JP2024003388A - Countermeasure pile against liquefaction and countermeasure method against liquefaction using therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a countermeasure pile using a substitute material having high permeability and capable of suppressing degradation of draining performance caused by mixing of sand, in place of conventional ballast, to thereby develop suppressing effect of liquefaction occurrence over a long period, and a liquefaction countermeasure method using the countermeasure pile.

SOLUTION: A countermeasure pile is used in a liquefaction countermeasure method of driving a countermeasure pile for a liquefaction countermeasure, composed of ballast in ground. The countermeasure pile is structured by using crushed shell in place of ballast.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

Application for application of Article 30, Paragraph 2 of the Patent Act Public Interest Incorporated Association Japan Geotechnical Society Kanto Branch 18th Japan Geotechnical Society Kanto Branch Presentation GeoKanto2021 <Abstract> 4th venue Disaster Prevention 5 Disaster Prevention 5-6 p. 44 Published on October 22, 2021 (Publications, etc.) Japan Geotechnical Society Kanto Branch 18th Japan Geotechnical Society Kanto Branch Presentation GeoKanto2021 <Collection of Abstracts> 4th Venue Disaster Prevention 5 Disaster Prevention 5-6 Online Presentation (ZOOM) Held on October 22, 2021

The present invention relates to a liquefaction countermeasure pile and a liquefaction countermeasure construction method using the countermeasure pile.

Many liquefaction damages have been confirmed and reported as an effect of past large-scale or medium-sized earthquakes.
Conventionally, the gravel drain construction method is generally known as one of the liquefaction countermeasure construction methods for suppressing damage caused by liquefaction. What is the gravel drain construction method? By driving anti-liquefaction piles made of crushed stone into soft ground, the drainage distance is shortened, and liquefaction is suppressed by the early dissipation of excess pore water pressure in the liquefied ground. This is a construction method that performs According to the gravel drain construction method, by driving the countermeasure pile into loosely piled sandy ground, liquefaction can be suppressed and prevented with simple construction and low cost.

In other words, the gravel drain construction method shortens the horizontal drainage distance by installing countermeasure piles made of crushed stone in sandy ground, suppressing the increase in pore water pressure that occurs during earthquakes, and preventing liquefaction. Out.

However, in recent years, earthquakes that have caused liquefaction have caused surrounding sand to get mixed into the gaps between the crushed stones that make up the countermeasure pile, narrowing the drainage performance range of the countermeasure pile made of crushed stone, and causing the countermeasure pile to The problem was that the water permeability of the area would decrease, and if another earthquake were to occur, the liquefaction suppression effect would decrease.

In other words, when constructing the conventional gravel drain method, when an earthquake that causes liquefaction occurs, the sand around the driven countermeasure piles gets mixed into the gaps between the crushed stones that make up the countermeasure piles. This caused a problem in that the drainage performance of the countermeasure pile deteriorated.

If the drainage performance of the countermeasure pile deteriorates and, for example, earthquakes that cause liquefaction occur repeatedly in a short or long period of time, the liquefaction suppressing effect of the countermeasure pile will further deteriorate, resulting in liquefaction. It was pointed out that there is a concern that the damage caused by natural disasters will become even more serious.

Japanese Patent Application Publication No. 2015-101938

Thus, the present invention was devised to solve the above-mentioned conventional problems, and it is possible to replace the conventional crushed stone with an alternative material that has high water permeability and can suppress the deterioration of drainage performance due to sand contamination. The object of the present invention is to provide a countermeasure pile that can be used as a pile material and exhibit a long-term liquefaction suppressing effect, and a liquefaction countermeasure construction method using the countermeasure pile.

In the past, there have been cases where many earthquakes that caused liquefaction were observed, and cases where multiple earthquakes that caused liquefaction occurred in a short period of time, including foreshocks, mainshocks, and aftershocks over several days. Even when seismic motions that cause liquefaction occur continuously, it is possible to prevent sand from entering the gap between the alternative material that makes up the countermeasure pile from the sand layer, which is the liquefaction layer, and thereby prevent liquefaction from occurring for a long period of time. Therefore, it is possible to provide countermeasure piles that can exhibit the effect of suppressing liquefaction, and a liquefaction countermeasure construction method using the countermeasure piles.

