JPH0465164B2 - - Google Patents

Description

[Detailed description of the invention] The present invention improves sandy ground that is easily liquefied, obtains a safe foundation ground that is free from liquefaction even during an earthquake, and constructs footings and foundation piles with large bearing capacity. Regarding liquefaction prevention structure of foundation ground.

There are already many known cases in which sand layered ground liquefies during an earthquake, loses its supporting capacity, and structures subside and collapse. The cause of the liquefaction mentioned above is that the pore water pressure in the sandy ground saturated with water increases rapidly due to shear stress during an earthquake, resulting in excess pore water pressure that causes the sandy ground to lose its bearing capacity. In general, it is said that there is a risk of liquefaction in loose sandy ground or fine sandy ground that is saturated with water, depending on the ground density, grain size, groundwater level, etc.

Conventionally, as a measure to prevent the above liquefaction,
For the purpose of increasing the relative density of the ground (increasing the N value) or replacing it with sand of a grain size that is difficult to liquefy, methods are generally used to improve the ground by driving sand piles using the composer method or the vibro method. However, this method of driving sand piles does not prevent or dissipate the sudden increase in pore water pressure that occurs during an earthquake, and there is a risk of liquefaction regardless of the strength of the earthquake.

The present invention aims at reducing the hydraulic conductivity of the ground (sand: 10 ^-2 to ^{10 -3} cm/sec,
Gravel and gravel: 10 ^-1 to 10 ^-2 cm/sec), focusing on the fact that excessive pore water pressure does not occur in gravel or gravel with good permeability, Drain pillars of a predetermined length made of fine stone, slag, and other materials with good water permeability were installed, and the high water permeability of these drain pillars was used to prevent and dissipate sudden increases in pore water pressure during earthquakes. It is something.

Generally, in the case of a foundation with a footing on the foundation ground, as shown in the drawing, the first foundation pile that supports the structure on the ground is the second foundation pile.
As shown in the figure, the piles are driven deep into the ground up to the support layer 3, and for friction piles, they are driven into the upper layer as shown in Figure 3.
A footing is added to the top of these foundation piles 1 to support a structure on the ground. The foundation pile 1
In either case, if the structure penetrates the sand layer 4 that is at risk of liquefaction (Fig. 2) or is located in the sand layer 4 that is at risk of liquefaction (Fig. When the ground beneath the supporting footing becomes liquefied, the footing loses its supporting capacity and the supporting capacity of the foundation piles completely. Furthermore, stress is generated in the ground below the footing that supports the structural load, restraining earthquakes even in normal times other than during earthquakes, and therefore it is difficult to prevent and dissipate a sudden increase in pore water pressure during earthquakes.

In the present invention, drain pillars 5 made of the above-mentioned material with good water permeability are cast in the sandy ground that is at risk of liquefaction below the footing that supports the structure, and are made of the above-mentioned material with good water permeability along almost the outer periphery of the footing to prevent sudden rises in the event of an earthquake. It dissipates the pore water pressure caused by
In particular, in the present invention, by providing a lateral overhanging water relief section made of the above-mentioned material at approximately the same height on the side of the footing in the upper part of the above-mentioned Doren column 5, the pore water pressure that is not likely to rise rapidly during an earthquake can be reduced. This further enhances the liquefaction prevention effect of the sandy ground below the footing, prevents the decline and loss of the supporting capacity of the footing and the supporting capacity of the foundation piles that support the structure, and improves the safety of the structure. This system is characterized in that it is designed to prevent pore water from flowing out or overflowing to the ground.

Next, specific embodiments of the present invention will be explained using illustrated examples.

Example Figures 1 to 3 show that the footing that supports the structure is located at the lower part of the structure a on the foundation ground.
The figure shows a case where a plurality of independent footings 2a are arranged at important points in the sand layer 4, which is at risk of liquefaction, along the entire circumference of the footing 2a built on top of the foundation pile 1. Drain columns 5 that reach the bottom of the footing are arranged and driven at appropriate intervals, and the diameter of the head of the drain column 5 is expanded at a position that approximately corresponds to the outer periphery of the footing, as shown in the figure.
The enlarged diameter portion is formed as an overhanging water escape portion 5a. In this case, since it has an enlarged diameter portion, it is possible to more effectively dissipate excess pore water pressure that occurs during an earthquake, and it is also possible to prevent pore water from flowing to the ground and overflowing. The upper end of the drain column 5 is provided at or near the ground surface.

