JP7609372B2 - Load test method and analysis system - Google Patents

Description

The present invention relates to a load test method for steel pipe piles driven into bedrock, and an analysis system used in the load test.

The known load test methods for evaluating the bearing capacity of foundation piles include the static load test method, the dynamic load test method, and the rapid load test method. For example, the dynamic load test method involves a rapid load test with a relative load time Tr of 5 or more and less than 500, and an impact load test with a relative load time Tr of less than 5. In these load tests, a hammer driving machine or a hammer hammer is used as the loading device.

The Gunpile method (registered trademark) is also known as a method for driving steel pipe piles into bedrock. In the Gunpile method, a steel pipe pile with a reinforced tip is driven directly into the bedrock. Specifically, the steel pipe pile is vibrated vertically using a vibrator to crush the bedrock, and a jet of water is supplied to the tip of the steel pipe pile through the hollow part of the steel pipe pile, removing the crushed rock powder while driving the steel pipe pile.

Japanese Patent Application Publication No. 10-153497

However, the method described in Patent Document 1 requires a process of forming measurement holes near the steel pipe pile, which increases the effort and cost involved in the load test.

The load test method that solves the above problem is a load test method for a steel pipe pile driven using a vibrator, in which the steel pipe pile is vibrated in an up and down direction by the vibrator to crush the rock mass, and jet water is supplied to the tip of the steel pipe pile through the hollow part of the steel pipe pile to remove rock powder while driving the steel pipe pile, the supply of the jet water is stopped after the steel pipe pile reaches the supporting layer, the acceleration of the steel pipe pile is obtained when the steel pipe pile is vibrated using the vibrator as a force application device, and the obtained acceleration is used to calculate the ground resistance of the rock mass.

The present invention makes it possible to efficiently carry out load tests on steel pipe piles.

FIG. 1 is a schematic diagram showing a state in which a steel pipe pile to which an embodiment of a load test method is applied is being driven. FIG. 1 is a block diagram showing a schematic configuration of an analysis system. (a) Graph showing an example of the measurement results of the acceleration of a steel pipe pile, (b) graph showing the speed of the steel pipe pile based on acceleration, (c) graph showing the displacement of the steel pipe pile based on acceleration, (d) graph showing the load applied to the steel pipe pile by the vibrator, (e) graph showing an example of the ground reaction force against the steel pipe pile, (f) graph showing the relationship between the displacement of the steel pipe pile and ground resistance, (g) graph showing an example of the ground reaction force against the steel pipe pile using the CASE method, (h) graph showing the relationship between the displacement of the steel pipe pile and ground resistance using the CASE method.

An embodiment of a load test method and analysis system will be described with reference to FIGS. 1 to 3. FIG.
As shown in FIG. 1, in the Gunpile method (registered trademark), a hollow steel pipe pile 12 with a reinforced tip is driven into a bedrock 11 by a vibrator 13. In the Gunpile method, the vibrator 13 vibrates the steel pipe pile 12 in the vertical direction to crush the bedrock 11. At the same time, low-pressure jet water is supplied to the tip of the steel pipe pile 12 through a supply path 14 arranged inside the steel pipe pile 12, so that the steel pipe pile 12 is driven while removing the crushed rock powder. In this embodiment, the hollow part of the steel pipe pile 12 after driving is filled with a grout material made of a cement-based material such as mortar. It is not necessary to fill the hollow part of the steel pipe pile 12 with a grout material.

The load test method of this embodiment is performed on the steel pipe piles 12 driven in by the gun pile method described above, using a vibrator 13 as a force application device. By using the vibrator 13 as a force application device, a load test equivalent to an impact load test can be performed.

The vibrator 13 has a box 15 , a gripping portion 16 , and a vibration driving source 17 .
The box 15 is suspended, for example, by a crane (not shown). The gripper 16 is supported at the lower end of the box 15. The gripper 16 grips the steel pipe pile 12 by being provided with a driving force from a gripping drive source (not shown). The vibration drive source 17 is housed in the box 15. The vibration drive source 17 in this embodiment is an electric type. The vibration drive source 17 may be a hydraulic type. When driven, the vibration drive source 17 vibrates the gripper 16 in the up and down direction, thereby applying force to the steel pipe pile 12.

