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Focus-Information

Geotechnology >> Borehole Measurements

Geotechnology Hydrogeology Monitor ing

Solexperts provides services to measure

the depth and position of boreholes and

buried pipes. The wide range of availa-

ble instrumentation allows selection of

the correct measurement system to

meet the specific site characteristics and

conditions (borehole length, diameter,

direction, type of casing).

The EZ-Trac is often used to measure

boreholes and pipes without steel

casing. The Maxibor and Gyrosmart are

used to measure boreholes with steel

casing. Vertical boreholes are measured

with a special borehole inclinometer

which uses installation rods to maintain

the reference direction.

• Survey measurements may be used to determine the positioning of explo-ratory boreholes relative to depth thus providing the locations of collected soil specimens relative to a future structure.

• Bearing capacity and effectiveness of earth and rock anchors can be influ- enced by the anchor’s relative posi-tions. When new anchors are being added to a site it is important that they are correctly positioned to avoid

EZ-Trac, Gyrosmart, Maxibor, Borehole Inclinometer:

Measurement systems and services of Solexperts AG

Borehole Measurements

Solexperts Services

impairing the performance of existing anchors.

• The position of boreholes used in the construction of pipe curtains, grouting and ground freezing must be within specified limits if a load-bearing arch or a continuous barrier against ground-water is to be successfully constructed. The same is true for monitoring bore- holes which contain temperature mea- suring chains to overview ground free-zing projects.

• The position of blasting drill holes must be accurately known for the planning of blast loads and the determination of blasting effects (dangers due to blasting operations, excavated mass of rock).

• By making directional measurements as the borehole is drilled the current posi-tion of the borehole can be checked in a timely manner. This allows corrective measures to be taken to adjust the drilling direction assuring that the desi-red borehole location is achieved.

Borehole Measurements (Frutigen, Switzerland)

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Applications of Borehole Position Measurements

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Borehole Position Measuring Systems:

• EZ-Trac

The EZ-Trac probe is fitted with an electronic magnetic compass that determines

the direction of the probe with reference to the Earth’s magnetic pole. The strength

of the Earth’s in-situ magnetic field is recorded and is taken into account in the

interpretation of the results. The EZ-Trac is used at sites where the disturbance to

the Earth’s magnetic pole is small. It cannot be used (or used only in a limited way) if

the borehole has a steel casing or is in the proximity of earth anchors, pipe curtains,

earth reinforcement, steel components or magnetically active rock. It is often possible

to use the EZ-Trac if only the start of the borehole is cased because the disturbance

to the Earth’s magnetic field decreases at depth. In this situation the position of the

cased borehole section is determined by means of geodetic measurement and by

extrapolation of the borehole direction from the undisturbed borehole section.

Important characteristics:

• Open uncased boreholes to great depths

• Probe size: Length: 1.03 m; diameter: 35 mm; the probe

should be centred in the borehole when measured

• Accuracy: slope: +/- 0.25°, azimuth: +/- 0.35°

• Gyrosmart

The Gyrosmart probe determines the direction of the borehole using a gyroscopic

compass. Within the probe a freely spinning gyroscope maintains the direction of

its axis of rotation. The direction of the probe with reference to this axis of rotation

is used to measure the direction of the borehole. Gyrosmart works independently

of the Earth’s magnetic field and therefore exhibits no magnetic deviation. However,

a deviation from the actual borehole direction can result from a rapid self-initiated

movement of the measuring probe. Gyrosmart is used mainly in boreholes having

a steel casing.

Important characteristics:

• Probe size: Length: 1.8 m; diameter: 40 mm; the probe should be centred in the

borehole when measured

• Vertical boreholes can only be measured with the aid of a calibration device

• Accuracy: slope: +/- 0.2° azimuth +/- 0.5°

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• Maxibor

Maxibor is an optical measuring deflectometer with an integrated angle gauge.

The probe is moved in a stepwise manner along the borehole, one half probe lengths

at a time. At each position the change in direction of the borehole with respect to the

previous measuring section is determined. Maxibor works independently of the

Earth’s magnetic field and therefore exhibits no magnetic deviation. Although the

Maxibor can have a deviation from the actual borehole direction due to an accumu-

lation of error along the borehole, its accuracy its quite high.

