JP4566634B2 - Ground improvement method - Google Patents

Description

The present invention relates to a ground improvement method for preventing settlement of these structures when a house, a road, a retaining wall, or the like is built on a soft ground.

When building houses on the soft ground created by lakes and paddy fields, the ground may sink rapidly even if solid foundations are used, and some ground improvement is necessary to prevent this. As an example of this ground improvement, a solid layer such as cement is sprinkled and stirred to a depth of about 1m, and the entire ground is hardened by solidification of the solidified material. If it cannot be overcome, a columnar improvement method for constructing a pillar in which solidified material and soil are mixed in the ground, a steel pipe pile method for driving a metal pipe, and the like can be mentioned. In addition to these methods, a method as described in Patent Document 1 below has been developed, and a construction method for preventing ground subsidence has already been established.
Japanese Patent No. 3450725

  The surface layer improvement method and the columnar improvement method as described above have many construction results so far, and their effects have been recognized but have drawbacks. First, in the surface layer improvement method, when there is a humus layer in the ground, the cement may not solidify, and depending on the geology, there is a risk that harmful substances such as hexavalent chromium may be generated due to chemical reaction with the cement. In addition, all of the surface layer improvement method, columnar improvement method, and steel pipe pile method will be in a state where concrete objects such as concrete blocks and piles are buried in the ground, and if the land is sold later, these artifacts will be removed. There are concerns that are required. And if these removals are actually carried out, it will be necessary to bear a large expense, which is expected to affect land transactions.

  The method according to Patent Document 1 forms a pile using crushed stone in the ground. In this case, the crushed stone is simply buried in the ground, and when the land is sold, it is removed to restore the current state. do not have to. However, when actually carrying out the invention, pressurized air and water are required, and in addition to the excavator, mechanical equipment for handling these fluids becomes large, and an increase in cost is inevitable. Therefore, for housing applications with tight budgets, adoption is often postponed even if the advantages are taken into account.

The present invention was developed on the basis of such circumstances, and when building a structure such as a house on soft ground, it is possible to reliably prevent land subsidence at the lowest possible cost and to give a great change to the ground. The purpose is to provide ground improvement methods that are also environmentally friendly.

The invention according to claim 1, which solves the above problem, is a cylindrical and tapered body having a diameter equivalent to a hole formed in the ground, and a blade spirally joined around the body, The projecting length of the blade is 1/5 to 20 times the maximum diameter of the fuselage. by bite into the ground, when you form a hole by burying the screw drill thrust by the blade to a predetermined depth, water squeezed out around the press and while seeking the hole to ground in the radial direction of the screw drill by fuselage after forming the modified region flowability is reduced is, in order to prevent collapse of the reforming zone, withdrawing the screw drill from the ground while feeding air into the hole from the body of the tip, the center of the reforming zone Building a reinforcing layer packed aggregate the formed hole, a method for improving the soil, characterized in that supporting a structure by reinforcing layer.

  In the present invention, a hole is constructed in a soft ground with a screw drill, and aggregates such as crushed stone are filled in the holes, and a load of a structure such as a house is received by a reinforcing layer made of the aggregate. The screw drill has an elongated shape, and a machine that imparts rotation to the opposite base end side is attached with a sharp tip facing the ground. In addition, a spiral blade is joined to the outer periphery of the screw drill. When the screw drill is brought upright and brought into contact with the ground, and then the screw drill is rotated, a propulsive force is generated by the blade, so that it is self-supporting. It will be buried in the ground.

  When the screw drill is buried, the soft ground is pushed out in the radial direction of the screw drill to form a hole. At this time, pressure is applied to the ground by extrusion, so the density of the soil increases and moisture is squeezed out. As a result, a modified zone with reduced fluidity is formed, and the soil wall around the hole is hardened and hardly collapses. Therefore, after the screw drill is buried to a predetermined depth determined at the time of design, the soil wall constituting the hole does not collapse even after the screw drill is extracted, and the hole can be filled with aggregates such as crushed stone. When this aggregate is solidified and a strengthening layer is built into the surrounding ground, the aggregate is pushed into the ground, and the load is dispersed over a wide range, thereby suppressing the ground subsidence.

