Diamond drilling is used in geotechnical studies of the characteristics of underground rocks required for the construction of infrastructures. The drilling operation provides core samples taken from the depths with undeniable accuracy, as this is the preferred method for studying rocks.
Piezometer profiles are drilled to:
1. Compliance Monitoring
2. Groundwater
3. soil formation
When drilling and installing holes for the piezometer, the movement of the earth and the presence of water are determined. These, combined with the identification and delineation of soft, cracked and unstable areas, represented from core samples, are used to identify any potential soil destruction.
The following discussion of piezometric drilling is the actual procedure from one of the operations on an underground mining ledge in Asia using the block collapse method. The hole profile with the piezometer sections was planned in accordance with the geological sections and information collected on the mapping of underground and surface geological characteristics, as shown below.
Hole data:
1. Hole size:
PQ - 4 1/2 inches dia.
HQ - 3 1/2 inches dia.
2. Slope - Vertical
3. Depth:
4 1/2 inches - 50 meters
3 1/2 inches - 120 meters
4. Water level - 8 meters
5. Installed pipes for piezometer - 2 sets
Diameter 1 inch. from 0 to 50 meters - to measure the water level
Diameter 1 inch. from 0 to 120 meters - to measure the horizontal movement of the earth
6. Pea gravel - diameter from 1/8 to 1/4 inch
Procedure:
For this project, a Longyear 44 drill was used. Since the drilling site is at the top of the subterranean compliance zone, we expect that the drilling of the well will cause difficulty due to the highly destructive rock, and if there is ground movement, the hole will be tight. It was decided that the use of bentonite drilling mud and additives is necessary for success, although this will certainly cause water loss.
Drilling began with HQ size bits for maximum core size and recovery from the collar to 10 meters. To drill an unstable rock, select a bit longyeard that is suitable for the formation of highly destructive diorites, otherwise the performance of the bits will be shorter and the cost of the bits will increase. After 10 meters, the hole was enlarged by drilling with a 4-inch tri-cone diameter. A pipe with a diameter of 4 1/2 inches, called the HW casing in diamond drilling terminology, was lowered into the hole. After that, a standard cement mixture was pumped into the casing, which allowed the HW to enter the collar of the hole outside the casing. The reason is to cement cracks in the overburden or the top of the reservoir to prevent surface water from seeping into the hole. Cement was allowed to harden for five hours; At the same time, the HW hull moved up and down every 30 minutes along the cement wall to ensure that it does not get stuck in the cement cement.
The drilling was used using a Longyear HQ two-pipe core (diameter 3 1/2 inches). Starting to drill cement inside the HW hull to 10 meters, after which the HW hull was planted and replaced with a PQ-sized frame. The speed of diamond drilling penetration is somewhat slower compared to the usual one, since the formation was broken down, the core was easily clogged, less disturbance was required on the reservoir and substantial core recovery.
A mud thickener such as Liquipol Baroid NL was used to seal cracks, clean the hole from cuttings, and preserve core samples, although it is expected to lose circulation of the drilling water. The use of bentonite mud (for example, Baroid Quik-gel) did not encourage the construction of mud cakes around walls and cracks, where it would be difficult to remove them in the final process of measuring water.
The proper drilling methodology for the project was very important. The kernel should be discarded each time a kernel lock occurs and occurs. If the resulting core samples are already with smooth edges already earlier, the main unit previously occurred, but was not observed by the driller. Usually the recovery is very small due to the grinding of the core inside the barrel. Most importantly, the soft parts of the core sample, such as the notch, are dissolved in this case. Please see My other article on blocking prevention and methods.
I gave several previous examples to avoid problems later.
Drilling with a PQ size is supported from 10 meters to 50 meters. Then the hole is cleaned of the material of the cave and drill cuttings by flushing with a drilling thickener (Liquipol) from the collar to 50 meters. The HW case with the impregnated casing at the lower end is then lowered and installed at a distance of 50 meters. Drilling will continue with a reduced hole diameter using the next smaller frame size HQ with the required depth from 50 to 120 meters. Again, the hole has been cleaned. The open HQ rod remained in the hole to prevent the wall from breaking down when installing piezometer pipes.
