JP6772098B2 - Ground improvement method - Google Patents

Description

The present invention relates to a ground improvement method for constructing sand piles in the ground and compacting the ground to improve the ground.

As an example of a ground improvement method for compacting and improving the ground, a sand press-fit type static compaction method is known.
The sand press-fit type static compaction method has a rod that press-fits fluidized sand into the ground from the lower end, penetrates the rod to a predetermined depth, and press-fits the fluidized sand from the rod into the ground until it reaches a predetermined pressure. By expanding the diameter of the fluidized sand in the ground, the surrounding ground is compacted. By doing this from a predetermined depth upward, sand piles are created in the ground to compact and improve the ground.

In this sand press-fit type static compaction method, the design target improvement rate is obtained in advance, the press-fit amount of fluidized sand into the ground is calculated from the design target improvement rate, and fluidization is performed based on this press-fit amount. Press the sand into the ground. The target improvement rate in design is obtained by an appropriate calculation method that has been conventionally used.
However, the N value and density of the ground vary depending on the ground and the depth, and the target improvement rate in the design obtained in advance is greatly affected by these variations.
That is, in the sand press-fit type static compaction method, fluidized sand is press-fitted based on the press-fit amount calculated from the design target improvement rate, and sand piles are created in the ground to compact the ground. During the construction of this sand pile, the fluidized sand press-fitted into the ground may cause a large uplift of the ground surface or a lateral displacement that displaces in the horizontal direction in the shallow part of the ground.

Therefore, conventionally, in the sand press-fit type static compaction method, a vibrator is attached to the lower end of the rod, the rod is penetrated to a predetermined depth, and after penetration, the vibrating ground is vibrated and compacted. Subsequently, while pulling out the rod at a predetermined pitch, a predetermined amount of fluidized sand is press-fitted to compact the surrounding ground. This is done from a predetermined depth to the top. At this time, the volume decrease due to vibration and the volume increase due to press-fitting of fluidized sand into the ground are made the same. As a result, it is possible to reduce the occurrence of a large uplift of the ground surface or lateral displacement in a shallow part of the ground when the sand pile is constructed (see Patent Document 1).

However, in this sand press-fit type static compaction method, compaction is performed by vibration, and then compaction is performed by press-fitting fluidized sand. After that, compaction is performed again by vibration, and then compaction is performed by press-fitting the fluidized sand. That is, compaction by vibration and compaction by press fitting of fluidized sand are alternately performed, and this is performed from a predetermined depth to the upper side. Therefore, it takes a lot of time to construct one sand pile, and there is a risk that the construction period for ground improvement will be long. In addition, the equipment used for work is equipped with a vibrator attached to a rod that presses fluidized sand into the ground so that both compaction by vibration and compaction by press fitting of fluidized sand can be performed. It is a dedicated machine with a complicated structure and high cost. Therefore, the cost of ground improvement work is high.

Japanese Unexamined Patent Publication No. 2014-177977

The present invention has been made in view of such a problem, and an object of the present invention is to shorten the construction period and reduce the cost in the ground improvement work for compacting and improving the ground.

The present invention has a first rod-shaped member that can penetrate and pull out into the ground and is equipped with a vibration / impact generating means that generates vibration or impact, and penetrates the first rod-shaped member to a predetermined depth. , The first step of compacting the surrounding ground by applying vibration or impact to the surrounding ground by means of vibration / impact generating means, and compacting the surrounding ground by vibration or impact from a predetermined depth upward, and enabling penetration and withdrawal into the ground. It also has a second rod-shaped member that goes up and down to discharge the sand material from the lower end, and after the first step, the second rod-shaped member penetrates to a predetermined depth and the sand material is discharged from the second rod-shaped member into the ground. The ground improvement has a second step of expanding the diameter of the sand material to compact the surrounding ground, and expanding the diameter of the sand material to compact the surrounding ground from a predetermined depth upward to create a sand pile. The method.

