WO2000053852A1

WO2000053852A1 - Method for controlling pile casting

Info

Publication number: WO2000053852A1
Application number: PCT/IL2000/000133
Authority: WO
Inventors: Magali Shachar
Original assignee: Magali Shachar
Priority date: 1999-03-07
Filing date: 2000-03-07
Publication date: 2000-09-14
Also published as: AU2937700A; IL128856A0

Abstract

A method for coordinating the lifting velocity of a drilling rod and the amount of concrete poured into a borehole to cast a pile from the bottom towards the surface. The concrete is poured through a pipe which is part of the drilling rod. A positive pressure is maintained at the bottom of the drilling rod by analyzing the tensile force in the lifting cable. As a pressure develops at the bottom of the drilling rod, a force is generated and upwardly pushes the drilling rod. The force is due to the 'piston effect' of the drilling rod geometry and reduces the minimal tensile force in the lifting cable.

Description

WO 00/53852 PCTtILOO/00133

METHOD FOR CONTROLLING PILE CASTING

Wherever it says "concrete^" it should be read as "concrete and/or mortar and/or cement and/or grout and/or lime and/or cement water and/or cement grout".

Wherever it says "auger" it should be read as "auger and/or drilling rod and/or drilling string and/or Kelly bar and/or ground displacement'"

Technical Field

In piles that are cast from the bottom up, through a pipe that is part of the auger (Continue Flight Auger, Cast Auger. Omega), there is a problem of coordinating the lifting velocity of the auger and the amount of concrete inserted to the pile. When the auger comes up, a space is created beneath it. This space must be immediately filled up with concrete, otherwise there might be a collapse of the hole's walls and the material that composes the hole^'s walls will occupy part (or all) of the concrete's space. In such case, the pile's capacity to carry the designated load is impaired. At the point of collapse, there may be a narrowing or even separation in the pile.

Background Art

In order to handle the above-described problem, and since there is no way to control the process through visual inspection, it is customary to use control and/or monitoring systems. The available control systems perform part or all of the following measurements:

1. Concrete pressure in the drilling rod head.

2. Depth of the auger.

3. Volume of concrete inserted to the pile as a function of the depth.

4. Lifting velocity of the auger.

5. Amount of concrete inserted into the pile relatively to the theoretical amount of concrete as a function of the depth.

6. Total amount of inserted concrete.

7. Total amount that is inserted relatively to the theoretical amount. Based on these measurements, all or part of them, the operator has to set the lifting velocity of the auger while assuring that no space is formed at the bottom of the auger, and that in any case, the amount of concrete entering the system, at any given point of time and height, will be equal or more than the physical volume evacuated from the bottom of the auger.

Control systems based on the above measurements (all or part of them) have the following disadvantages:

1. The measurement of the concrete pressure is taken at the auger head yet the pressure that actually influences the structure of the pile is the pressure at the bottom of the auger. There is no direct correlation between the two pressures, as the pressure at the auger head may be very high whereas the pressure at the bottom of the auger may be very low and even negative when, for instance, there is a blocking at any point along the auger.

2. There may be a situation opposite to the one described on section 1 above. Measuring the pressure in the auger head will show a very low pressure or even negative (vacuum) whereas the pressure at the bottom of the auger will be high. This phenomena takes place when concrete flows well inside the auger but the operator lifts the auger in such a velocity that the amount of concrete entering the system is smaller than the volume of the space evacuated at the bottom of the auger. At the head of the auger, suction is created but the pressure at the bottom of the auger, as a result of the static pressure of the concrete inside the auger, may be very high.

3. Calculating the volume of concrete entering the system is based in most cases on the fact that most concrete pumps are piston pumps that compress concrete through one or two pistons, and which operation is based on a suction-compression process. Due to the batch nature of the concrete pumps, the motion of concrete in the pipes, as well as the concrete pressure, behave as pulses. Most controllers exploit the phenomena described above and by maintaining a follow up of the concrete pressure, they attempt to identify the pulses of the compression pistons. The number of pulses multiplied by the volume of concrete flo n in each stroke of the concrete piston should give the volume of concrete inserted to the system. This method of measuring (calculating) the concrete volume is problematic and unreliable. The pressure pulses produced by the concrete pump depend on the type of pump, its level of wear, length of pipes, type of concrete and activity of the concrete pump^'s, and the drilling machine^'s operators. In order to coordinate between the controller and concrete pump, several mathematical parameters should be set in the controller/monitor. Any change in the pump requires a change in the parameters so that the results of the calculation also depend on the accuracy of using the parameters.

Another method to measure (calculate) the amount of concrete fed into the system is based on a magnetic flow rate meter. The magnetic flow rate meter also depends on the parameters since various kinds of aggregates as well as types of cement and sand affect the accuracy of its operation. An additional disadvantage of this method is derived from the motion of concrete that is in batches and not continuous. In the total calculation, the accuracy of the magnetic flow rate meter is adequate but dividing in time (depth) is unreliable. The magnetic flow rate meters available in the market are unreliable and many problems are involved in their operation.

