JPH06287965A - Foundation for weak ground, and method for constructing foundation in weak ground - Google Patents

Abstract

PURPOSE:To stably keep a tall building constructed on a weak ground for a long period by working the buoyancy of a resin foamed block laid in a frame body to the whole foundation as a pulling force. CONSTITUTION:A plurality of steel sheet piles are embedded in a weak ground 1 to form a frame body 12. A resin foamed block 13 is laid in the frame 12. The maximum pulling force received by the resin foamed block 13 from the weak ground 1 is substantially equilibrated with the weights of a foundation member 18 and a construction 19 on the foundation member 18. Since the foundation member 18 and the construction 19 are supported by the buoyancy of the resin block 13, the consolidation settlement over a long period is prevented. The ratio of the length of the steel sheet pile forming the frame body 12 to the depth of the resin foamed block 13 is set within the range of 2:1-50:1. Since the frame body 12 is embedded deep in the weak ground 1, the opposing force to horizontal and bending moments is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foundation for a structure constructed in soft ground and a method for constructing this foundation. More particularly, the present invention relates to a foundation having a high stability such that a tall building can be constructed even in extremely deep soft ground and a method of constructing this foundation.

[0002]

BACKGROUND OF THE INVENTION When building a tall building such as a steel tower on soft ground, conventionally, a large amount of soil is applied to the entire area where the building is to be built to improve the soft ground. After that, the method of building the foundation was adopted. However, with this method, the range of land to be constructed is extremely wide when trying to build a stable foundation. In addition, the whole soft ground is not improved, only the soft ground near the part where the foundation is constructed is improved, and the increase in load due to the soil acts as an increase in load on the lower soft ground. However, the stability of the foundation over time is not reliably guaranteed with this method, since this increase in load causes consolidation settlement over a long period of time.

As an improvement method for constructing a foundation on such soft ground, a method of constructing on a support pile foundation, a method of constructing on a friction pile foundation, a method of constructing on a deep foundation stirring pile, etc. are known. ing. Among these improvement methods, for example, the support pile foundation method is a method of constructing a foundation on support piles that reach the bedrock, and is a method with high reliability and less influence on the surroundings. If is deep,
There are economic problems such as the need for very long piles. In addition, the friction pile foundation method uses a foundation built on a large number of piles that have frictional force against the surrounding soft ground, so the number of piles is large, so horizontal resistance is also generated due to the group pile effect and stable. However, even with long piles, the temporal stability of bearing capacity is not so high, so there is a problem that a large number of piles are required to ensure stability. In addition, the deep foundation stir pile method is said to have almost the same capacity as friction piles without the need to discharge sediment when driving the piles,
This construction method has the same problem as the above-mentioned friction pile, and also has the problem that the pile itself is easily sheared, and therefore, as a basis for constructing a tall building, maintenance against horizontal stress is required. Stability about ability becomes an issue.

As described above, the conventional method for constructing a tall building on soft ground has room for improvement in terms of economy and stability. In particular, the foundation of a tall building must have sufficient stability in the horizontal direction, and in the above conventional method, the stability in the horizontal direction,
Furthermore, there is a problem that the reliability of resistance against bending moment is not sufficient.

[0005]

It is an object of the present invention to provide a foundation for soft ground and a method for constructing this foundation, which enables a building to be stably maintained for a long time even when a tall building is constructed on soft ground. It is an object. More specifically, the present invention is
It is an object of the present invention to provide a foundation for soft ground, which has no increased stress in the ground, has little influence on dense settlement and surrounding ground, and has high resistance to horizontal and bending moments, and a method for constructing this foundation.

[0006]

SUMMARY OF THE INVENTION The foundation for soft ground of the present invention is a frame body formed by a plurality of steel sheet piles buried in the soft ground, a resin foam block laid in the frame body, and the laid base body. The resin foam block, which is formed on the resin foam block by engaging with the frame body and is constructed, is embedded in the frame body, and the resin foam block is loaded by the building constructed on the foundation member. It is characterized by being laid at a depth that produces a maximum lifting force that is almost in balance with the weight of the product.