According to the present invention, the work of applying vibration or impact to the ground by the vibration / impact generating means of the first step to compact the ground, and discharging the sand material of the second step into the ground to expand the diameter of the sand material to expand the ground. By performing the compaction work individually instead of alternately performing the work as in the conventional case, each work can be performed efficiently and the construction period can be shortened.
Further, as the apparatus, the apparatus used in the first step and the apparatus used in the second step are separated, and each apparatus is made into a machine having a simple structure and inexpensive. As a result, the work can be performed without using a dedicated machine having a complicated structure and expensive as in the conventional case, and the cost in the ground improvement work can be reduced.

It is explanatory drawing of the 1st apparatus used in the ground improvement method of this invention. It is explanatory drawing which shows the operation of the vibration / shock generating means of the 1st apparatus. It is explanatory drawing of the 2nd apparatus used in the ground improvement method of this invention. It is explanatory drawing which shows the 1st step of the ground improvement method of this invention. It is explanatory drawing which shows the 2nd step of the ground improvement method of this invention. It is explanatory drawing which shows the working state of the 1st process and 2nd process. It is a schematic diagram for demonstrating the state of the ground in the 1st step and the 2nd step. It is explanatory drawing which shows the state of the ground when the ground is improved. It is explanatory drawing which shows the work of the 3rd process. It is explanatory drawing which shows the state of the displacement which occurs in the existing structure.

An embodiment of the ground improvement method of the present invention will be described with reference to the drawings.
The ground improvement method is roughly a first step of penetrating a first rod-shaped member to a predetermined depth, applying vibration or impact to the surrounding ground to compact it, and performing this from a predetermined depth upward. After the process, the second rod-shaped member is penetrated to a predetermined depth, the sand material is discharged into the ground, the diameter of the sand material is expanded to compact the surrounding ground, and this is performed from the predetermined depth upward to the sand pile. It has a second step of creating the above.

In the ground improvement method of the present embodiment, in the second step, the ground improvement by the sand press-fit type static compaction method, which is one of the ground improvement methods, will be described as an example. However, the ground improvement is not limited to this, and the ground may be improved by other construction methods such as the sand compaction pile construction method.

The device for improving the ground by this ground improvement method is composed of a first device 1 used in the first step and a second device 2 used in the second step.
FIG. 1 is an explanatory view of the first device used in the ground improvement method of the present embodiment, FIG. 2 is an explanatory view showing the operation of the vibration / impact generating means of the first device, and FIG. 3 is the ground improvement of the present embodiment. It is explanatory drawing of the 2nd apparatus used in the method.

As shown in FIG. 1, the first device 1 has a self-propelled construction machine 10, and the construction machine 10 is, for example, a general construction machine having an arm 11. The construction machine 10 has a first rod-shaped member 12 at the tip of the arm 11, and the first rod-shaped member 12 is a casing that goes up and down so that it can penetrate and pull out into the ground.

A vibration / shock generating means 13 that generates vibration or shock is attached to the first rod-shaped member 12. Here, the vibration / shock generating means 13 generates a shock S. As shown in FIG. 2A, the vibration / impact generating means 13 is provided with a weight 14 that moves up and down and an air cylinder 15 that moves the weight 14 inside the first rod-shaped member 12. Four wedge-shaped sliders 16 are provided under the weight 14, and four impact generating plates 17 are provided so as to face the four sliders 16, and the impact generating plates 17 project horizontally from the first rod-shaped member 12. ..

In the operation of the vibration / impact generating means 13, as shown in FIG. 2 (B), the weight 14 located above is pushed down vigorously by the air cylinder 15, and the slider 16 is pushed down by the weight 14, and FIG. As shown in (C), the four impact generating plates 17 project vigorously in the horizontal direction from the first rod-shaped member 12. The impact S can be applied to the ground by the protrusion of the impact generating plate 17.

The vibration / impact generating means 13 attached to the first rod-shaped member 12 is not limited to that of the above-mentioned mechanism, and may be of another mechanism. Further, the vibration S may be generated instead of generating the impact S. Although not shown, the vibration / shock generating means 13 that generates vibration is provided with, for example, a rotating motor and an eccentric weight that rotates eccentrically inside the first rod-shaped member 12, and the first rod-shaped member is rotated by the rotation of the eccentric weight. A type that vibrates the member 12 or a type in which a vibration generator is attached to the upper end of the first rod-shaped member 12 and the entire first rod-shaped member 12 is vibrated by the vibration generator may be used.