The present invention
A countermeasure pile used in a liquefaction countermeasure construction method in which a countermeasure pile made of crushed stone is driven into the ground,
The countermeasure pile was constructed using crushed shells as an alternative material to crushed stone.
It is characterized by
or
The construction using the crushed shells was constructed so that the relative density (Dr) was 60% to 80%.
It is characterized by
or
The crushed seashell has a particle size of 75 mm or less and has a flat plate shape.
It is characterized by
or
This is a liquefaction prevention construction method that involves building and constructing countermeasure piles to prevent liquefaction in the ground consisting of a liquefaction layer.
producing crushed seashells in the form of flat plates having a predetermined particle size composition by crushing seashells;
A countermeasure pile made of the generated crushed seashells is constructed in the liquefaction layer ground using a pile construction device,
The countermeasure pile was constructed by sending out the crushed shells in a stacked state in the ground of the liquefaction layer, and setting the relative density (Dr) of the sent out crushed shells to 60% to 80%.
It is characterized by
or
This is a liquefaction prevention construction method that involves building and constructing countermeasure piles to prevent liquefaction in the ground consisting of a liquefaction layer.
producing crushed seashells in the form of flat plates having a predetermined particle size composition by crushing seashells;
The countermeasure piles made of the generated crushed seashells are constructed using a pile construction device by burying a plurality of countermeasure piles in a distributed manner in a target area of the ground in the liquefaction layer,
The crushed seashells were sent out in a stacked state into the ground, and the relative density (Dr) of the sent out crushed seashells was set to 60% to 80%.
It is characterized by
or
This is a liquefaction prevention construction method that involves building and constructing countermeasure piles to prevent liquefaction in the ground consisting of a liquefaction layer.
producing crushed seashells in the form of flat plates having a predetermined particle size composition by crushing seashells;
The construction of countermeasure piles made of the generated crushed seashells using a pile construction device involves distributing a plurality of countermeasure piles over the target area of the ground in the liquefaction layer at the intersections of vertical and horizontal lines forming a grid pattern. It will be buried as much as possible,
The crushed seashells were sent out in a stacked state into the ground, and the relative density (Dr) of the sent out crushed seashells was set to 60% to 80%.
It is characterized by
or
Shell mats are formed in the exposed upper end openings of the countermeasure piles, which are buried and constructed in a dispersed manner, and are covered with crushed shells stacked so that the upper end openings are connected.
It is characterized by
or
The sending of the crushed seashells in a stacked state in the ground is performed by compacting the crushed shells in a horizontally stacked state.
It is characterized by this.

According to the present invention, crushed shells, which have high water permeability and can suppress the deterioration of drainage performance due to sand contamination, are used as countermeasure piles in place of conventional crushed stone, thereby preventing liquefaction over a long period of time. The present invention has the excellent effect of providing a countermeasure pile that can exert a suppressing effect and a liquefaction countermeasure construction method using the countermeasure pile.

It is a top view of a vibration device. FIG. 3 is a front view of the vibration device. It is a front view of an earthen tank. It is an external view of the vibrating device shown in the photograph. This is a plan view of the earthen tank. This is a photo showing piles containing crushed stone. This is a photo showing a pile that prevents crushed shells from entering. This is a photograph showing piles containing crushed stone and crushed shells installed in an earthen tank. This photo shows the sheet being removed from the countermeasure pile. This is a table showing the cases tested. It is a table showing experimental results. FIG. 1 is a diagram (1) showing a waveform of acceleration. It is a figure (1) showing the result of a pore water pressure meter. FIG. 2 is a diagram (2) showing a waveform of acceleration. It is a figure (2) showing the result of a pore water pressure meter. FIG. 3 is a diagram (3) showing a waveform of acceleration. It is a figure (3) showing the result of a pore water pressure meter. FIG. 4 is a diagram (4) showing a waveform of acceleration. It is a figure (4) showing the result of a pore water pressure meter. FIG. 5 is a diagram (5) showing a waveform of acceleration. It is a figure (5) which shows the result of a pore water pressure meter. FIG. 6 is a diagram (6) showing a waveform of acceleration. FIG. 6 is a diagram (6) showing the results of a pore water pressure meter. FIG. 3 is a diagram showing the relationship between period and acceleration when uniform vibration is applied for a certain period of time. FIG. 2 is an explanatory diagram showing a schematic configuration of a liquefaction countermeasure construction method. FIG. 2 is an explanatory diagram illustrating the configurations of a shell mat according to the present invention and a conventional gravel mat. FIG. 2 is an explanatory diagram showing the particle size distribution when shells are crushed with heavy equipment. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram illustrating the configuration of a countermeasure pile construction device according to the present invention.

