JPS642726B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a construction method for improving the ground by constructing a large number of sand piles in soft ground.

When constructing a large number of sand piles in soft ground to improve the ground, in order to obtain a uniformly improved ground, either the sand pile diameter or the sand pile strength, or both, should be adjusted in response to changes in the soil properties of the original ground. It has been previously proposed by the present applicant to construct each sand pile while changing the sand piles (see Japanese Patent Application No. 56-149708 and Japanese Unexamined Patent Publication No. 58-50216).

When carrying out this prior invention, it is necessary to detect the soil properties of the original soil at the sand pile construction point prior to sand pile construction. By performing the process of penetrating the hollow tube, the sand pile construction can be carried out efficiently and accurately.

Hereinafter, the present invention will be specifically described with reference to the drawings.

For constructing each sand pile in the construction method of the present invention, a hollow pipe 1 for constructing sand piles as illustrated in FIG. 1 is used.

A sand discharge/compaction member 3 that is forcibly moved up and down by a hydraulic piston/cylinder device 2 is provided at the lower end of the illustrated hollow pipe 1 for sand pile construction. Although hollow tubes are preferred for the present invention as will be clear from the following description, the hollow tubes for constructing sand piles used in the present invention do not have to be of this type.

When using the illustrated hollow pipe 1 for sand pile construction, the sand pile construction is carried out by moving the sand pile construction hollow pipe 1 from the ground surface A at the construction point to a predetermined depth in the ground, as shown in Figure 2A. Penetrate up to B (penetration process), and then pull out the sand pile construction hollow pipe 1 while removing the sand discharge and compaction member 3.
The sand in the hollow pipe 1 for sand pile construction is forcibly discharged and compacted by the operation of the sand pile, and the sand pile is successively constructed up to the ground surface (construction process), but in the method of the present invention, in the penetration process, As shown in FIG. 2B, the original ground soil properties (original ground strength) are detected for each depth (GL ₁ to _{GL o} ).

The method of detecting the soil texture of the original ground is arbitrary; for example,
Possible methods include a method of detecting stress by installing stress measurement gauges, load cells, etc. at appropriate locations in hollow pipes for sand pile construction, and methods of detecting from changes in the penetration speed of hollow pipes for sand pile construction. The sand discharge and compaction member 3 of the hollow tube 1 may be used for detection as follows.

In FIG. 1, when the switching valve 4 is placed in the neutral position, the liquid flows in the direction of the arrow in the pipe line 5 leading to the upper chamber of the cylinder of the hydraulic piston-cylinder device 2 through the switching valve 4 and the pilot-operated check valve. If the hollow pipe 1 for sand pile construction penetrates into the ground in this state, the hydraulic pressure corresponding to the penetration resistance acting on the sand discharge/compaction member 3 will be completely blocked by the pipe 5. Occurs in liquid. Therefore, by detecting this hydraulic pressure with the pressure sensor 7, the soil properties of the ground can be known.

It is also possible to operate the sand discharge/compaction member 3 during penetration of the hollow pipe 1 for sand pile construction, and detect the soil properties of the original ground from the hydraulic pressure of the pipe 5 immediately before its maximum extension. Needless to say, the check valve 6 is unnecessary in this case.

The penetration depth of the hollow pipe for sand pile construction is detected with a conventionally known depth meter, and the relationship between the detected depth and the soil properties of the original ground is recorded on the recording paper of the recorder.

In the construction method of the present invention, in the construction process following the penetration process, either or both of the diameter and strength of the construction sand pile is changed at each depth to correspond to the soil properties of the original soil detected as described above. Sand piles are constructed one after another in the upward direction, but in terms of the diameter of the sand piles, detecting and changing the diameter to correspond to the soil properties of the original soil means detecting the soil properties of the original soil ( In places where the actual original soil strength a) is lower than the design original soil property value (average strength b), the diameter of the construction sand pile is made larger than the standard pile diameter D determined in the design, depending on the degree. On the other hand, if it is large, it should be made smaller as well (see Fig. 3), and the specific value is calculated from a correlation formula prepared in advance based on experience.

This calculation is completed before the construction process begins,
The results are recorded or displayed or stored in a storage device.

The operation to obtain a predetermined diameter, etc. may be performed by an operator while looking at the above-mentioned record or display, or may be performed automatically based on a signal from a storage device.

The sand pile diameter is typically controlled by adjusting the pulling speed of the sand pile construction hollow pipe 1, but in addition to this, it is also possible to consider adjusting the stroke length, lifting speed, and cycle time of the sand discharge/compaction member 3. It will be done.

In addition, to control the sand pile strength (sand density), it is necessary to add or stop micro-vibrations to the sand discharge/compaction member 3, and to adjust the frequency and amplitude of the micro-vibrations being applied. It is conceivable to change one or both of them.

In addition, when increasing the pile diameter or increasing the pile strength, a consolidation agent such as lime or cement may be added as an supplement.

The method of the present invention forms a uniform improved ground using sand piles as described above, but in particular, the soil properties of the original soil at each depth are detected when the hollow pipe for sand pile construction is penetrated. Before moving on to the sand pile construction process, it is possible to decide how to construct sand piles at each depth, and in this respect, uniform improved ground formation can be performed efficiently and accurately.

Although the above description has been made regarding sand piles, the present invention is also applicable to piles using sand-like materials such as gravel and crushed stone.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an example of a device for carrying out the construction method of the present invention, and FIGS. 2A and 2B and 3A and 3B are explanatory diagrams of the present invention construction method. In the figure, 1...Hollow pipe for sand pile construction, 2...Hydraulic piston/cylinder device, 3...Sand discharge and compaction member, 4
...Switching valve, 6...Check valve, 7...Pressure sensor.

Claims (1)

[Scope of Claims] 1. In a construction method for improving the ground by constructing a large number of sand piles in soft ground, a step of penetrating a hollow pipe for sand pile construction to a predetermined depth into the soft ground when constructing each sand pile. In the process of detecting the soil properties of the original soil at each depth and creating sand piles while pulling out the hollow pipe for sand pile construction, the soil properties of the original soil are detected at each depth in order to correspond to the soil properties of the original soil detected in the penetration process. A method for improving soft ground using sand piles, which is characterized by forming uniform improved ground by changing either or both of the diameter and strength of the sand piles. 2. A hollow pipe for sand pile construction is equipped with a hydraulically operated sand discharge and compaction member at the lower end, and the sand pile construction is performed using the sand discharge and compaction member to detect the soil texture of the original ground and to create sand piles. A soft ground improvement method using sand piles according to claim 1.