JP2000180561A - Ground investigation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground investigation method for accurately, easily, and rapidly investigating stratum sections, ground strength in each stratum, and the like even under the ground at a depth being relatively shallower from the earth's surface and in the ground with a complex stratum structure. SOLUTION: A shell 10 with at least either one being selected from an accelerator, a load meter, and a pore water pressure meter in a tip part 12 is penetrated into the ground whose base is to be investigated, the penetration resistance of the shell 10 is measured at each stratum L for composing the ground, at the same time an elastic wave E is generated from the shell tip part 12 when the shell is penetrated, and either one of a direct wave D and a reflection wave R being reflected on each stratum boundary surface C out of the elastic wave E is measured by a vibration receiver 3, thus estimating the condition of stratum such as the ground strength and stratum section of each stratum L.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground survey method, and more particularly to a ground survey method applicable to a landfill or the like having a complicated stratum.

[0002]

2. Description of the Related Art Conventionally, a shallow layer reflection method is used for estimating a subdivision of a stratum constituting a ground, and an elastic wave is applied from a vibration source (eg, an air hammer) provided on the surface of the ground toward the underground. The elastic waves reflected mainly from the boundary surface of each layer are captured and measured by a geophone installed on the ground surface, and the obtained elastic wave waveform record is recorded in various waveforms such as filtering and amplification. A method of estimating an underground stratum division by performing processing and judging a boundary surface has been used in some cases.

[0003] Also, a cone penetration test method is used, in which a single-pipe or double-pipe pipe having a cone-shaped tip and a load cell or the like at the tip is penetrated into the ground. There is also a method of estimating the ground strength of each layer and the geological division of the ground by measuring the penetration resistance in each layer using a load cell provided at the tip.

[0004]

However, of the above-mentioned conventional methods, the shallow layer reflection method has the following problems.

[0005] That is, in the shallow layer reflection method, this method was originally developed for the purpose of exploring the approximate location of an underground resource such as an oil reservoir existing underground at a large depth of several thousand meters underground. As in the case of the ground survey conducted in the civil engineering field, it is necessary to conduct accurate and detailed survey and measurement of the boundary position of the stratum existing there in a relatively shallow depth of about several tens of meters underground. In order to use it for surveys that require accuracy, extremely high know-how is required for various waveform processing and arithmetic processing, and technical difficulties are involved.
There was a problem that increase in survey cost and decrease in survey efficiency were unavoidable.

[0006] Moreover, although it is possible to confirm the stratum boundary, it is difficult to accurately estimate the stratum depth.

Therefore, for example, when the shoaling method is applied to a liquefaction study by applying the shallow layer reflection method in a place where the stratum is complicated, such as a landfill, the measurement results obtained and the judgment results based on the results are as follows. I have to say that the reliability is poor.

Accordingly, the present invention has been made in view of such a conventional problem. Even if the ground is relatively shallow from the surface of the ground and the ground has a complicated stratum structure, the formation of the stratum and the location of each land can be improved. It is an object of the present invention to provide a ground survey method capable of accurately, simply, and quickly examining a ground strength in a layer.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and has a tube provided with at least one selected from an accelerometer, a load meter, and a pore water pressure gauge in a tip portion. The body penetrates into the ground to be subjected to the ground survey, measures the penetration resistance of the pipe in each layer constituting the ground, and generates an elastic wave from the tip of the pipe at the time of penetration of the pipe, whereby the elasticity is increased. By measuring at least one of the direct wave and the reflected wave reflected at each layer boundary surface with the geophone, it is possible to estimate the geological condition such as the ground strength and stratum classification of each layer. Features.

[0010]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 (a) is an explanatory view schematically showing a penetrating device for penetrating a pipe in the ground survey method of the present invention.
(B) is sectional drawing which showed the internal structure of the front-end | tip part of this pipe.

Here, as a penetrating device used for performing a penetration test for penetrating the pipe 10 into the ground, for example, as shown in FIG.
Penetration device 20 that enables continuous or intermittent vertical movement of zero, depth measuring device 21 that measures the penetration depth of pipe 10 to be penetrated, various measurement signals from penetration device 20 and depth measuring device 21, and the like. And a signal receiver 22 that receives the signal.

Further, the pipe body 10 in the ground survey method of the present invention has at least a length corresponding to a depth penetrating into the ground,
A rod portion 11 having a strength capable of withstanding the pushing force into the ground applied from the penetrating device 20; and a cone-shaped, mainly steel-shaped tip portion provided at the tip of the rod portion 11 and called a cone 12. The outer shape of the cone and the inside of the cone are shown in FIG.

That is, the cone 12 has a shape, for example,
A cone having a tip angle 12a of 60 ° and a bottom area 12b of about 10 cm ² is appropriate, and a filter 12c for measuring pore water pressure is provided in a collar shape on the peripheral surface. And partially measure the pressure. However, for the tip angle 12a and the bottom area 12b,
Particularly, the bottom area 12b is appropriately changed according to the hardness of the ground and the strength of the generated elastic wave. Although not shown, the cone 12 includes an accelerometer (not shown) for measuring the penetration state of the pipe body 10 into the ground, and a load cell for measuring the penetration resistance in each layer.

When actually performing a penetration test, the filter 12c is saturated in advance with a liquid such as degassed water or glycerin, and is temporarily covered with a rubber sleeve or the like until the filter 12c reaches the target depth to reduce the saturation. It is preferable to keep it. After such a pipe body 10 is mounted on the above-described penetrating device 20, and the penetrating device 20 itself is securely fixed to the ground by an anchor 23 or the like which is a fixing device so that the penetrating device 20 itself can withstand a penetrating reaction force, a test is performed. Start.