Further, the method for constructing a foundation in soft ground according to the present invention is such that a plurality of steel sheet piles are embedded in soft ground to form a frame, and then a resin foam block is formed in the frame by the soft ground. The resin foam block is laid at a depth at which the maximum pulling force received by the resin foam block and the weight loaded by the foundation member constructed on the resin foam block and the structure constructed on the foundation member are substantially balanced. Then, a base member engaged with the frame is constructed on the laid resin foam block.

The foundation for soft ground of the present invention comprises a frame body formed by combining a plurality of steel sheet piles buried in the soft ground, a resin foam block laid in the frame body, and a block on the block. And is composed of a frame and a basic member that is locked. By adopting such a configuration, buoyancy is applied to the resin foam block, and this buoyancy acts as a lifting force on the entire foundation. Therefore, if a building having a weight that is in balance with the pulling force is constructed on the foundation of the present invention, the foundation itself will not sink due to the weight of the construction. Moreover, since the frame body formed of the steel sheet pile is deeply embedded in the soft ground, a counter force is exerted between the frame body and the soft ground against a horizontal stress and a bending moment.

That is, the foundation for soft ground of the present invention has a function similar to that of a floating pile by integrating the frame made of steel sheet pile, the resin foam block and the foundation member as a whole.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Next, the foundation for soft ground of the present invention will be specifically described along with its construction method.

FIG. 1 is a cross-sectional view schematically showing a cross section of a foundation for soft ground of this embodiment constructed in soft ground.
FIG. 2 is a cross-sectional view showing an engagement state between a frame body made of steel sheet pile and a base member, and FIG. 3 is a plan view showing a state of a resin foam block laid on the frame body made of steel sheet pile. Yes,
FIG. 4 is an enlarged plan view showing a contact portion between the frame body made of steel sheet pile and the resin foam block.

As shown in FIGS. 1 to 4, the foundation for soft ground of the present embodiment comprises a frame body 12 formed by combining a plurality of steel sheet piles 11 embedded in the soft ground 1, and a frame body. The resin foam block 13 is laid on the base, and the foundation member 18 is formed on the laid resin foam block 13 in a state of being engaged with the frame 12.

The steel sheet pile 11 has various shapes, but in the present embodiment, the steel sheet has a convex cross section and has an engaging portion 14 for engaging an adjacent steel sheet pile at the edge of the convex portion. A sheet pile is used. Such steel sheet piles 12 are arranged so that the convex portions are alternately arranged, and at the time of this arrangement, the engaging portions 14 of the steel sheet pile 11 are arranged.
And the adjacent steel sheet piles are mutually locked to form the frame body 11. The length of the steel sheet pile used here is determined in consideration of the height and weight of a building constructed on the basis of the present invention, but at least the resin foam laid in the frame body. A steel sheet pile having a length twice the depth of the block is used. That is, when the length of the steel sheet pile is a and the depth of the resin foam block to be laid is b in FIG. 1, a is preferably longer than 2b, and a is 3
It is particularly preferable that it is longer than b. From the viewpoint of stability of the foundation, it is preferable that the steel sheet pile is long, but considering the balance of both economic efficiency and stability, even if a steel sheet pile with a exceeding 50b is used, the stability due to the lengthening of the steel sheet pile is considered. Is no longer expected, and more generally, a is 10b
Even if a steel sheet pile exceeding 10 is used, the improvement in stability is not significantly manifested. That is, the length of the steel sheet pile is usually a length that can withstand the buoyancy of the resin foam block due to the rise of groundwater, and withstand the lifting force from the upper structure and the horizontal force, and Determined to withstand the rotational moment.

