U0737756University of East London

14/5/20102010

Cornwall Geology Field Course Exercises

Nima Golzar Soufiani

ContentsMonday’s field log – Fistral Beach, Towan Beach and Watergate Bay....................................1

Fistral Beach...........................................................................................................................2

Bed (M AM 1)....................................................................................................................2

Bedding Plane (M AM 2)...................................................................................................2

Joints (M AM 3).................................................................................................................2

Cleavage (M AM 4)............................................................................................................3

Rock Mon A (M AM 5)......................................................................................................3

Rock Mon B (M AM 6)......................................................................................................3

Rock Mon C (M AM 7)......................................................................................................4

Quartz/Calcite (M AM 8)...................................................................................................4

Group average Dip and Dip Direction for the discontinuities of the Fistral beach rock mass (M AM 9)...................................................................................................................4

Sketch of rock face at back of beach annotate to indicate stability (M AM 10)................5

Gabbions (M AM 11).........................................................................................................6

Geology/geological processes controlling the shape of the land (M AM 12)....................6

Towan Beach..........................................................................................................................7

Stack (M AM 13)................................................................................................................7

Sketch of great circles for discontinuities and faces of stack (M AM 14)..........................8

Geo (M AM 15)................................................................................................................12

Stable rock face (M AM 16).............................................................................................12

Unstable rock face (M AM 17).........................................................................................12

Plane (transitional) failure (M AM 18).............................................................................13

Wedge failure (M AM 19)................................................................................................13

Evidence of failure (M AM 20).......................................................................................13

Sketch of rock faces annotate to indicate stability/instability (M AM 21).......................14

Geology/geological processes controlling the shape of the land (M AM 22)..................15

Watergate Bay......................................................................................................................16

Beds (M PM 1).................................................................................................................16

Bedding planes (M PM 2).................................................................................................16

Joints (M PM 3)................................................................................................................16

Igneous intrusion (M PM 4)..............................................................................................17

Fossils (M PM 5)..............................................................................................................17

Baked margin (M PM 6)...................................................................................................17

Area of instability (M PM 7)............................................................................................18

Rock Mon D (M PM 8).....................................................................................................18

Rock Mon E (M PM 9).....................................................................................................18

Rock Mon F (M PM 10)...................................................................................................18

Geology/geological processes controlling the shape of the land (M PM 11)...................19

Tuesday’s field log – Bude......................................................................................................20

Whales rock/Saddle rock area..............................................................................................21

Beds (T AM 1)..................................................................................................................21

Bedding plane (T AM 2)...................................................................................................21

Joints (T AM 3).................................................................................................................21

Rock Tues A (T AM 4).....................................................................................................22

Rock Tues B (T AM 5).....................................................................................................22

Ripple marks/fossilised sea bed (T AM 6).......................................................................22

Plane (transitional) failure (T AM 7)................................................................................22

Wedge Failure (T AM 8)..................................................................................................23

Pericline (T AM 9)............................................................................................................23

Dip and Dip direction of pericline (T AM 10)..................................................................23

Cliff section between break water and lock.........................................................................24

Syncline (T AM 12)..........................................................................................................24

Anticline (T AM 13).........................................................................................................24

Dip and dip direction of syncline (T AM 14)...................................................................24

Dip and dip direction of anticline (T AM 15)...................................................................25

Cliff section prior to swimmimg pool..................................................................................26

Sketch section of cliff with labels (T PM 1).....................................................................26

Cliff section just after swimming pool.............................................................................27

Turbidites (T PM 2)..........................................................................................................27

Plane failures (T PM 3).....................................................................................................27

Wedge failures (T PM 4)..................................................................................................27

Crooklets beach – cliff sections adjacent to the stairs..........................................................28

Syncline (T PM 5).............................................................................................................28

Anticline (T PM 6)............................................................................................................28

Fault in cliff face (T PM 7)...............................................................................................28

Vertical beds (T PM 8).....................................................................................................29

First cove..............................................................................................................................29

Chevron folds (T PM 9)....................................................................................................29

Intensely folded zone (T PM 10)......................................................................................29

Cliff section above Maer Low Cliff beach...........................................................................30

Head (T PM 11)................................................................................................................30

Tension crack (T PM 12)..................................................................................................30