Important characteristics:

• The Maxibor is often used to measure cased, magnetically disturbed boreholes.

Typical applications are sub-horizontal boreholes for anchors, pipe curtains and

ground freezing

• Size of measuring probe: Length: 8.5 m or 6.5 m; diameter: 44 mm; the probe

should be centred in the borehole when measured

• Limitation: Not suitable for boreholes that are vertical or inclined up to +/- 10°

from the vertical

• Accuracy: 1/1000 of the

borehole length, i.e. over

a 100 m length of borehole

it is +/- 0.1 m from the

position of the borehole

Unique construction and measuring principle: An image of concentric rings is projected onto a sensor within the probe. The position of the projected rings on the sensor changes when the probe expe-riences a deflection while passing along the borehole. The position change allows the deflection to be measured.

• Borehole Inclinometer

The borehole inclinometer consists of a biaxial, high precision slope sensor. The

probe is kept aligned using stiff torsion installation rods. The probe is fitted with a

centring device and moved in a stepwise manner along the borehole. The influence

of errors is largely minimised because each measurement of the borehole inclination

is carried out at two positions.

Important characteristics:

• Suitable for the vertical direction and up to approx. +/- 10° from the plumb line.

Both cased or uncased boreholes can be measured. This probe is used mainly for

vertical boreholes up to a depth of about 50 m

• Probe Size: Length: 1.5 m; diameter: 70 mm; the probe should be centred in the

borehole when measured

• Accuracy: slope: +/- 0.5 mm/m, azimuth +/- 2°, typical value for 30 m is

+/- 20 mm

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FLEXIT: SmartTool drillhole survey result table.

Survey name : VV1INSurvey date : 29/09/2010 11:16:45Printed on 03.05.2011 07:48:01

Page 1 of 2

Station Dip Azimuth Easting Northing Elevation UpDown LeftRight ShortfallMetres Degrees Degrees Metres Metres Metres Metres Metres Metres

0.0 -7.67 261.00 0.00 0.00 0.00 0.00 0.00 0.006.0 -7.72 261.00 -5.87 -0.93 -0.80 0.00 0.00 0.00

12.0 -7.48 261.00 -11.75 -1.86 -1.60 0.01 0.00 0.0018.0 -6.56 261.00 -17.63 -2.79 -2.33 0.07 0.00 0.0024.0 -6.17 261.00 -23.52 -3.72 -3.00 0.21 0.00 0.0030.0 -6.01 261.00 -29.41 -4.66 -3.63 0.38 0.00 0.0036.0 -5.76 261.00 -35.31 -5.59 -4.25 0.56 0.00 -0.0142.0 -5.35 261.00 -41.20 -6.53 -4.83 0.79 0.00 -0.0148.0 -4.85 261.00 -47.11 -7.46 -5.36 1.06 0.00 -0.0254.0 -3.95 261.62 -53.02 -8.36 -5.82 1.40 0.03 -0.0360.0 -3.50 260.81 -58.94 -9.28 -6.21 1.81 0.05 -0.0466.0 -2.85 258.84 -64.83 -10.34 -6.54 2.28 -0.07 -0.0672.0 -2.39 260.14 -70.73 -11.43 -6.82 2.81 -0.23 -0.0978.0 -1.91 260.56 -76.64 -12.44 -7.04 3.39 -0.29 -0.1284.0 -1.92 261.27 -82.56 -13.38 -7.24 3.99 -0.30 -0.1590.0 -1.92 260.87 -88.48 -14.31 -7.44 4.59 -0.30 -0.1896.0 -2.79 261.22 -94.40 -15.25 -7.69 5.15 -0.29 -0.20