A strain gauge 18 and an acceleration gauge 19 are attached to the steel pipe pile 12. The strain gauge 18 measures the strain of the steel pipe pile 12 when vibrations are applied from the vibrator 13. The acceleration gauge 19 measures the acceleration of the steel pipe pile 12 when vibrations are applied from the vibrator 13. The measured values of the strain gauge 18 and the acceleration gauge 19 are input to an analysis system 20. The analysis system 20 is a system that analyzes a load test of the steel pipe pile 12 that was performed using the vibrator 13 as a load application device. The load test is performed before the hollow part of the steel pipe pile 12 is filled with grout material, or when the filled grout material is in an unhardened state.

As shown in FIG. 2, the analysis system 20 includes an information processing device 21 as a main component.
The information processing device 21 acquires various types of information and executes various processes based on the acquired various types of information, as well as programs and various data stored in memory. The information processing device 21 may be configured as a circuit including one or more dedicated hardware circuits such as ASICs, one or more processors that operate according to computer programs (software), or a combination thereof. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute processes. Memory, i.e., computer-readable media, includes any medium that can be accessed and used by a general-purpose or dedicated computer.

In addition to the above-mentioned distortion measuring device 18 and acceleration measuring device 19, an input device 22 and a display device 23 are electrically connected to the information processing device 21.
The input device 22 includes a keyboard, a pointing device, etc. The input device 22 inputs various information, instructions to execute various processes, etc. to the information processing device 21.

The display device 23 displays the measurement values of the acceleration measuring device 19 and the results of various processes executed by the information processing device 21. The information processing device 21 has a processing unit 25 and a data storage unit 26.

The processing unit 25 executes various processes. When an analysis start operation is performed on the input device 22, the processing unit 25 executes the analysis process.
In the analysis process, the processing unit 25 stores the strain ε input from the strain measuring instrument 18 and the acceleration a input from the acceleration measuring instrument 19 in the data storage unit 26 in association with each acquisition timing for a predetermined fixed period from the analysis start operation. The processing unit 25 uses the stored strain ε and acceleration a to calculate the ground resistance Rsoil of the rock mass 11. The processing unit 25 of this embodiment calculates the static resistance component Rw of the rock mass 11 by the unloading point method, and calculates the calculated static resistance component Rw as the ground resistance Rsoil.

A method for calculating the static resistance component Rw using the unloading point method will be described.
When a load F acts on the steel pipe pile 12, an inertial resistance component Ra of the steel pipe pile 12 (= mass M of the steel pipe pile 12 × acceleration a), a static resistance component Rw and a dynamic resistance component Rv that the tip of the steel pipe pile 12 receives from the bedrock 11 are generated in the opposite direction of the load F. On the other hand, when the steel pipe pile 12 displaced downward by the load F bounces off the bedrock 11, the steel pipe pile 12 is in a stationary state. In other words, no dynamic resistance component Rv is generated. For this reason, if the value obtained by subtracting the inertial resistance component Ra from the load F is taken as the reaction force Fsoil from the bedrock 11, the reaction force Fsoil at the time of the maximum displacement of the steel pipe pile 12 becomes the static resistance component Rw.

(Load test procedure)
The procedure of the load test will be described. Prior to the load test, target information on the steel pipe pile 12 is input to the information processing device 21 via the input device 22. The target information is information indicating mechanical properties of the steel pipe pile 12, such as the Young's modulus of the steel pipe pile 12, as well as the inner diameter, outer diameter, and mass M of the steel pipe pile 12. The processing unit 25 of the information processing device 21 stores the input target information in the data storage unit 26.

The load test is carried out after the steel pipe pile 12 has been driven to a specified depth that reaches the supporting layer, and the supply of jet water is stopped. In the load test, the vibrator 13 is first driven, and then an operation to start the analysis is performed using the input device 22. In this way, by using the vibrator 13 that was used to drive the steel pipe pile 12 as a force application device that applies a load F to the steel pipe pile 12, a force application device such as a Monken is not required for the test.

