -Saxon period. Apparently the richest source of information are the Anglo-Saxon charters which record grants of land and their attached boundary Clauses. The charters and boundary clauses contains evidence of early farming systems (Malcom et al 2000). Ridge and furrow in site shows past Agricultural activities. The quarry in the site area dates back 100-120 years ago as interpreted from the historic maps.
3.1 Field Survey
In March, 2017 Geomorphological mapping was conducted on the site area. The mapping started on the 8th of March and ended on the 10th. Mapping was conducted by a group of Engineering Geologist led by Dr Andy Gibson, Dr Malcom Whitworthand Dr Steve Penn. The field equipment’s used for mapping of the area are: compass clinometer, mapping boards, ranging poles, measuring tapes, pencils, A3 ordnance survey maps, Lidar maps and aerial A3 maps.
3.2 Geomorphological Features Encountered
A brief account of the geomorphological features encountered during the three days mapping are presented in the tables below(Table 3.1 to 3.3).
Table 3.1 Day 1 Mapping (8th March, 2017)
|
Weather |
Cloudy |
|
Time of Arrival |
12:49pm |
|
Location |
Off A44 road next to the road leading to Broadway high street |
|
Geology |
Marlstone Rock Formation and Dyrham |
|
Encountered Features during mapping |
1. Old mechanical quarry with three layers of marlstone rock formation. Highly weathered limestone with very closely spaced discontinuity, orange in colour and fossiliferous. 2. Evidence of recent flow. Flow occurring with tension cracks. Spring encountered during 30×30 geomorphological mapping. Lobate feature was seen on the 30×30 mapping area which is 14 to 18m long and 10m wide. Photography of features mapped for both locations is shown in Appendix G. |
Table 3.2 Day 2 Mapping (9th March, 2017)
|
Weather |
Sunny and windy |
|
Time of Arrival |
09:15am |
|
Location |
Off A44 road next toFish Hill |
|
Geology |
Whitby Mudstone Formation |
|
Encountered Features during mapping |
1. Evidence of recentrotational land slide flow occurring. There was presence of tension crack suggesting age to be less than 10 years of age. 2. Evidenceof relictlandslide (Old rotational landslide). This is suggested to be 50 to 100 years old. 3. Spring pouring out large volume of water was found on the middle area of site.Evidence of Marlstone Rock Formation on site area, seen around tree roots. Photography of features mapped for the locations is shown in Appendix G2. |
Table 3.3 Day 3 Mapping (9th March, 2017)
|
Weather |
Cloudy and Cold |
|
Time of Arrival |
09: 20am |
|
Location |
Colliers knap and Farncombe House |
|
Geology |
Marlstone Rock Formation and Dyrham |
|
Encountered Features during mapping |
1. Relict landslide (Old rotational landslide) were seen around Colliers Knap with presence of spring. 2. Bench area at Farncombe house which is made of Whitby Mudstone Formation. Tension cracks occurred in the bench area. Photography of features mapped for both locations is shown in Appendix G3. |
4.1 Geological Ground Conditions
Geologicalformations of the study area generally conforms to past research literature. This is shown on table 4.1.
Table 4.1 Typical description of the geology formations and slope formations seen on the site study area.
|
Formation |
Description |
Surface Morphology |
|
Birdlip Limestone Formation (Inferior Oolite Group) |
Comprises mainly OoidLIMESTONE, shell fragmental LIMESTONE and Sandy LIMESTONE |
Cambering and multiple rotational landslide. Steep scarp face (250m OD) |
|
Bridport Sand Formation |
Comprises of fine to medium grained SANDSTONE |
Landsliding and Cambering features. |
|
Whitby Mudstone Formation |
Comprises of dark grey micaceous mudstone with fossils preserved in pinkish ARAGONITE |
Gentle angle slope with remains of relict landslide (old rotational landslide). |
|
Marlstone Rock Formation |
Brown to grey variablyferruginous SANDSTONE containing limonitic Ooids |
Cap rock to mid slope lithological bench. Mechanical quarry present in a part of the formation. |
|
Dyrham Formation |
Comprises grey mudstone, with interbeds of highly micaceous, weakly cemented SILTSTONE or fine grained SANDSTONE |
Steep scarp faces below the lithological bench (marlstone rock formation). Occasionally extensive rotational landslides (seen at Colliers knap). |
|
Charmouth Mudstone Formation |
Dominated by dark grey CLAY with occasional bands of argillaceous limestone. |
Occurs down slope. Enveloped by superficial deposits. |
4.2 Geomorphology
The study area is predominant of rotational landslide, mainly of relict and few occurring recent rotational landslide. Othersections of study area comprises of translational slide and mudflows with tension cracks present on site. Spring and hummocky surfaces present on site. Detailed geomorphological features are shown in the base map. Data was gathered from desk study and field mapping of study area. A number of geomorphology and geological features can be seen in the study area. These are:
- Rotational landslide- Rotational landslide is predominant in the study area. At colliers knap there is an extensive rotational landslide down a lithologic bench, which is the marlstone rock bench. The geology of the bench area is marlstone rock formation and beneath it (gentle slope) is the dyrham formation. This have a potential to flow when triggered and this pose an area of concern for engineering work.
- Translational landslide- Translational landslide occurred at the south – south part of the study area and also around the bench mark at farncombe estate. These are old relict translational landslide which comprises of active mudflows/slide flow.
- Tension cracks- Tension cracks are other common features in site area. This feature occurred at the bench mark leading to farncombe house and it is of Whitby mudstone formation. Tension cracks were also seen in other areas of recent landslide in the site. These cracks at the head of landslide suggests strongly that instability is imminent. It is not advisable for a pipeline route to pass through this area.