Further, the volume of the resin foam block to be laid / laminated is such that the increase amount of the effective underground stress applied to the lower end of the steel sheet pile in the ground is greater than the allowable bearing capacity of the ground and the consolidation stress. It is preferable to set the volume so that

The shape of the frame body 11 thus formed is not particularly limited, and the cross-sectional shape can be various shapes such as square, rectangular and circular. Frame body 12 as described above
Are formed in the soft ground 1 having an average N value of 3 or less. That is, the soft ground in the present invention means the ground having an average N value of 3 or less. Here, the average N value is JIS-
63.5Kg according to the standard penetration test specified in a-1219
The number of times required for the standard penetration tester to penetrate the ground of 30 cm by the energy of dropping the weight of 75 cm from the height of 75 cm. Therefore, for example, an N value of 0 means a soft ground where the standard penetration tester sinks under its own weight without being hit.

According to the method of the present invention, this average N value is 1
It is highly effective even for extremely soft ground such as the following.
For example, in an area where humus soil is deposited on a clay layer, such as a lowland near a large river, the average N value is often low as described above. In such lowlands, the groundwater level is high, and it is not uncommon for the groundwater level to fall below 50 cm from the surface. In Fig. 1, the groundwater level is indicated by a dashed line.

After the frame 12 made of a plurality of steel sheet piles is formed in the soft ground as described above, the earth and sand inside the frame 12 are removed. The depth of the earth and sand to be removed is basically the total depth obtained by adding the thickness of the foundation layer 15 and the thickness of the foundation member buried in the ground to the total thickness of the resin foam blocks to be laid in layers. That's it.

The soft ground foundation of the present invention is configured such that the increased stress generated in the ground due to the difference between the resin foam block and the wet unit volume weight of the soil is 0 or less than the consolidation stress. That the buoyancy generated when the resin foam block is in water (ground containing a large amount of water) and the lift from the structure are resisted by the frictional force of the steel sheet pile. Due to the soil and the weight of the steel sheet pile surrounded by the construction, it is possible to counter the rotational moment and to share a larger horizontal resistance on the wall surface of the steel sheet pile.
It is possible to build on super-soft ground (that is, soft ground containing a large amount of water) or even on large tower buildings with low stability.

In the construction method of the present invention, since the frame body 12 is formed of the steel sheet pile as described above, the frame body 12 is deeply buried even though the groundwater level is higher than the bottom of the removed sand. As a result, the water-blocking effect is obtained to some extent, so that when removing the earth and sand, it is possible to suppress to some extent the amount of groundwater discharged from the portion where the earth and sand have been removed.

After removing a predetermined amount of earth and sand in this way, a base layer 15 is attached to the bottom of this portion. This underlayer 15
Has a function of forming a flat surface for laying the resin foam block and blocking groundwater coming up from the lower portion to a certain extent. Normally, on the surface from which the soil has been removed,
Sand, gravel, etc. are spread, concrete is poured on this, and the base layer 15 is formed.

After the base layer 15 is formed in this manner, a resin foam block is laid and laminated on the base layer. This resin foam block is a block formed of resin foam such as styrene foam, urethane foam, and polyolefin foam, and the size of this resin foam block is usually several tens of cm square to a long edge. It is possible to use even a rectangular parallelepiped having a length of 10 m or less. For example, the outer size of a resin foam block for civil engineering is often 50 × 100 × 20.
It is about 0 (unit cm). In the future, the outer dimensions of civil engineering resin foam blocks will be 100 x 200 x 600 (unit:
It is preferable to use a large one (cm). However, these dimensions are merely examples, and it goes without saying that the resin foam block used in the present invention is not limited to these dimensions.

Such a resin foam block has 20 to 20
It has a specific gravity of 30 Kg / m ³ (measured by JIS-K-7222) and 10
It has a compressive strength of up to ²⁰ tf / m ² (measured by JIS-K-722). Therefore, this resin foam block is extremely lightweight and has very high compressive strength. As is apparent from the specific gravity, this 1 m ³ resin foam block produces a buoyancy of about 970 to 980 kg when immersed in water. Further, even if a load is applied so as to be balanced with the buoyancy (lifting force) generated at this time, the compressive strength is sufficient to withstand this load as described above.