As shown in FIG. 3, the second device 2 has a self-propellable construction machine 20, and the construction machine 20 has a mast 21 erected in front of the mast 21 and a second rod-shaped member along the mast 21. 22 has. The second rod-shaped member 22 is a casing that faces up and down, and allows penetration and withdrawal into the ground, through which fluidized sand (sand material) and compressed air pass. The upper part of the second rod-shaped member 22 has a rotating portion 23 for rotating the second rod-shaped member 22 and an elevating portion 24 for penetrating or pulling out the second rod-shaped member 22 into the ground. Further, at the lower end of the second rod-shaped member 22, a discharge port 25 for discharging fluidized sand into the ground is provided.
Here, the fluidized sand is a sand material that has been fluidized by mixing a fluidizing agent with the sand.
Further, the sand material is not limited to fluidized sand. For example, when the ground is improved by the sand compaction pile method in the second step, the sand material is sand, crushed stone, slag, or a mixture thereof. ..

Further, the second device 2 has a peripheral equipment 30 for supplying fluidized sand to the second rod-shaped member 22 of the construction machine 20, and the peripheral equipment 30 mixes a fluidizing agent with the sand to generate fluidized sand. The fluidized sand generator 31 is provided, and the fluidized sand is sent out from the fluidized sand generator 31 by a pressure pump 32, and the fluidized sand is supplied to the second rod-shaped member 22 via the pressure gauge 33.

Next, the ground improvement method of this embodiment will be specifically described.
FIG. 4 is an explanatory diagram showing the first step, FIG. 5 is an explanatory diagram showing the second step, and FIG. 6 is an explanatory diagram showing the working states of the first step and the second step.

In the first step, as shown in FIG. 4A, the first rod-shaped member 12 of the first device 1 is penetrated to a predetermined depth, for example, 5 to 6 m from the ground surface. After the penetration, as shown in FIG. 4B, the vibration / impact generating means 13 attached to the first rod-shaped member 12 is operated to apply an impact S to the surrounding ground to compact it. After compaction, the first rod-shaped member 12 is pulled upward by, for example, 50 to 100 cm. After that, as shown in FIG. 4C, the vibration / impact generating means 13 is operated again to apply an impact S to the surrounding ground to compact it. As shown in FIG. 4 (D), this is repeated from a predetermined depth upward, and as shown in FIG. 4 (E), the ground is compacted by the impact S to the vicinity of the ground surface.
The compaction of the ground by the impact S is sequentially performed at a plurality of predetermined locations P1. That is, as shown in FIG. 6A, the ground compaction portion P1 by the impact S is performed at intervals of 1 to 2 m in a range of, for example, 10 m in width and 20 m in length. The ground surface sinks due to the compaction of the ground by this impact S.

The second step after the first step is performed based on the result of compaction of the ground by the impact S of the first step, and as shown in FIG. 5 (A), the second rod shape of the second device 2. The member 22 is penetrated to a predetermined depth, for example, 5 to 6 m from the ground surface. After the penetration, as shown in FIG. 5 (B), a predetermined amount of fluidized sand R is press-fitted (discharged) into the ground from the discharge port 25 while pulling out the second rod-shaped member 22 upward by, for example, 20 to 30 cm. The fluidized sand R press-fitted inside is expanded in diameter to compact the surrounding ground. After that, as shown in FIG. 5C, while pulling out the second rod-shaped member 22 upward by, for example, 20 to 30 cm, a predetermined amount of fluidized sand R is press-fitted into the ground from the discharge port 25 to remove the surrounding ground. Compact. As shown in FIG. 5 (D), this is repeated from a predetermined depth upward, and as shown in FIG. 5 (E), the ground is compacted by press-fitting the fluidized sand R into the ground near the ground surface. Do up to. As a result, a sand pile T whose diameter is expanded from a predetermined depth to the vicinity of the ground surface is created.
The compaction of the ground by press-fitting the fluidized sand R into the ground is sequentially performed at a plurality of predetermined locations P2. That is, as shown in FIG. 6B, the portion P2 for compacting the ground by press-fitting the fluidized sand R into the ground is predetermined in the vicinity of the portion P1 for compacting the ground due to the impact S in the first step. It is performed at intervals, for example, at intervals of 1 to 2 m. The compaction of the ground by press-fitting the fluidized sand R into the ground (creating a sand pile T that expands in diameter) raises the ground surface that sank in the first step, thereby eliminating the subsidence of the ground surface. Return to the original flat surface.