The inventors of the present invention first believe that if the crushed shell 7 of a scallop or the like has a predetermined particle size, even if the crushed shell 7 is affected by vibrations such as an earthquake, the particles from the upper sand layer to the lower layer It has been confirmed that sand from the sand layer is difficult to mix into the crushed shell layer composed of crushed shells 7 with a large diameter.

Based on this confirmation, by using crushed seashells 7 such as scallops as a substitute pile material for the countermeasure pile 2, sand contamination from the sand layer around the pile into the countermeasure pile during liquefaction is suppressed, and sand contamination is suppressed. This invention is capable of suppressing the decline in drainage performance associated with water discharge.

That is, the present inventors compared the characteristics of sand being mixed into a countermeasure pile 2 made of crushed stone 6, which is a conventional countermeasure pile 2, and a countermeasure pile using crushed shells 7 as a substitute material for the crushed stone 6 due to earthquake motion. We evaluated the decrease in drainage performance due to sand contamination and verified the mechanism of the decrease in drainage performance. This revealed the effectiveness of the countermeasure pile 2, which can suppress the generation of excessive pore water pressure and thereby suppress the deterioration of drainage performance even in repeated earthquake motions, that is, the liquefaction prevention countermeasure pile 2 using crushed shells 7. That's what I did.
Furthermore, we have also invented a liquefaction countermeasure construction method that is effective in preventing liquefaction by using countermeasure piles 2 using the crushed shells 7 as pile materials.

Therefore, below, we will first describe the details of the experiment that revealed the effectiveness of the liquefaction prevention countermeasure pile 2 using crushed seashells 7, and then explain the liquefaction countermeasure that is effective in preventing liquefaction using the countermeasure pile 2. The invention of the construction method will be explained.

(Experiment to understand three-dimensional sand mixing characteristics using small vibrator 1)
In this experiment, we used a vibration device 1 and a pore water pressure gauge 4 to examine the acceleration settings, the increase in pore water pressure due to liquefaction, and the three-dimensional mixing of sand into the countermeasure pile 2 due to large-scale vibration, which caused a decrease in drainage performance. A qualitative evaluation was conducted. We also confirmed changes in the drainage performance of countermeasure pile 2 depending on the scale of the earthquake, and sand contamination characteristics due to differences in the relative density (Dr) of the sand layer, which is the liquefaction layer.

(Summary of vibration device experiment)
FIG. 1 shows a plan view of the vibration device 1, FIG. 2 shows a front view of the vibration device 1, and FIG. 3 shows a front view of the soil tank 3. The soil tank 3 has a height of 406 mm, a width of 780 mm, and a depth of 280 mm. FIG. 4 shows an external view of the vibrating device 1 shown in a photograph. FIG. 5 is a plan view of the soil tank 3. Countermeasure pile 2 consists of an acrylic plate with a thickness of 3 mm and a diameter of 50 mm, and a coarse geotextile rolled into a cylindrical shape, which are glued together and filled with crushed stone 6 or crushed seashells 7. Countermeasure pile 2 with crushed stone As shown in FIG. 6, a pile 2 for preventing crushed shells was installed in a soil tank 3 as shown in FIG. 7 (see also FIGS. 3 and 8).

Note that a sheet was wrapped around the countermeasure pile 2 to prevent dry sand from entering the gap between the countermeasure piles 2. For the water inlet, the pipe is cut in half and is long enough to reach the bottom of the soil tank 3. Gauze was packed at the tip of the pipe to prevent sand from flowing back from the water inlet. The pore water pressure gauge 4 was installed between the two countermeasure piles 2 containing crushed stone 6 and the countermeasure pile 2 containing crushed shells at positions 50 mm and 100 mm from the ground surface, respectively (see Figure 3).

(Physical properties of sample)
The sample is a mixture of crushed stones No. 5, No. 6, and No. 7 (see Figure 6) adjusted to a grain size of 4.75 to 19 mm for the countermeasure pile 2 of crushed stone 6, and a sample prepared by heavy machinery crushing for the countermeasure pile 2 of crushed shell 7. Crushed scallop shells 7 from Aomori Prefecture were used (see Figure 7), Toyoura sand was used to generate the liquefied layer and the non-liquefied layer, and these three types of samples were used.

(Experimental procedure)
A soil tank 3 is attached to the vibration device 1, and a pore water pressure gauge 4 is installed. Measure the mass of the sample to be used, and shovel the measured dry Toyoura sand into the soil tank 3 to create a non-liquefaction layer with a relative density Dr = 69.8% (ρ _d = 1.58 g/cm ³ ). Then, use a sand compaction vibrator to compact the soil until the non-liquefied layer reaches a height of 100 mm from the bottom of the soil tank 3.