The screw drill is composed of a cylindrical body and blades spirally joined around the body , and the body is formed in a tapered shape toward the tip. The fuselage has a generally cylindrical shape with a hollow interior, and is equipped with blades formed by joining steel plates in a spiral shape around the fuselage, using the same principle as wood screws. Propulsion in the direction is generated. When the screw drill is buried in the ground, the space pushed by the trunk becomes a hole for filling the aggregate. Therefore, the body and the hole necessarily have the same diameter.

  Moreover, the circumference of a hole can be strengthened most effectively by making the protrusion length of the blade | wings joined to the circumference | surroundings of a screw drill into the range of 1/5 to 1/20 of the largest diameter of a fuselage | body. Here, the protruding length of the blade indicates the distance from the outer periphery of the fuselage to the outer edge of the blade. If the protruding length is short, the propulsive force by the blade is insufficient and the blade cannot be buried in the ground. If it is large, the friction between the blade and the ground will increase, so it will be necessary to increase the rotational force and the blade will disturb the surroundings of the hole. Considering such points, by setting the protrusion length of the blade to the above numerical range, it is possible to construct a more healthy hole with a small rotational force.

  When the screw drill reaches a predetermined depth and is extracted from the ground, the soil wall around the hole may be weakened due to the pressure drop in the ground depending on the geology, depending on the geology. Therefore, when the screw drill is extracted from the ground, air is sent into the hole from the front end of the trunk to prevent the reformed region from collapsing. By sending air into the hole in this way, when extracting the screw drill, the pressure drop in the hole can be prevented and the soundness of the hole can be maintained.

  As in the first aspect of the invention, the screw drill is buried in the ground, and the surrounding ground is pushed outward to apply pressure to the ground, the water is squeezed out, the fluidity is reduced, and the screw drill is removed. Later, a hole equivalent to the shape of the screw drill is formed, and the surrounding earth wall does not collapse. Therefore, aggregates such as crushed stones can be fully packed, and a reinforcing layer that is tightly intertwined with the ground by solidifying the aggregate is built, and the load of the structure built on the reinforcing layer is thereby grounded Can be dispersed widely, and land subsidence can be suppressed. Moreover, the ground is only filled with aggregates such as crushed stone, and problems such as generation of harmful substances and removal of buried objects do not occur. Furthermore, the present invention can be basically constructed with a screw drill and a machine that rotates the screw drill, can reduce the equipment cost, and can shorten the time required because the operation is simple.

  In addition, when pulling out the screw drill from the ground, by sending air from the tip of the fuselage into the hole, the pressure drop inside the hole formed between the ground and the screw drill tip can be prevented, and the surrounding earth wall collapses To improve work reliability.

  FIG. 1 shows an outline of a method for improving the ground 5 according to the present invention in time series. First, FIG. 1 (A) is a stage before the work is started, and the ground 5 is in a soft state where it gradually sinks when a load is applied. In order to drive the screw drill 1 there, it is suspended vertically with the tip downward. Lower. When the screw drill 1 is gradually lowered, the tip of the screw drill 1 pierces into the ground 5. At this stage, when the screw drill 1 is rotated in a predetermined direction around the axis, the blade 4 at the tip of the blade 3 pierces the ground 5 and then the blade 3 bites into the ground 5 so that the screw drill 1 is buried in the ground 5. Propulsion is generated. FIG. 1B shows a state where the screw drill 1 is rotated in the direction indicated by the arrow and embedded to a predetermined depth. The screw drill 1 is formed with an introduction portion that tapers toward the tip. Therefore, as shown by an arrow in the figure, the ground 5 is pushed out in a substantially horizontal direction, and dehydration is caused by an increase in pressure at this time. Since the action and the compacting action work, the fluidity of the surrounding ground 5 is lowered to be in a tightly tightened state, whereby the hole 6 is formed in the ground 5.

  When the screw drill 1 reaches the depth determined at the time of design, the rotation method is reversed as shown in FIG. 1C, and this is extracted from the ground 5 by the propulsive force of the blades 3. The periphery of the hole 6 is compacted to a range corresponding to the diameter of the screw drill 1 to form a modified region 13 having changed soil properties. Therefore, the earth wall does not collapse rapidly, but aggregate 7 such as crushed stone is put into the hole 6 as soon as possible. The aggregate 7 is spread with a high density so as not to generate a cavity in the middle, and is further solidified by using a compactor or the like in order to prevent sinking over time. As a result, the reinforcing layer 8 in which the aggregate 7 is spread vertically is formed, and the foundation 10 is constructed on the structure 10 as shown in FIG. To prevent. Prior to the construction of the foundation 10, it is desirable to apply a force about three times the design load to the reinforcing layer 8 to confirm that there is no sinking.