- Mudflow/Slide flow- Mudflow features occurred twice within the colliers knap area. The first flow occurred at about 10m north-east of the abandoned old quarry. Here, a 30 x 30 geomorphologic mappingwas conducted, spring was encountered with a northward flow direction. Whilst the second mudflow occurred just before the lithologic bench leading to farncombe house. Mudflow in the site is bound to extend over time. Generally the geomorphological features are vividly shown in the base map.
- Cambering- This feature occurred at the Broadway tower region which is located at the southern part of site area. There was a separation between two joints leading to downward movement of rock formation in opposite directions thereby forming a gull in the site. This was a restricted area.
The plan and cost for intrusive investigation was completed with the use of the bill of quantities (UK specification for ground investigation).
Bill of Quantities: Percussion boring
|
ITEM |
DESCRIPTION |
UNIT |
QUANTITY |
RATE (£) |
AMOUNT (£) |
|
B |
Percussion boring |
||||
|
B1 |
Transport/mobilisation of cable percussion rig and personnel to site and removal on completion of works |
nr |
Not required |
300.00 |
300.00 |
|
B2 |
Set up, dismantle and move rig between boreholes |
each move |
4 |
70.00 |
280.00 |
|
B3 |
Excavate starter pit |
each move |
4 |
50.00 |
200.00 |
|
B4 |
Extra over for breaking out concrete etc. re-excavate starter pit |
each move |
2 |
90.00 |
180.00 |
|
B5 |
Boring/advance by light cable percussion rig between ground level and 10m |
Per (m) |
10m by 4 boreholes |
20.00 |
800.00 |
|
B6 |
As item B5 but between 10m to 15m |
Per (m) |
5m by 4 boreholes |
25.00 |
500.00 |
|
B7 |
As item B6 but between 15m to 20m |
Per (m) |
5m by 4 boreholes |
32.00 |
640.00 |
|
D |
Trial pits and trenches |
||||
|
D1 |
Transport machine, driver and qualified geologist to supervise, log pits, take reports and bulk sampling |
Per day |
3 days |
1350.00 |
4050.00 |
|
F |
Cone Penetration Testing |
||||
|
F1 |
Mobilisation of rig per day on-site and reporting |
Per day |
3 days |
2000.00 |
6000.00 |
|
E |
Probing |
||||
|
E1 |
Probing |
Per day |
3 days |
800.00 |
2400.00 |
|
Sub-total |
15350.00 |
Bill of Quantities: Sampling
|
ITEM |
DESCRIPTION |
UNIT |
QUANTITY |
RATE (£) |
AMOUNT (£) |
|
J |
Sampling |
||||
|
J1 |
Take small disturbed samples (1kg) with split-barrel tubes from ground level to depth of 10m (at every 2m) |
Per sample |
5 per borehole (20) |
2.00 |
40.00 |
|
J2 |
Take 100mm undisturbed samples from ground level to 15m (every 3m) |
Per sample |
5 per borehole (20) |
18.00 |
360.00 |
|
J3 |
Take 45kg bulk disturbed samples not exceeding 10m depth below ground level |
Per sample |
5 per borehole (20) |
5.00 |
100.00 |
|
J4 |
Take representative water samples |
Per sample |
5 per borehole (20) |
5.00 |
100.00 |
|
Sub-total |
600.00 |
Bill of Quantities: In-situ testing
|
ITEM |
DESCRIPTION |
UNIT |
QUANTITY |
RATE (£) |
AMOUNT (£) |
|
H |
Standard Penetration Test (SPT) |
||||
|
H1 |
SPT from Ground level to 15m |
Per borehole |
4 boreholes |
12.50 |
48.00 |
|
H2 |
Permeability Test |
||||
|
H 2.1 |
Permeability-Falling head (Head modified) for up to 4 days |
4 boreholes |
58.00 |
232.00 |
|
|
H3 |
Point Load Test |
||||
|
H 3.1 |
Point Load |
4 boreholes |
65.00 |
260.00 |
|
|
H4 |
Shear box Test |
||||
|
H 4.1 |
Shear box |
4 boreholes |
330.00 |
1320.00 |
|
|
Sub-total |
1860.00 |
Bill of Quantities: Instrument
|
ITEM |
DESCRIPTION |
UNIT |
QUANTITY |
RATE (£) |
AMOUNT (£) |
|
I |
Standpipe |
||||
|
I1 |
Install standpipe 50mm diameter |
Per metre |
10m per borehole (40) |
15.00 |
600.00 |
|
I2 |
Protective cover re above and re-instatement |
Per each standpipe |
4 |
100.00 |
400.00 |
|
Sub-total |
1000.00 |
Bill of Quantities: Laboratory testing
|
ITEM |
DESCRIPTION |
UNIT |
QUANTITY |
RATE (£) |
AMOUNT (£) |
|
K |
Classification Tests |
||||
|
K1 |
Determination of Moisture Content |
Nr |
4 |
4.00 |
16 |
|
K2 |
Determination of Liquid & Plastic Limits and Plasticity Index |
Nr |
4 |
27.50 |
110 |
|
K3 |
Bulk/Dry Density |
Nr |
4 |
15.00 |
60 |
|
K4 |
Particle Size Distribution – Sand and Gravel |
Nr |
4 |
26.50 |
106 |
|
K5 |
Particle Size Distribution -Fine Grained Soils |
Nr |
4 |
30.00 |
120 |
|
K6 |
Soil Chemical Test |
||||
|
K 6.1 |
Organic content |
Nr |
4 |
20.00 |
80 |
|
K 6.2 |
Soluble Sulphate content (Soil- 2:1) |
Nr |
4 |
16.00 |
64 |
|
K 6.3 |
Soluble Sulphate content (Water) |
Nr |
4 |
16.00 |
64 |
|
K 6.4 |
pH value (Soil)
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