When actually performing the ground survey method of the present invention,
For example, various devices are arranged as shown in FIG. Here, (a) shows the situation immediately before the pipe body 10 penetrates into the ground in the ground survey method of the present invention, and (b) shows the situation where the pipe body 10 penetrates into the ground to perform measurement. FIG.

In the ground survey method of the present invention, the pipe 10
As the devices used other than the penetrating device, the elastic wave E generated continuously or at an arbitrary time from the cone 12 at the tip of the tube 10 when penetrating the tube 10, for example, by hitting or vibrating the tube 10. A group of geophones 30 for receiving ground G,
A receiving point switch 32 for switching the vibration of each of the geophones 31 according to the survey plan and the propagation state of the elastic wave with respect to the geophone group 30 and a waveform signal transmitted by the geophone 31 according to the elastic wave E received. An amplifier 33 that amplifies the signal to an appropriate level, an arithmetic processing / recording device 34 that performs arithmetic processing on the amplified waveform signal and performs appropriate recording, and monitors the above investigation status and records all investigation results as necessary. There is a monitor recorder 35 and the like.

As a procedure for performing a ground survey, the above-described devices are arranged on the surface G as shown in FIG. 1A, the cone 12 is directed underground, and the pipe 10 is set in the penetrating device 20. Here, an elastic wave E is generated from the cone 12 and a reflected wave R reflected from the boundary surface C of the stratum L is measured to determine the sensitivity of the group of geophones 30 and which geophone 31 receives the elastic wave E. Adjustment is suitable for subsequent measurements.

Next, the penetrating device 20 is operated to operate the cone 12.
With the tip as the tip, the pipe body is penetrated into the ground, and the penetration resistance according to the ground strength of each layer L at that time is measured,
Cone 1 from filter 12c under the pore water pressure in the ground
2 Pore water pressure transmitted to the inside is detected by various sensors. The speed at which the pipe 10 penetrates into the ground is preferably, for example, about 1.0 to 2.0 cm / s.

Further, in parallel with the penetration test using the tube 10, an elastic wave measurement test for receiving and capturing the elastic wave E generated from the vicinity of the tip of the tube 10 by the group of geophones 30 on the ground surface G is performed. When the pipe 10 penetrates, the elastic wave E generated by, for example, impact or vibration on the pipe 10 from the cone 12 at the tip of the pipe 10 is applied to the geophone G on the ground G according to a predetermined generation pattern.
1 to receive. The elastic wave E is composed of a reflected wave R that is emitted from the cone 12 and then reaches the stratum boundary C and is reflected there toward the ground surface G, and a direct wave D that is directly transmitted from the cone 12 to the ground surface G, For example, it is possible to know the stratum boundary surface C by receiving the reflected wave R, and to clearly know the depth position of the cone 12 by receiving the direct wave D.

The elastic wave E received by the vibration receiver 31 is transmitted as a waveform signal to the amplifier 33 and amplified to an appropriate level. After that, calculation processing such as removing unnecessary waveforms superimposed on the desired elastic wave waveform and estimating the position of the stratum boundary surface C from the elastic wave velocity and the response time to the geophone is performed by various computers and the like. This is performed by the device 34.

The measurement data of the penetration resistance and the like obtained as described above are recorded every moment and are provided for the subsequent analysis. May be estimated, or may be brought back from the site to perform a more detailed analysis.

Further, the tube shown in the present embodiment may be formed in advance so that at least one selected from an accelerometer, a load meter, and a pore water pressure gauge is provided inside the distal end portion thereof. Alternatively, a tip portion related to an end portion of a ready-made tube may be provided detachably.

[0024]

As described above in detail, according to the ground survey method of the present invention, a ground survey at a relatively shallow depth of about several tens of meters underground, such as a ground survey conducted in the field of civil engineering, etc. , Accurate and detailed survey and measurement of the boundary position of the existing stratum,
Various waveform processing and arithmetic processing of the measured elastic wave can be performed easily and efficiently, which leads to a reduction in research cost and an improvement in research efficiency.

In addition, it is possible to confirm the stratum boundary by measuring the reflected wave of the elastic wave reflected from the stratum boundary, and it is also possible to measure the direct wave directly traveling from the cone to the ground surface. It is also possible to accurately estimate the depth of each layer by measuring the cone penetration depth during the cone penetration test.

Therefore, for example, even when liquefaction is examined in a place where the stratum is complicated, such as a landfill,
A measurement result having both high reliability and high accuracy and a determination result based on the measurement result can be obtained.

[Brief description of the drawings]

FIG. 1A is an explanatory view schematically showing a penetrating device that penetrates a pipe in the ground survey method of the present invention, and FIG. 1B is a cross-sectional view showing an internal structure of a distal end portion of the pipe. is there.

FIG. 2 (a) shows a state immediately before a pipe is penetrated into the ground in the ground survey method of the present invention, and FIG. 2 (b) shows a state where a pipe is penetrated into the ground and measurement is being performed. FIG.

[Explanation of symbols]

 L formation layer E elastic wave D direct wave R reflected wave C formation layer boundary surface 10 pipe 12 tip part, 31 geophone

Claims (1)

[Claims] 1. A pipe having at least one selected from an accelerometer, a load meter and a pore water pressure gauge penetrates into the ground to be subjected to a ground survey into the inside of the tip portion to form a ground. While measuring the penetration resistance of the pipe in the layer, an elastic wave is generated from the tip of the pipe when the pipe penetrates, and at least one of a direct wave and a reflected wave reflected at each layer boundary surface among the elastic waves. A ground survey method that estimates the geological condition of each layer, such as the ground strength and stratum classification, by measuring either of these with a ground-based geophone.