JPH02225711A - Liquefaction preventive construction of foundation ground - Google Patents

Abstract

PURPOSE:To make it possible to disperse pore water pressure in the ground which is going to be boosted driving drain columns into the sand layer ground likely to liquefy, and flowing out the pore water through the drain columns in case of an earthquake. CONSTITUTION:Foundation piles 2 are driven into the foundation ground 1, and drain columns 3 having high permeability consisting of materials such as gravel, crushed stone, thrown stone and the like are arranged scatteredly to drive from the vicinity of the ground surface to the bottom of the sand layer 5 which is likely to liquefy. Then, the heads of the drain columns 3 is widened in diameters in the vicinity of the ground surface, and projected parts 4a are formed in the horizontal direction. In case of an earthquake, the pore water in the ground is flown out through the drain columns 3 and, at the same time, it is dispersed to the projected parts 4a. According to the constitution, the occurrence of excessive pore water pressure or the liquefaction of the peripheral ground of the foundation piles 2 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves sand layered ground that is easily liquefied, obtains a safe foundation ground even in the event of an earthquake, and improves the liquefaction of the foundation ground in order to construct foundation piles with large bearing capacity. Regarding prevention structure.

There are already many known cases in which the ground of a sand tank liquefies during an earthquake and loses its supporting capacity, resulting in structures sinking and collapsing. The cause of the above liquefaction is that the pore water pressure in the sand layer saturated with water increases rapidly due to shear stress during an earthquake.
As a result, excess pore water pressure is generated and the bearing capacity of the sand layer ground is lost.Generally, depending on the density of the ground, grain size, groundwater level, etc., it is said that water-saturated loose sand layer ground or fine sand layer It is said that there is a risk of liquefaction in the ground.

Conventionally, as a measure to prevent the above liquefaction, sand piles have been constructed using the Comboser method, Vibro method, etc. for the purpose of increasing the relative density of the sandy ground (increasing the N value) or replacing it with sand with a grain size that is difficult to liquefy. The commonly used method is to improve the ground by driving sand piles, but this method of driving sand piles does not prevent or dissipate the sudden increase in pore water pressure that occurs during earthquakes, There is a risk of liquefaction.

In particular, terrestrial structures are directly based on the base 1i! 3 (Do not drive resistors! Whether it is a single or pile foundation, it is supported by the supporting capacity of the foundation ground, but if the sand layer ground that is at risk of liquefaction during an earthquake becomes liquefied, the support of the foundation ground will be lost. This will cause the foundation pile to lose its bearing capacity.

Therefore, the present invention proposes that the occurrence of excessive pore water pressure, which is the main cause of liquefaction, is caused by the hydraulic conductivity of the ground (sand:
ee s Gravel and gravel: xo-'~10-2es+/5ee
), focusing on the fact that excessive pore water pressure does not occur in gravel or gravel with good water permeability, we installed a predetermined length of water-permeable material made of gravel, fine stone, slag, or other material in a sandy ground that is at risk of liquefaction. The purpose of this invention is to prevent and dissipate a sudden increase in pore water pressure during an earthquake by using the high water permeability of these drain columns. By providing an overhang at the top of each drain column that is made of the same material as the drain column and that extends laterally from the drain column, it is possible to more effectively dissipate the pore water pressure that tends to rise rapidly during an earthquake. It is characterized by further enhancing the effect of preventing liquefaction of the foundation ground and the liquefaction of the ground around the foundation piles, thereby ensuring the safety of the structure, and also preventing the outflow of pore water to the ground and masuda. It is something to do.

Next, specific embodiments of the present invention will be described based on the drawings.

Example (Il Figures 1 and 2 show an example in which the base li!! type is a direct base II (solid foundation) that does not use drag, and the foundation ground (1) at the bottom of the above-ground structure is Drain columns (3) that reach the lower part of the sand layer (5) that is at risk of liquefaction are installed in a scattered manner within a range that substantially surrounds the structure, and the heads of the drain columns (3) are installed. Expanded diameter using the same material,
The enlarged diameter portion is formed as a laterally extending portion (4a). In this case, since the overhang is provided, excess pore water pressure generated during an earthquake can be more effectively dissipated, and
It can prevent pore water from flowing to the ground and causing masuda. The upper end of the drain column (3) is provided at or near the ground surface.

