Inclinometer Casing

Inclinometer Casing

Inclinometer casing is a special purpose pipe used in inclinometer installations. It performs three functions:

  • It maintains access for the inclinometer probe, allowing it to obtain subsurface measurements.
  • It controls the orientation of the probe via internal grooves.
  • It conforms to movement of the surrounding ground.
cross sectional view of inclinometer casing

Casing Diameter & Groove Shape

Casing Diameter
Movement of the ground causes the casing to deform. Eventually, the casing is sheared off or pinched closed. When that happens, the probe can no longer pass through, and no more readings can be obtained. In general, larger diameter casing will offer a longer useful life, because it can accommodate more deformation before access is closed to the probe.
  • 85 mm / 3.34 inch casing is the largest diameter. It is suitable for all uses and especially recommended for landslides and long-term monitoring. It is also appropriate for monitoring multiple shear zones or very narrow shear zones.
  • 70 mm / 2.75 inch casing is suitable for construction projects. It can also be used for slope stability monitoring if only a moderate degree of deformation is expected.
  • 48 mm / 1.9 inch casing is used only deformations are expected to be very small and are distributed over broad zones. It is generally not installed in soils.
Groove Shape

inclinometer casing sizes groove shapeGroove Shape

The accuracy of inclinometer measurements is directly influenced by the quality of the casing grooves. The best grooves provide a regular, flat surface for the wheels of the probe.

The grooves should be slightly wider than the wheels, to permit some side to side movement as the probe passes through curves. If the grooves are too tight, the wheels will climb out of the grooves and degrade the reading.

Coupling Style

QC Casing
QC Casing QC casing is Slope Indicator's most popular style of casing. It offers precision grooves, flush self-sealing, joints, and snap-together convenience. Casing sections have built-in couplings that snap together. O-rings ensure that the joint is grout proof. There is no need for solvent cement or tape. QC casing is offered in 70 and 85 mm diameters. Accessories include grout valves, casing anchors, telescoping sections, and splice kits.
Standard Casing
Standard CasingThis is Slope Indicator's traditional glue and rivet style of casing. It features precision grooves and strong, flush joints that provide superior resistance to twisting and bending. Casing sections and couplings are glued together, riveted, and sealed with mastic and tape. Standard casing is offered in 48, 70, and 85 mm diameters. Accessories include grout valves, casing anchors, and telescoping sections.
EPIC Casing
Epic casing couplingEpic casing is an economical casing that withstands rough handling. It can be cut and coupled anywhere along its length, so it is easy to extend and easy to repair. Its strong, oversize couplings provide superior resistance to twisting and bending. Casing sections and couplings are glued together, riveted, and sealed with mastic and tape. The injection molded couplings provide an interference fit for better sealing. Epic casing is offered only in 70 mm diameter. Accessories include grout valves, casing anchors, and simple telescoping couplings.
CPI Casing
CPI CasingCPI casing features precision grooves, self-sealing couplings, and rapid assembly. Its oversize, injection-molded couplings can withstand twisting and bending. CPI casing can be used in weather that is too cold for snap or glued couplings. It is also suitable for temporary installations that require repeated assembly and disassembly. The coupling is pressed onto the casing section and an nylon shear wire is inserted to lock the joint. An O-ring inside the coupling makes the joint grout proof. CPI casing is offered in 48, 70, and 85 mm diameters. Accessories include grout valves, casing anchors, and telescoping sections.
Shear Wire Casing
Shear Wire Casing Shear Shear wire casing is a cold-weather alternative to QC casing. It provides precision grooves, self-sealing flush joints, and rapid assembly. Shear wire casing can be disassembled, but it is not designed for repeated disassembly. Casing sections have integral couplings. Sections are pressed together and a nylon shear wire is inserted to lock the joint. An O-ring makes the joint grout proof. Shear wire casing is offered in 70 and 85 mm diameters.