4. The flow of concrete in the pipes is in batches (due to the properties of the concrete pump) whereas the lifting velocity of the drilling rod is uniform. Since the lifting velocity of the drilling rod. which is uniform, defines the evacuated volume, and since the flow of the concrete into the system is what fills up the gap that is created and it is in batches, there's a problem of coordination between the two systems. The problems aggravate as the volume of concrete entered to the system in each stroke of the concrete pump grows bigger and as the diameter of the pile grows smaller. A possible solution to the problem presented above may give an answer, that is mathematically reasonable, but no one really understands what^'s going on at the physical level.

5. As the volume of concrete inserted to the system in each stroke of the concrete pump is relatively high (say 50 liter per stroke) and the diameter of the pile is relatively small (say 600 mm.), then each pump stroke fills up about 170 mm. of the pile's height. In most measurement and control systems, the data are displayed (and perhaps saved) each 100 mm. Hence the amount of concrete should be "divided^", at least from a calculative point of view, between two consecutive heights of calculation. No one can tell, with reasonable certainty, what is the nature of this dividing so that some assumptions should be made and/or some mathematical operations should be carried out. These actions are not necessarily compatible with the physical reality.

Making sure that the inserted volume of concrete equals or exceeds the evacuated volume at the bottom of the auger does not necessarily assure the quality of the pile. There are cases where the drilling rod penetrates through an underground cavity (cave). In such cases, there may be a situation where some concrete is swallowed in the cave. The calculation system will show that the amount of inserted concrete is "correct^" and that the pile is "adequate^" but in fact there may be a discontinuity of the concrete. One way to overcome this situation is to assure a minimum concrete pressure in the concrete feed line. As stated above, measuring the concrete pressure is also inaccurate and unreliable. From an operational point of view, it is not simple to demand from the operator to maintain a balance between the amount of concrete coming in relatively to the volume that is evacuated from the bottom of the drilling rod, and maintain a specific concrete pressure at the same time.

Disclosure of Invention

Using the force in which the concrete pushes the auger upward (referred as concrete upward force) as a criterion to determine the lifting velocity of the auger. It is possible, of course, to apply in addition techniques such as those that are described within the Background Art.

One can regard the auger - soil mass as a piston rod encased in a casing (cylinder). The concrete pressure exerts force on the bottom of the auger and pushes it upwards exactly as hydraulic pressure pushes a piston rod inside a cylinder ( Fig . i and ) ■ The force that is applied by the concrete pressure to push the auger upwards (the concrete upward force) equals the concrete pressure at the bottom of the auger multiplied by the effective area of the bottom of auger. The effective area is. for practical purposes, the cross section of the auger minus the cross section of the pipe in which concrete is flown ( fiQ . 3) .

Maintaining a certain amount of concrete upward force using the concrete pressure (fι( M) is a way to assure that there^'s no space between the bottom of the auger and the last (top) surface of concrete and that the concrete is in a continuous contact with the bottom of the auger.

Maintaining a certain amount of concrete upward force, using the concrete pressure, is independent of concrete supply technique, operator of the concrete supply system, type of drilling machine, type of concrete, type of soil, mathematical and/or statistical functions or the structure of the auger.

The weight of the auger and ground on it, including the weight of the mechanical systems plus the friction force between the soil and the auger, minus the concrete upward force of the concrete equals the lifting force that the mechanical system of the drilling rig should apply ( F/ ₉, 2) ,

The concrete upward force is the concrete pressure multiplied by the effective area ( Rg. 3) . With a pile diameter of 700 mm, and a concrete pipe diameter of 125 mm., the effective area is about 0.37 square meter. A pressure of 0.1 Mpa will result in a lifting force of 37 kN.

The weight of the auger including the mechanical systems and soil on it (for drilling at a depth of 16 m. and 700 mm. Pile diameter) is approximately 100 KN.

The lifting force of the concrete constitutes about 37% of the load, a magnitude that can be easily and reliably identified.

The above mentioned calculative example is not binding and is brought for the sake of clarification only. The friction force between the soil and the auger (including the soil on the auger) may be measured, calculated, estimated, eliminated or ignored.

The friction force may be measured by performing a test pile with no concrete injection and measuring the force that is required to lift the auger (as a function of the depth) and at a second stage subtracting the self-weight.

The friction force may be calculated through geo-mechanical theories.

The friction force may be estimated based on the accumulated experience.

The friction force may be eliminated through a continuous rotation of the auger around its axis. If the linear velocity of rotation of the auger^'s perimeter is higher than the lifting velocity of the drilling rod. most of the friction between the auger and soil is exerted in the horizontal plane and neutralized by the rotation system of the auger. Friction in the vertical direction, the one that resists the upward motion of the auger, is very low hence negligible.

The weight of the auger, including the weight of the mechanical systems and soil, may be measured, estimated or calculated.

The auger could be pulled out and its weight including the weight of the mechanical systems and soil on it may be measured.

The weight of the auger including the mechanical systems and soil may be estimated.

The weight of the drilling rod, the mechanical systems and soil may be calculated.

