How much do you know about casing oscillators?

What is casing oscillator? The casing oscillator is a kind of construction auxiliary equipment for rotary drilling rigs. It is mainly used for sinking and pulling out casing during construction in unstable strata. This kind of casing oscillator has two hydraulic drive modes. One is directly connected to the drilling rig and uses the hydraulic system of the drilling rig to provide power; the other is equipped with an additional hydraulic station and uses the hydraulic station to provide power. During construction, the casing oscillator can provide torque and pressure several times greater than that of the drilling rig, and its ability to sink and pull out the casing is much greater than that of the casing driver.

The structure of the casing oscillator mainly includes chassis, casing chuck, variable, diameter slips, oil cylinder, hydraulic system, electrical system, remote control box and mechanical interface board.

First at all, let’s introduce what is full casing construction and how casing oscillator works in that.

What is full casing construction? Full casing construction means the casing will reach the bottom of piles.

Full casing construction is mainly suitable for the following strata:

- Soft soil strata: The principle of full casing construction is to insert casings into the soil layer and use the squeezing and compacting effect of the casings on the surrounding soil layers to form a load-bearing structure. Therefore, soft soil strata are ideal for full casing construction because they are softer and prone to compression and compaction.

- Aquifer: The full casing construction can be carried out in the aquifer, because the casing can effectively isolate the groundwater and prevent the impact of water flow on the construction. At the same time, the water in the aquifer can also be discharged through the casing, which is beneficial to the smooth progress of the construction.

- Pebbles and boulders: Full casing construction can be applied to pebbles and boulders because the casing can pass through pebbles and boulders of different sizes and fix them in predetermined positions. At the same time, the sand and gravel in the pebble and boulder formation can also be discharged through the casing, which is beneficial to improving the bearing capacity of the formation.

- Hard ground: Full casing construction can also be applied to hard ground, such as rock formations, hard soil layers, etc. In this case, full casing construction can break and compact the hard ground through the casing to form a load-bearing structure.

It should be noted that full casing construction may not be suitable in the following strata:

- Large boulder formation: The large boulder formation is not easy to be penetrated and fixed by casing due to the larger stones, so full casing construction is not suitable.

- Mudstone and soft rock formations: Mudstone and soft rock formations are soft in texture and are prone to extrusion and deformation, making it difficult to form a load-bearing structure, so full casing construction is not suitable.

- Areas with high groundwater levels and thick fine sand layers in the soil: When carrying out full casing construction in these areas, special attention needs to be paid to prevent the difficulty of pressing in/out due to excessive density of the sand layer. If the groundwater level at the construction site is high and the soil layer contains a relatively thick layer of fine sand, careful consideration should be given to whether to carry out full casing drilling construction.

Devices required in full casing construction:

1. Rotary drilling rig - Torque≥200KN-M

2. Pipe rubbing machine - Caliber 1500-2500

3. Pipe rubbing machine power station - Optional

4. Rotary kelly bar -Short kelly bar≤12 meters

5. Land - Remove the pressure plate and install the connecting plate

6. Flower tube drive - The upper part is connected to the power head connection plate, and the lower part is connected to the casing

7. Casing - 2m/pc, 3m/pc, 4m/pc

8. Casing boots - Select cutter teeth according to the formation

Features of full casing construction:

1. Efficient construction: the pipe rolling machine drives the casing (hole formation and wall filling throughout the entire process), and the rotary excavator extracts soil from the casing (efficient drilling)

2. Safe construction: The hole forming and pouring casing are double isolated, which will not disturb the foundation of surrounding buildings (near subway and high-rise building construction)

3. Environmentally friendly construction: no mud discharge, dry drilling, and the drilled rock and soil can be recycled.

4. Broad-spectrum construction: suitable for various complex strata, gravel layers, and strongly weathered rock strata; soft layer casing is advanced and hard layer drill bit is advanced.

5. Casing verticality: The shallow rotary excavation machine controls the verticality, and the deep pipe rolling machine controls the verticality.

6. Pipe rubbing machine power: independent pumping station (pipe rubbing machine and rotary excavator operate independently and do not interfere with each other), or borrow the power of the rotary excavator.

Processes of full casing construction:

1. Measurement

2. Equipment in place: Rotary drilling rig and casing oscillator.

3. Buried casing: The power head of the rotary drilling rig drives the first section (with pipe boots) of the casing to run vertically. Or the casing oscillator rubs in the first section of casing.

4. Rub into the casing

5. Rotary drilling

6. Drill the casing to the depth of the pile: Pipe rubbing and rotary drilling are carried out simultaneously, casing is added and the ground is drilled section by section until the bottom of the hole is reached.

7. Setting into steel cage: Clean the bottom of the hole after drilling the casing to the designed pile depth. The crane is lowered into the steel cage.

8. Pouring concrete

9. Pull out the casing: The tremie pipe is sunk below the liquid level and concrete is poured. Every time a truck of concrete is poured, a section of casing need to be pulled out. The casing oscillator shakes and pulls out the casing.

10. Pile formed: After the pouring is completed, the first section of casing is pulled out and the pile is formed. The rotary drilling rig and casing oscillator move to the next pile position at the same time.

Drilling methods in different strata (pipe rubbing and rotary drilling)

- Soft soil layer (N≤5): The casing is drilled 1-2m in advance, and the soil is taken from the casing of the rotary drill bit to control the verticality.

- General soil layer, clay layer, pebble layer, and backfill riprap layer (N=6-30): The soil layer casing leads 0.3-1m, and the hard soil layer and pebble layer drill bit drills 0.2-0.5m ahead in the casing. , guide casing follow-up.

- Hard strata and strongly weathered rock strata (N≥30): The rotary drill bit drills in advance and assists the hammer to impact the broken rock. The casing is followed and rubbed into the rock formation (rock embedded at the bottom of the pile)

Technical measures for special occasions

- Large depth and hard-biting piles: For fully-cased piles and hard-biting piles exceeding 60 meters, it is recommended to use a full-rotation drilling rig in conjunction with a rotary drilling rig to take advantage of full-rotation cutting and efficient drilling of rotary excavation in complex strata with high water levels.

- Large-depth rock-embedded piles: Use hammers and grab buckets to assist in impacting broken rock, and use rotary excavation inside the casing to clear the bottom. The full-rotation casing can effectively cut through strong weathering and enter the weathered hard rock layer. The rock-embedded depth is 5- 10m.