JP7606952B2 - How to build a structure on existing ground - Google Patents

Description

The present invention relates to a method for constructing a structure on existing ground, which is carried out when constructing a structure at a height higher than the ground surface of the existing ground (original ground).

For example, when distributing multiple structures (facilities) that utilize the difference in elevation (water level difference) between them, such as a water purification plant, on an existing flat ground surface, the structures are constructed so that there is an elevation difference between the base of the foundations of each structure and the water flows downstream.

However, excavating the ground to construct a structure requires a lot of temporary construction work, such as installing retaining walls and struts, and therefore costs more and takes longer than building embankments. From this point of view, building embankments with different top heights for each of the areas of multiple structures on the existing ground is a rational method, as it reduces overall costs, including the cost of constructing the structures, while shortening the construction period.

Methods for constructing embankments on existing ground mainly include a method in which an embankment is constructed on the ground surface, and then piles are driven from the top of the embankment to reach the existing ground (see Patent Document 1), and a method in which piles are driven into the ground with their upper sections protruding above the ground surface, and then embankment material is laid using fiber reinforcement to ensure integrity with the piles (see Patent Document 2).

JP 2011-202427 A (Claim 1, Claim 3, Paragraphs 0009 to 0013, Figure 1) JP 2011-26792 A (Claim 3, paragraphs 0007, 0010 to 0022, Figures 1 to 4)

In Patent Document 1, after the embankment is constructed, ground improvement piles are constructed from the top of the embankment to reach the original ground before the embankment was constructed (Claim 3, paragraph 0013), which makes it necessary to install a ground improvement machine on the top surface of the embankment, but the work of moving the ground improvement machine from the original ground to the top of the embankment and the removal of the machine can be difficult.

For example, it is necessary to create a gentle slope from the original ground surface to the top surface of the embankment to allow for the movement of ground improvement equipment, and this requires time and money for additional work in addition to the actual construction. As the slope is unrelated to the embankment as a structure, it will be removed once the embankment is completed unless it has any useful value.

In addition, the creation of a slope requires extra land on either side of the entire embankment to allow for the construction of the slope, so the amount of land required to build the embankment is limited. If there is not enough land available for the slope, it is not possible to create the slope, making it impossible to install a ground improvement machine on the embankment and therefore impossible to construct piles. Furthermore, if the top surface of the constructed embankment is narrow, it may be difficult to load and maneuver heavy machinery such as a ground improvement machine or pile driver.

Furthermore, because the piles in Patent Document 1 are ground improvement piles, the heads of the completed piles will be located below the ground surface, and the piles cannot be completed with the upper section of the pile protruding (exposed) above the ground surface as in Patent Document 2. Therefore, before the construction of the embankment, piles with their heads located on the top surface of the planned embankment cannot be constructed. This also applies when the piles are in-situ construction piles (cast-in-place piles).

In Patent Document 2, piles are driven into the original ground before the embankment is constructed, and the upper section of the pile protrudes from the ground surface, thus avoiding the problems associated with forming a slope required for the installation of a pile driver, which occurs when driving piles from above the embankment.

However, the piles in Patent Document 2 are placed in reinforced soil embankment A so as to penetrate the entire embankment layer 2 across the entire embankment layer 2 in order to ensure the integrity of the multiple layers of embankment layer 2, which are made of fiber reinforcement material 1 and embankment material and are formed on the original ground (paragraphs 0002, 0007, 0010, Figures 3 and 4), and the reinforced soil embankment A is installed at the foot of the slope so as to act as a dam to prevent the collapse of the embankment on the slope it faces (paragraph 0007, Figure 4). In this regard, since the heads of the piles are ultimately buried in the uppermost embankment material (paragraphs 0021, 0022, Figure 4), it is not envisaged that above-ground structures will be constructed on the heads of the piles.

If we focus only on the results, since in Patent Document 1 a deck slab is constructed on the top surface of the ground improvement piles (claim 1, paragraphs 0009 and 0013, Figure 1), it would appear that by combining Patent Document 2 with Patent Document 1, it would be easy to construct the foundation of a structure on the top surface of the piles in Patent Document 2.

