3.0 INVESTIGATION PROCEDURES 3.1 General 3.2 · PDF file3.2 Boreholes The geotechnical ... the...

INTERIM GEOTECHNICAL DATA REPORT - OLRT TUNNEL

December 2010 Report No. 10-1121-0068-1 3

3.0 INVESTIGATION PROCEDURES

3.1 General The geotechnical and hydrogeological field investigation for this project was carried out from May 3 to August 11,

2010. The field investigation included borehole drilling, downhole geophysics logging and testing and seismic

surveys, all of which are discussed in detail below.

3.2 Boreholes The geotechnical drilling for this investigation was carried out between May 3 and July 15, 2010. During that

period, twenty-three boreholes (numbered T-1 to T-23, inclusive) were drilled at the locations shown on Figure

1.2. Fourteen environmental boreholes shown on Figure 1.2 were also drilled during this period, but are

discussed in the report “Factual Report, Scoped Phase II Environmental Site Assessment, Preliminary Design,

Ottawa Light Rail Transit Tunnel, Ottawa, Ontario”, Report Number 10-1121-0068 (5000) dated September

2010.

The following table lists the borehole locations along the alignment, borehole dip, dip direction (relative to True

North), drilled lengths and vertical depths:

Table 3.1: Summary of Boreholes

Borehole No. Location Borehole Dip /

Dip Direction Drilled Length (m) Drilled Depth (m)

T-1 West Portal 68 / 141 31.9 29.6

T-2 West Portal 70 / 270 33.2 31.2

T-3 Tunnel 72 / 053 51.8 49.3

T-4 Downtown West Station 72 / 053 52.8 50.2

T-5 Downtown West Station 68 / 243 54.4 50.4

T-6 Tunnel 68 / 243 52.9 49.0

T-7 Downtown East Station 67 / 243 52.7 48.5

T-8 Downtown East Station 73 / 139 54.5 52.1

T-9 Tunnel 70 / 058 57.6 54.1

T-10 Rideau Station 69 / 332 45.3 42.3

T-11 Rideau Station 70 / 251 45.0 42.3

T-12 Tunnel - Bedrock Valley 90 / NA 36.1 36.1(1)

T-13 Tunnel - Bedrock Valley 89 / 027 40.5 40.5

T-14 Tunnel 69 / 060 38.7 36.9

T-15 Tunnel 69 / 234 38.0 35.5

T-16 Tunnel 71 / 206 35.0 33.1

T-17 Tunnel 67 / 200 33.0 30.4

T-18 Campus Station 87 / 133 27.8 27.8

T-19 Campus Station 90 / NA 27.4 27.4

T-20 Tunnel 88 / 112 27.9 27.9

T-21 Tunnel 90 / NA 25.1 25.1



Borehole No. Location Borehole Dip /

Dip Direction Drilled Length (m) Drilled Depth (m)

T-22 East Portal 88 / 179 21.0 21.0

T-23 East Portal 88 / 211 21.4 21.4

Total 904.8

Note: (1) Borehole T-12 was not drilled to its planned depth of 40.4 metres due to several factors such as limited work hours and difficult soil conditions.

After the final depth was reached, the boreholes were left open (with flushmount cover in place) for up to

approximately one month to conduct geophysical logging within the boreholes.

On completion of the drilling operations, the soil and rock samples from the boreholes were transported to

Golder Associates’ laboratory for testing and to an off-site storage facility for examination by the project

engineer.

Due to the proximity of existing underground utilities, it was necessary to remove the pavement structure and the

first few meters of the overburden soils at boreholes T-5, T-9 and T-12 using hydro-vacuuming techniques.

Following the geophysical logging of boreholes T-5 and T-12 and decommissioning of borehole T-9, the backfill

and pavement structure were reinstated at those respective boreholes. In addition, the asphalt was removed

and reinstated at borehole T-4 due to damage caused by flush water.

Landscape repairs were carried out at boreholes T-1, T-2, T-17, T-18, T-19 and T-20 after all the fieldwork was

completed.

