Construction: Hand Rotary and Hand Percussion Methods

A. The Hand Rotary Method

1. Overview of Method

This method of well sinking has been commonly referred to as boring. Sometimes percussion techniques are included under the general title of bored wells. Because of the limited soil conditions in which simple rotary methods are effective, it is often useful to have percussion tools available. However, for clear explanation, simple rotary and percussion techniques are discussed separately here.

Where sophisticated drilling methods are available for well sinking, hand augering is used only for taking soil samples at relatively shallow depths. It is cheap and provides very accurate soil samples, but requires time and effort and is limited to unconsolidated noncaving formations.

An auger, which functions as a drill bit, is attached to the bottom of a length of drilling rod and turned with the handle, which is attached to the top of the drilling rod. (Fig. 12-1.)

The auger serves first to loosen soil at the bottom of the hole and second to remove it. As the auger is turned, the loosened soil accumulates in or on the auger.

When the auger is full, it is lifted to the surface and emptied and then returned to the hole to continue sinking. Lengths of drilling rod are added to the tool string as the hole is deepened. It has been estimated that 70 to 80% of the time required for this sinking method is taken up by raising and lowering the tool string.

2. Advantages and Disadvantages

There are several advantages to this method.


FIG. 12-1. HAND AUGERING

It has, however, certain disadvantages.

3. Equipment

Excavating equipment includes:

a. cylindrical bucket type - different variations used for hand or power drive. (See Fig.12-2.)

b. open blade type - used mainly with power equipment (continuous spiral) although some are available with hand drive. (See Fig. 123.)


FIG. 12-2. BUCKET AUGERS


FIG. 12-3. OPEN BLADE AUGERS

The following are examples of types of connections that have been used.

- Threaded pipe and coupling is probably the most frequently used connection because it is so readily available.

- Another connection involves slipping the two connecting ends of the drill shaft into a slightly larger piece of pipe and bolting them in place. Only one bolt needs to be removed to disconnect the two shaft sections. That can usually be easily done because it has been found that the bolts need only be finger tight. An alternative to using a regular nut and bolt could be to use a toggle type bolt.

NOTE: A magnet can be a fishing too] for small items dropped into the hole.


FIG. 12-4.

4 The Sinking Process


FIG. 12-5. ADDED WEIGHT NECESSARY TO PENETRATE HARD GROUND

If the auger encounters rock you still have several options. Try to remove the entire rock from the hole with a ram's horn (spiral auger). (See Fig. 12-6.) This will work only if the rock is smaller than the hole.

Although a spiral auger is a piece of equipment listed in the literature for removing rocks from augered holes, field experience has found that percussion techniques work better. (See Hand Percussion, p. 155.) A percussion rock bit would be attached to a rope and dropped in the hole or attached to the end of the drill shafts just as the auger is. Abandon the hole and try some other place if you have no equipment to penetrate a rock layer or if it is too thick or hard to be penetrated by whatever tools you have.


FIG. 12-6. SPIRAL AUGER

If the hole continues to cave in permitting you to go no deeper, you have two options. If you have hit water at the same time, see "Bottom Section." If the hole is still dry, however, you must evaluate your situation to decide whether you want to continue sinking this hole. The hole will usually be caving because the earth is loose sand. To go deeper you will need to sink a casing to hold the walls in place. Determine how much deeper you can go and whether it is worthwhile.

If the tool string is not long enough to go further, abandon this hole and try another location.

5. Time Saving Suggestions

B. The Hand Percussion Method

1. Introduction

This method has usually been classified as a variation or useful addition to hand augering. It makes use of the same methods that are used on a larger scale in cable-tool percussion drilling with large rigs.

The basis of this method is the up and down motion used to sink a hole. The tool string is lifted by an appropriate means and dropped, causing the bit at the bottom of the string to come into sudden, forceful contact with the bottom of the hole. The heavier the tool string, the harder it will strike the bottom of the hole.

It is usually useful to have several different bits suitable for varying ground formations. All of these bits are operated by dropping them onto the bottom of the hole. It will often be useful to turn the bit in the hole, either with a wrench or with a handle, that can be attached similar to an auger handle to make drilling easier and help ensure a round hole.

Cuttings can be removed from the hole in several different ways depending on the particular bit being used. Hard rock cuttings and very loose, caving material is usually removed with a bailer. (See Fig. 1210.) Non-caving soil can usually be packed into a hollow bit. (See Fig. 12-9.)

2. Advantages and Disadvantages

The hand percussion method is suitable for use in a wide range of ground conditions, and may be effective where an auger is not.

This method can be slow, especially in hard formations.