It should be noted that the ground compaction points P2 due to the press-fitting of the fluidized sand R into the ground are performed at predetermined intervals in the vicinity of the ground compaction points P1 due to the impact S in the first step. Based on the result of compaction of the ground by the impact S in the first step, the locations P2 may be performed at arbitrary locations instead of at predetermined intervals.

Next, the principle that the ground surface subsides in the first step and the ground surface subsided in the second step rises and returns to the original flat surface will be described.
FIG. 7 is a schematic diagram for explaining the state of the ground in the first step and the second step. Here, the gap ratio is shown in order to make the relative density Dr of the ground easy to understand.
FIG. 7A shows the state of the ground before the work of the first step, for example, the initial gap ratio e0 when the relative density Dr is 45%.
FIG. 7B shows a state of the ground when the ground is compacted by applying an impact S to the ground by the vibration / impact generating means 13 in the first step, and the relative density Dr increases from 45% to 65%. The gap ratio e1 is also reduced by that amount, indicating that the volume is reduced (broken line portion in the figure) due to the impact S.
FIG. 7C shows the state of the ground when the fluidized sand R is press-fitted into the ground to expand the volume of the fluidized sand R and compact the ground in the second step. It shows a state in which fluidized sand R having the same volume Δe as the volume decreased when the ground is compacted by applying an impact S is press-fitted into the ground. As a result, the relative density Dr increases from 65% to 75%, and the ground is compacted.
That is, in this ground improvement method, the volume decrease due to the impact S and the volume increase due to the press-fitting of the fluidized sand R into the ground are made the same. According to such a principle, the ground surface subsided in the work of the first step rises in the work of the second step, the subsidence of the ground surface disappears, and the original flat surface is restored. In addition, after the second step, the ground surface does not rise significantly or lateral displacement in the shallow part of the ground does not occur.

As described above, according to the ground improvement method of the present embodiment, in the first step, only the work of applying an impact S to the ground by the vibration / impact generating means 13 to compact the ground is performed, and in the second step, the flow is performed. Only the work of press-fitting (discharging) the fossilized sand R (sand material) into the ground to expand the diameter of the fluidized sand R and compact the ground is performed. As a result, the work of applying an impact S to the ground to compact it and the work of press-fitting the fluidized sand R into the ground to expand the diameter of the fluidized sand R and compacting the ground are not performed alternately. By performing each of the steps individually, each work can be performed efficiently and the construction period can be shortened.
Further, for example, when the work of the second step after the first step is performed, the two works can be performed in parallel by performing the work of the first step at another place, and this also allows the construction period. Can be shortened.

In the ground improvement method, in the first step, the ground is compacted by the impact S without press-fitting the fluidized sand R, and in the second step, the result of the compaction of the ground by the impact S in the first step (first step). Based on the amount of ground subsidence caused by the compaction of the ground due to the impact S of the process), the fluidized sand R is press-fitted to compact the ground. As a result, the amount of fluidized sand R press-fitted into the ground in the second step can be adjusted to an appropriate amount, and the ground can be improved with high accuracy. Further, by eliminating the useless use of fluidized sand R and reducing the amount of fluidized sand R used, it is possible to reduce the cost in the ground improvement work.

As for the device, the device used in the first process (first device 1) and the device used in the second process (second device 2) are separated, and each device is made into a machine having a simple structure and inexpensive. .. As a result, the work can be performed without using an expensive dedicated machine capable of both compaction by vibration and compaction by press-fitting of fluidized sand, and the cost in the ground improvement work can be reduced.