Monitoring wells were installed in boreholes T-5, T-10, T-12, T-13, T-19 and T-23 to allow subsequent

measurement of the stabilized groundwater level at the site and for field permeability (rising head) testing. In situ

hydraulic conductivity (packer) testing was also carried out within select boreholes (refer to Section 3.2.2).

Boreholes in which monitoring wells were not installed were backfilled with a cement-bentonite grout.

The field work was supervised by experienced Golder personnel who located the boreholes, directed the drilling

operations, geotechnically logged the boreholes, took custody of the samples, and carried out the in situ testing.

The borehole locations were selected and located in the field by Golder Associates personnel and the locations

and elevations were subsequently surveyed by Annis O’Sullivan Vollebekk Ltd. The elevations are referenced to

Geodetic datum (Canadian Vertical Datum 1928).

3.2.1 Drilling

Nineteen boreholes were advanced using truck-mounted drill rigs and one borehole was advanced using a track-

mounted drill rig operated by George Downing Estate Drilling Ltd. of Grenville-sur-la-rouge, Quebec. Three

boreholes were also advanced using a truck-mounted drill rig operated by Marathon Drilling Company Ltd. of

Ottawa, Ontario. The boreholes were advanced to depths which varied from 20.8 to 54.0 metres below ground

surface.



Standard penetration tests (ASTM D698) were conducted at regular depth intervals in boreholes T-18 to T-21,

inclusive, and borehole T-23. Samples of the soils encountered were recovered using drive-open sampling

equipment. In-situ vane testing was carried out within the silty clay at boreholes T-18 and T-19 to evaluate the

undrained shear strength of this soil unit.

Within boreholes where bedrock was estimated to be deeper (T-12, T-13, T-18 and T-22) the soil was sampled

using PQ sized rotary soil coring equipment along with standard penetration tests (ASTM D698) at regular

intervals of depths.

Five relatively undisturbed, 75-millimetre diameter thin-walled Shelby tube (ASTM D1587) samples of the silty

clay were obtained using a fixed piston sampler; three of which were extracted from borehole T-19 and two from

borehole T-20.

All boreholes were advanced into the underlying bedrock using HQ sized rotary core drilling equipment and a

triple tube core barrel. The bedrock core was sequentially placed into core boxes for transport and storage.

Fifteen boreholes were drilled at an inclination of 70 degrees from horizontal to lengths varying from 31.9 to

57.6 metres which corresponds to depths of about 30 to 54 m below ground surface. The inclined boreholes

were primarily intended to provide information on bedrock quality and geotechnical properties as only limited

sampling and in situ testing was possible within the overburden of the inclined boreholes.

Fracture and discontinuity data was recorded based on a visual inspection of the recovered rock core extracted

from the core barrel. The orientation of the core was determined using a core orientation tool (ACE

manufactured by Reflex Instruments); an electronic instrument which records the orientation with regard to its

original position after it has been removed from the ground.

3.2.2 Hydrogeological Testing

In-situ hydraulic conductivity testing was carried out in selected boreholes to assess the permeability

characteristics of the rock formations and rock structure encountered. The packer test locations ranged from

approximately 4 to 50 m vertically below ground surface. Packer testing was carried out within boreholes T-1,

T-3, T-5 to T-11, T-13 to T-16 and T-19.

The downhole testing equipment consisted of a single pneumatic packer lowered down the HQ-sized drill rods

using AQ-sized rods, the packer was subsequently inflated with nitrogen gas to isolate the test interval. A

vibrating wire pressure gauge was used to monitor and record real-time pressure responses during the tests.

The packer equipment was manufactured by RST Instruments Ltd. Falling head and/or constant head tests were

conducted to determine hydraulic conductivity values for the test intervals.

For a falling head test, a hydraulic head was applied to the test interval via a column of clean water within the

AQ-sized rods. The drop in the hydraulic head (or water level) was then monitored over time as it recovered to

the pre-test static water level. The recovery data of the falling head tests were analyzed using Hvorslev’s (1951)

method to calculate the hydraulic conductivity of the rock mass interval.