  FIG. 2 shows a shape example of the screw drill 1 according to the present invention. 2A is a plan view, FIG. 2B is a front view, and FIG. 2C is a cross-sectional view taken along line AA. This product is composed of a fuselage 2 having a circular cross section using a general-purpose steel pipe and a blade 3 surrounding the periphery of the fuselage in a spiral shape, and a grip portion 12 using a square bar for attaching an auger or the like to the upper portion of the fuselage 2. Is formed. The upper part of the body 2 is a simple cylindrical shape, but the lower part is tapered in a conical shape so that the ground 5 can be smoothly spread. Furthermore, since the most advanced contact of the screw drill 1 with the ground 5 is the most intense, the tip is sharply formed after increasing the thickness. The blade 3 is joined to the entire body 2 at the same pitch, and the tip of the blade 3 is provided with a sharp face 4 formed so as to be able to bite into the ground 5 smoothly. When you hit them, push them out. In addition, a pipe 26 a that functions as air supply means 21 a described later is inserted into the body 2, and this end is exposed to the outside above the body 2.

  The screw drill 1 depicted in FIG. 2 has a total length of 2.3 m, the maximum diameter of the fuselage 2 is 400 mm, the length of the tapered section of the fuselage 2 is 1.5 m, and the pitch of the blades 3 joined in a spiral shape. Is 200 mm, and the protruding length from the body 2 is 25 mm throughout. The thickness of the blade 3 is 12 mm from the face 4 to the second pitch, but the subsequent intermediate portion is 9 mm and the proximal end is 6 mm. By changing the thickness of the blade 3 in this way, both securing strength and reducing friction are achieved, and finishing processing is performed so that an extreme step does not occur at the portion where the thickness of the blade 3 changes. . As for the size of the screw drill 1, the size depicted here is standard, but an optimum shape is selected and used depending on the conditions such as geology and load resistance.

  The state at the time of using the screw drill 1 is shown in FIG. 3A is before the start of work, and FIG. 3B is being worked. In order to rotate the screw drill 1, the grip portion 12 is fitted in the auger 16, and the auger 16 is attached to the tip of the arm 15 of the self-propelled excavator 14. Since the excavator 14 can move freely, the position adjustment is very simple, and the height of the screw drill 1 can be adjusted by changing the posture of the arm 15. For this reason, it is possible to quickly move to a target position and immediately start work, and when the same work is repeated at different locations, the efficiency is extremely high. The auger 16 is driven by hydraulic pressure, which is supplied from the power shovel 14 and can be started and stopped, and the rotation direction can be switched by operating the lever from the driver's seat.

  When constructing the hole 6, when the position of the power shovel 14 is adjusted and the auger 16 is operated and the arm 15 is lowered, the tip of the screw drill 1 comes into contact with the ground 5 and the blade 3 is grounded. Start biting into 5. After this, propulsive force is generated by the blade 3, so that the arm 15 can be freely moved and waits for the screw drill 1 to reach a predetermined depth. In addition, after the screw drill 1 is buried, when scooping up the earth and sand using the blade 3, the arm 15 is fixed and only the auger 16 is operated. When the screw drill 1 is extracted from the ground 5, the rotation direction of the auger 16 is reversed. At this time, the arm 15 is also lifted in synchronization.

  FIG. 4 shows a construction method in the case of scooping up the earth and sand in the ground 5 with the screw drill 1 and is applied when the earth pressure is high. FIG. 4 (A) shows the construction of the hole 6, and the screw drill 1 rotates in the direction indicated by the arrow and moves downward. When the predetermined depth is reached, the screw drill 1 continues to rotate as shown in FIG. Then, the earth and sand pushed out by the screw drill 1 is pushed back to the periphery of the screw drill 1 by the reaction force, the earth and sand are scooped up by the blades 3 as indicated by arrows, and the discharged earth 20 accumulates on the ground surface. When a certain amount of earth and sand is picked up, the periphery of the hole 6 is gradually stabilized and the earth and sand are not pushed back. Therefore, the screw drill 1 is not rotated as shown in FIG. Finally, the hole 6 surrounded by the modified region 13 as shown in FIG. 4D is completed, and thereafter, the reinforcing layer 8 is constructed in the same manner as in FIG.