Inclinometer Casing Accessories

Casing Anchor
casing anchorWhen grout backfill is still a fluid, it exerts an uplift force that can force even water-filled casing out of the borehole. The obvious way to counter this buoyancy - holding the casing down from the top - has some unfortunate side-effects. Held down from the top, the casing goes into compression and snakes from side to side in the borehole. Thus casing curvature is present from the start, and slight changes or errors in the positioning of the probe will produce reading errors - the larger the curvature, the larger the error. The best way to counter buoyancy is to anchor the casing at the bottom, either by weighting it or by using a convenient casing anchor. When the bottom is anchored, the rest of the casing self-centers in the borehole and becomes very straight. The casing anchor shown here has spring loaded arms that are activated when a pin is pulled. The leaf spring in the casing anchor will expand the anchor approximately 10 inches (25cm) from tip to tip. Therefore, the casing anchor should only be utilized in boreholes that have a diameter of less than 10 inches (25cm). Once the anchor catches the side of the borehole, the anchor will continue to expand such that the distance from tip to tip is 19.5 inches (50cm). This final expansion will allow the casing to travel upwards up to 4.5 inches (11.5cm), assuming no deformation of the in-situ soils. Casing anchors are available for 70 mm • 2.75" and 85 mm • 3.34" casing sizes. Combination anchors + grout valves are also available.
Grout Valve
inclinometer grout valve drawingA grout valve provides a way to deliver grout backfill when there is no room in the borehole for an external grout pipe. The grout valve is a one-way valve installed in the bottom of the casing. After the casing is in place, a grout pipe is lowered through the casing to mate with the valve and deliver the grout. The gasket-type grout valve is shown at right. You can see the gasket at the base of a smaller diameter pipe. A larger diameter grout pipe slides over the smaller pipe to rest on the gasket. Grout can then be pumped through the valve. When grouting is finished, the remaining grout in the pipe is flushed with water (just enough to displace the grout in the pipe) and then withdrawn from the casing. Grout valves are easy to use, but require a slightly deeper borehole. Also grout must be mixed carefully so that it does not have lumps that could be caught in the valve mechanism. The grout pipe is nominal 1.25" pipe. A 1.25" schedule 40 pipe has an ID of 1.35" (35mm). The smaller diameter pipe, which is part of the grout valve, is 3/4" pipe. It has an OD of 1.07" (27 mm).

Grout Mixes for Inclinometers

Grout Mix for Hard and Medium Soils
Materials Weight Ratio by Weight
Portland cement 94 lb (1 bag) 1
Water 30 gallons 2.5
Bentonite +/- 25 lbs. (See Notes Below) 0.3
Mix cement with water first. Then mix in the bentonite. Adjust the amount of bentonite to produce a grout with the consistency of heavy cream. If the grout is too thin, the solids and the water will separate. If the grout is too thick, it will be difficult to pump. The 28 day compressive strength of this mix is about 100 psi, similar to hard clay. The modulus is 10,000 psi.
Grout Mix for Soft Soils
Materials Weight Ratio by Weight
Portland cement 94 lb (1 bag) 1
Water 75 gallons 6.6
Bentonite +/- 39 lbs. (See Notes Below) 0.4
Mix cement with water first. Then mix in the bentonite. Adjust the amount of bentonite to produce a grout with the consistency of heavy cream. If the grout is too thin, the solids and the water will separate. If the grout is too thick, it will be difficult to pump. The 28 day compressive strength is about 4 psi, similar to very soft clay.
Grout Mix Notes
  • It is not really practical to try to match the strength of the grout to the strength of the soil, since the properties of grout and soil are so different. The cement-water ratio controls the strength of the grout. To decrease the strength of the grout, add more water.
  • Drillers are accustomed to mixing water and bentonite first, but this will not allow you to control the water-cement ratio. Mix water and cement first. Then add bentonite. There is no particular amount of bentonite that you must add. The thickness of the grout varies with water, temperature, and agitation, so the amount of bentonite required will vary.
  • The quantity of the third ingredient to be added must be adjusted to obtain a suitable consistency. A watery mix is NOT acceptable. A mix that is too thick cannot be pumped. The Marsh funnel number of the liquid grout should be about 55 seconds +/- a few seconds.
  • If you mix cement and water first, the amount of bentonite has to be adjusted. The amount is rarely ever equal to exactly 25 lbs. The final quantity also varies with the type of bentonite used, the method of mixing and the pH of the water.
  • If you mix bentonite and water first, the mix usually gets so thick with one bag of cement that it cannot be pumped. There is also a high risk of a flash-set. The cement content must usually be lowered. That results in a higher w/c ratio, lower strength and probably a higher permeability.
  • If the mix is left too watery, not only do you get shrinkage, but segregation occurs: cement on the bottom, then bentonite and water on top (bleed). This is not acceptable.

Countering Casing Buoyancy

Why Casing Floats in Grout

Grout backfill has a higher density than water-filled casing. During installation, when the grout is still a fluid, it exerts an uplift force on the bottom cap of the casing. This uplift force is greater than the down force exerted by water-filled casing. The net uplift can be calculated as the density of grout minus the density of water filled casing x depth of casing x area of bottom cap. Lateral forces do not contribute to uplift.

