Geophysics for Pipelines and Cable Routes Pipelines and cable routes present a set of unique developmental and geotechnical challenges. TerraDat has designed an integrated geophysical survey approach, providing data that is useful to all stages of a project. Archaeological assessments and UXO detection; Due to the large distances covered by pipelines and cable routes, the chance of encountering archaeological features is high. in order to mitigate this, TerraDat use a 4m wide magnetometry rig towed behind a 4x4 vehicle or ATV, this system provides corridors of archeological geophysical; data that can be interpreted by our in-house archaeologist to provide detailed maps of archaeological remains along the proposed route. Using this system up to 50km per day of pipeline can be surveyed, depending on site conditions. This system will also detect shallow ferrous metallic items, useful in areas where UXO is of concern Bedrock profiling and geological structure surveys; Resistivity tomography surveys effectively map buried geological structures. This technique can be adapted to gather data for a range of depths and profile lengths. Measuring the electrical properties of the subsurface enables identification of structures such as bedrock variation, fault zones and weathered / clay-rich layers. The models can be calibrated with the help of physical observation of direct samples. Seismic surveys provide information on the depth and strength (rippability) of underlying ground materials. Seismic data can be acquired using surface-based P and S-wave refraction and /or MASW techniques. On sites with limited survey area or variable geology, seismic data can be obtained via boreholes. By combining the derived seismic P and S-wave velocities with density information, it is possible to calculate Poisson’s Ratio along with a range of elastic moduli (Shear, Young’s and Bulk).
58.23 Hedge
60.09
n
65.204
Grass
60.51
q
60.92
k
Ht=2.0m
,
59.48
60.23
p
q
General scatter of small magnetic anomalies 1009
1007 58.021
Soil Resistivity/Corrosistivity Testing; Resistivity tomography surveys are used to provide information on the shallow geology and soil electrical properties for earthing design. This approach is more accurate than the traditional 4-pin method as it is possible to derive more reliable resistivity values. Thermal properties of the soil can be analysed by using a thermal resistivity meter to acquire data either at surface, or within trial pits.
c
61.49
60.85
o
, n
61.09
Magnetic anomalies - possible UXO
h
m
Hedge Ht=2.2m 57.65 57.64
58.94
57.12
Archaeological survey data and interpretive CAD drawing
UXO survey plan Upper resistive layer
Conductive clay-rich layer Chainage (m)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
25
250
260
270 25
Elevation (m OD)
20
20
Conductive peat layer
15
15
10
10
5
5
0
0
-5 -10
67.28
57.67
Pond
Ht=2.2m
61.17
Hedge
61.06
58.92
TH
57.52
j
59.80
57.74
f 62.77
Grass
62.13
g
e
b
1005 62.533
58.71
63.75
Ht=2.0m
e
,
Existing buried service
Hedge
62.80
Grass
n
a
61.61
n
n
h
62.95
,
*Cost Effective *Non-invasive *Rapid Ground Coverage *Environmentally Friendly *Swift Mobilisation/Global Coverage
River crossings; Seismic refraction and resistivity tomography surveys provide detailed cross sections along the routes of proposed pipelines or cables. These can be of particular benefit in areas where the opportunity for intrusive investigations are limited, such as river road or railway crossings, or in environmentally sensitive areas where the presence of a drill rig may be prohibited.
Pipelines/Cable routes
TechnicalNote
-5
Lower resistive Siltstone Layer
Localised conductive bedrock feature - fracture zone
Resistivity tomography Section
, Archaeological Surveys , Rock Head Detection Surveys
Resistive Siltstone strata
-10
, Geotechnical information , Earthing Measurements , Unexploded Ordnance Detection
Seismic refraction profile over a river valley Contact Simon Hughes for more info; simon@terradat.co.uk
TerraDat (UK) Ltd - Tel (08707 303050) www.terradat.co.uk