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Proposed Pipeline Route Analysis

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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

Hydrogeology

BirdlipLimestone Formation- Moderate Aquifer

BirdportSand formation.

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.

Recommendations

Constraints

Restriction of some potential accessible sites. Topography of the site.

Proposedpipeline routing

Proposed pipeline route is approximately 1.09km. This is subdivided into 3 zones.

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:

  1. Major Aquifer High
  2. Major Aquifer Intermediate
  3. Major Aquifer Low
  4. Minor Aquifer High
  5. Minor Aquifer Intermediate
  6. 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:

  1. Landslide form and Cambering
  2. Slope changes
  3. Ground mass movement
  4. 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 30x30 geomorphological mapping. Lobate feature was seen on the 30x30 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)

Nr

4

6.00

24

K 6.5

pH value (Water)

6.00

K 6.6

Chloride content

Nr

4

15.00

60

K 6.7

Remould Soil sample/ Adjust Moisture content

Nr

4

27.50

110

K7

Soil Strength Test

K 7.1

One dimensional Consolidation

Nr

4

60.00

240

K8

Rock Strength Test

K 8.1

Uniaxial (Rock cores)

Nr

4

45.00

180

Sub-total 1234.00

General Summary

BILL NO.

DESCRIPTION

AMOUNT (£)

2 (B-E)

Boring and Coring/ Drilling

15350.00

3 (F)

Sampling

600.00

4 (G-J)

In-situ Tests

1860.00

5 (K)

Instrumentation

1000.00

6 (L-O)

Laboratory Tests

1234.00

Sub-total £20044.00

 

 

Decision making for the purpose of assessing and managing risks should be seen relative to the occurrence of hazards; i.e. risk management in the situations before, during and after the events of hazards. Before a hazard occurs the issue of concern is to optimise investments into preventive measures such as e.g. protecting societal assets, adequately designing and strengthening societal infrastructure as well as developing preparedness and emergency strategies (Faber 2008).

Hazard/Risk Type

Cause of hazard

Construction Stage

Consequences

Mitigation

Following Mitigation Stage

probability

Impact

Risk Rating

probability

Impact

Risk Rating

Slipping

Not wearing the right shoes or slippery surfaces

4

2

8

Bone fracture and other fatal injuries

Avoid slippery surfaces and always wearing protective safety shoes and hard hart.

2

1

2

Mud Flow

Wet soil due to rainfall and spring on site

3

3

9

Cover route parts, affect high way road and destroy close by settlement.

Dewatering might be required during excavation

Avoid areas with potential mudflows.

1

1

1

Slope instability

Landslide

4

5

20

Instability

Addressed in material specification.

Detailed site investigations of foundation and track

locations will be carried out at the pre-construction

stage, prior to detailed construction designs being

Produced.

Detailed construction designs will be produced with

Input from a geotechnical engineer.

The geotechnical risk register will be updated following

site investigations and detailed design at the

Preconstruction stage.

A programme of geotechnical inspections will be

Implemented during excavation works.

1

2

2

Variations from Design Assumptions

Unexpected ground conditions

4

4

16

Settlement and slope failure

Appropriate geotechnical design

.

Geotechnical monitoring during construction.

Programme contingency

2

1

2

Uncertainty of Construction Technique

Variable ground soil type

4

4

16

Delay

Detailed site investigation will be carried out at the pre-construction stage, prior to detailed construction design being produced.

Detailed construction design will be produced with input from a geotechnical engineer.

The geotechnical risk register will be updated following site investigations and detailed design at the preconstruction stage.

A programme of geotechnical inspections will be implemented during excavation works.

3

1

3

Design changes during pipeline installation

Changes in bearing

4

5

20

Various but could include slope failure, bearing failure.

Design changes to be reviewed by geotechnical specialist

1

2

2

Unexpected Ground Conditions

Ground condition different from those indicted for project ground condition

4

4

16

Construction delayed/ design review required

Detailed site investigations of foundation and track

locations wi


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