When an analysis start operation is performed on the input device 22, the processing unit 25 of the information processing device 21 starts the analysis process. In the analysis process, the processing unit 25 stores the strain ε and the acceleration a in the data storage unit 26. Then, the processing unit 25 calculates the load F acting on the steel pipe pile 12 at each acquisition timing based on the strain ε and the Young's modulus of the steel pipe pile 12 stored in the data storage unit 26, and then the processing unit 25 calculates the static resistance component Rw by the unloading point method using the load F, the mass M of the steel pipe pile 12, and the acceleration a.

3(a) to 3(f) are graphs showing examples of the results of an actual load test.
As shown in Fig. 3(a), the acceleration a obtained in the load test shows spike-like behavior that changes significantly in a short period of time. Such spike-like behavior of the acceleration a is obtained by using a vibrator 13 as a force application device for a steel pipe pile 12 driven into a rock mass 11. In Fig. 3(a), the downward acceleration a is shown as a negative value.

As shown in FIG. 3B, the velocity is an integrated value of the acceleration a, and therefore exhibits a gentler behavior than the acceleration a.
As shown in FIG. 3C, the displacement is an integrated value of the velocity, and therefore exhibits a gentler behavior than the velocity.

As shown in FIG. 3D, the load F exhibits spike-like behavior, although not as much as the acceleration a, and more so than the velocity and displacement.
As shown in FIG. 3( e ), the reaction force Fsoil from the bedrock 11 exhibits spike-like behavior similar to that of the acceleration a.

Figure 3(f) is a graph showing the relationship between ground resistance and the displacement of the steel pipe pile 12, with the reaction force Fsoil from the bedrock 11 being the ground resistance. In Figure 3(f), the downward displacement is shown as a positive value. As shown in Figure 3(d), the ground resistance is the reaction force Fsoil minus the inertial resistance component Ra of the steel pipe pile 12 (= mass M of the steel pipe pile 12 × acceleration a), and therefore exhibits spike-like behavior similar to acceleration a. The maximum value at the time of maximum displacement is then calculated as the static resistance component Rw, i.e., the ground resistance Rsoil.

The CASE method is known as another method for calculating such ground resistance Rsoil. The CASE method measures the input wave and reflected wave, and calculates the total resistance of the ground (static resistance component Rw + dynamic resistance component Rv) based on the measured input wave and reflected wave. The static resistance component Rw, which is obtained by separating the dynamic resistance component Rv from the total resistance, is then calculated as the ground resistance Rsoil.

Figure 3(g) shows the reaction force Fsoil of the rock mass 11 calculated by applying the acceleration a shown in Figure 3(a) to the CASE method. Figure 3(h) shows the relationship between the ground resistance and the displacement of the steel pipe pile 12. Figure 3(g) is shown on the same scale as Figure 3(e), and Figure 3(h) is shown on the same scale as Figure 3(f).

As shown in Figures 3(g) and 3(h), in the CASE method, the behavior of the reaction force Fsoil and ground resistance was gentler than that of the reaction force Fsoil and ground resistance obtained by the above analysis process. This is because the dynamic resistance component Rv is calculated using the speed of the steel pipe pile 12, and therefore cannot reflect the spike-like behavior of the acceleration a. As a result, the ground resistance Rsoil calculated by the CASE method was smaller than the ground resistance Rsoil calculated by the above analysis process.

The inventors compared the ground resistance Rsoil calculated by the above analysis process with the ground resistance Rsoil calculated by a method other than the CASE method. Specifically, they compared it with the ground resistance Rsoil calculated using a PDA (Pile Driving Analyzer). The PDA is an impact load testing system (manufactured by Pile Dynamics, Inc.) that can calculate the ground resistance Rsoil with high accuracy. As a result of the comparison, it was confirmed that the ground resistance Rsoil calculated by the above analysis process is approximately equal to the ground resistance calculated by the PDA.

The effects of this embodiment will be described.
(1) The above-mentioned load test method is a load test method for a steel pipe pile 12 driven using a vibrator 13, in which the steel pipe pile 12 is vibrated in an up and down direction to crush the bedrock 11, and jet water is supplied to the tip of the steel pipe pile 12 through the hollow part of the steel pipe pile 12 to remove crushed rock powder while driving the steel pipe pile 12, and after the steel pipe pile 12 reaches the supporting layer, the supply of jet water is stopped, and the acceleration of the steel pipe pile 12 is obtained when the steel pipe pile 12 is vibrated using the vibrator 13 as a force application device, and the ground resistance Rsoil of the bedrock 11 is calculated using the obtained acceleration.