In zones with higher permeability, where the falling head testing showed rapid hydraulic head loss, constant

head tests were performed and the data was processed using Hvorslev’s constant head interpretation method

(Hvorslev, 1951). The constant head tests were carried out using the Lugeon method, which consisted of

inducing varying constant pressure head intervals using a pump on surface and monitoring the flow rate, with a

flow meter.



The following table lists the number of packer tests, the test interval and elevation for each packer test.

Table 3.2: Summary of Packer Testing

Borehole No. No. of Packer TestsDownhole Interval

(m along borehole)

Elevation Interval

(m above sea level)

T-1 3 9.0 – 15.3 m

13.6 – 21.3 m 20.1 – 31.9 m

57.2 – 51.5 m 53.1 – 46.0 m 47.1 – 36.1 m

T-2 None - -

T-3 1 24.2 – 35.0 m 51.2 – 40.9 m

T-4 None - -

T-5 3 26.3 – 34.7 m 36.3 – 45.4 m 46.3 – 54.4 m

38.3 – 29.9 m 29.1 – 21.6 m

T-6 1 19.7 – 52.9 m 53.6 – 22.8 m

T-7 3 9.3 – 22.6 m

22.6 – 39.3 m 37.6 – 53.0 m

62.7 – 50.5 m 50.5 – 35.1 m 36.6 – 22.5 m

T-8 3 11.3 – 28.9 m 28.3 – 43.9 m 41.1 – 53.5 m

61.8 – 45.0 m 45.5 – 30.6 m 33.3 – 21.4 m

T-9 3 8.7 – 18.1 m

17.9 – 36.3 m 34.9 – 57.6 m

66.0 – 57.2 m 57.4 – 40.1 m 41.4 – 20.1 m

T-10 3 4.1 – 14.8 m

13.3 – 30.0 m 28.3 – 45.3 m

63.1 – 53.1 m 54.5 – 38.9 m 40.5 – 24.6 m

T-11 3 16.3 – 26.9 m 25.2 – 36.0 m 34.3 – 45.0 m

49.7 – 39.8 m 41.4 – 31.2 m 32.8 – 22.8 m

T-12 None - -

T-13 2 8.7 – 21.0 m

19.3 – 40.0 m 55.1 – 42.8 m 44.5 – 23.8 m

T-14 2 6.3 – 19.7 m

18.6 – 39.5 m 58.3 – 45.7 m 46.8 – 27.1 m

T-15 2 8.1 – 22.7 m

20.3 – 38.0 m 61.5 – 47.7 m 50.2 – 33.3 m

T-16 2 7.6 – 18.4 m

16.7 – 35.0 m 62.9 – 52.7 m 54.3 – 37.1 m

T-17 None - -

T-18 None - -

T-19 1 19.3 – 27.4 m 46.5 – 38.4 m

T-20 None - -

T-21 None - -



Borehole No. No. of Packer TestsDownhole Interval

(m along borehole)

Elevation Interval

(m above sea level)

T-22 None - -

T-23 None - -

Groundwater levels were measured and in situ rising head permeability tests were carried out between July 26

and August 11, 2010 in the monitoring wells installed in boreholes T-5, T-10, T-12, T-13, T-19 and T-23. Water

level dataloggers were installed in each of the monitoring wells to record daily water levels.

3.2.3 Geotechnical Logging

The following geotechnical parameters were routinely recorded as part of the geotechnical logging:

Rock Type and Geotechnical Description;

Total Core Recovery (TCR);

Solid Core Recovery (SCR);

Rock Quality Designation (RQD);

Fractures per 0.25 metre;

Weathering Classification;

Hardness;

Major Structures;

Discontinuity Type;

Discontinuity Dip; and,

Discontinuity Properties.

Total Core Recovery (TCR) is the total amount of core recovered expressed as a percentage of the measured

length drilled for each core run.

Solid Core Recovery (SCR) is estimated by measuring the cumulative length of solid core, recovered at full

diameter and is expressed as a percentage of the total core run.