Embodiment FIGS. 4 and 5 show a drain having a continuous footing 2b in which the footing arranged on the foundation ground is a continuous footing 2b, and which has an overhanging drainage part 5a with an enlarged diameter at the upper part along both longitudinal walls of the footing 2b. This shows the case where columns 5 are placed in rows at regular intervals. In this case as well, the drain pillar 5 is usually driven to the bottom of the sand layer 4, which may be in a liquefied state.

Embodiment FIGS. 6 and 7 show that in place of the enlarged diameter overhanging water relief part 5a of the head of the drain column 5 cast along the outer periphery of the footing 2 in the above-mentioned embodiments [] and [], An embodiment is shown in which the head is connected in a wall-like (groove-like) manner at a peripheral portion of the ground surface that approximately corresponds to the outer periphery of the footing, and the connected portion is formed as an overhanging water escape portion 5b. In the case of this example, in addition to achieving the same purpose as Example [] [],
Since each drain column 5 is connected by an overhanging water escape part 5b, water collection and drainage becomes easier.

In addition, although each of the above embodiments is an example in which a foundation pile is used on the bottom surface of the footing, the footing 10 can also be used in a so-called solid foundation that does not use foundation piles.
The drain pillar 5 having an overhanging water escape part on the upper part can be installed in the same manner as described above, and in this case, the drain pillar 5 is installed on the lower surface of the footing 10 as shown in FIGS. 8 and 9. It is also possible to drive foundation piles instead of foundation piles. In the case of this embodiment, the pore water pressure that rises rapidly in the earthquake area can be effectively dissipated in the ground below the footing.

As shown in FIGS. 10 to 12, the method for manufacturing the drain column 5 includes a casing 10 having a lid 11 at its tip that can be closed when inserted and opened by hanging under its own weight when pulled out. , by driving it into a predetermined location in the ground using a vibration exciter 12 such as a vibrohammer, and after driving it to a predetermined length, pull out the casing 10 while pouring gravel, fine stone, slag, and other materials for constructing a drain pillar into the casing 10. Drain pillars 5, which are appropriately compacted, are constructed on the ground pillars. 13
indicates the input port for the material for constructing the drain pillar. In addition,
The drain column 5 having an overhanging water escape part 5a with an enlarged diameter at the head as shown in Example [][] has a casing 1 whose upper part is enlarged in diameter instead of the casing 10 described above.
0' (see Figure 13), and as in Example [], the wall-like (groove-like) overhanging water escape part 5b connecting the upper part of the drain pillar 5 can be created by digging a trench with an excavator after the drain pillar is constructed. However, drain pillar construction material can be poured into the groove. Furthermore, the cross-sectional shape of the drain column 5 in the present invention 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 under the footing does not undergo a sudden rise in pore water pressure due to shear stress during an earthquake, in the present invention, the outer periphery of the footing is applied to the sandy layer of ground under the footing that is at risk of liquefaction. Since drain columns 5 made of gravel or gravel, which have much better permeability than sand, are installed along the drain column, pore water is discharged through the drain columns 5, and the pore water pressure that is about to rise rapidly is dissipated. , the range of underground stress in the ground below the footing that supports the building load (stress in the ground caused by the footing supporting the load) by the drain pillars cast along the footing at important points in the foundation ground. range), the above-mentioned excess pore water pressure is effectively dissipated. In addition, even if the structure is large and requires a vast site, by driving drain columns in rows along the footing, excessive pore water pressure can be prevented even in the ground below the footing built in the center of the site's ground. is effectively dissipated without causing the footing to lose its supporting capacity. Furthermore, since the drain column 5 has an overhanging water escape section at the upper part of the drain column 5 at approximately the same height on the side of the footing, water collection in this upper overhang water escape section is difficult.
Due to the drainage effect, excess pore water pressure is quickly, reliably, and more effectively dissipated, and together these can reliably prevent the generation of excess pore water pressure itself in the ground below the footing during an earthquake, and the It is possible to completely prevent liquefaction of the ground and surrounding ground, without lowering or losing the supporting capacity of the footing, and while accelerating the flow of pore water within the drain column that occurs during the dissipation process, it also prevents water from gushing to the ground. This method also provides the following excellent effects not found in conventional methods, such as the ability to prevent the occurrence of earthquakes and to obtain a footing that has a safe supporting capacity even in the event of an earthquake.