Next, the countermeasure pile 2 containing crushed stone 6 packed with crushed stone 6 at a relative density Dr = 60.2% (ρ _d = 1.56 g/cm ³ ) and the crushed scallop shell 7 were packed at a relative density Dr = 59.9% (ρ d = 1.56 g/cm 3 ). A countermeasure pile 2 containing crushed seashells 7 packed with _d = 0.909 g/cm ³ ) was installed as shown in the drawing in FIG. 3 and the photographic image shown in FIG. 8.

Thereafter, dry sand was placed in the soil tank 3 using a funnel and uniformly dropped in the air to a relative density of Dr = 29.9% or Dr = 48.8% (ρ _d = 1.47 g/cm ³ , ρ _d = 1.52 g/cm ³ ) and compacted slowly.
When adding sand by the aerial drop method, a bag was placed over the countermeasure pile 2 to prevent dry sand from getting mixed into the countermeasure pile 2. Next, we inserted a hose connected to the water tank into the water inlet pipe and started injecting water (see the photographic video in Figure 4).

In order to prevent the sand layer, which will become the liquefaction layer 5, from vibrating and causing boiling in an unsaturated state, water was slowly poured for about 2 hours until the water level reached the ground surface to saturate the sand layer. After water was poured, a hose connected to a water vacuum cleaner was inserted into the pipe to drain the water, and the water level was lowered to a non-liquefied layer (if the sheet was pulled out while the water level was at ground level, the impact of pulling it out would cause This is to prevent liquefaction or to prevent sand from getting mixed into the countermeasure pile 2).

After that, the sheet to prevent dry sand from being mixed in was slowly pulled out (see the photo in Figure 9), water was poured again until the water level reached the ground surface, and then the vibration device 1 was set at a frequency of 5.1 Hz and 10 waves. , vibration time was set to 2 seconds, acceleration was set for each case, and horizontal sine wave vibration was applied.

After the vibration, the water in the soil tank 3 was drained using a water vacuum cleaner, the surrounding sand was removed to prevent sand from getting into the countermeasure pile 2, and the countermeasure pile 2 was taken out. The mixed sand, crushed stones 6, and crushed shells 7 in the countermeasure pile 2 were taken out into a container and dried in a drying oven (110±5°C) for 24 hours.

After drying in the drying oven, the sand, crushed stones 6, and crushed shells 7 were sieved, and the mass of the sand was measured. Then, the average saturated hydraulic conductivity due to sand contamination was calculated, and the deterioration in drainage performance of Pile 2 containing 6 pieces of crushed stone and Pile 2 containing 7 pieces of crushed shells when sand was mixed was evaluated.

(Experimental case)
Figure 10 shows an experimental case. In the experimental case shown in FIG. 10, the wave number was 10 waves, the vibration frequency was 5.2 Hz, the vibration time was 2 seconds, the number of vibrations was 1 time, and the acceleration was set for each experimental case to give a sinusoidal horizontal vibration. We compared and confirmed the amount of sand mixed in due to the influence of the magnitude of the earthquake due to the difference in the magnitude of the maximum acceleration.

In actual construction, driving countermeasure pile 2 compacts the ground around countermeasure pile 2, so in this experiment, the loosely compacted relative density Dr = 29.9% (ρ _d = 1.47 g /cm ³ ) and the surrounding ground was compacted by driving two countermeasure piles, we conducted an experiment with a relative density Dr = 48.8% (ρ _d =1.52 g/cm ³ ). Therefore, the amount of sand mixed in due to the difference in relative density (Dr) of the liquefaction layer 5 was also compared.

(Experimental results and discussion)
The experimental results are shown in FIG. The basic mixed amount before applying vibration is: crushed stone: 86.6 g, crushed shells: 81, 82 g when relative density Dr = 29.9%, crushed stone: 93.40 g, crushed shells when relative density Dr = 48.8% :96.73 g.

Case A has a maximum acceleration of 101 gal (acceleration waveform: see Figure 12, pore water pressure gauge results: see Figure 13), case B has a maximum acceleration of 149 gal (acceleration waveform: see Figure 14, pore water pressure gauge results: see Figure 15) , caseC has a maximum acceleration of 188 gal (acceleration waveform: see Figure 16, pore water pressure gauge results: see Figure 17), caseD has a maximum acceleration of 55 gal (acceleration waveform: see Figure 18, pore water pressure gauge results: see Figure 19) ), caseE has a maximum acceleration of 95 gal (acceleration waveform: see Figure 20, pore water pressure gauge results: see Figure 21), caseF has a maximum acceleration of 192 gal (acceleration waveform: see Figure 22, pore water pressure gauge results: Figure 23) ).