Slip circle (shear plane) (T PM 13)..................................................................................30

Looking down at beach from the cliff path above Crooklets beach.....................................31

Wave cut platform (T PM 14)...........................................................................................31

Fault in wave cut platform (T PM 15)..............................................................................31

Horizontal anticline/syncline (T PM 16)..........................................................................31

Geology/geological processes controlling the shape of the land (T PM 17)....................32

Cheesewring Quarry, Rock Slope stability exercise................................................................33

Introduction.......................................................................................................................34

Rock mass description......................................................................................................34

Assessment of angle of friction........................................................................................34

List of hammer readings...................................................................................................34

IS(50) readings...................................................................................................................35

Rock slope stability analysis.............................................................................................36

Report................................................................................................................................37

Portreath...................................................................................................................................38

Desk study............................................................................................................................39

Introduction.......................................................................................................................39

Maps..................................................................................................................................40

Superficial deposits...........................................................................................................41

Rock type..........................................................................................................................41

Accessibility......................................................................................................................42

Faults/folds........................................................................................................................42

Location............................................................................................................................42

History of the site..............................................................................................................42

Stability assessment..........................................................................................................43

Tunnel analysis.................................................................................................................44

Ground profile across the beach for bridge foundation....................................................46

Ground profile...................................................................................................................48

Reference..................................................................................................................................49

Monday’s field log – Fistral Beach, Towan Beach and Watergate Bay

1

Fistral Beach

Bed (M AM 1)

This picture shows a bed. A bed is a layering of sheet like units called beds or strata.

Bedding Plane (M AM 2)This picture shows a bedding plane. A bedding plane is essentially a planar surface that separates a layer of bed from another.

Joints (M AM 3)

This picture shows me pointing to a joint. The definition of a joint is a brittle fracture in a rock of which there have been little to no movement parallel to the plane of the fracture.

2

Cleavage (M AM 4)

This picture shows cleavage. This is the formation of a set of fractures along closely spaced, parallel surfaces in a rock

Rock Mon A (M AM 5)

Highly weathered, Very large Blocky, with narrow jointing, dark-greyish-black, medium grained Slate. Moderately strong rock, non-permeable through the discontinuity sets (4).

Rock Mon B (M AM 6)

Moderately weathered, large blocky, light greyish white, coarse grained sandstone. Moderately strong rock, permeable through the discontinuity sets (4)

3

Rock Mon C (M AM 7)

Moderately weathered, large blocky, light brownish white, fine grained Mudstone. Strong rock, permeable through the discontinuity sets (4)

Quartz/Calcite (M AM 8)

This picture shows calcite in the rock. This is the basic component of chalk, marble and Limestone. It is a common form of natural calcium carbonate.

Group average Dip and Dip Direction for the discontinuities of the Fistral beach rock mass (M AM 9)

Dip Dip Direction54 25245 23246 260

Average Dip and Dip Direction

48⁰/248⁰

4

Sketch of rock face at back of beach annotate to indicate stability (M AM 10)

5

Gabbions (M AM 11)

6

This picture shows a Gabion. It is basically a mesh cage that contains earth or rock in order to support the slope.

Geology/geological processes controlling the shape of the land (M AM 12)

The geology of the land when looking from a plan view forms a kind of semi-circle as seen to the left. This is due to the harder rock being less susceptible to erosion than the softer rock. As a result the softer rock has been eroded away more than the harder rock.

7

Towan Beach

Stack (M AM 13)

In this picture, a stack is shown. This is a pillar or block of rock which have sides that are nearly vertical. At one point it was one with the main cliff but due to erosion, has been separated as shown in this picture.

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Sketch of great circles for discontinuities and faces of stack (M AM 14)

North side

9

East Side

10

South side

11

West side

12

Geo (M AM 15)

In this picture is a geo. A geo is a narrow inlet of a clogged coastline, which has developed along a major near vertical joint or fault.

Stable rock face (M AM 16)

This picture shows a stable rock face. The reason as to why it is a stable rock face is because the discontinuities are not sliding towards this face

.

Unstable rock face (M AM 17)

As can be seen on this picture, this is a unstable rock face. This can be seen by the rubbles that have been left on the ground as a result of sliding.

13

Plane (transitional) failure (M AM 18)

Similar to the previous picture, due to the rubble that has been left on the ground, one can assume that plane (transitional) failure has occurred.