Rock Quality Designation (RQD) is defined as the percentage of core recovered from intact pieces of

100 millimetres (mm) or more in length for the total length of core run. The RQD does not include core with an

unconfined compressive strength of less than 1 MPa or mechanical breaks in the core. The RQD value is

calculated after Deere and Deere (1988) and defined as:

RQD(%) = 100 x length of hard, sound core in pieces 100 mm or longer

length of core run

Natural fractures were measured at 0.25 metre increments for each run. Values of fracture frequency,

expressed as the number of fractures per metre, were subsequently calculated.



The hardness scale shown on Table 3.3, which is based on the International Society of Rock Mechanics (ISRM)

guidelines, was used for field estimation of the intact rock strength during field mapping and for the rock

descriptions.

Table 3.3: Field Estimation of Rock Hardness

Grade Description Field Identification Approx. UCS Range (MPa)

R0 Extremely weak rock

Indented by thumbnail. 0.25 – 1

R1 Very weak rock Material can be shaped with a pocket knife or can be peeled by a pocket knife. Crumbles under firm blows of pick (or point) of geological hammer.

1.0 – 5.0

R2 Weak rock

Knife cuts material but too hard to shape into triaxial specimens or material can be peeled by a pocket knife with difficulty. Shallow indentations (< 5mm) made by firm blow with pick (or point) of geological hammer.

5.0 – 25

R3 Medium strong rock

Cannot be scraped or peeled with a pocket knife. Hand held specimens can be fractured with single firm blow of geological hammer.

25 – 50

R4 Strong rock Hand held specimen requires more than one blow of geological hammer to fracture it.

50 – 100

R5 Very strong rock Specimen requires many blows of geological hammer to break intact rock specimens (or to fracture it).

100 – 250

R6 Extremely strong rock

Specimen can only be chipped under repeated hammer blows, rings when hit.

> 250

The degree of weathering and/or alteration was recorded on a per run basis during the geotechnical core

logging. The weathering process describes the breakdown of rock by physical process, while the hydrothermal

and/or supergene alteration processes cause the alteration and breakdown of the intact rock by chemical

processes. The degree of weathering or alteration tends to cause a reduction in the rock strength and

competency.

Table 3.4 was used to describe the degree of weathering as defined by the ISRM (1981). It provides a

qualitative measure of the degree of weathering for the original rock material. The same table was adopted to

define the degree of alteration of the rock.



Table 3.4: Weathering Classification (after ISRM 1981)1

Term Symbol Description Discoloration

Extent Fracture

Condition Surface

Characteristics

Residual soil

W6

All rock material is converted to soil. The mass structure and material fabric are destroyed. There is a large change in volume, but the soil has not been significantly transported.

Throughout N/A Resembles soil

Completely weathered

W5

100% of rock material is decomposed and/or disintegrated to soil. The original mass structure is still largely intact.

Throughout Filled with alteration minerals

Resembles soil

Highly weathered

W4

More than 50% of the rock material is decomposed and/or disintegrated to a soil. Fresh or discoloured rock is present either as a discontinuous framework or as corestones.

Throughout Filled with alteration minerals

Friable and possibly pitted

Moderately weathered

W3

Less than 50% of the rock material is decomposed and/or disintegrated to a soil. Fresh or discoloured rock is present either as a discontinuous framework or as corestones.

Visible texture of the host rock still preserved. Surface planes are weathered (oxidized or carbonate filling) even when breaking the “intact rock”.

>20% of fracture spacing on both sides of fracture

Discoloured, may contain thick filling

Partial to complete discoloration, not friable except poorly cemented rocks

Slightly weathered

W2

Discoloration indicates weathering of rock material on discontinuity surfaces (usually oxidized). Less than 5% of rock mass altered.

<20% of fracture spacing on both sides of fracture

Discoloured, may contain thin filling

Partial discoloration

Fresh W1 No visible sign of rock material weathering.