Example (n) Figures 3 and 4 show examples of pile foundations in which the foundation type is piles, excluding the part where the foundation piles (2) are driven into the foundation ground (1) at the bottom of the structure. Drain pillars (3) each having a diameter-expanded overhang (4a) at the top are scattered and installed in a sand layer that is at risk of liquefaction.

Embodiment (III) FIG. 5 shows a case in which drain columns (3) are placed at equal intervals (a) in Examples CI) and (II).

Example (IV) Figure 6 shows an example in which the drain columns (3) are arranged in a pattern in the ground around the foundation pile (2) in Examples (1) and (II). 2) and the drain pillar (3) are placed closer together than the distance between the other drain pillars (3) and (3). In this case, it is more effective in preventing liquefaction of the ground around the foundation piles.

Example (V) Figures 7 and 8 show the overhanging part (4a) due to the enlarged head diameter of the drain column (3) cast in the foundation ground (1) in Examples [1] to (IV). In place of this, an embodiment is shown in which a wall-shaped (groove-shaped) projecting portion (4b) extending laterally so as to connect the head is provided.

In this case, since the respective drain columns (3) are connected by the wall-like overhang (4b), water can be easily collected and drained, and the effect of dissipating excess pore water pressure is also great.

Example (Vr) Figures 9 and 10 show that in Example (V), drain columns (3) are placed and placed in the ground (l'') equivalent to the lower part of the structure, and each drain This is an embodiment in which a wall-like overhang part (4b) connecting the upper part of the column (3) in the peripheral area of the ground surface is formed in a mesh shape on the inner metal body of the lower part of the ground (l'),
In particular, as shown in the figure, the end (4b') of the overhang (4b)
) is derived outside the ground equivalent to the upper part of the structure ffi (1'), the effect of Example (V) is further enhanced and the ground bearing capacity is increased.

Example [■] Figures 11 to 13 show drain pillars (3) installed in the same manner as in Examples (I) to EV) as an overhang extending laterally from the upper part of the drain pillars at the periphery of the ground surface. (3) Connect the layered overhang (4c) to the foundation ground (1)
An example is shown in which it is formed on the entire surface, and in this case as well, collection and drainage of pore water is easy, and the effect of dissipating excess pore water pressure is even greater, and the bearing strength of the ground is increased.

As shown in Figures 14 to 16, the above drain pillar (3) is constructed by attaching a lid (It) at its tip that can be closed when driven in and opened by hanging under its own weight when pulled out. The provided casing (10) is passed through a vibration exciter (12) such as a vibrohammer.
) at a predetermined location in the ground, and after driving to a predetermined length, gravel, fine stone, slag, and other materials for constructing drain columns (13) are poured into the casing (10).
), and the drain pillar (3) is properly tightened.
is created in the ground. (14) indicates the input port for materials for constructing drain pillars. In addition, Example (1) ~
As shown in (IV), the drain column (3) provided with an overhang (4a) due to an enlarged head diameter can be created by using a casing (10') whose upper part is enlarged in diameter instead of the above-mentioned casing OO). 17), and as in Example (V), the wall-shaped (groove-shaped) overhang (4b) that connects the upper part of the drain column (3) is made by cutting a thin groove with an excavator after the drain column is constructed, and then inserting it into the groove. It can be created by inputting the materials for constructing drain pillars.

Furthermore, the cross-sectional shape of the drain column (3) in the present invention is
The casing may be either circular or rectangular, and a casing with a cross-sectional shape suitable for each may be used.

The present invention has the above configuration, and even if the ground is subjected to shear stress during an earthquake and the pore water pressure does not rise rapidly, the present invention provides water permeability far more than sand to the sand layer ground that is at risk of liquefaction of the foundation ground. Drain pillars made of good quality gravel or gravel (
3) is installed, the pore water flows into the drain column (
The pore water pressure that is drained through the drain column (3) and is about to rise rapidly dissipates immediately, especially since the upper part of the drain column (3) is provided with a laterally extending overhang made of the same material. Excess pore water pressure can be dissipated quickly, reliably, and effectively through water collection and drainage effects, and the occurrence of excess pore water pressure itself during an earthquake can be reliably prevented, and liquefaction of the foundation ground can be completely prevented. In addition, while accelerating the flow of pore water within the drain column that occurs during the dissipation process, it can also prevent water from gushing out onto the ground, making it possible to obtain a foundation with completely safe bearing capacity even in the event of an earthquake. , it has the following excellent effects not found in conventional methods.