Wedge failure (M AM 19)

This picture shows a wedge failure. This is a common type of failure where sliding will take place on two planes.

Evidence of failure (M AM 20)

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Sketch of rock faces annotate to indicate stability/instability (M AM 21)

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Geology/geological processes controlling the shape of the land (M AM 22)

The stack is formed due to a weakness found in a particular area of the cliff. This weakness is attacked by the sea which is weakened further and then eroded away. It is a feature of erosion.

16

Watergate Bay

Beds (M PM 1)

This picture shows beds. A bed is a layering of sheet like units called beds or strata.

Bedding planes (M PM 2)This picture shows a bedding plane. A bedding plane is essentially a planar surface that separates a layer of bed from another.

Joints (M PM 3)

This picture shows me pointing to a joint. The definition of a joint is a brittle fracture in a rock of which there have been little to no movement parallel to the plane of the fracture.

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Igneous intrusion (M PM 4)

This picture shows an igneous intrusion. These are formed when magma solidifies below the surface of the earth. Later, they may be exposed at the surface. (Waltham, 2003)

Fossils (M PM 5)

This picture contains a fossil. It is essentially the remains of an organism that once lived in the past.

Baked margin (M PM 6)

This picture shows a baked margin. This is when sediment comes into contact with any hot igneous body and alters the sediment. The result is the exposed surface appears as a baked margin. (Nicholas , 2000)

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Area of instability (M PM 7)

As can be seen in the picture, the large amount of rubbles that are gathered indicate plane failure that has occurred and instability.

Rock Mon D (M PM 8)

Moderately weathered, medium blocky, light yellowish brown, medium grained sandstone. Moderately weak rock. Permeable through discontinuity sets (3).

Rock Mon E (M PM 9)

Moderately weathered, very large blocky, light brownish grey, fine grained Rhyolite. Strong rock. Non permeable through discontinuity sets (5).

Rock Mon F (M PM 10)

Slightly weathered, large blocky, light brownish grey, fine grained shale. Strong rock, non-permeable through the discontinuity sets (5).

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Geology/geological processes controlling the shape of the land (M PM 11)

The igneous intrusion has caused the country rocks around it to heat at such a rate that the layers in the shale have fused together. If one was to look further away from the igneous intrusion they would find the shale to have obvious layers.

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Tuesday’s field log – Bude

21

Whales rock/Saddle rock area

Beds (T AM 1)This picture shows a bed. A bed is a layering of sheet like units called beds or strata.

Bedding plane (T AM 2)This picture shows a bedding plane. A bedding plane is essentially a planar surface that separates a layer of bed from another.

Joints (T AM 3)This picture shows me pointing to a joint. The definition of a joint is a brittle fracture in a rock of which there have been little to no movement parallel to the plane of the fracture.

22

Rock Tues A (T AM 4)

Highly weathered, very large blocky, dark reddish brown, medium grained sandstone. Moderately strong, permeable rock through the discontinuity sets (5).

Rock Tues B (T AM 5)

Highly weathered, very large, blocky, dark brownish grey, medium grained limestone. Strong rock, low permeable through discontinuity

Ripple marks/fossilised sea bed (T AM 6)

This picture shows a ripple mark/fossilised sea bed. These are basically sand waves which were made by wave or wind on top of a bed.

Plane (transitional) failure (T AM 7)

This picture shows a plane (transitional) failure. This can be seen by the rubble of rocks that look to have been sliding down.

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Wedge Failure (T AM 8)

This picture shows a wedge failure. This is when two discontinuities intersect behind the face. (Wyllie, Mah, & Hoek, 2004)

Pericline (T AM 9)

This picture shows a Pericline. A Pericline is a form of anticline whose length is longer than its width which were made from sediments that were deposited.

Dip and Dip direction of pericline (T AM 10)

Dip Dip Direction28 16022 16022 140

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Cliff section between break water and lock

Syncline (T AM 12)

This picture shows a syncline. It is a fold whose hinge is downwards with the outer layer being the oldest and the inner layer being the youngest.

Anticline (T AM 13)

This picture shows a Anticline. It is a gold whose hinge is upwards with the outer layer being the youngest and the inner layer being the oldest.