However, the invention in Patent Document 2 is a reinforcement structure for embankments, and since the pile heads are completed with the pile heads embedded in the uppermost embankment material (paragraphs 0010, 0021, 0022), it is not anticipated that a structure will be constructed on top of the unfinished pile heads.

In light of the above background, the present invention proposes a method for constructing a structure on the existing ground, which makes it possible to build a structure at a height higher than the ground surface.

The method of constructing a structure on the current ground as described in claim 1 comprises the steps of driving a plurality of piles horizontally spaced apart into the current ground from a position corresponding to the position where the foundation of a structure to be constructed higher than the ground surface of the current ground will be formed, with their upper sections exposed above the current ground, constructing an embankment on the current ground to a height where at least a portion of the axial direction of the heads of the piles is exposed, constructing the foundation of the structure on or including at least a portion of the heads of the piles, and constructing the superstructure of the structure on the foundation.
The method for constructing a structure on the existing ground described in claim 2 has the constituent feature of the method of claim 1, in which a top surface around the head of the pile is formed which is relatively lower than the top surface of the uppermost part of the embankment.

"A position corresponding to the formation position of the foundation of the structure to be constructed" refers to the construction position of the foundation of the structure to be constructed on the embankment, or the installation position. "Installation" refers to the installation of prefabricated products such as precast concrete members. "Spaced horizontally" mainly refers to the piles being spaced apart in two horizontal directions, but this is not always necessary, and depending on the size and shape of the structure, it may be sufficient to space the piles apart in only one horizontal direction.

"With the upper section exposed above the current ground" means that the driving (driving) of the piles is completed with a section near the top of the pile, including the head of the pile, exposed (protruding) above the ground surface of the current ground. The piles are prefabricated piles such as concrete piles and steel piles, excluding on-site construction piles (cast-in-place piles). The tip (bottom end) of the pile reaches underground in the current ground. If it is a bearing pile, the tip reaches the supporting layer.

The "height at which at least a part of the axial direction of the head of the pile is exposed" refers to the exposure of the head 2a or a part of the part corresponding to the head 2a to the entirety when the embankment 3 is constructed on the current ground 1 as shown in FIG. 1-(b). After the embankment 3 is constructed, only the top surface 2b of the pile head 2a may be exposed on the top surface (ground surface) 3a of the embankment 3 at the time of construction of the foundation 41. By exposing at least a part of the axial direction of the head 2a of the pile 2 , unlike the pile of Patent Document 2, it is possible to construct the foundation 41 of the structure 4 directly on the pile head 2a as shown in FIG. 1-(c) and to have the pile 2 directly support the structure 4, and it is not necessary to remove the soil around the pile head 2a to construct the foundation 41.

"Constructing the foundation of a structure on the head of the pile or including at least a part of the head" means that the degree of exposure of the head 2a varies depending on whether the foundation 41 is pin-connected, semi-rigidly connected, or rigidly connected to the head 2a of the pile 2. In addition, as shown in Figure 2-(c), the foundation 41 may be placed on the top surface 2b of the pile head 2a so that it can slide horizontally.

In the case of a pin joint or a sliding joint, the foundation 41 can be joined or placed (supported) on the top surface 2b of the head 2a as shown in Figure 2-(c), so the foundation 41 is constructed on the head 2a. In the case of a semi-rigid or rigid joint, a part of the head 2a near the top surface 2b is joined so as to be incorporated into the foundation 41 as shown in Figure 1-(c), so the foundation 41 is constructed to include part of the head 2a. The superstructure 45 of the structure 4 is constructed on the foundation 41.

To summarize, when the foundation 41 is pin-jointed to the pile head 2a, the embankment 3 should be constructed so that the top surface 3a of the embankment 3 is aligned with the top surface 2b of the pile head 2a as shown in Fig. 2-(b), and when the foundation 41 is semi-rigidly or rigidly joined, the embankment 3 should be constructed so that at least a part of the pile head 2a, including the top surface 2b, is exposed as shown in Fig. 1-(b). The top surface 3a of the embankment 3 is not necessarily constant (same height) as in the example shown in Fig. 1.