The first pipe with a diameter of 1 inch (BI) is filled from 0 to 114 meters and perforated at 110-120 meters (6 meters below). The goal is to allow any groundwater from 75 to 120 meters to go inside the pipe to monitor a possible second aquifer at this depth. As mentioned above, the main task of the first pipe is to determine any horizontal movement of the soil. The size of the perforation is 1/8 inch and is drilled 6 inches vertically apart with four rows of holes around the pipe from end to end. The lower end of the pipe must be screwed on with a lid to avoid scraping the walls during lowering, so blocking the pipe with rock particles and causing the wall to break. The pipe can be connected using a pipe coupling, but we did not use it, because it can scrape the walls and also cause a jumper when gravel of gravel is scattered throughout the pipe. Another alternative is gas welding that connects the pipes of all pipes. To ensure that the inside diameter of the weld does not form, a smaller diameter cylinder of 6 inches is lowered inside a 1-inch pipe each time one length is welded to check that the pipe is free and no foreign material is inside.
The next step is to pre-fill the pea gravel inside the hole, but outside the 1-inch pipe of the piezometer. While it is scattered, the water also passes around the circumference of the pipe to avoid clogging pea gravel. The HQ boom also drops out every 6 meters to prevent the wall from breaking down. The 1-inch pipe with the screwed-in coupling is just left standing in the hole, and the HQ gradually decreases. Pea gravel is poured from 120 to 75 m and will serve as a filtering medium, so small particles cannot get inside the pipe.
At a height of 75 meters by 6 meters (69 m) a buffer will be installed. This is for cement buffer that prevents infiltration to a lower depth. The cement buffer consists only of an old newspaper, rolled around a piezometer pipe 6 meters high and forged HQ rods until it reaches 69 - 75 meters down. The cement mixture will be injected through the HQ rod at a height of 6 meters (63 m). Cement is kept for 5 hours. After the cement setting time, the hole is washed using fresh water to pump cement. However, the lower end of the HQ rod must be at least 10 meters above the cement level when flushing, as it can also wash off the cement.
Coarse sand is scattered around the first pipe of the piezometer from 63 meters to 50 meters. Throughout the rod, the HQ also folds to avoid sticking. At a distance of 50 m, the size of the hole is now much larger. The HQ rods roll out of the hole, as there is another body in the hole (PQ or HW). The PQ rods will now be used to flush and clean the hole.
Now the second pipe of the piezometer with a diameter of 1 inch will be lowered. The entire length of the length is perforated, except for the top 10 meters. The pipe is again lowered down through the welding hole and then checks the inside for obstructions. So the second pipe is fixed at a depth of 50 meters on rough sand and near the first pipe. After installing the pipe, the cement buffer is made again from 10 m to 5 m. Now the folded newspaper buffer is placed around the two tubes of the piezometer and is forged and sealed with a PQ rod. Then the cement is again loved from 5 m to the collar and allowed to harden. Two pipes are protected from above, screwing up the closed coupling.
After completing all the above procedures, the piezometer tubes are now ready for monitoring the water level (short tube) and for detecting any movement in the piezometer long tube. To measure two targets, we used only one electrical probe, consisting of a 200-meter roll of duplex wire, an electrical tester connected to one end at the end of the roller and an open end wire at the other end. The open end is inserted in dia. 6 inches by 3/4 inches. PVC pipe with wire held by hardened candle. As soon as the wire enters the water, a surge of electric current is indicated in the tester's device. This indicates an increase in water level. If the probe is lowered in the long tube of the piezometer and cannot pass, there may be movement at this depth.
The above procedure is very simple and simple, but requires proper planning and careful implementation.