Dip and dip direction of syncline (T AM 14)

Dip Dip Direction31 00235 35015 32656 18040 16226 132

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Dip and dip direction of anticline (T AM 15)

Dip Dip Direction40 25243 23245 26045 18045 16640 150

26

Cliff section prior to swimmimg pool

Sketch section of cliff with labels (T PM 1)

27

Cliff section just after swimming pool

Turbidites (T PM 2)

This picture shows Sedimentary deposit laid down by a turbidity current.

Plane failures (T PM 3)

This picture shows a plane falure. This is a failure which occurs by sliding along a single plane which daylights into a slope face. (Bell, 2004)

Wedge failures (T PM 4)

This picture shows a wedge failure. This is when two planar discontinuities intersect with each other. The wedge is formed daylighting into the face. (Bell, 2004)

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Crooklets beach – cliff sections adjacent to the stairs

Syncline (T PM 5)

This picture shows a syncline. It is a fold whose hinge is downwards with the outer layer being the oldest and the inner layer being the youngest.

Anticline (T PM 6)

This picture shows an Anticline. It is a gold whose hinge is upwards with the outer layer being the youngest and the inner layer being the oldest.

Fault in cliff face (T PM 7)

This picture shows a fault in a cliff face. This can be seen by the beds at the bottom having been separated from each other.

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Vertical beds (T PM 8)This picture shows a vertical bed.

First cove

Chevron folds (T PM 9)

This picture shows a Chevron fold. Its feature includes an angular fold which have straight limbs and small hinges.

Intensely folded zone (T PM 10)

This picture shows an intensely folded zone.

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Cliff section above Maer Low Cliff beach

Head (T PM 11)

This picture shows a head. A head is essentially a mixture of soil and scree.

Tension crack (T PM 12)

This picture shows a tension crack.

Slip circle (shear plane) (T PM 13)

This picture shows a slip circle

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Looking down at beach from the cliff path above Crooklets beach

Wave cut platform (T PM 14)

This picture shows a wave cut platform. This is a feature created by the action of waves hitting against the cliff face which forms a wave cut notch, eventually enlarging to a cave, the roof of the cave collapses which breaks to smaller pieces and/or washed into sea.

Fault in wave cut platform (T PM 15)

This picture shows a wave cut platform with a fault.

Horizontal anticline/syncline (T PM 16)

This is a picture of a anticline/syncline.

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Geology/geological processes controlling the shape of the land (T PM 17)

The wave cut platform is a geological feature that is created by the action of waves. The constant action of waves over geological time causes the cliff face to form a wave cut notch. His wave cut notch eventually turns into a cave over geological time. The roof of the cave then collapses and the waves wash away the broken pieces into the sea. The end result is a wave cut platform.

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Cheesewring Quarry, Rock Slope stability exercise

34

Introduction

Due to the proposal to reopen the quarry, it was decided to assess the stability of each of the rock faces. In this report, the strength and the results of the stability of each rock face is determined.

Rock mass description

Slightly weathered, very large blocky, light greyish grey, coarse grained Granite. Very strong non permeable through discontinuity sets (3).

Assessment of angle of friction

5 readings of the angle of friction were taken and an average was obtained. The angle of friction was founded to be 34⁰. This was done by gaining two sample of rock and placing them one on top of each other on a flat clipboard. The clipboard was raised from one end until the rock slid off of the rock beneath it. The dip was taken and the whole process done 4 more times with the average being the angle of friction.

List of hammer readings

Schmidt hammer readings were taken to estimate the compressive strength of the rock. The following results were gathered:

Schmidt hammer readings32343532Average : 33

35

IS(50) readings

P(KN) W(mm) D(mm) Is F Is(50) De^2 Reference

1 8.31 89.3 18.9 3.867031 0.966526 3.737588 2148.936 Nima and Yosef

2 7.02 78.9 27.2 2.5691 1.020208 2.621016 2732.474 Nima and Yosef

3 3.89 52.1 27 2.171891 0.927713 2.014891 1791.066 Nima and Yosef

4 5.37 60.2 23.2 3.019811 0.926216 2.796997 1778.257 Nima and Yosef

5 7.59 7.59 31 25.33542 0.62041 15.71836 299.5805Adam and Michael

6 5.77 39.2 66.6 1.735823 1.066202 1.850737 3324.072Adam and Michael

7 14.83 53.8 65.2 3.320482 1.139462 3.783565 4466.219Adam and Michael

8 2.08 4.09 28.1 14.21424 0.528038 7.505654 146.3321Adam and Michael

9 3.55 28.5 53.2 1.838915 0.943493 1.735003 1930.486Adam and Michael

10 3.8 21.5 22.5 6.169536 0.729639 4.501534 615.9296prajee and Craig

11 5.02 30 36.8 3.571285 0.878489 3.137335 1405.656prajee and Craig

12 6.4 89.6 49.3 1.137928 1.20013 1.365661 5624.256prajee and Craig

Average IS(50) = 4.99

36

Rock slope stability analysis

Each face was measured and its stability was determined through the use of stereonets which can be found in Thursday’s appendix. The position of each face can also be found in Thursday’s appendix.

Face Stability analysis1 All are stable2 All are stable3 All are stable4 All are stable5 All are stable6 Man made7 Man made8 Man made9 Wedge failure along DS3/DS4 and DS4/DS110 All are stable11 Plane slide failure along DS112 Plane slide failure along DS1 and wedge failure along DS1 and DS313 All are stable14 Wedge failure along DS1/DS3 and plane slide failure along DS115 Wedge failure along DS5/DS116 Wedge failure along DS1/DS417 Failed face18 All are stable19 Wedge failure along DS5/DS420 All are stable21 All are stable22 Wedge failure along DS5/DS423 All are stable24 All are stable25 All are stable

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Report

To reopen this entire quarry would be unadvisable due to the amount of instability found on site. Though it is not possible to open this entire quarry, it may be partially open due to the instability’s which are mainly situated towards the north and west of the quarry as indicated on the map.

All of the rock faces along the east and south are stable except for one, face 22. To stabilise the north and west side of the quarry, a number of stabilisation techniques can be used. One of the most effective ways could be to reduce the face angle which would decrease the chance of a plane failure occurring.

The quarry though is overall not stable and it is not recommended to reopen this quarry unless stabilisation techniques are used or the quarry is partially opened.

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Portreath

39

Desk study

IntroductionAccording to the cornwallguide website, portreath is a small resort with a very narrow harbour located about 5 miles north of Redruth. Though it only now shelters the occasional fishing boat, it was at one point a busy port which imported and exported coal. It was even hard to navigate through the harbour entrance and required high level of skill to navigate.

The old tram roads that were used for transporting ore though have now been converted to cycle paths which makes it possible to ride from Portreath to Devoran.

Portreath is now very known for its sandy beach and it a magnet for surfers and bodyboarders alike.

40

MapsBelow is a map from Edina of Portreath

41

Below is an ordnance survey map of Portreath

Superficial depositsOn the beach Shingle, sand, silt and clay; may be bedded or chaotic; beach deposits may be in the form of dunes, sheets or banks. The age is in the QUATERNARY period.

On battery hill Alluvium deposits can be found. These are Normally soft to firm consolidated, compressible silty clay, but can contain layers of silt, sand, peat and basal gravel. A stronger, desiccated surface zone may be present.

Rock typeThe bedrock is called the PORTHTOWAN FORMATION which consists of Interbedded slaty mudstone, grey and grey-green, and sandstone. Subordinate sandstone beds are up to 2m thick, typical turbidites. Its age ranges from the Fransnian to Eifelian which are in the Devonian period 

42

AccessibilityThere exists a footpath leading to the site which makes it easy for people to access the beach however, for cars choices are very limited. There is a car park that is situated very close to the beach as shown below.

Faults/foldsThere are no observed faults or folds on site

LocationLocation were obtained from the digi map with co ordinates 165198, 45419

History of the siteThere are mining history in portreath that date back to the 1830’s where above all, porteath was a mineral harbour. Its industrial significance is thus bound up with this link to the local copper mines, at first around Scorrier, and later Camborne. Portreath is a key place when it comes to Cornish industrial history as the earliest phase of the development of railways and the parallel development of railways and port development occurred there. A big role was played when it portreath was used as a holiday base for the workers of the Camborne-Redruth mining districts in the 19th and 20th centuries.

43

Stability assessment

Each face was measured and its stability was determined through the use of stereonets which can be found in Friday’s appendix. The position of each face can also be found in Friday’s appendix.