None Closed or discoloured

Unchanged

Any major geological structures encountered during drilling were logged. Where fracture zones or broken core

were encountered, dip angles were taken along the contacts of the structure. The following major structure

identifications were used:

Fault (FLT) – Natural break with displacement evident. Typically consists of a zone of generally greater

than 0.5 m of altered, weak and typically clay gouge and/or crushed and/or broken rock. Extensional faults

were also noted as smaller zones of healed breccia material, with a slight discoloration and alteration and

carbonate veining.

1 ISRM 1981. Rock characterization, testing and monitoring. International Society for Rock Mechanics, Suggested Methods, Pergamon Press, Oxford. Brown, E.T. (ed.).



Shear (SH) – Natural break with displacement evident. Typically consisted of a series of tightly spaced

joints/fractures, slickensides, and possibly folded and healed relic rock fabric. The discontinuities

associated with the shears would be noticeably more altered than those in the surrounding rock. This is

commonly seen in weaker argillaceous seams found between more competent limestone.

Fracture Zone (FZ) – Small zone of broken rock fragments, possibly in combination with slightly weaker or

altered material. A network of joints and/or fractures is associated with this zone that likely broke further

due to drilling processes.

Broken Core (BC) – Small zones of broken rock fragments, possibly in combination with slightly weaker

material. There would not be a trend of fractures associated with the broken core and the broken core may

have resulted from the drilling process.

All natural discontinuities were described and measured for their dip angle. The following types of discontinuities

were identified:

Bedding (BD) – If the rock fabric showed a preferential trend in stratigraphic layering, the discontinuities

associated with this trend were identified. The designation HBD was used to represent bedding that was

not broken.

Joint (JN) – This type of discontinuity shows; persistence, full separation, some aperture, and typically

some form of staining, alteration, coating or infill. A joint would typically be associated with the major and

minor joint sets within the rock mass structural domain. Occasionally a healed joint was identified and

denoted as HJN.

Vein (VN) – Typically formed of calcite (carbonate) seams. The designation HVN was used for veins that

were not broken, i.e., “healed”.

Fracture (FR) – Not a mechanical break, but a discontinuity likely broken from drilling which follows a

previously healed discontinuity feature, or trend of weakness. The fractures were typically tight, with clean

to some alteration along the surfaces. The fractures were often not completely broken, with jagged contact

surfaces, which likely broke along a preferential plane associated with a weakness trend such as a healed

joint.

Contact (CO) – A discontinuity formed by a contact between different rock types, or a rock type and an

intrusive. The designation HCO represents healed contact boundaries.

The surface conditions of the logged discontinuities were described using the parameters Joint Roughness (Jr)

and Joint Alteration (Ja), from the Barton et al. (1974) Q system of classification. The values assigned for logging

Jr and Ja are shown in Table 3.5 and Table 3.6, respectively.



Table 3.5: Joint Roughness, Jr (after Barton et al. 1974)2

Description Jr

Rough and wavy 3.0

Smooth and wavy 2.0

Rough and planar 1.5

Smooth/planar/filled 1.0

Slickensided/planar 0.5

Table 3.6: Joint Alteration, Ja (after Barton et al. 1974)2

Unfilled or Coated Joints Filled

Description Ja Description Ja

Clean/staining only – either fresh rock or discoloration of discontinuity. The physical appearance and texture of the host rock is unaltered.

1

Sand/crushed rock (>1 mm) – continuous filling of sand and crushed rock material (altered or otherwise) which completely covers joint face, with loss of rock on rock contact reducing frictional strength of joint (Jr=1).

5

Slightly altered – includes slight oxidation, slight carbonate/clay/pyrite alteration. The majority of rock texture (roughness) is still visible, and discontinuities show good rock on rock contact, although with slightly lower material contact strengths.

2

Stiff clay (<5 mm) – includes filling with stiff clay material such as chlorite/talc/epidote (>1 mm). No rock on rock contact, little frictional resistance (Jr=1).

6

Sandy/silty coatings – includes physical sand/silt materials, and harder mineral materials such as calcite/carbonate. Less than 1 mm of coating covering the majority of the joint face. Material can typically be wiped off with finger or peeled with knife (carbonates). Discontinuity will still show relatively good roughness with majority rock/rock contact.

