JPH0328534B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an enclosure foundation for stably supporting a structure such as an oil tank on soft ground such as loose sand.

As shown in Figure 1A, the conventional foundation construction method for soft ground involves laying piles 2 up to supporting layer 1 such as bedrock.
The long piles 2 can be used to support the structure 3, or as shown in Fig. 1B, a ground improvement method such as a sand compaction method or a vibroflotation method can be used to cover a wide area and deep layer. The ground was improved to provide support.

However, with the above conventional construction method, even though the load level of the structure is not so large, large-scale construction work such as pile driving and ground improvement work is required, which not only takes a long time and increases construction costs, but also causes noise. There were drawbacks such as pollution caused by vibration and vibration.

In addition, in sandy ground in particular, liquefaction phenomenon occurs during earthquakes, and there is a risk of serious damage and disasters to structures such as oil tanks, but no countermeasures are being taken. Alternatively, the reality is that countermeasures have been taken by implementing extensive ground improvement as described above, and drastic measures have been desired.

The present invention has been made in view of the above points, and
The purpose of this is to eliminate the need for large-scale construction works such as pile construction and ground improvement work, even in soft ground with deep supporting layers, and without causing pollution such as noise and vibration. Not only can it be constructed in a relatively short period of time and at an extremely low cost, but it can also effectively prevent ground liquefaction during earthquakes.
The goal is to provide an extremely stable and earthquake-resistant foundation.

An embodiment of the present invention will be described below with reference to the drawings.

In FIGS. 2 and 3, 4 is an oil tank as a structure, which is constructed on soft ground 5. An enclosure foundation 6 consisting of an underground closing wall is constructed around the ground 5' that supports the oil tank 4 so as to surround it. The underground closure wall can be constructed, for example, by excavating a trench around the ground 5' directly beneath the structure and sequentially placing panel-shaped concrete plates, pressure-resistant plastic plates, etc. therein, or by constructing steel sheet piles. It is constructed by sequentially connecting and inserting them along the periphery of the ground 5' directly beneath the ground.
Incidentally, the above-mentioned underground closure wall may be constructed by continuously erecting pipe-shaped or rod-shaped concrete or plastic.

Therefore, in the support system without the enclosure foundation 6 as shown in Fig. 4, the ground supporting the load of the oil tank 4 tends to slide and break as shown in the figure, and the sliding resistance R is the counterforce. It will be supported by the holding force P′ by the soil around ′.

On the other hand, according to the above embodiment, as shown in FIG. 3, the ground 5' below the oil tank 4 is surrounded by the enclosure foundation 6 and separated from the external ground 5. The load of the oil tank 4 is integrated with the ground 5' and acts on the ground 5 below the enclosure foundation 6, due to the sliding resistance R and holding force P, as well as the frictional force N acting on the outer surface of the enclosure foundation 6. It will be supported. Therefore, in this embodiment, the enclosure foundation 6
As the actual bottom of the foundation becomes deeper, the soil cover increases accordingly, and the holding force P increases to the fourth level.
It can be seen that this is significantly greater than the holding force P' of the shallow supporting ground shown in the figure, and that a new frictional force N is generated, increasing the overall supporting force.

It has been found that if the enclosure foundation 6 is constructed of a water-permeable material such as a water-permeable concrete plate, the liquefaction phenomenon during an earthquake can be further prevented. In other words, as shown in Figure 5A, sand grains S in loose sandy ground trap groundwater W inside, and when an earthquake occurs, the sand grains S vibrate and move, trapping it as shown in Figure 5B. The water pressure of the water W increases, acting on the surrounding sand grains and dispersing them mutually as shown by the arrows, liquefying the entire sand layer and rapidly reducing its supporting force.

Therefore, if the enclosure foundation 6 is made of a permeable material as described above, as soon as an earthquake occurs, the water in the ground 5' directly below will be sucked into the permeable enclosure foundation 6 as shown by the arrow. and rises to the upper end 6a.
Since water is drained from the sand grains S and dissipated, the water pressure in the sand grains S does not increase and there is no risk of liquefying the ground 5' directly below, and the ground is still stably maintained with a large supporting force.

Furthermore, instead of constructing the entire enclosure foundation 6 from a water-permeable material as in the above embodiment, for example, in the case of an enclosure foundation 6 made of sheet piles 7, the enclosure foundation 6 shown in FIGS.
As shown in the figure, a water-permeable plate 8 may be attached to the inside thereof. In this case, holes may be made in the sheet piles 7 to allow water in the external ground to also dissipate.

In addition, although the above explanation was about soft ground,
The ground targeted by the present invention is not limited to this, and the depth of the underground closing wall is appropriately set according to various conditions such as the size and load of the structure, or the properties of the ground. Furthermore, this enclosure foundation can be used not only as a foundation for oil tanks, but also as a foundation for buildings such as houses and towers, retaining walls, factory floors, or under roads.

As described above, the enclosure foundation of the present invention is constructed by constructing an underground closed wall around the ground directly beneath the structure, so it is not only easy to construct, shortens the construction period, and is inexpensive, but also reduces noise and vibration. It does not generate any pollution, provides stable strength over a long period of time, and by composing all or part of the underground closure wall with a permeable material, an effective earthquake-resistant foundation can be obtained in soft ground. There are advantages such as

[Brief explanation of drawings]

Fig. 1 is a diagram showing a conventional structure support method on soft ground, Fig. 2 is a perspective view showing a method for supporting an oil tank using an enclosed foundation according to the present invention, and Fig. 3 is a diagram showing support using an enclosing foundation according to the present invention. Fig. 4 is an explanatory diagram showing the force increase. Fig. 4 is an explanatory diagram of the supporting force by conventionally commonly used support methods. Fig. 5 is an explanatory diagram of the principle of liquefaction of an underwater sand layer. Fig. 6 is a diagram of a permeable enclosure foundation. 7 and 8 are plan views of another embodiment in which a permeable plate is attached to the inside of an enclosing foundation made of steel sheet piles. 4... Oil tank, 5... Ground, 5'... Directly below ground, 6... Enclosure foundation, 7... Sheet pile, 8... Permeable plate, N... Frictional force, P, P'... Holding force, R,
R'...Slip resistance, S...Sand grains.

Claims (1)

[Claims] 1. An enclosing foundation characterized by constructing an underground closing wall around the ground directly beneath the structure, and constructing all or part of the underground closing wall from a water-permeable material.