In this way, by constructing the embankment 3 to a height where at least a part of the axial direction of the head 2a of the pile 2 is exposed, the foundation 41 of the structure 4 can be directly joined to or supported by the pile 2 regardless of the joining conditions such as pin joints, so there is a high degree of freedom in the joining between the pile 2 and the foundation 41. In other words, since the joining conditions between the foundation 41 and the pile 2 can be selected according to the scale of the structure 4, it is easy to accommodate (follow) differences in the scale (mass) and structural type of the structure 4 when having a plurality of piles 2 support the structure 4.

In the present invention, by driving piles 2 with their upper sections 2A exposed prior to the construction of the embankment 3 on the existing ground 1, the work of installing a pile driver on the top surface 3a of the embankment 3 and removing (collecting) it, which is required in Patent Document 1 in which the construction of the embankment 3 precedes, is unnecessary. As a result, it is no longer necessary to form a slope between the ground surface of the existing ground 1 and the top surface 3a of the embankment, saving time and costs for slope formation. In Patent Document 1 in which a deck is constructed on the top surface of the ground improvement piles, the ground improvement piles cannot be constructed before the construction of the embankment as described above, which has the disadvantage of sacrificing construction time and costs.

As mentioned above, the formation of a slope requires a site around the embankment large enough to lay the slope, and if the site for laying the slope is not secured, it is impossible to form the slope and install a pile driver, and in Patent Document 1, it is not possible to drive piles. In contrast, the present invention does not require the formation of a slope, so it can be implemented even in places where there is no extra site secured around the embankment (embankment ground), making it possible to build the embankment 3 and construct the structure 4 on top of it.

In particular, if the pile 2 located on the outermost side in a plane as shown in Fig. 1-(b) is located on the inner side of the edge of the top surface 3a of the embankment 3 (claim 3 ), it becomes easier to avoid exposure of the piles and the resulting reduction in the bearing capacity of the piles when a part of the embankment near the edge collapses, as in the case of arranging piles along the edge of the embankment as in Patent Document 1. "On a plane" means when viewed from a plane.

In claim 3, even if a part of the embankment 3 near the edge collapses, the piles 2 are prevented from being immediately exposed, ensuring the stability of the structure 4 supported by the piles 2 and eliminating the need for a surface protection material for the embankment such as the layer thickness management material of Patent Document 1. In addition, it is also possible to construct an upper embankment 6 so as to surround and restrain the foundation 41 of the structure 4 on a plane as shown in Figure 1-(c) (claim 4 ).

In this way, in claim 3 , if an upper embankment 6 is constructed on the top surface 3a of the embankment 3 on the outer periphery of the foundation 41, surrounding the foundation 41 from the outer periphery (claim 4 ), the foundation 41 of the structure 4 is restrained from the outer periphery, thereby further improving the stability of the structure 4, especially against seismic forces.

Because piles with exposed upper sections are driven into the existing ground prior to the construction of the embankment on the existing ground, there is no need to install and remove (collect) a pile driver on the top surface of the embankment, which is required when the embankment is constructed first. As a result, there is no need to form a slope between the surface of the existing ground and the top surface of the embankment, saving time and money for slope formation. Because there is no need to form a slope, it is possible to build the embankment and structures on top of it even in places where there is no extra land available around the embankment ground.

In addition, because the embankment is constructed to a height where at least a portion of the axial direction of the head of the pile is exposed, the foundation of the structure can be directly joined to the pile, regardless of the joining conditions such as pin joints, etc. As a result, the joining conditions between the foundation and the pile can be selected according to the scale of the structure, so that the structure can be supported by multiple piles while responding to differences in the scale and type of structure.

1A to 1C are longitudinal cross-sectional views showing the work procedure from driving a pile into the existing ground to constructing a structure on the pile and embankment when forming a footing that includes the pile head on the head of the pile. 1A to 1C are longitudinal cross-sectional views showing the work procedure from driving piles into the existing ground to constructing a structure on the piles and embankment when constructing a mat slab as a foundation on the pile heads.

Based on Figures 1-(a) to (c), the work procedure from driving multiple piles 2 into the existing ground 1 to constructing a structure 4 on the piles 2 will be explained.