3

Soft clay (<5 mm) – soft filling (low friction material) includes >1 mm of soft (altered minerals) such as chlorite/talc/epidote. No rock on rock contact. No frictional resistance, and low cohesive strength (Jr=1).

8

Soft mineral coatings (<1 mm) – includes thin coating of clay/talc over the majority of the joint face. The coating will visibly decrease the roughness of the joint face, however the material would still show reasonable frictional characteristics.

4

Hydrating clays (<5 mm) – filling of material which is very soft when saturated (“soupy”). No frictional resistance and little to no cohesive strength (Jr=1).

12

The conditions along the joint surface of a discontinuity, recorded in order to assess the strength and behaviour

of the discontinuity, were also recorded using the Bieniawski RMR76 system.

2 Barton, N.R., Lien, R. and Lunde, J. 1974. Engineering classification of rock masses for the design of tunnel report. Rock Mech. 6(4), 189-239.



According to the Bieniawski criteria, the general condition of the discontinuities or series of discontinuities within

a recorded interval are assigned a particular value according to their roughness, continuity, aperture, alteration,

and infill. A Joint Condition (Jcon) value is assigned according to Table 3.7.

Table 3.7: Joint Condition, Jcon (after Bieniawski 1976)3

Fracture Condition RMR76

Very rough surfaces, fractures not continuous, no separation, unweathered. 25

Slightly rough surfaces, separation < 1 mm, slightly weathered. 20

Slightly rough surfaces, separation < 1 mm, highly weathered. 12

Slickensided surfaces OR Gouge < 5 mm thick OR Separation = 1-5 mm Continuous fractures. 6

Soft gouge > 5 mm thick OR Separation > 5 mm. Continuous fractures. 0

3.3 Borehole Geophysical Logging 3.3.1 Methodology

The geophysical logging of the bedrock boreholes was preformed to collect information on the geological

structure and hydrogeological characteristics of the overburden and rockmass.

There were three different suites of logs performed, which are summarized in the following table:

Table 3.8: Summary of Geophysical Logging Suites

Purpose Full Suite Partial Suite

Stratigraphy Natural Gamma

Apparent Conductivity Natural Gamma

Apparent Conductivity

Structure and Engineering Properties

Acoustic Televiewer Optical Televiewer Mechanical Caliper

Hydrogeophysics Fluid Temperature

Fluid Resistivity Heat Pulse Flow Meter

Note: The hydrogeophysical testing, when carried out, was conducted under both ambient and pumping conditions when possible, to stress the well.

For the full suite logging (typically carried out in rock drillholes) the boreholes were cased to the bedrock surface

and open below. For the partial suite logging typically carried out in overburden boreholes, the boreholes were

uncased and PVC lined.

3 Bieniawski, Z.T. 1976. Rock mass classification in rock engineering. In Exploration for rock engineering, proc. of the symp., (ed. Z.T. Bieniawski) 1, 97-106. Cape Town: Balkema.



Descriptions of each geophysical probe follow below:

Natural Gamma

The natural gamma log provides a measurement (recorded in counts per second – cps) that is proportional to

the natural radioactivity of the formation. The sample volume for the γn log is typically a 25 to 30 centimetre (cm)

radius. The log is used principally for lithologic identification and stratigraphic correlation.

The tool used for logging employs a scintillation NaI detector. The gamma–emitting radio-isotopes that naturally

occur in geologic materials are Potassium 40 and nuclides in the Uranium 238 and Thorium 232 decay series.

Potassium 40 occurs with all potassium minerals including potassium feldspars. Uranium 238 is typically

associated with dark shale’s and uranium mineralization. Thorium 232 is typically associated with biotite,

sphene, zircon and other heavy minerals.

Apparent Conductivity

This measurement records the apparent conductivity of the rock or soil mass surrounding the borehole using the

inductive electromagnetic technique. The probe provides a radial bulk measurement of the material 0.1 metre to

1.0 metre from the borehole wall over a distance of 1.0 metre. The measurement is unaffected by conductive

borehole fluid or the presence of plastic casing. This log is generally used in conjunction with the Natural

Gamma log to identify variations in lithology/stratigraphy.