In the ground improvement method, the press-fitting (discharge) of the fluidized sand R (sand material) into the ground in the second step is such that an appropriate amount of the fluidized sand R (sand material) is press-fitted (discharged) into the ground. The press-fitting amount (discharge amount) is calculated, and the fluidized sand R (sand material) is discharged into the ground based on the calculated press-fitting amount (discharge amount). The press-fitting amount (discharge amount) of the fluidized sand R (sand material) is calculated based on the result of compaction of the ground due to vibration or impact in the first step.

The amount of fluidized sand R press-fitted into the ground is calculated as follows.
First, the improvement rate as1 generated by the compaction of the ground due to the vibration or impact of the first step is obtained, and the target improvement rate as2 is determined from this improvement rate as1. This target improvement rate as2 is obtained by subtracting the improvement rate as1 generated by the compaction of the ground due to the vibration or impact of the first step from the design target improvement rate as obtained in advance.
That is, the formula for obtaining the target improvement rate as2 is as2 = as-as1.
From the target improvement rate as2 thus obtained, the press-fitting amount of the fluidized sand R so as to reach the target improvement rate as2 after the press-fitting of the fluidized sand R is calculated.
Here, the improvement rate is a value indicating an effect when improving the ground, and is sometimes called a replacement rate.

Next, a design target improvement rate as and a method of obtaining an improvement rate as1 caused by compaction of the ground due to vibration or impact in the first step will be described.

FIG. 8 is an explanatory diagram showing a state of the ground when the ground is improved.
Before the improvement of the ground, as shown in FIG. 8 (A), the ground has a volume of 1 + e0. After the improvement of the ground, as shown in FIG. 8B, the fluidized sand R corresponding to Δe (e0-e1) is press-fitted to improve the ground. The basic calculation formula of the design target improvement rate as at this time is shown by the following formula. In addition, e0 is the gap ratio of the initial ground, and e1 is the gap ratio of the ground after improvement, and these are obtained from a preliminary test conducted in advance or an existing relational expression.

From this calculation formula, the target improvement rate as in design can be obtained.

Next, the improvement rate as1 generated by the compaction of the ground due to the vibration or impact of the first step is obtained. In this case, first, the average subsidence amount S of the ground is obtained. The average subsidence amount S of the ground is expressed by the following equation. In addition, e0 is the gap ratio of the initial ground, e1 is the gap ratio of the ground after improvement, and H is the thickness of the layer to be improved.

The improvement rate as1 is obtained from the average subsidence amount S of the ground obtained by this calculation formula. Since Δe / (1 + e0) in the equation for obtaining the average subsidence amount S of the ground is the improvement rate as1, the improvement rate as1 is expressed by the following equation.

From this calculation formula, the improvement rate as1 caused by the compaction of the ground due to the vibration or impact of the first step can be obtained.

As described above, according to the ground improvement method of the present embodiment, an appropriate amount of fluidized sand R (sand material) is press-fitted (discharged) into the ground in the second step, so that the first step When the ground surface subsided in the above is raised, it is possible to prevent the ground surface from being raised more than the original flat surface or lateral displacement in the shallow part of the ground. Further, by eliminating the use of wasteful fluidized sand R (sand material), rationalization can be achieved and the cost in the ground improvement work can be reduced.

Next, another embodiment of the ground improvement method of the present invention will be described.
The ground improvement method has the same first step and second step as in the above-described embodiment, and has a third step after the second step.
In the third step, as in the first step, the first rod-shaped member 12 is penetrated to a predetermined depth, and the surrounding ground is compacted by applying vibration or shock S by the vibration / shock generating means 13, and the surroundings due to vibration or shock. The ground is compacted from a predetermined depth to the upper side.

The ground improvement method having such a third step is effective for ground improvement in the place where the existing structure K exists.
FIG. 9 is an explanatory diagram showing the work of the third step, and FIG. 10 is an explanatory diagram showing a state of displacement occurring in the existing structure.
That is, when the ground is compacted by press-fitting the fluidized sand R into the ground in the second step in the ground near the existing structure K, the adjacent existing structure K is displaced and the existing structure K is installed. There is a risk of adversely affecting the structure K. Therefore, in a place close to the existing structure K, as shown in FIG. 9, after the second step, the ground is compacted by vibration or impact S, which is less likely to adversely affect the existing structure K (third step). I do. The ground compaction portion P3 due to the vibration or impact S in the third step is narrower than, for example, the interval of the ground compaction portion P1 in the first step. As a result, the ground at a location close to the existing structure K can be reliably compacted and the ground can be improved without adversely affecting the existing structure K.