3. Equipment Overview

- A cutting bit is needed for hard formations. (See Figs. 12-7 and 12-8.) Heavy bits with sharp hard edges are used to smash and chip rock. The bit action cuts and mixes the drill cuttings with a small amount of water added to hole to form a paste which can be easily removed with the bailer (too much water will slow drilling). While a solid piece of regular steel can be used to make the rock bit, it is a good idea to face or fit the cutting edges of hard steel. This can be done by building up the tip with welding steel and grinding it down to the desired shape. The bit will require less frequent sharpening and will last longer. The bit can be worked either hanging by rope or cable, or connected to drill shafts.

Rope or cable will tend to wear and may break during the drilling process. If this happens, the bit will have to be "fished" from the hold. (p. 163.) Although rope wears faster, it does have one advantage over cable. When rope suddenly reaches the end of its fall, it gives a quick little turning motion to the bit which helps prevent the bit sticking in the hole. For the very heavy (80 kg) bits which are more effective in harder rock, rope or cable seems far more suitable than drill shafts. With an 80 kg bit, five to seven people are needed and they require frequent rests (every 50 to 100 strokes). The best action with a rock bit can be achieved with short (50 cm) rapid strokes.


FIG. 12-7. PERCUSSION BIT


FIG. 12-9. DETAIL OF PERCUSSION BIT

- A hollow rod bit can be easily made locally from a piece of heavy metal pipe. (See Fig.129.) Galvanized iron pipe is sufficient. It can be made with either a sharpened straight bottom edge as in the figure or a jagged bottom edge. The straight edge is simply sharpened with a file while the jagged edge can be Cut with a hack saw. The opposite end of the bit should be fitted so that it can connect to a drill shaft or rope. It will probably be better with this type of bit to attach it to a drill shaft so that the bit can be forcibly turned or pushed down as necessary. It will be very useful to leave or cut a narrow slot almost the entire length of the bit so that drill cuttings that have been packed up into the bit can be removed by prying with a piece of re-rod or something similar.


FIG. 12-9. HOLLOW ROD BIT

NOTE: If you reach rock, it is usually advisable to continue drilling for three to five days to get an idea of whether this is an isolated boulder; a thin, easily penetrable rock layer; or a virtually impenetrable thick rock layer. After about 50 cm penetration into rock, it is normally possible to identify a boulder, because a boulder will usually break up.


FIG. 12-10. BAILER

- A bailer is the most commonly used tool in loose soils. It is a long cylindrical tube with a valve in the bottom end which permits material to be forced up into the tube but will not permit it to fall back out (See Fig.12-10.) Bailers used with hand equipment are most often equipped with flap valves. The bailer is lowered to the bottom of the hole. Lift it 1 to 2 meters and drop it. The impact of the bailer on the bottom of the hole will force some of the loose soil up into the hollow core. Continue lifting and dropping until the bailer is full or until it has picked up as much of the loose material as it can. Experience will show how long to continue lifting and dropping the bailer to get the maximum usage. When the bailer is full, pull it up to the surface and empty it away from the well.

A bailer has several uses in different situations. It removes rock pieces loosened by rock bit; it removes sand in caving formations from inside the casing; it functions to remove loose material that cannot be packed or retain its shape.


FIG. 12-11. FISHING TOOL - WHICH CAN BE USED TO PICK UP BROKEN ROPE OR CABLE

4. The Sinking Process

5. Sinking Variations

There are three variations of this sinking process that can be used depending on the ground conditions encountered.

Here are some comments and suggestions that may help. It may be necessary to add water to the hole to facilitate sinking because either too much or not enough soil is sticking to the bit. Rotating the bit in the hole is sometimes useful to loosen the bit after it has been dropped and to help maintain a round hole. Leaning the tool string against the rod support or tripod to empty the bit, as opposed to laying it down, saves time and energy. Where the handle is needed to turn the bit, it will be most useful if it can simply be clamped into the tool string wherever desired. This can be long hard work but a system of alternating work and rest periods for teams of workers has proved efficient.

As the bit fills with the loosened soil, it picks up less and less with each stroke until it becomes so packed that it can no longer loosen and pick up any soil. Because different soils pack differently, the bit may be as little as one third full when it must be removed and emptied. With experience, one quickly gains a feel for when the bit needs to be emptied.

In loose, caving formations like saturated sand, a bailer can be operated inside the casing to sink the hole as the casing is sunk or driven. (See Fig. 12-10.) The outside diameter of the bailer should be slightly less than the inside diameter of the casing being installed.

If the casing will sink by itself, the bailer is simply worked up and down inside the casing pipe to pick up loose ground material. As the bailer picks up the material from the bottom of the hole, the casing should sink under its own weight. (If the casing does not sink, it can be driven.) When the bailer fills up, it will need to be removed from the hole and emptied.

The casing can be driven at the same time that the bailer is being worked or it can be driven down about .5 m and then bailed. This particular process of driving and bailing is very commonly used to penetrate loose caving formations.

6. Problems in Sinking