Mechanical Caliper

This measurement records the borehole diameter as indicated by the average deflection of three spring-loaded

arms pressed against the wall of the borehole. Abrupt shifts to larger diameter (kicks) can indicate the locations

where fractures intersect the borehole wall. However, the thickness of the caliper arms and the mechanical

enlargement of fractures that can occur during drilling result in an approximate, qualitative relation between

fracture aperture and the size of the caliper deflection. Changes in borehole diameter indicated by the caliper

log complement other geophysical logs – e.g., accurate changes in borehole diameter are needed for

interpretation of structure from acoustic and optical televiewer logs.

Acoustic Televiewer

This measurement produces an image of the pattern of reflection of an ultrasonic pulse from a source that scans

the borehole wall as the logging probe is slowly moved along the borehole. The televiewer probe also records

telemetry so that the azimuth of the scan and the deviation of the borehole can be measured during logging.

The reflection is uniformly bright wherever the borehole wall is solid and smooth. The reflected pulses are

scattered wherever a fracture or other irregular opening intersects the borehole wall. Strike and dip are

determined by matching a template to the apparent shape of a fracture. The accuracy of this measurement

depends on the degree to which the shape of the feature represents that predicted for a planar feature and by

the degree of damage and/or erosion during the drilling process associated with the point where the fracture

intersects the borehole wall.

Optical Televiewer

This measurement produces a continuous, oriented 360° image of the borehole wall using an optical imaging

system as the logging probe is slowly moved along the borehole. The televiewer probe is magnetically

orientated so that the azimuth of the scan and the deviation of the borehole can be measured during logging.



Fluid Column Temperature and Resistivity

This measurement records the temperature and resistivity of the fluid filling the borehole. These measurements

apply to the fluid (water) in the borehole and may not be the same as the temperature and resistivity of the rocks

surrounding the borehole. The characteristics of these measurements (changes in slope or abrupt shifts in

values) can often be related to flow in the borehole at the time of logging. This measurement was recorded

under ambient (static) and dynamic (steady-state pumping) conditions when possible to better characterize the

hydrogeological characteristics in the vicinity of the borehole.

Heat Pulse Flowmeter

This measurement records the vertical flow at a given depth in the borehole when the probe is held stationary

long enough to eliminate the effects of probe movement on the fluid column. The measurement gives the time

required for vertical flow to move a thermally tagged parcel of water a distance of 2 cm up or down borehole after

heating by capacitor discharge onto an electrical grid. The probe measures flow through a cylindrical

measurement section where the borehole annulus surrounding this cylinder is blocked by a flexible disk (the

diverter). Flowmeter response times are converted to flow rates using calibration formulas provided by the probe

manufacturer. Two flow profiles were made, under ambient conditions first, and then under steady pumping

conditions. The heat-pulse flowmeter has a low flow detection limit of about 0.01 gpm (0.038 L/min). The device

also has an upper flow detection limit associated with the thermal inertia of the thermistors, which cannot

respond quickly enough to detect flow if the flow exceeds about 1.5 gpm (5.68 L/min) in either direction (up or

down).

3.3.2 Geophysical Logging Procedure

The following table indicates the geophysical logging techniques that were carried out in each of the boreholes

for this investigation:

Table 3.9: Summary of Geophysical Logging for Each Borehole

Borehole No. Geophysical Logging

T-1 Full suite completed.


T-3 No dynamic fluid column temperature and resistivity or ambient heatpulse flow metering due to low water table. Remainder of full suite completed.




T-7 No dynamic fluid column temperature and resistivity or ambient heatpulse flow metering due to low water table. Remainder of full suite completed.




T-11 Full Suite completed.

T-12 Gamma conductivity only.



Borehole No. Geophysical Logging


T-14 Optical televiewer to 17 m only (image obscured below). An attempt was made to flush the drillhole to clear the field of view but no return was achieved (~5000 L pumped into drillhole). Remainder of full suite completed.