With conventional methods of preventing liquefaction by compacting or replacing sandy ground, there is a risk of liquefaction due to the strength of an earthquake, but in the present invention, as described above, the drain column with an overhanging water escape part is used to increase pore water pressure. Because it prevents this, there is no risk of liquefaction, regardless of its strength, even in the event of an earthquake, and the ground and footings can be secured with sufficient supporting capacity, making the structure completely safe even in the event of an earthquake. .

Drain columns are constructed only in the ground around the foundation piles below the footings, which are directly affected by earthquakes, so there is no waste, and they are extremely economical and safe for the foundation piles.

Since drain columns are installed in a row along the outer periphery of the footing, liquefaction can be completely prevented from occurring in the sandy layer of ground below the footing, which supports the construction load, and around the stress in the ground below the footing, and the footing itself is highly safe. Therefore, the supporting capacity of footings and foundation piles will not decrease or be lost. Furthermore, the horizontal bearing capacity of the footing is also enhanced due to the rigidity of the drain column existing near the outer periphery of the footing, that is, the rigidity of the constituent materials of the drain column, such as gravel, fine stone, ore slag.

By constructing a drain pillar in the ground, it has the effect of compacting the surrounding ground and replacing the grain size, and the drain pillar itself is less likely to liquefy and has the effect of improving the ground.

In particular, due to the presence of an enlarged diameter overhang at the top of the drain column or a wall-like overhang that connects the tops of the drain column, pore water pressure may leak or overflow to the ground as it dissipates through the drain column. pore water pressure is more effectively dissipated, and the effect of preventing ground liquefaction is further enhanced. In the case of the above-mentioned wall-shaped overhanging water escape section, it is easy to collect and drain water to the outside of the structure.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, and Fig. 1 is a schematic plan view showing an embodiment in the case of an independent footing, and Figs. 2 and 3 are longitudinal cross-sectional views of the same with different foundation piles. , FIG. 4 and FIG. 5 are a schematic plan view and a longitudinal sectional view showing an embodiment in the case of continuous footing,
Figures 6 and 7 are a schematic plan view and longitudinal cross-sectional view showing an example in which an overhanging water relief section connecting the upper part of the drain column is provided, and Figures 8 and 9 are examples of the implementation in the case of a solid foundation. A schematic plan view and a longitudinal sectional view showing an example, and FIGS. 10 to 13 are longitudinal sectional views illustrating a method for forming a drain pillar. 1...Foundation pile, 2a...Independent footing, 2b
...Continuous footing, 4...Sand layer with a risk of liquefaction, 5...Drain pillar, 5a, 5b...Permeable pit.

Claims (1)

[Scope of Claims] 1. A sand layer of ground that is at risk of liquefaction under the footing that supports the structure is made of materials such as gravel, crushed stone, gravel, slag, metal, and synthetic resin pieces along almost the outer periphery of the footing. A foundation characterized in that drain columns of a predetermined length are cast in a row, and a water escape part made of the above-mentioned material and extending to the side is provided at approximately the same height on the side of the footing at the upper part of the drain column. Structure to prevent ground liquefaction. 2. The foundation ground liquefaction prevention structure according to claim 1, wherein the diameter of the upper part of the drain column is expanded to form an overhanging water escape part. 3. The foundation ground liquefaction prevention structure according to claim 1 or 2, wherein the upper part of the drain column is connected in a wall shape to form an overhanging water escape section.