Such a resin foam block has a load of a base member arranged on the resin foam block and a structure constructed on the base member and a lifting force (buoyancy) due to the resin foam block. ) And are laid and laminated in an amount that almost balances them. This resin foam block 13
First, as shown in FIG. 3, first, the resin foam blocks of the first layer are laid in a zigzag pattern on the underlayer 15. Further, as shown in FIG. 3, the resin foam blocks of the second layer, the third layer, ... Are laminated on the resin foam block of the first layer. At this time, the resin foam blocks to be laminated are preferably laminated in a zigzag pattern also in the depth direction. Further, when laying / stacking the resin foam blocks, it is preferable to connect the blocks to each other in order to prevent the blocks from being displaced. For this connection, a connecting tool that is usually used for connecting resin foam blocks can be used. In addition, recesses and protrusions are provided on the surface of the resin foam block, and the recesses provided in each block are provided. It is also possible to lay and stack the resin foam blocks so that the convex portions fit in.

Further, since the frame body 12 is formed by the steel sheet pile 11, the frame body 12 has the concave portion 20 and the convex portion with respect to the center line XX of the steel sheet piles connected as shown in FIG. 21. Normally used resin foam block 13
Does not have a form corresponding to the concave portion 20 and the convex portion 21. Therefore, if a resin foam block that is normally used is laid, the convex portion 21 is not filled with the resin foam block. . Therefore, in the present invention, it is preferable that the convex portion 21 is also filled with the resin foam. Since the convex portion 21 and the concave portion 20 are similar to each other, a resin foam having a thickness corresponding to the thickness corresponding to the sectional thickness h of the steel sheet pile is prepared, and the resin foam is formed into the steel sheet pile 11. When punched out according to the cross-sectional shape of No. 3, the punched portion has the same shape as the cross-sectional shape m of the steel sheet pile, and the cross-sectional shape of the remaining punched-out portion has the same shape as n. Therefore, this m
By combining and n as shown in FIG. 4, the resin foam can be filled in the convex portion formed by the resin foam block 13 and the steel sheet pile 11. The resin foam filled in the convex portion formed on the frame body 12 is efficiently filled as described above, but the present invention is not limited to this method, and the same shape as the convex portion is formed. Of course, it is also possible to adopt other methods such as separately molding the resin foam block that it has.

After laying and laminating a predetermined amount of the resin foam block 13 in the frame body 12 as described above, the base member 18 is constructed on the resin foam block 13. The foundation member 18 usually includes a concrete floor board 16 and a concrete foundation 17. The frame 12 is usually engaged with a concrete floorboard 16.

The frame 12 and the concrete floor plate 16 are engaged with each other by, for example, welding a reinforcing bar (not shown) embedded in the concrete floor plate 16 to the frame body 12 to integrate them.

After the reinforcing bars and the frame body 12 are welded and engaged with each other as described above, concrete is poured so that the reinforcing bars are embedded to form the concrete floorboard 16. A concrete foundation 17 is constructed on the concrete floor board 16 thus formed to form a foundation member 18.

A building 19 is built on the base member 18. FIG. 1 shows an aspect in which the building 19 is a steel tower. In the present invention, the compression pressure (load) C from the building constructed on the foundation for soft ground, the pull-out force T from the building constructed on the foundation for soft ground,
A member constituting the foundation for soft ground of the present invention so that the value Lb of (length L of steel sheet pile × perimeter b of foundation) satisfies the relations of the following equations [I], [II], and [III]: It is preferable to select the structure.

C ≧ (γ _w −γ _EPS ) V _EPS −W ・ ・ ・ [I] T ≦ (γ _t −γ _EPS ) V _EPS −W ・ ・ ・ [II] Lb ≧ T / μ ・ ・ ・ [ III] where W is the weight of the base, V _EPS is the total weight of the resin foam block, γ _EPS is the unit volume weight of the resin foam block, γ _w is the unit volume weight of water, and γ _t is The wet volumetric weight of soil, μ, represents the frictional force between the steel sheet pile and the soil.

Further, in the present invention, considering the consolidation yield stress P _y , the members and structures constituting the foundation for soft ground of the present invention are set so that the above T satisfies the relation of the following formula [Ia]. It is particularly preferable to select it.