■ Conventional methods of preventing liquefaction by compacting or replacing sandy ground leave a risk of liquefaction due to the strength of an earthquake, but in the present invention, as described above, the drain pillar and its upper part extend laterally. Since it prevents the rise in pore water pressure itself, there is no risk of liquefaction regardless of the strength of the earthquake, and the ground has sufficient supporting capacity, ensuring that the structure remains completely intact even in the event of an earthquake. It is.

■ Drain pillars with good water permeability are scattered over almost the entire surface of the foundation ground at the bottom of the structure, which is directly affected by an earthquake, so there is no risk of liquefaction of the underlying ground and it is safe.

■ By constructing drain pillars in the ground, the surrounding ground is compacted, and the rigidity of the foundation ground is increased by replacing the particle size, and the drain pillars themselves are less susceptible to liquefaction, which has the effect of improving the ground.

■ In particular, due to the presence of an overhang due to the enlarged diameter of the upper part of the drain column or a wall-like overhang that connects the upper parts of the drain column, pore water may flow out to the ground or leak when the pore water pressure is dissipated through the drain column. pore water pressure is more effectively dissipated, and the effect of preventing ground liquefaction is further enhanced. In particular, when the end of the wall-like overhang is led out to the outside of the site ground, it is easy to collect and drain water to the outside of the structure.

■ If drain columns are placed at equal intervals, the dissipation effect of excess pore water pressure will be uniform, and the ground beneath the structure will be uniformly stabilized. In addition, if drain columns are placed densely around the foundation piles,
It is more effective in preventing liquefaction of the ground around the piles, that is, the ground within the underground stress range around the foundation piles that support the structure load.

■ If overhangs are provided in a layered manner all over the ground around the ground surface so as to connect the drain column heads, the above effect (■) will be even greater and the bearing capacity of the ground will also increase.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, and FIGS. 1 and 2 are a schematic plan view and a vertical cross-sectional view showing an embodiment of a direct foundation without using piles, and FIGS. 3 and 4 are piles. A schematic plan view and a longitudinal cross-sectional view showing an example of the foundation; FIG. 5 is a schematic plan view showing an example in which drain columns are arranged at equal intervals;
Fig. 6 is a schematic plan view showing an example in which drain columns are densely arranged around the foundation pile, and Figs. 7 and 8 show an example in which a wall-like overhang is provided to connect the upper part of the drain column. A schematic plan view and a vertical sectional view, FIGS. 9 and 10 are a schematic plan view and a vertical sectional view, and FIG. - Fig. 13 is a schematic plan view when a layered overhang is provided, and a vertical cross-sectional view taken along lines 12-12 and 13-13 in the figure, and Figs. 14 to 17 show a method of constructing a drain pillar. It is a longitudinal cross-sectional view to illustrate. (1)...Ground, (lo)...Lower part of the structure) ■This ground, (2)...Foundation pile, (3)
......Drain column, (4a)...Overhanging part due to diameter expansion, (4b)......Wall-shaped overhanging part, (4C
)...Layered overhang, (5)...Sand layer that may be liquefied. Gij6. '>1''?'Division! ;”j 'L'L'
2 STT: 2) Figure 1 Patent Applicant: Takechi Construction Co., Ltd. Figure 3 Figure 5 Figure 9 Figure 1O Figure 17

Claims (1)

[Claims] 1. Drain pillars made of materials such as gravel, fine stones, gravel, and slag, as well as metals and synthetic resins, are scattered in the sandy layer of ground that is at risk of liquefaction in the foundation ground that supports the structure. A structure for preventing liquefaction of foundation ground, characterized in that an overhang part made of the above-mentioned material and extending laterally from the drain pillar is provided at the upper part of each drain pillar. 2. The foundation ground liquefaction prevention structure according to claim 1, wherein the overhanging portion is formed by expanding the diameter of the head of the drain column. 3. The foundation ground liquefaction prevention structure according to claim 1, wherein the overhang portion has a wall shape extending so as to connect the upper part of the drain column. 4. Claim 3, in which the drain columns are arranged and cast throughout the ground corresponding to the lower part of the structure, and the ends of the wall-like overhanging parts connecting each drain column are led out of the ground corresponding to the lower part of the structure. Liquefaction prevention structure for foundation ground as described in section. 5. The foundation ground liquefaction prevention structure according to claim 1, wherein the overhanging portion is provided in a layered manner over the entire foundation ground so as to connect the upper part of the drain column in the surrounding ground.