In cases B, C, and F, the pore water pressure increases, indicating that liquefaction has occurred. However, in the case of liquefaction, the value of the pore water pressure gauge GL-10cm would normally rise to 10 g/cm ² , but the experimental results showed it to be 5 to 8 g/cm ² . It is conceivable that this result occurred because the soil tank 3 was not completely saturated.

In cases A, D, and E, the pore water pressure did not increase, indicating that liquefaction did not occur. The amount of sand mixed in when there is no liquefaction does not change much compared to the basic amount, so it is thought that sand will not be mixed in if it is a small earthquake that does not cause liquefaction.

Comparing the amount of sand mixed in (crushed stone: 128.05 g, crushed shells: 137.12 g) due to manually applied vibration (1 vibration) and the experimental results of this experiment, it was found that 6 pieces of crushed stone and 2 piles were crushed. Since the amount of mixed sand in both shells 7 and 2 has a maximum acceleration of 149 gal, and is less than the mixed amount of sand in case C, which has a maximum acceleration of 188 gal, in the manual experiment, vibrations with a maximum acceleration of 149 to 188 gal were detected. It is possible that

Although acceleration is not a value representing seismic intensity, FIG. 24 shows the relationship between period and acceleration when uniform vibration is applied for a certain period of time.
From this relationship, in this experiment, vibration was applied using a small vibration device 1 with a constant acceleration, period (T = 0.196 seconds), and amplitude, so the estimated seismic intensity was approximately 5 lower for cases B, C, and F. I understand.

In the case of an earthquake that causes liquefaction with a seismic intensity of less than 5, crushed shells 7 can be used as the liquefaction countermeasure pile 2 to prevent the deterioration of drainage performance due to the mixing of sand caused by vibrations during liquefaction. It was confirmed from the experimental results shown in FIG. 11, such as the value of the sand mixing ratio, that it can be made smaller than when using the sand.
It was also confirmed that by using crushed shells 7 for the liquefaction countermeasure pile 2, it would be possible to cope with repeated earthquakes and exert a long-term liquefaction suppressing effect.

Since the maximum acceleration of caseC, 188gal, and the maximum acceleration of caseF, 192gal, are about the same acceleration, when comparing the sand contamination due to the difference in the relative density (Dr) of the liquefaction layer 5, it is found that the relative density Dr = 29.9% and the sand is loose. The amount of sand mixed in compacted case C is crushed stone: 136.26 g, crushed shell: 139.67 g, whereas the mixed amount of sand in case F, compacted with relative density Dr = 48.8%, is crushed stone: 124. 00g, crushed shells: 113.07g.
From this, it was confirmed that the looser the sandy ground, the more sand gets mixed in.

In addition, in this experiment, the results are shown by comparing the amount of sand mixed in, the sand mixing rate, and the hydraulic conductivity of Pile 2 containing 6 crushed stones and Pile 2 containing 7 crushed shells. Pile 2 containing 7 shells was superior, and it was confirmed that the use of Pile 2 containing 7 crushed shells could exert a long-term liquefaction suppressing effect.
In particular, when comparing the sand contamination rate, it was confirmed that the difference between Pile 2 with 6 pieces of crushed stone and Pile 2 with 7 pieces of crushed seashells was significantly smaller in all cases. can.

Here, the value of the permeability coefficient (m/sec) is determined by how much the voids of the pile 2 containing crushed shells 7 and the pile 2 containing crushed stones 6 are filled with incoming sand.

That is, it is assumed that sand has entered the void. In that case, even if the amount of sand mixed in is the same, the amount of voids that the pile 2 with 6 crushed stones and the pile 2 with 7 crushed shells have is significantly different, and the pile 2 with 7 crushed shells has The amount of voids is overwhelmingly larger. Therefore, even if the same amount of sand is mixed into the voids, the water permeability of the crushed shell 7 prevention pile 2 does not decrease.

As a result, it can be seen from the results shown in Figure 11 that in all cases A to F, the value of the sand contamination rate is overwhelmingly smaller for the countermeasure pile 2 containing 7 crushed shells, and its water permeability is It can be recognized that performance, in other words, drainage performance, does not deteriorate.