Figure 1-(c) shows the state after a structure 4 has been constructed on the heads 2a of multiple piles 2, or while the structure 4 is being constructed, where the number of piles 2 according to the scale (mass) of the structure 4 to be constructed on the embankment 3 is spaced horizontally into the existing ground 1 as shown in (a), and driven to the required depth using a pile driver 5 as shown in (a). The upper section 2A of the piles 2, including the heads 2a, protrudes above the ground surface of the existing ground 1. The piles 2 are prefabricated piles such as concrete piles, and include friction piles and support piles.

The length of the upper section 2A protruding from the ground surface corresponds to the thickness (depth) of the embankment 3 to be constructed on the current ground 1, but as shown in Figure 1-(b), when the embankment 3 is constructed, the head 2a of the pile 2 protrudes above the top end 3a of the embankment 3. As shown in Figure 2-(b), the length of the upper section 2A may become equal to the thickness of the embankment 3 at the time of construction of the foundation 41. The thickness of the embankment 3 is the distance from the ground surface of the current ground 1 to the top surface 3a of the embankment 3, but the height (level) of the top surface 3a may differ depending on whether it is around the pile 2 or not, as shown in Figure 1-(b).

If the length of the upper section 2A ultimately matches the thickness of the embankment 3, at the time of construction of the foundation 41 after completion of the embankment 3, as shown in Figure 2-(b), only the top surface 2b of the head 2a of the pile 2 will be exposed on the top surface 3a of the embankment 3, and if it is smaller than the thickness of the embankment 3, at least a part of the axial direction of the head 2a will protrude from the top surface 3a of the surrounding embankment 3, as shown in Figure 1-(b).

After the piles 2 are driven, as shown in Figure 1- (b), an embankment 3 is constructed on the existing ground 1 up to a height where at least a part of the axial direction of the heads 2a of the piles 2 is exposed. There are no particular restrictions on the material of the embankment 3, but in order to restrain the multiple piles 2 after construction and suppress vibrations in the upper section 2A, materials containing cement-based materials such as ground improvement soil or fluidized soil are effective.

In the example shown in Figure 1, as shown in (c), the lower end of the foundation beam 43 is located on the top surface 3a of the top of the embankment 3, and the foundation 41 is constructed so that the lower end of the footing 42 is located at a position lower than that position (level), so a top surface 3a that is relatively lower than the top is formed at the position of the lower end of the footing 42, which is lower than the top surface 3a. In the example in Figure 1, a working space for constructing the footing 42 is secured around the footing 42, with a large planar area above the bottom surface of the footing 42, and this space is filled with backfill soil, materials for the embankment 3, etc. after the footing 42 is constructed.

After the embankment 3 is constructed, the foundation 41 of the structure 4 is constructed in a state in which it is supported by the piles 2 as shown in (c). Figure 1 shows an example of the formation of the foundation 41 in which a footing 42 (independent foundation) is constructed to surround the head 2a of each pile 2, and a foundation beam 43 is constructed or laid between the footings 42, 42. In this case, the embankment 3 is constructed so that the head 2a including the top surface 2b of the pile 2 is exposed as shown in (b). When constructing the footing 42, if the embankment 3 is constructed once so that only the top surface 2b is exposed, some of the soil around the head 2a is removed when the footing 42 is formed.

Following the construction of the foundation 41, a superstructure 45, which is the main body of the structure 4, is constructed continuously on top of the foundation 41. When the footing 42 surrounds the head 2a, the footing 42 is semi-rigidly or rigidly connected to the head 2a of the pile 2, and the unity of the foundation 41 including the foundation beams 43 and the multiple piles 2 is easily ensured.

Figure 1-(c) particularly shows an example of a case where an upper embankment 6 is constructed on the embankment 3 around the foundation 41 in order to restrain the foundation 41 from the surroundings on a plane and increase the stability of the structure 4 against seismic forces. In anticipation of the construction of this upper embankment 6, in (b) the piles 2 located on the outermost side on a plane are positioned on the inner side of the edge of the top surface 3a of the embankment 3 on a plane, and a distance for the construction of the upper embankment 6 is secured between the edge of the embankment 3 and the piles 2 on the outer side. There is no restriction on the material of the upper embankment 6, but in order to increase the stability of the structure 4, by using a material containing cement-based materials or fluidized soil for the upper embankment 6, the upper embankment 6 will be improved in ground condition, making it possible to restrain the piles 2 and resist horizontal forces (earthquakes, etc.).