Face Stability analysisWestern hill1 Wedge failure along DS/DS42 All are stable3 Wedge failure along DS1/DS5 and plane failure along DS44 Plane failure along DS2 and plane failure along DS45 Wedge failure along DS1/DS4Battery hill6 All are stable7 All are stable8 Plane failure along DS39 Plane failure along DS3

Overall, western hill and battery hill are unstable as there are a number of wedge and plane failure that occur there.

Lift shaft analysis

1Since the lift shaft is round, this would mean that the face is infinite. Therefore every discontinuity that is greater than the angle of friction is a potential failure.

The left shaft then has:

Wedge failure along DS1/DS5 Wedge failure along DS1/DS2 Wedge failure along DS1/DS4 Wedge failure along DS5/DS2 Wedge failure along DS5/DS4 Plane failure along DS1 Plane failure along DS2 Plane failure along DS4 Plane failure along DS5

Building a lift shaft would cause huge amounts of problems therefore a lift shaft to be built here is not recommended.

1 The lift shaft stereonet can be found in Friday’s appendix44

Tunnel analysis

2A tunnel for western hill was proposed for which the analysis has been performed.

Face 1 (the face that is facing towards north) has a wedge failure along DS1/DS2 which intersect within the danger area therefore this side is unstable. On face 2 (directly opposite) the face is stable as there is no plane or wedge failure. The recommendation to the client would be to stabilise face 1 as it has a potential wedge failure with retaining or supporting walls.

The picture above shows where the location of the proposed tunnel will be.

2 The stereonet for the tunnel can be found in Friday’s appendix. 45

2.5 meters

2.0 meters

3.34 meters

Face 1Face 2

Face 3

Fracture in rock

Diagram of proposed tunnel

As can be seen from the diagram above, the beds are inclined and are sloping into the roof. The fractures are shows in two locations which intersect the inclined. If the fractures were not present then it would be recommended to construct this tunnel. As it is though, there are two fractures that could cause severe problems for the roof of the tunnel and can lead to roof collapse . There are remedial procedures that can take place to make the tunnel stable but this would be uneconomical and highly laborious.

46

Fracture in rock

Ground profile across the beach for bridge foundation

Electrode separate (a)

Meter Reading (ohm) apparent resistivity

Cumalitive apparent resistivity

1 10.42 65.47 65.472 2.57 32.30 97.773 0.80 15.08 112.854 0.15 3.77 116.625 0.33 10.37 126.986 0.18 6.79 133.777 0.18 7.92 141.698 0.14 7.04 148.729 0.11 6.22 154.94

10 0.12 7.54 162.48

Graph can be viewed on the next page

47

48

Dry sand

Capillary

Saturated sand

Hard rock

Ground profile

The ground profile gained from the resistivity drill will inform us of the ground conditions for a foundation to be built for the bridge. As can be seen on the graph, the water table is hit when the potential nodes have been spaced 4 meters apart. What is found is dry sand, capillary, saturated sand, gravel sand and hard rock. This does not make the ground conditions viable to lay foundations on. Piled foundations would be recommended in this case since these are used for conditions where suitable foundation conditions are not present or to transmit loads to a lower level of subsoil. (Chudley & Greeno, 2006)

It is worth noting the reason why the resistivity graph does not show the lines completely joining each other. This is due to observations that were made on site. There are only four layers that should be expected which are dry sand, capillary, saturated soil and hard rock. Since no gravely sand was observed, it is assumed that there was a slight error in the reading.

49

2 meters

3 meters

4 meters and water table

Dry sand

Capillary

Saturated sand

Hard rock

Ground level

Ground profile

Reference

Bell, F. G. (2004). Engineering geology and construction. London: Spon Press.

Chudley, R., & Greeno, R. (2006). Building Construction Handbook sixth edition. Oxford: Elsevier.

Nicholas , C. J. (2000). Exploring Geology on the ISle of Arran. Cambridge: Cambridge University Press.

Waltham, T. (2003). Foundations of Engineering Geology second edition. Oxford: Spon Press.

Wyllie, D. C., Mah, C. W., & Hoek, E. (2004). Rock slope engineering: civil and mining. Oxon: Institute of Mining and Merallurgy.

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