(summary)
The vibration given by the vibration device 1 is considered to be on the same scale as an earthquake that causes liquefaction, and by using the crushed shells 7 as the liquefaction countermeasure pile 2, it is possible to reduce the amount of sand mixed in due to the vibration during liquefaction. The results showed that the deterioration of the drainage performance of Countermeasure Pile 2 could be suppressed and the liquefaction suppressing effect could be exerted over a long period of time.

Furthermore, it was confirmed that the lower the relative density (Dr) of the sandy ground of the liquefaction layer 5, the more easily sand contamination occurs. The actual problem is that the surrounding ground is compacted due to confining pressure generated in the ground due to driving of countermeasure pile 2, embankment, and overload from building structures, and sand gets mixed into countermeasure pile 2 due to vibration. It is thought that the trend of decline in drainage performance accompanying this will become even more gradual.

Next, the invention of the liquefaction countermeasure construction method using the countermeasure pile 2 containing crushed seashells 7 according to the present invention will be explained.
As shown in FIG. 25, the ground on which countermeasure piles 2 are constructed to take measures to prevent liquefaction is the ground consisting of a liquefaction layer 5. The ground consisting of the liquefaction layer 5 consists of sandy soil in a water-containing state, and during an earthquake, saturated water flows between the sand grains due to vibration, and the intergranular bonds of the sand grains are broken, causing the soil to behave like a liquid. This is considered to be the layer that loses its supporting capacity.

When the liquefied layer 5 liquefies, the water pressure of the fluidized pore water rapidly increases, and excess pore water is generated.
In the present invention, as shown in FIG. 25, countermeasure piles 2 for liquefaction prevention measures are constructed in the ground consisting of the liquefaction layer 5, and a liquefaction prevention construction method is implemented.
First, the countermeasure piles 2 for preventing liquefaction are preferably constructed by burying a plurality of piles scattered over the entire area of the liquefaction layer 5.

Here, the liquefaction countermeasure pile 2 used in the gravel drain construction method, which is one of the liquefaction countermeasure construction methods, is used to drain excess pore water in the liquefaction layer 5 upward during an earthquake. It is constructed as a columnar body buried in the formed layer 5 in a substantially vertical direction.

That is, a plurality of countermeasure piles 2 are buried in the entire target area of the ground in the liquefaction layer 5 at predetermined intervals (horizontal intervals), for example, in a grid pattern (see FIG. 26). .
Depending on the area to be buried, it may be divided into a plurality of equilateral triangles and dispersed, and the countermeasure piles 2 may be buried at the vertices of the triangles.

As mentioned above, the countermeasure pile 2 for liquefaction countermeasures used in the conventional gravel drain construction method is a countermeasure pile 2 containing crushed stone 6. However, the present inventors focused on seashells that exist in large quantities in Japan, which is an island nation. When shells are crushed, most of them become flat and flat. It never becomes block-shaped. The shell originally has more voids inside than the crushed stone 6. By paying attention to the characteristics of these shells, we came up with the idea of using the crushed shells 7 as the filling material for the countermeasure piles 2.

We believe that shells with many voids and high drainage capacity are suitable for the countermeasure pile 2 for liquefaction prevention measures that require good drainage performance, and we crush the shells with a roller using heavy equipment and crush them into the specified size. A countermeasure pile 2 made of crushed shells 7 having a grain size is used. By crushing with heavy equipment, crushed shells 7 having a particle size accumulation curve (particle size distribution) as shown in FIG. 27 can be easily produced. It is possible to easily obtain crushed seashells 7 having a particle size that is effective as the pile 2 for preventing crushed seashells 7 from entering.

After obtaining a large amount of crushed seashells 7 having a predetermined particle size through the above process, a plurality of piles 2 containing crushed seashells 7 are constructed in the area where liquefaction prevention measures should be taken, that is, in the area of the ground of the liquefaction layer 5. Get to work.
As a device for burying and constructing the countermeasure pile 2, it is preferable to use an excavation device 12 shown in FIG. 28, such as a so-called sand compaction pile.

The excavation device 12 is provided with a cylindrical excavation tool 10 as a cutting member. This excavating tool 10 is provided with a crushed shell inlet 11 on its upper end side, and is configured such that crushed seashells 7 of an appropriate particle size can be introduced into the hollow part of the excavating tool 10 from the crushed shell inlet 11. ing.

Further, an opening 13 for sending out crushed shells is provided at the lower end of the digging tool 10, and the crushed shells 7 stored in the hollow portion can be sent out into the ground through this opening 13.