  FIG. 5 shows a construction method adapted to the case where the ground 5 is relatively hard. The ground drill 17 is used before the screw drill 1 is used, and FIG. This is the stage where 18 is being constructed. The earth drill 17 scoops up the earth and sand scraped off at the tip along a spiral, and is supported by a construction machine such as an auger and supported by a base end. In this case, when the pilot hole 18 is constructed, there is almost no change in the properties of the surrounding earth wall, and after the earth drill 17 is extracted, the earth wall may collapse in a short time. Therefore, after the formation of the pilot hole 18 is completed as shown in FIG. 5B and the ground drill 17 is extracted, the periphery of the pilot hole 18 is quickly pressed and hardened using the screw drill 1 as shown in FIG. A more healthy hole 6 is formed. FIG. 5 (D) shows a state in which the screw drill 1 has been extracted, and thereafter, the reinforcing layer 8 is constructed in the same manner as in FIG.

  FIG. 6 shows an example of a method for constructing the reinforcing layer 8 and shows a method for packing the aggregate 7 after extracting the screw drill 1. First, FIG. 6 (A) is a stage where the construction of the hole 6 is finished, and the inside is a simple cavity and the depth is about 2 m. Thereafter, the aggregate 7 is put into the hole 6 as shown in FIG. 6 (B), but once the height reaches about 0.5 m, the filling is once finished, and thereafter, as shown in FIG. 6 (C). In this way, after the rolling pressure pipe 9 is inserted into the hole 6 and the pressurizing portion 19 is brought into contact with the aggregate 7, a load about twice as much as the design load is applied and hardened. The rolling pipe 9 has substantially the same shape as the body 2 of the screw drill 1, and the pressurizing portion 19 on the bottom surface has increased strength so that deformation does not occur. Since the gap between the hole 6 and the rolling pipe 9 is small, the aggregate 7 does not rise during the tamping, and the earth wall of the hole 6 does not collapse by impact. Once the tamping is completed, the aggregate 7 is again packed by a height of about 0.5 m as shown in FIG. 6 (D), and then tamped with the compaction pipe 9 as shown in FIG. 6 (E). Thus, the reinforcing layer 8 as shown in FIG. 6F is completed. Note that the depth of the holes 6 and the amount of aggregate 7 to be introduced at a time are different each time, and what is described here is merely an example.

  FIG. 7 is a cross-sectional view showing a situation when the ground improvement according to the present invention is performed and a structure 11 such as a house is built thereon. When the hole 6 is formed in the ground 5 with the screw drill 1 as described above and then the aggregate 7 is packed in a high density to form the reinforcing layer 8, the aggregate 7 widely bites the surrounding ground 5 and applies a load. Since it can disperse | distribute in a wide range, even if the structure 11 is mounted on this, ground subsidence hardly arises. In addition, there is a limit to the load that can be received at one reinforced layer 8, and in general, construction is performed continuously at intervals of several meters, and if the building is partly double-storey, the load will be biased. Correspondingly, the arrangement of the reinforcing layer 8 may be adjusted. As shown in this figure, the ground 5 is usually composed of a plurality of formations depending on the depth, and generally the side close to the ground surface tends to be soft. However, in the present invention, the reinforcing layer 8 is expected to have a certain strength such as viscous soil. Achieving the desired layer and exhibiting the required performance.

  By the way, as shown in FIG. 1B, when the screw drill 1 is driven into the ground 5 and reaches a predetermined depth, the screw drill 1 is reversely rotated as shown in FIG. As 1 rises, the hole 6 surrounded by the ground 5 and the screw drill 1 has no room for air to enter from the outside, and the pressure may decrease and the soil wall may become unstable.