C ≧ {(γ _w −γ _EPS ) V _EPS −W} −P _y ... [Ia] In the above formula [Ia], P _y represents a consolidation yield stress, and W, V _EPS. , Γ _EPS and γ _w have the same meanings as described above.

In the foundation for soft ground according to the present invention constructed in this way, since the uniform pressure is applied to the steel sheet pile from all directions below the portion where the resin foam block is laid, the steel sheet pile is pressed. Substantially no increase in underground stress due to increase in burial depth. Therefore, damage to the steel sheet pile due to underground stress hardly occurs.

The foundation for soft ground of the present invention has the above-mentioned constitution, and the resin foam block laid / laminated gives a pulling force to the foundation for soft ground.
Since the pulling force and the weight of the building are balanced, the stability in the vertical direction such as the sinking of the foundation on the soft ground is excellent, and this stable state can be maintained for a long time. Further, a frictional force acts between this frame and the soft ground around the frame, and this frictional force imparts stability to the building in the horizontal direction and resistance to bending moment. . That is, the underground effective stress applied increases as the steel sheet pile becomes deeper, but in the present invention, the increase amount of the underground effective stress normally applied to the lower end portion of the steel sheet pile is the allowable bearing force of the ground and the consolidation stress. Since the frame body is made of steel sheet pile with a length smaller than both of them, the horizontal stress and bending moment from the building are absorbed by the frictional force between the embedded frame body and the soft ground. To be done.

With the mechanism as described above, the soft ground foundation of the present invention ensures the stability in the vertical direction and the horizontal direction, and the length of the steel sheet pile is such that the above stability is exhibited. It can be shortened by changing the shape of the sheet pile. For example, as shown in FIGS. 5 and 6, an anchor or stabilizing wing 23 can be provided at the lower end portion of the steel sheet pile 11. By providing the stabilizing blades 23, the stability of the frame body against the stress in the lateral direction of the building is increased, so that the length of the steel sheet pile embedded in the soft ground can be shortened.
Further, as shown in FIG. 6, by using the steel sheet pile 11 in which the anchor 24 is pivotally attached to the tip portion of the steel sheet pile 11 so as to be openable and closable, the driving of the steel sheet pile becomes easy.

As shown in FIG. 7, the foundation for soft ground of the present invention has a vertical hole formed in the depth direction in the ground from the lower end of the frame body 12 made of steel sheet pile 11 with a cylindrical boring lot. A reinforcing bar 27 having a wire 26 wound by a tip is inserted into the boring rod, and then mortar 28 is injected into the boring lot to remove the boring rod. Due to the pressure from the soft ground around the ground anchor thus formed, a stress is generated against the foundation of the invention against longitudinal stresses and rotational moments. After arranging the plurality of ground anchors 25 as described above, the steel sheet pile 11 is arranged thereon to form the frame body 12. The frame body composed of the ground anchor 25 and the steel sheet pile 11 is engaged by a usual engaging means, for example, a bolt and the like. After forming the frame body 12 in this manner, the underlayer 15 is formed in the same manner as above, and the resin foam block 13 is laid and laminated on the underlayer 15. Next, the foundation member 18 including the concrete floor board 16 and the concrete foundation 17 is constructed on the laid / laminated resin foam block 13. A building is constructed on the base member 18. FIG. 7 shows a state in which the steel tower 19 is constructed. The ground anchors 25 are usually provided at at least four corners of the frame body 12, but can be provided at an intermediate portion of the corner portions of the frame body 12. Further, when the ground anchor 25 is provided on the base layer 15, a through hole penetrating the base layer 15 is formed, and the ground anchor 25 as described above is arranged here. Since the reinforcing bars are not usually buried in the underlayer 15, the ground anchor 25 is
5 An iron plate having tower holes is arranged on the upper surface, and a reinforcing rod constituting a ground anchor or the like is inserted into this iron plate and screwed with a screw 30 to engage with the underlayer 15. Therefore, the number of the ground anchors 25 is usually 4 or more, and the height of the building constructed on the basis of the present invention,
The number of the resin foam blocks can be appropriately set in consideration of the volume and the like.