The process of sending the crushed shells 7 underground and constructing the pile 2 to prevent the crushed shells 7 from entering is as shown in FIG. It is sent underground through the opening 13. The locus of movement of the lower end of the excavating tool 10 at that time is as shown in FIG. The crushed shells 7 sent into the ground must be compacted to a predetermined degree of compaction. Therefore, in order to achieve a predetermined degree of compaction, the crushed shells 7 are compacted by applying vibrations or the like when being sent underground. The degree of compaction of the crushed shell 7 can be expressed by the relative density (Dr) of the crushed shell 7. The relative density (Dr) of the crushed shell 7 required here is a numerical value of 60% to 80%.

The crushed seashells 7 constituting the countermeasure pile 2 have many voids inside and are in a flat plate-like shape with a predetermined grain size in the crushed state. Therefore, when the above-mentioned vibration etc. are applied, the crushed shells 7 are arranged vertically in the direction of the outer circumferential surface of the countermeasure pile 2 so as to be located in a direction parallel to the vertical surface of the countermeasure pile 2. . Therefore, the arrangement of the crushed shells 7 further prevents sand from entering from the liquefied layer 5.

In addition, around the axial direction of the countermeasure pile 2, many crushed seashells 7 having a flat plate-like shape are piled up horizontally in a layered state. In combination with the crushed shells 7 vertically arranged in the direction of the outer circumferential surface of the countermeasure pile 2, it is possible to reliably prevent sand from entering from the liquefaction layer 6 outside.

In the conventional countermeasure pile 2 containing crushed stones 6, not all of the crushed stones 6 have a flat flat shape. Most crushed stone shapes are block-shaped.

However, if the seashells are crushed, all the crushed seashells 7 will almost automatically become flat and flat. Therefore, if this flat-shaped crushed seashell 7 is used as the pile material for the countermeasure pile 2, the intrusion of sand will be better than the countermeasure pile 2 containing crushed stone, combined with the fact that the shell has more voids inside than the crushed stone. This makes it possible to prevent the deterioration of the drainage performance of the countermeasure pile 2.

In addition, a spiral digging blade is provided on the outer circumferential surface of the drilling tool, and by rotating it while penetrating, it excavates underground in a cylindrical shape, and after excavating to a predetermined underground depth, the drilling tool is inserted into the excavated hole. It is also possible to use a construction method in which crushed shells 7 are dropped while pulling out shells 10 to spread the shells. However, by applying vibration during this dropping, the crushed shells 7 to be spread can be made to have a predetermined compaction degree, in other words, a relative density (Dr) consisting of a predetermined numerical value. Here again, the optimal relative density (Dr) of the filled crushed shells 7 is preferably 60% to 80%.

The construction of the piles 2 to prevent crushed shells 7 is carried out by dispersing them, for example, at the intersections of vertical and horizontal lines forming a grid in the ground of the liquefaction layer 5 where liquefaction prevention measures are to be taken, and burying them in a scattered manner. Constructed.

The upper end opening surface of the pile 2 for preventing crushed seashells 7 buried in the liquefaction layer 5 is exposed to the ground surface, but the exposed upper end opening surface is covered with crushed seashells 7 and covered. becomes. This is the formation of a so-called shell mat 9. By forming the shell mat 9 composed of the crushed shells 7, excess pore water that has passed through the inside of the pile 2 for preventing crushed shells 7 and has risen can be drained horizontally very smoothly. In other words, water can be drained onto the ground surface at a predetermined location. Here, the shell mat 9 of the present invention is formed of crushed shells 7 as described above, and is not formed into a planar mat shape of crushed stones 6 as in the conventional case, but is structured into a lattice mat shape as shown in the figure. There is.
With this configuration, faster and smoother horizontal drainage can be achieved.

In addition, referring again to the construction of the countermeasure pile 2 using the crushed shells 7, the crushed shells 7 are placed on the interface between the outer peripheral surface of the excavation hole and the ground of the liquefaction layer 5 so that the crushed shells 7 are parallel to the interface. The crushed seashells 7 are vibrated and released so as to stand upright, and are compacted. Further, near the axial direction of the countermeasure pile 2, the crushed shells 7 are released and compacted so as to be piled up perpendicular to the boundary surface.