102.0 -3.51 261.43 -100.33 -16.15 -8.02 5.62 -0.26 -0.22108.0 -4.10 261.45 -106.25 -17.04 -8.42 6.03 -0.21 -0.23114.0 -4.77 261.19 -112.16 -17.94 -8.88 6.37 -0.18 -0.24120.0 -5.48 261.16 -118.07 -18.86 -9.42 6.63 -0.16 -0.25126.0 -6.02 261.35 -123.97 -19.77 -10.02 6.83 -0.13 -0.25132.0 -6.83 261.96 -129.87 -20.63 -10.69 6.96 -0.06 -0.26138.0 -7.27 262.01 -135.76 -21.46 -11.43 7.03 0.04 -0.26144.0 -7.75 261.66 -141.65 -22.31 -12.21 7.05 0.12 -0.26150.0 -8.34 261.54 -147.53 -23.18 -13.05 7.01 0.19 -0.26156.0 -8.85 261.65 -153.40 -24.04 -13.95 6.91 0.25 -0.26162.0 -9.49 261.59 -159.26 -24.91 -14.90 6.76 0.31 -0.26168.0 -9.93 261.57 -165.11 -25.77 -15.91 6.54 0.37 -0.27174.0 -10.42 261.53 -170.95 -26.64 -16.97 6.28 0.43 -0.27180.0 -10.98 262.20 -176.78 -27.48 -18.09 5.96 0.52 -0.28186.0 -11.51 262.43 -182.62 -28.26 -19.26 5.59 0.65 -0.29192.0 -11.87 262.54 -188.44 -29.03 -20.47 5.17 0.81 -0.31198.0 -12.19 262.75 -194.26 -29.78 -21.73 4.71 0.97 -0.33204.0 -12.60 262.77 -200.07 -30.52 -23.01 4.22 1.15 -0.35210.0 -12.83 262.21 -205.88 -31.29 -24.33 3.69 1.31 -0.38216.0 -13.11 262.02 -211.67 -32.09 -25.68 3.14 1.42 -0.41222.0 -13.40 262.13 -217.45 -32.89 -27.05 2.55 1.53 -0.44228.0 -13.76 262.04 -223.23 -33.70 -28.46 1.94 1.64 -0.47234.0 -14.20 261.92 -229.00 -34.51 -29.91 1.28 1.74 -0.51240.0 -14.60 261.95 -234.75 -35.32 -31.41 0.57 1.83 -0.55246.0 -15.05 262.57 -240.50 -36.10 -32.94 -0.17 1.96 -0.60252.0 -15.28 262.59 -246.24 -36.85 -34.51 -0.95 2.12 -0.65258.0 -15.57 263.13 -251.98 -37.57 -36.11 -1.76 2.31 -0.71264.0 -15.75 262.85 -257.71 -38.28 -37.73 -2.60 2.51 -0.77270.0 -15.81 262.40 -263.44 -39.02 -39.36 -3.44 2.67 -0.83276.0 -15.95 261.76 -269.15 -39.81 -41.00 -4.30 2.78 -0.89282.0 -16.06 261.43 -274.86 -40.66 -42.65 -5.17 2.84 -0.96288.0 -16.31 261.12 -280.56 -41.53 -44.32 -6.06 2.87 -1.02294.0 -16.55 261.49 -286.24 -42.40 -46.02 -6.97 2.90 -1.09300.0 -17.09 262.16 -291.93 -43.22 -47.76 -7.92 2.98 -1.17306.0 -17.37 260.70 -297.60 -44.07 -49.54 -8.92 3.03 -1.25

Solexperts AG

Mettlenbachstrasse 25

P.O. Box 81

8617 Mönchaltorf

Switzerland

Tel +41 (0) 44 806 29 29

Fax +41 (0) 44 806 29 30

info@solexperts.com

www.solexperts.com

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Principle of Borehole Measurement

The relative borehole position is given by section-wise measurements of the slope

and direction (azimuth) over the length of the borehole. The position calculation assu-

mes that the borehole is uniform between the measuring points. For determination

of the absolute borehole position the coordinates, direction and slope at the start

of the borehole must be taken into account. The starting slope is measured using a

slope sensor and the direction is measured with an electronic magnetic compass, a

gyroscopic compass, an angle gauge or a measuring rod.

Data Acquisition, Evaluation and Presentation of Results

The data from all the systems are electronically measured and stored. Measurements

can be evaluated immediately after the survey is completet and the results can be

displayed graphically and numerically. The borehole position with depth is given

relative to a coordinate system or as a deviation from a given initial borehole direction

and slope.

0.50

1.00

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