In this ground improvement method, the displacement that occurs in the existing structure K will be described.
The displacement generated in the existing structure K is measured by a displacement pile installed in the immediate vicinity of the existing structure K.
As shown in FIG. 10, when the ground is compacted by the vibration or impact S in the first step, a displacement Da on the retracting side that tries to attract the existing structure K from the existing structure K toward the compacted portion occurs. .. Next, when the ground is compacted by press-fitting the fluidized sand R into the ground in the second step, the extruding side that tries to extrude the existing structure K from the compacted portion toward the existing structure K. Displacement Db occurs. Next, when the ground is compacted by the vibration or impact S in the third step, the displacement Dc on the retracting side that tries to attract the existing structure K from the existing structure K toward the compacted portion is generated again.

That is, in the first step, the displacement Da on the pull-in side is generated, in the second step, the displacement Db on the push-out side is generated, and in the third step, the displacement Dc on the pull-in side is generated. As a result, the displacement Db on the extrusion side generated in the second step is corrected by the displacement Dc on the pull-in side generated in the third step, and finally the displacement generated in the existing structure K is within the allowable range (FIG. It can be stored in the shaded area inside) so as not to adversely affect the existing structure K.

1 ... 1st device, 2 ... 2nd device, 10 ... Construction machine, 11 ... Arm, 12 ... First rod-shaped member, 13 ... Vibration / shock generating means, 14 ... Weight, 15 ... Air cylinder, 16 ... Slider, 17 ... Impact generator, 20 ... Construction machine, 21 ... Mast, 22 ... Second rod-shaped member, 23 ... Rotating part, 24 ... Elevating part, 25 ... Discharge port, 30 ... Peripheral equipment, 31 ... Fluidized sand generator, 32 ... Pressure pump, 33 ... Pressure gauge.

Claims (4)

It is a ground improvement method that creates sand piles in the ground to compact the ground and improve the ground.
It has a first rod-shaped member that can penetrate and pull out into the ground and is equipped with a vibration / shock generating means that generates vibrations and shocks, and penetrates the first rod-shaped member to a predetermined depth to vibrate / shock. The first step in which vibration or impact is applied to the surrounding ground by the generating means to compact the surrounding ground, and the surrounding ground is compacted by vibration or impact from a predetermined depth upward.
It has a second rod-shaped member that can penetrate and pull out into the ground and that discharges sand material from the lower end, and after the first step, the second rod-shaped member is penetrated to a predetermined depth to allow the second rod-shaped member to penetrate. The sand material is discharged into the ground from the ground, the diameter of the sand material is expanded to compact the surrounding ground, and the surrounding ground is compacted by expanding the diameter of the sand material from a predetermined depth to the upper side to create a sand pile. 2 steps and
A ground improvement method characterized by having. In the ground improvement method according to claim 1,
The improvement rate caused by the compaction of the ground due to vibration and impact in the first process is obtained, the target improvement rate is set from this improvement rate, and the amount of sand material discharged into the ground in the second process is calculated from the target improvement rate. A ground improvement method characterized in that sand material is discharged into the ground based on the calculated discharge amount. In the ground improvement method according to claim 2,
The target improvement rate is a ground improvement method characterized in that it is obtained by subtracting the improvement rate generated by compaction of the ground due to vibration or impact in the first step from the design target improvement rate obtained in advance. In the ground improvement method according to any one of claims 1 to 3,
After the second step, the first rod-shaped member is penetrated to a predetermined depth, and the surrounding ground is compacted by applying vibration or shock by the vibration / shock generating means, and the surrounding ground is compacted by the vibration or shock to the predetermined depth. A ground improvement method characterized by having a third step performed from the top to the top.

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