Figure 2 shows an example of a case where a mat slab 44 is constructed as a foundation 41 on the top surface 2b of the piles 2. In this case, the mat slab 44 rests on the top surfaces 2b of the multiple piles 2, and the integrity between the foundation 41 and the multiple piles 2 is relatively lower than in the example of Figure 1, so as shown in Figure 2-(a), more piles 2 are driven in than in the example of Figure 1. In this case, too, the piles 2 are driven in with the upper section 2A of the piles 2, including the heads 2a, protruding from the ground surface of the current ground 1.

After the piles 2 are driven, as in the example of Fig. 1, the embankment 3 is constructed on the existing ground 1 up to a height where at least a part of the axial direction of the heads 2a of the piles 2 is exposed, as shown in (b). As in the example of Fig. 1, when constructing the upper embankment 6 on the embankment 3 around the foundation 41, a distance for constructing the upper embankment 6 is secured between the edge of the embankment 3 and the piles 2 on the outer periphery.

After the embankment 3 is constructed, a foundation 41 of the structure 4 is constructed in a state in which it is supported by the piles 2 as shown in (c). In the example of Fig. 2, a mat slab 44 is constructed on the top surface 2b of the piles 2, so there is no need to form a footing 42 to incorporate the heads 2a of the piles 2 as in the example of Fig. 1. In this relationship, after the embankment 3 is constructed to a height where a part of the axial direction of the heads 2a is exposed , only the top surfaces 2b of the piles 2 need to be exposed at the time of constructing the foundation 41. In this example as well, a superstructure 45 is constructed continuously on the mat slab 44 as the foundation 41.

1(c) shows an example in which a mat slab 44 as a foundation 41 is placed horizontally and slidably on the top surface 2b of the pile 2. In this example, the top surface 2b of the pile 2 and the top surface 3a of the embankment 3 are aligned at the time of construction of the foundation 41 , so the mat slab 44 is placed on the top surface 2b of the pile 2 and the top surface 3a of the embankment 3 and is supported slidably by both. Even if the mat slab 44 is slidable on both top surfaces 2b, 3a, frictional forces, etc. can be set so that sliding occurs only when a horizontal force of a certain level or more is applied to the structure 4.

In this example, in order to restrain the foundation 41 from the surroundings on a planar surface and increase the stability of the structure 4 against seismic forces, an upper embankment 6 is constructed on the embankment 3 surrounding the foundation 41.

1...Current ground condition,
2... Pile, 2a... Head, 2b... Top surface, 2A... Upper section,
3... embankment, 3a... top surface,
4: Structure, 41: Foundation, 42: Footing, 43: Foundation beam, 44: Mat slab, 45: Superstructure,
5... Pile driver,
6...Upper embankment.

Claims (4)

A plurality of piles are driven into the existing ground at intervals horizontally from a position corresponding to the position of the foundation of a structure to be constructed higher than the ground surface of the existing ground, with the upper section exposed above the existing ground;
After constructing an embankment on the existing ground to a height where at least a part of the axial direction of the head of the pile is exposed,
A method for constructing a structure on existing ground, comprising constructing the foundation of the structure on or including at least a portion of the head of the pile, and constructing the superstructure of the structure on the foundation. 2. The method for constructing a structure on an existing ground according to claim 1, characterized in that a top surface is formed around the head of the pile that is relatively lower than the top surface of the uppermost part of the embankment. A method for constructing a structure on existing ground as described in claim 1 or claim 2, characterized in that the pile that is located most outer on a plane among the plurality of piles is positioned inner than the edge on a plane of the top surface of the embankment. 4. A method for constructing a structure on an existing ground as described in claim 3 , characterized in that an upper embankment is constructed on the top surface of the embankment on the outer periphery side of the foundation, surrounding the foundation from the outer periphery side.

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