From all that was stated above, it is clear that performing a pile as the concrete composing it is cast from the bottom up through a special pipe that is part of the auger, where the load applied by the lifting system (lifting force) is measured (as a function of depth), may be controlled only by measuring the load that is applied in the lifting system (lifting force). When the auger rotates around its axis at the time of lifting, the accuracy of measurement and calculation increases since most of the friction between the soil and the auger is cancelled by the rotation system of the auger. The load applied by the auger^'s lifting system (lifting force) may be directly measured by a series connection of a load cell ( rjg , 1 and 2. ) to the lifting system, by an indirect measurement of the load in the lifting system, by measuring the pressure in the hydraulic system (if any) that activates the lifting system, by measuring the tension in the cable and/or chain of the lifting system (if any) or by measuring the forces and/or reactions to the forces that are developed by the mechanical lifting system (if any).

A control system that uses the force applied in the auger^'s lifting system (lifting force) in piles that are cast from the bottom up through a pipe that is part of the auger as a criterion (not necessarily a single criteria) has the following advantages:

1. Simplicity of measurement.

2. Independent of operators.

3. Independent of mathematical parameters.

4. Insensitive to the type of concrete.

5. Independent of the concrete pump (if any).

6. Applicable regardless of the concrete supply technique.

7. Very high level of confidence and reliability.

8. Independent of the drilling machine and/or drilling equipment.

9. Very high sensitivity of the control circuit.

10. Applicable to any drilling machine.

Brief Description of Drawings

Fiα 1 describes the drilling rig - auger - pile - ground picture.

Fl .2 illustrates the four main vertical forces. πC) . 3 is a zoom view of the bottom of the auger. /g. 4 is the depth - force diagram of the controlling cycle. Best Mode of Carrying Out the Invention

The easiest way to perform a pile installation using the above mentioned controlling loop is composed of six stages:

1. The operator lays the center of the auger on top of the marker, at ground level, while the lifting cable is loose. At that moment the controller/monitor measures the "zero^" depth and tension. Denoted "1". Fig. .

2. The operator lifts the auger rrom tne ground about 150 mm. At that moment, the controller/monitor measures the dead weight of the mechanical parts. Denoted "2'^",

F/g .4 .

3. The operator penetrates into the ground normally all the way to the designed depth. Denoted "3^", Fq. Jf .

4. The operator lifts the auger about 150 mm. At that moment, the controller/monitor measures the dead weight of the mechanical parts including the weight of the soil. Denoted

5. e operator lifts the auger while maintaining a concrete upward force as needed. The controller/monitor leads the operator to follow the solid line. (The doted line is the tension force in the cable when there is no concrete upward force.

Industrial Applicability

The preferable way to apply the invention is by using an electronic load cell connected to the end of the lifting cable and the body of the drilling rig. That load cell measures the tension forces acting and converts them to electronic signal f Fiq . 1 and 2). That signal is fed into the controlling/monitoring system and serves as one of the two main inputs. The second main input is a depth meter, which is tracing the longitudinal movement of that lifting cable.

More gauges may be applied.

The load cell measures the lift forces while the depth meter supplies depth references. The controller/monitor manipulates the input signals and guides the operator of the drilling rig regarding the lift velocity.

Claims

1. Using the force that is exerted in the drilling rod^'s lifting system in piles that are cast from the bottom up through a pipe that is part of the drilling rod as a way to measure the concrete pressure acting at the bottom of the drilling rod (auger).

2. Using the force that is exerted in the drilling rod's lifting system in piles that are cast from the bottom up through a pipe that is part of the drilling rod (auger) as a criterion to control the casting process.

3. Using the force that is exerted in the drilling rod's lifting system in piles that are cast from the bottom up through a pipe that is part of the drilling rod as a criterion to determine the lifting velocity of the drilling rod (auger).

4. Using the force that is exerted in the drilling rod's lifting system in piles that are cast from the bottom up through a pipe that is part of the drilling rod (auger) as stated on section 1 -3 above, yet in addition, using criteria that are derived from measuring the concrete pressure at the head of the drilling rod (or anywhere else along the concrete supply pipe) and/or measuring the concrete flow rate through a flow rate meter and/or measuring the concrete flow rate by counting the concrete pump^'s pulses and/or measuring the depth of the bottom of the drilling rod (auger) and/or measuring (or calculating) the lifting velocity of the drilling rod and/or measuring the velocity of rotation of the drilling rod and/or measuring the drilling rod^'s torque.

5. Controlling piles, that are cast from the bottom up through a pipe that is part of the drilling rod (auger), installation by analyzing the force that acts in the drilling rod's lifting system.

6. Controlling piles, that are cast from the bottom up through a pips that is part of the drilling rod (auger), installation by analyzing the force that acts in the drilling rod's lifting system yet in addition, using criteria that are derived from measuring the concrete pressure in the drilling rod's head (or anywhere else along the concrete supply pipe) and/or measuring the concrete flow rate through a flow rate meter and/or measuring the concrete flow rate by counting the concrete pump^'s pulses and/or measuring the depth of the bottom of the drilling rod and/or measuring (or calculating) the lifting velocity of the drilling rod and/or measuring the velocity of rotation of the drilling rod and/or measuring the drilling rods^" torque.