T-17 Full suited completed.

T-18 Full suited completed.

T-19 Gamma conductivity only.

T-20 Optical televiewer image obscured. Unable to clear hole. Remainder of full suite completed.

T-21 Borehole blocked at casing bottom and therefore unable to carry out geophysical logging.



3.4 Seismic Surveys 3.4.1 Methodology

For the VSP (Vertical Seismic Profiling) method, seismic energy is generated at the ground surface by an active

seismic source and recorded by a geophone located in a nearby borehole at a known depth. Two active sources

are generally used, to preferentially generate compression or shear waves, respectively. The time required for

the energy to travel from the source to the receiver (geophone) provides a measurement of the average

compression or shear-wave seismic velocity of the medium between the source and the receiver. Data obtained

from different geophone depths are used to calculate a detailed vertical seismic velocity profile of the subsurface

in the immediate vicinity of the test borehole.

The high resolution results of a VSP survey are often used for earthquake engineering site classification, as per

the National Building Code of Canada, 2005.



Example 1: Layout and resulting time traces from a VSP survey



Values for Poisson’s ratio (), Shear modulus (G), Deformation modulus (Ed) and Bulk modulus (K) may be

calculated from compression wave and shear wave velocities as follows:

Poisson’s Ratio: 1)(

1)(5.02

VV

2VV

S

P

S

P

Deformation Modulus: )1(2)1(

)21)(1(2

GV

Ed P

Shear Modulus:

2

)1(2 SVE

G

Bulk Modulus: G

V

)21(3

EK

34

2P

Where is the bulk density (in Kg/m3), VP is the compression wave velocity (m/s) and VS is the shear wave

velocity (m/s). Seismic testing results in very low strain being applied to the tested medium, and the calculated

moduli are therefore representative of low strain conditions. Moduli calculated for low strain conditions are often

termed dynamic moduli or maximum moduli (Gmax, Emax, Kmax).

3.4.2 Survey Procedures and Equipment

A VSP test was completed in borehole T-18 on Colonel By Drive on July 22, 2010. The borehole was cased with

a PVC pipe which was grouted in place at the time of testing.

Both compression and shear-wave seismic sources were used and both sources were located in close vicinity to

the borehole. The seismic source for the compression wave test consisted of a 7.3 kilogram sledge hammer

vertically impacted on a metal plate. The plate was located 1.24 metres from the borehole. The seismic source

for the shear-wave test consisted of the same metal plate, which was struck on alternate ends of the plate to

induce polarized shear waves. The shear source was also located 1.24 metres from the borehole. The

measurements started 1 metre below ground surface. Data were recorded in the borehole with a 3-component

receiver spaced sequentially at 1-metre intervals below the ground surface, to a depth of the 27 metres.

The seismic records collected for each source location were stacked five times to minimize the effects of

ambient background seismic noise on the collected data. The data was sampled at 0.020833 millisecond

intervals and a total time window of 0.3041 seconds collected for each seismic shot.

3.4.3 Data Collection and Processing

Processing of the VSP test results consisted of the following main steps:

1) Combination of seismic records to present seismic traces for all depth intervals on a single plot for each

seismic source and for each component;

2) Low pass filtering of data to remove spurious high frequency noise;

3) First break picking of the compression and shear-wave arrivals; and,



4) Calculation of the average compression and shear-wave velocity to each tested depth interval.

Processing of the VSP data was completed using the SeisImager/SW software package (Geometrics Inc.).

3.5 Geological Mapping Geological field mapping was carried out by Golder Associates in the downtown Ottawa region on April 7 and 8,

2010. Due to the urban setting of this project, there were a limited amount of bedrock exposures within close

proximity to the proposed tunnel alignment. The 4 sites that were structurally mapped are shown on Figure 3.1.

Geological mapping included descriptions of the lithology, measurements of the orientation of major joint sets,

descriptions of the joint characteristics and notes on groundwater seepage. The geological mapping data is

presented in Section 6.2.

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