The density of water-filled casing is about 62.4 pounds per cubic foot or 1000 kg per cubic meter. The density of ABS casing and the density of water are nearly the same. The density of bentonite-cement grout is about 80 pounds per cubic foot or 1280 kg per cubic meter. The area of the bottom cap of 2.75" (70mm) inclinometer casing is 0.0412 square feet or 3.8485E-3 square meters. Thus if the bottom cap is 100 feet deep, the uplift pressure on the 2.75 inch bottom cap will be about 72.5 pounds or 32.3 kg.

The Worst Way to Counter Buoyancy

Unfortunately, the easiest way to keep the casing in place - holding the casing down from the top - is also the worst way. The uplift force acts on the bottom of the casing, so if the casing is held in place from the top, the casing goes into compression. When the casing goes into compression, it tends to snake from side to side in the borehole. This problem is particularly severe in large diameter boreholes and in deep installations, where the uplift force is largest and where portions of the borehole may be enlarged. Snaked casing increases the potential for:

  • Kinked or Separated Casing: The combination of compressive force and eccentric loading (due to snaking in enlarged diameter boreholes) can produce strong bending moments in the casing. In some severe cases, this bending moment has caused snap-together joints to fail where the glue-and-rivet joints do not.
  • Depth Errors: In snaked casing, slight changes or errors in the positioning of the probe will produce reading errors. The larger the curvature, the larger the error. For example, if the change of inclination between adjacent reading increments is two degrees, and the probe is positioned 25 mm from the correct depth, the resulting error in displacement would be 1 mm.
Better Ways to Counter Buoyancy
  • Suspend a steel pipe or drill rods inside the casing. For the best results, suspend the pipe just an inch or so off the bottom cap of the casing.This ensures that the steel pipe remains straight and avoids resting the full weight of the pipe on the bottom cap. As the casing rises to meet the pipe, the down force of the pipe is activated to keep the casing in place. The main drawback to this method is that you must use the drill rig to suspend the pipe or you must return with the drill rig to retrieve the pipe. A variation is to rest the pipe on the bottom cap, which you must reinforce.

    Pre-install an anchor at the bottom of the casing. Simple prong anchors or packer types have been used. Slope Indicator has produced several prototypes of such anchors. Different soils may require different types of anchor.

  • Pre-attach a weight to the bottom of the casing. This method requires a weight, a safety line to prevent casing from sinking, a borehole drilled deeper to accommodate the weight, and calculation of the uplift force. It is best used in shallow boreholes.
  • Grout the borehole in stages. The uplift force of grout varies with the height of the grout column. If the column is short, the uplift force is low and the casing can be held in place by its own weight or with very little down-force applied from the top. When the grout sets, the bottom cap is isolated from the column of grout and there is no surface for the uplift force to act on. No more than two or three meters to 3 m need to be grouted in the first stage. If the normal bentonite/cement grout is used it needs to set for at least 12 hours before second-stage grouting. Avoid use of a quick-set grout, since the heat of hydration could melt and deform the plastic. The two stages can be placed via an outside tremie pipe. Alternatively the first stage can be placed before lowering the casing, provided that all is done efficiently so that there is no chance of the grout setting prematurely. If grout valve method is used, first stage grouting can be done through the valve, and then the valve is abandoned. An outside tremie pipe for the second stage is lowered with the casing, with its bottom at the level planned for the top of the first stage. After first stage grouting, the excess is flushed out via the tremie pipe, and then this is raised until the first stage has set.
  • Fill the casing with drilling fluid that is heavier than the grout. This is a sure and easy method, but requires disposal of the drilling fluid.

Datasheet and Documents

Datasheet and Documents

Please download the data sheet for Inclinometer Casing.

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Read the INCLINOMETER CASING FAQ

When you buy inclinometer casing, important features to consider are:

Inclinometer Casing Part Numbers

QC CASING 85MM · 3.34"
Casing Section, 10' (3.05 m) 51150310
Casing Section, 5' (1.52 m) 51150311
Section, Telescoping 51150320
Cap, Bottom 51150330
Cap, Bottom, Heavy Duty 51100520
Grout Valve, Gasket Type 51100830
Cap, Top 51100500
Cap, Locking 51100550
Splice Kit, Male 51150350
Splice Kit, Female 51150351
QC CASING 70mm · 2.75"
Casing Section,10' (3.05 m) 51150210
Casing Section, 5' (1.52 m) 51150211
Section, Telescoping 51150220
Cap, Bottom 51150230
Cap, Bottom, Heavy Duty 51101520
Grout Valve, Gasket Type 51100820
Cap, Top 51101500
Cap, Locking 51101550
Splice Kit, Male 51150250
Splice Kit, Female 51150251
STANDARD CASING 85mm · 3.34"
Casing Section, 10' (3.05 m) 51100100
Casing Section, 5' (1.52 m) 51100105
Telescoping Section 51106400
Coupling 51100200
Cap, Bottom, Heavy Duty 51100520
Grout Valve, Gasket Type 51100830
Cap 51100500
Cap, Locking 51100550
Pop Rivet AD44H 51103301
STANDARD CASING 85mm · 3.34"
Casing Section, 10' (3.05 m) 51100100
Casing Section, 5' (1.52 m) 51100105
Telescoping Section 51106400
Coupling 51100200
Cap, Bottom, Heavy Duty 51100520
Grout Valve, Gasket Type 51100830
Cap 51100500
Cap, Locking 51100550
Pop Rivet AD44H 51103301
STANDARD CASING 70mm · 2.75"
Casing Section, 10' (3.05 m) 51101100
Casing Section, 5' (1.52 m) 51101105
Telescoping Section 51107400
Coupling 51101200
Cap, Bottom, Heavy Duty 51101520
Grout Valve, Gasket Type 51100820
Cap 51101500
Locking Cap with Padlock 51101550
Pop Rivet AD42H 51003303
EPIC CASING 70mm · 2.75"
Casing Section, 10' (3.05 m) 51111100
Coupling 51111200
Telescoping Coupling 51111400
Cap, Bottom, Heavy Duty 51101520
Grout Valve, Gasket Type 51100820
Cap 51111500
Locking Cap with Padlock 51101550
Pop Rivet AD46H 51003310
Lubricant for Telescoping Coupling 57504000
CPI CASING 85mm · 3.34"
Casing Section, 10' (3.05 m). 57500100
Casing Section, 5' (1.52 m) 57500105
Telescoping Section 57506400
Coupling with 2 Shear Wires 57500200
Cap with Shear Wire 57500500
Cap, Bottom, Heavy Duty 51100520
Grout Valve, Gasket Type 51100830
Cap, Top 51100500
Spare Nylon Shear Wire 57500700
O-Ring Lubricant 57504000
CPI CASING 70mm · 2.75"
Casing Section, 10' (3.05 m) 57501100
Casing Section, 5' (1.52 m) 57501105
Telescoping Section 57507400
Coupling with 2 Shear Wires 57501200
Cap with Shear Wire 57501500
Cap, Bottom, Heavy Duty 51101520
Grout Valve, Gasket Type 51100820
Cap, Top 51101500
Spare Nylon Shear Wire 57501700
O-Ring Lubricant 57504000
CPI CASING 48mm · 1.9"
Casing Section, 5' (1.52 m) 57502105
Coupling with 2 Shear Wires 57502200
Cap with Shear Wire 57502500
Grout Valve, Gasket Type 57503700
Cap, Top 51102500
Spare Nylon Shear Wire 57502700/td>
O-Ring Lubricant 57504000
SHEAR WIRE CASING 85mm · 3.34"
10' (3.05 m) Casing Section 51160310
5' (1.52 m) Casing Section 51160311
Section, Telescoping 51160320
Cap, Bottom 51160330
Cap, Bottom, Heavy Duty 51100520
Grout Valve, Gasket Type 51100830
Cap, Top 51100500
Cap, Locking 51100550
SHEAR WIRE CASING 70mm · 2.75"
Casing Section, 10' (3.05 m) 51160210
Casing Section, 5' (1.52 m) 51160211
Section, Telescoping 51160220
Cap, Bottom 51160230
Cap, Bottom, Heavy Duty 51101520
Grout Valve, Gasket Type 51100820
Cap, Top 51101500
Cap, Locking 51101550
CASING ANCHORS
Casing Anchor, 85 mm (3.34") 51104385
Casing Anchor, 70 mm (2.75") 51104370
Anchor + Grout Valve, 85mm(3.34") 51104485
Anchor + Grout Valve, 70mm(2.75") 51104470
INSTALLATION ACCESSORIES
Mastic Sealing Tape 51003800
Vinyl Tape 51003900
Duct Tape 51004000
ABS Solvent Cement, 1/2 pint 51103401
ABS Solvent Cement, 1 pint 51103402
Pop Rivet Gun 50100202
Casing Clamp 50100200