Further, although the ground anchor has shown the mode of using the reinforcing bar, only the wire is inserted through the boring hole without using such a reinforcing bar, and after filling the mortar, the cylindrical object for boring is pulled out. It can also be formed.

Further, various improvements can be added to the steel sheet pile, the resin foam block and the like used in the method of the present invention within the range not impairing the object of the present invention. For example,
It is also possible to use a steel sheet pile or a reinforcing bar having a rustproof film attached to the surface of the frame body.

The foundation for soft ground of the present invention is a building having a high height such as a steel tower as described above, in other words, a building whose height is larger than the length of the building in the width direction. It is particularly suitable as a foundation for buildings, but is not limited to such buildings, but it is the basis of ordinary buildings such as houses, in other words, buildings whose height is smaller than the width of the building. Can also be used effectively.

[0039]

According to the foundation for soft ground of the present invention, when a building is constructed on soft ground, the building can be maintained in a stable state for a long period of time. That is, the foundation for soft ground of the present invention does not have an increase stress in the ground, has little influence on dense settlement and surrounding ground, and has high resistance to horizontal direction and bending moment.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a foundation for soft ground of the present invention.

FIG. 2 is a cross-sectional view showing a base member and its vicinity in the soft ground foundation.

FIG. 3 is a plan view showing a laid portion of the resin foam block of the soft ground foundation.

FIG. 4 is a plan view showing a laid state of a resin foam block near the frame body in the soft ground foundation.

FIG. 5 is a cross-sectional view showing a state in which stabilizing blades are provided at the lower end portion of the steel sheet pile.

FIG. 6 is a cross-sectional view showing a state in which an opening / closing anchor is provided at the lower end of the steel sheet pile.

FIG. 7 is a cross-sectional view showing an embodiment using a ground anchor in the foundation for soft ground of the present invention.

[Explanation of symbols]

 1 ... Soft ground 11 ... Steel sheet pile 12 ... Frame body 13 ... Resin foam block 14 ... Engagement portion 15 ... Underlayer 16 ... Concrete floorboard 17 ... Concrete Foundation 18 ... Foundation member 19 ... Steel tower 20 ... Frame concave portion 21 ... Frame convex portion 23 ... Stabilizing wing or anchor 24 ... Anchor 25 ... Ground anchor 26 ... Stranded wire 27 ... Reinforcing bar 28 ... Mortar

Front Page Continuation (72) Inventor Yutaka Tsuda 4-5-6 Sendagaya, Shibuya-ku, Tokyo Taisei Basic Design Co., Ltd.

Claims (5)

[Claims] 1. A frame body formed by a plurality of steel sheet piles embedded in soft ground, a resin foam block laid inside the frame body, and the frame body on the laid resin foam block. And a resin foam block embedded in the frame, the maximum lifting force being approximately in balance with the weight loaded by the building constructed on the base member. A foundation for soft ground characterized by being laid at a depth where 2. The length of the steel sheet pile embedded in the soft ground and the depth of the laid resin foam block are from 2: 1.
The foundation for soft ground according to claim 1, wherein the foundation is in the range of 50: 1. 3. A plurality of steel sheet piles are embedded in soft ground to form a frame body, and a resin foam block is then formed in the frame body.
A depth at which the maximum pulling force received by the resin foam block by the soft ground and the weight loaded by the foundation member constructed on the resin foam block and the building constructed on the foundation member are approximately balanced. A method for constructing a foundation in soft ground, which comprises laying a base member on a soft ground, and then constructing a foundation member engaged with the frame on the laid resin foam block. 4. The length of the steel sheet pile embedded in the soft ground and the depth of the laid resin foam block are from 2: 1.
The method for constructing a foundation according to claim 3, wherein the ratio is in the range of 50: 1. 5. A building constructed on the foundation member,
The method for constructing a foundation according to claim 3, wherein the building has a maximum height larger than a maximum width.