Photo of Model 3200.

Hydraulic Borehole Pressure Cells

Model 3200

The standard Borehole Pressure Cell (BPC) is used to measure rock stress changes and is designed to be grouted inside a borehole. The BPC is manufactured from two steel plates welded together around their periphery. The plates are deformed into a “dog bone” configuration so that they can be expanded easily without damage to the welds. Hydraulic oil fills the space between the two plates and a high-pressure stainless steel tube connects the plates to a stainless steel pressure gage and/or a pressure transducer.

Specifications
Standard Ranges 20, 35, 75 MPa
Resolution 0.25% of range (approximately)
Accuracy 0.25% F.S. (gage) 0.1% F.S. (VW transducer)
Borehole Size 57 mm
Temperature Range −20°C to +80°C
L × W × H 210 × 51 × 6 mm

Photo of Model 4300-EX, 4300-BX and 4300-NX.

Vibrating Wire Borehole Stressmeters

Model 4300

The Model 4300 Vibrating Wire Borehole Stressmeters are designed to measure stress changes in rock and can be installed in boreholes up to 100 feet deep. The Stressmeter consists of a high strength steel proving ring wedged tightly across one diameter inside a borehole and a vibrating wire tensioned across the other diameter inside the stressmeter. Changes in rock stress cause a related change in the resonant frequency of vibration of the tensioned wire providing output which is read by the Geokon Model GK-403 Readout Box.

Specifications
Range in Compression 70 MPa
Range in Tension 3 MPa
Resolution¹ 14 to 70 KPa
Temperature Range² −20°C to +80°C
Borehole Diameter

(4300-EX) 37 to 39 mm

(4300-BX) 58 to 61 mm

(4300-NX) 74 to 77 mm

¹Depends on rock modulus

²High temperature versions (up to 200°C) available on request

Photo of Model 4350.

Vibrating Wire Biaxial Stressmeters

Model 4350

The Model 4350 Vibrating Wire Biaxial Stressmeter is designed to measure compressive stress changes in rock, salt, concrete or ice. Three or six Vibrating Wire sensors oriented at 60° intervals allow the principal stress changes to be measured in the plane perpendicular to the stressmeter axis. The stressmeter consists of a high strength steel cylinder which is grouted (or frozen, in the case of ice) into a BX (60 mm) size borehole.

Specifications
Standard Range 70 MPa
Resolution¹ 14 to 70 KPa
Accuracy ±0.1% F.S.
Temperature Range² −20°C to +80°C
Borehole Diameter BX (60 mm)

¹Depends on rock modulus

²High temperature versions (up to 200°C) available on request

Photo of Model 4360.

Vibrating Wire Soft Inclusion Stress Cells (SISC)

Model 4360

The Model 4360 Vibrating Wire SISC is a larger version of the Model 4300 Borehole Stressmeters. The SISC is pre-loaded by wedging it into a large size diamond drill hole using an integral screw mechanism or hydraulic piston and can be set to measure both tensile and/or compression stress changes. It has been used successfully in 152 mm diameter overcoring holes (drilled to measure in situ stresses) to measure Aggregate/Alkali Reactions (AAR) in concrete dams.

Specifications
Standard Range¹ ±35 MPa
Resolution¹ 35 KPa
Temperature Range −20°C to +80°C
Borehole Diameter² NX, PQ, HQ, 152 mm

¹Proportional to rock modulus; figures given are for E = 0.03 × 106 MPa

²Other diameters available on request

Photo of Model 4370.

Vibrating Wire Concrete Stressmeters

Model 4370

The Model 4370 Concrete Stressmeter comprises a short vibrating wire load cell in series with a longer cylinder of concrete. This concrete cylinder has the same properties as the surrounding concrete but is de-bonded from it by means of a smooth-walled, porous plastic tube. It’s coupled at its ends to the surrounding concrete by means of two flanges equipped with sections of split rebar to provide a better grip. The vibrating wire load cell measures the load imposed on the inner concrete cylinder by stresses in the surrounding concrete. This load, when divided by the cross sectional area of the inner cylinder, gives the stress in the surrounding concrete.

Specifications
Standard Range −3 MPa to +25 MPa
Resolution 10 kPa
Accuracy¹ ±0.25% F.S.
Temperature Range −20°C to +80°C
Length × Diameter 600 × 76 mm (I.D. 66 mm)

¹Load cell accuracy.

Photo of Model 5000.

Borehole Deformation Gages

Model 5000

The Model 5000 Borehole Deformation Gage is the proven USBM-style gage used to measure in situ rock stresses using the overcoring technique in rock that is competent and elastic. The measurement of in situ stresses is important in the design of underground openings such as power houses, crushing stations, mines, tunnels and the like. It is also useful for determining the inherent stability of pit slopes, foundation excavations, mine pillars and dam abutments. A full line of ancillary equipment is available including readout units, biaxial modulus chamber, setting rods, etc.

Specifications
Borehole Diameter 38 mm EX-size diamond drill hole
Resolution 1.0 µε
Minimum Overcore Depth 203 mm (25 mm with reverse case)
Maximum Overcore Depth 15 m standard (60 m with extra cable)
Temperature Range −20°C to +80°C
Length × Diameter 267 × 35 mm

Products

Please Note: Geokon maintains an ongoing policy of design review and reserves the right to amend products and specifications without notice. Various instruments are discontinued over time and replaced with new, updated models.