This eliminates the need for processes such as attaching a force application device such as a Monken to the steel pipe pile 12 and forming measurement holes near the steel pipe pile 12. As a result, the effort and costs involved in the load test can be reduced. In addition, there is no need for space to wait for the attached force application device, making effective use of on-site space.

(2) In the above-mentioned load test method, the ground resistance Rsoil is calculated by the unloading point method using the acceleration a of the steel pipe pile 12. This makes it possible to calculate the ground resistance Rsoil of the bedrock 11 with high accuracy.

(3) Even if there is unhardened grout material in the hollow portion of the steel pipe pile 12, the vibration of the steel pipe pile 12 has little effect on the grout material. For this reason, the above-mentioned load test method may be performed when the grout material filled in the hollow portion of the steel pipe pile 12 is in an unhardened state. In other words, the load test process and the grout material filling process may be performed at the same time. This makes it possible to further reduce the costs associated with the load test.

Although one embodiment of the load test method and analysis system according to the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the spirit of the invention. For example, this embodiment can be modified as follows. This embodiment and the following modified examples can be combined with each other as long as they are not technically inconsistent.

The load test may be performed before filling with grout material or after the grout material has hardened.
The method of calculating the ground resistance Rsoil is not limited to the unloading point method, and may be any method that calculates the ground resistance Rsoil using the acceleration a itself, which exhibits spike-like behavior measured by the acceleration measuring instrument 19.

11...Rock, 12...Steel pipe pile, 13...Vibrator, 14...Supply channel, 15...Box, 16...Holding unit, 17...Vibration drive source, 18...Strain meter, 19...Acceleration meter, 20...Analysis system, 21...Information processing device, 22...Input device, 23...Display device, 25...Processing unit, 26...Data storage unit

Claims (4)

A load test method for a steel pipe pile driven using a vibrator, comprising:
The steel pipe pile is vibrated in the vertical direction by the vibrator to crush the rock mass, and jet water is supplied to the tip of the steel pipe pile through the hollow part of the steel pipe pile to remove the crushed rock powder while driving the steel pipe pile.
After the bearing layer is reached, the supply of the jet water is stopped, and the acceleration of the steel pipe pile is obtained when the vibration is applied to the steel pipe pile using the vibrator as a force application device.
and calculating the ground resistance of the rock mass by an unloading point method using the obtained acceleration. A load test method for a steel pipe pile driven using a vibrator, comprising:
The steel pipe pile is vibrated in the vertical direction by the vibrator to crush the rock mass, and jet water is supplied to the tip of the steel pipe pile through the hollow part of the steel pipe pile to remove the crushed rock powder while driving the steel pipe pile.
After reaching the supporting layer, the supply of the jet water is stopped and the hollow portion of the steel pipe pile is filled with grout material;
When the filled grout material is in an unhardened state, the acceleration of the steel pipe pile is obtained when vibration is applied to the steel pipe pile using the vibrator as a force application device;
calculating the ground resistance of the rock mass using the obtained acceleration. An analysis system used in a load test of a steel pipe pile that is driven while crushing rock by vibrating the steel pipe pile in the vertical direction using a vibrator and removing rock crushed powder by supplying jet water to the tip of the steel pipe pile through a hollow part of the steel pipe pile,
an acceleration measuring device that measures the acceleration of the vibration applied to the steel pipe pile using the vibrator as a force application device while the supply of the jet water is stopped;
and an information processing device that calculates the ground resistance of the rock mass by an unloading point method using the acceleration. An analysis system used in a load test of a steel pipe pile in which a rock mass is crushed by vibrating the steel pipe pile in the vertical direction using a vibrator, and a jet of water is supplied to the tip of the steel pipe pile through the hollow portion of the steel pipe pile to remove rock crushed powder, and then the hollow portion is filled with grout material .
an acceleration measuring device that measures the acceleration of vibration applied to the steel pipe pile using the vibrator as a force application device when the supply of the jet water is stopped and the grout material filled in the hollow portion is in an unhardened state; and
and an information processing device that calculates the ground resistance of the rock mass using the acceleration.