By filling in this way, even if there is an earthquake that causes liquefaction, the crushed shells 7 standing on the boundary surface can further firmly prevent sand from entering from the liquefaction layer 5. Also, near the axial direction where the crushed shells 7 are stacked and compacted perpendicular to the boundary surface, the crushed shells 7 stacked in layers further prevent sand from entering from the liquefied layer 5. This can be prevented.

Therefore, due to the countermeasure pile 2 containing a plurality of crushed shells 7 built in the liquefaction layer 5, excess pore water flows into the countermeasure pile 2 during an earthquake that causes liquefaction, and The shell mat 9 is discharged to a desired location on the ground surface. Therefore, in the liquefaction layer 5, an increase in the excess pore water pressure ratio is suppressed, and liquefaction is prevented.

In addition, it has been pointed out that if excess pore water in the liquefaction layer 5 is drained into the countermeasure pile 2 during an earthquake, the liquefaction layer 5 may condense and cause ground subsidence. If a paved road or a ground improvement layer is formed above layer 5, it is thought that even if some ground subsidence occurs, significant ground subsidence can be prevented from occurring.

The present invention is applicable not only to the drain construction method as a liquefaction countermeasure construction method, but also to other liquefaction countermeasure construction methods such as the compaction construction method.

1 Vibration device 2 Countermeasure pile 3 Soil tank 4 Pore water pressure gauge 5 Liquefaction layer 6 Crushed stone 7 Crushed shells 9 Shell mat 10 Excavation tool 11 Crushed shell inlet 12 Drilling device 13 Opening

Claims (8)

A countermeasure pile used in a liquefaction countermeasure construction method in which a countermeasure pile made of crushed stone is driven into the ground,
The countermeasure pile was constructed using crushed shells as an alternative material to crushed stone.
A liquefaction prevention pile characterized by:
The construction using the crushed shells was constructed so that the relative density (Dr) was 60% to 80%.
The liquefaction prevention pile according to claim 1, characterized in that:
The crushed seashell has a particle size of 75 mm or less and has a flat plate shape.
The liquefaction prevention pile according to claim 1 or claim 2, characterized in that:
This is a liquefaction prevention construction method that involves building and constructing countermeasure piles to prevent liquefaction in the ground consisting of a liquefaction layer.
producing crushed seashells in the form of flat plates having a predetermined particle size composition by crushing seashells;
A countermeasure pile made of the generated crushed seashells is constructed in the liquefaction layer ground using a pile construction device,
The countermeasure pile was constructed by sending out the crushed shells in a stacked state in the ground of the liquefaction layer, and setting the relative density (Dr) of the sent out crushed shells to 60% to 80%.
A liquefaction prevention construction method using countermeasure piles for liquefaction prevention measures, which is characterized by the following.
This is a liquefaction prevention construction method that involves building and constructing countermeasure piles to prevent liquefaction in the ground consisting of a liquefaction layer.
producing crushed seashells in the form of flat plates having a predetermined particle size composition by crushing seashells;
The countermeasure piles made of the generated crushed seashells are constructed using a pile construction device by burying a plurality of countermeasure piles in a distributed manner in a target area of the ground in the liquefaction layer,
The crushed seashells were sent out in a stacked state into the ground, and the relative density (Dr) of the sent out crushed seashells was set to 60% to 80%.
A liquefaction prevention construction method using countermeasure piles for liquefaction prevention measures, which is characterized by the following.
This is a liquefaction prevention construction method that involves building and constructing countermeasure piles to prevent liquefaction in the ground consisting of a liquefaction layer.
producing crushed seashells in the form of flat plates having a predetermined particle size composition by crushing seashells;
The construction of countermeasure piles made of the generated crushed seashells using a pile construction device involves distributing a plurality of countermeasure piles on the intersections of vertical and horizontal lines forming a grid pattern for the target area of the ground in the liquefaction layer. It will be buried as much as possible,
The crushed seashells are sent out in a stacked state into the ground, and the relative density (Dr) of the sent out crushed seashells is set to 60% to 80%.
A liquefaction prevention construction method using countermeasure piles for liquefaction prevention measures, which is characterized by the following.
Shell mats are formed in the exposed upper end openings of the countermeasure piles, which are buried and constructed in a dispersed manner, and are covered with crushed shells stacked so that the upper end openings are connected.
A liquefaction prevention construction method using the liquefaction prevention countermeasure pile according to claim 5 or claim 6.
The sending of the crushed seashells in a stacked state in the ground is performed by compacting the crushed shells in a horizontally stacked state.
A liquefaction prevention construction method using the liquefaction prevention countermeasure pile according to claim 5, claim 6, or claim 7.