  As a countermeasure for preventing this, as shown in FIG. 8, there is a method of preventing the pressure drop in the hole 6 by providing an air supply means 21 a in the screw drill 1. This air supply means 21a is composed of a vent 22a, a valve 23a, a fulcrum 24a, a stopper 25a, and a pipe 26a, and exhausts air from the vent 22a formed by cutting out the body 2 near the tip of the screw drill 1 to the outside. To do. However, the vent 22a needs to be closed so that dirt and the like do not enter the body 2 at the time of excavation, and is therefore provided with a valve 23a. The valve 23a is rotatably supported by a fulcrum 24a attached to the body 2, and its movement range is restricted by a stopper 25a and a pipe 26a. When the external pressure is high, the valve 23a is in close contact with the stopper 25a and the vent 22a is completely sealed. However, when the external pressure is reduced, the valve 23a is moved to open the vent 22a, and the air Is sent to the outside. This air is supplied from a pipe 26a penetrating the inside of the fuselage 2, but the end of the pipe 26a protrudes to the outside at the base end of the fuselage 2 as shown in FIG. To do.

  During excavation, as shown in FIG. 8A, the valve 23a is pushed by the outer earth and sand and comes into contact with the stopper 25a, so that the sealing performance is maintained. When the excavation is finished and the retreat is started, the pressure near the tip of the screw drill 1 is reduced, and the valve 23a is pushed by the air from the pipe 26a to be opened as shown in FIG. Can supply.

  Since the rolling pipe 9 also surrounds the periphery with the earth wall when the aggregate 7 is hardened, the pressure between the pressurizing part 19 and the aggregate 7 may be lowered when the aggregate is pressed after being pressed. . Therefore, as shown in FIG. 9, an air supply means 21 b is also provided in the pressurizing portion 19 of the rolling pipe 9, so that air can be sent from the vent 22 b when the external pressure is reduced. This structure is the same as that shown in FIG. 8, the valve 23 b is supported so as to be rotatable around a fulcrum 24 b, and the pipe 26 b passes through the rolling pipe 9. FIG. 9 (A) shows a state where tamping is being performed, and the valve 23b is received and sealed by the stopper 25b. In FIG. 9 (B), the pressure around the pressurizing unit 19 decreases. Then, the valve 23b is opened by being pushed by the air from the pipe 26b. The valve 23b does not open any more by contacting the pipe 26b.

The figure which shows the outline | summary of the ground improvement method by this invention in a time series, and work progresses in order of (A) (B) (C) (D). The example of the shape of the screw drill by this invention is shown, (A) is a top view, (B) is a front view, (C) is AA sectional drawing. It is a figure which shows the example of a method at the time of constructing a hole using a screw drill, (A) is before work start, (B) is working. It is a figure which shows the construction method in the case of scooping up the earth and sand in the ground with a screw drill, and work advances in the order of (A) (B) (C) (D). It is a figure which shows the outline | summary of the construction method applied when the ground is comparatively hard in time series, and work advances in order of (A) (B) (C) (D). After extracting a screw drill, it is a figure which shows the operation | work which builds a reinforcement layer by tamping an aggregate with a rolling compaction pipe in time series, (A) (B) (C) (D) (E) (F) Work proceeds in order. It is sectional drawing which shows the example of a situation at the time of ground improvement by the method by this invention, and building structures, such as a house, on this. It is sectional drawing which shows the specific example of the air supply means with which a screw drill is equipped, (A) is in the state where the valve was closed at the time of excavation, etc., (B) is the state where the pressure at the tip of the screw drill dropped and the valve was opened It is. It is sectional drawing which shows the specific example of the air supply means with which a compaction pipe is equipped, (A) is in the state where the valve was closed at the time of tamping, etc., (B) It is in an open state.

DESCRIPTION OF SYMBOLS 1 Screw drill 2 Body 3 Blade 4 Face 5 Ground 6 Hole 7 Aggregate 8 Strengthening layer 9 Rolling pipe 10 Foundation 11 Structure 12 Grip part 13 Reform area 14 Power shovel 15 Arm 16 Auger 17 Earth drill 18 Pilot hole 19 Pressure part 20 Exhaust soil 21a, 21b Air supply means 22a, 22b Vents 23a, 23b Valves 24a, 24b Support points 25a, 25b Stoppers 26a, 26b Pipes

Claims (1)

A cylindrical and tapered body (2) having a diameter equivalent to the hole (6) formed in the ground (5), and a blade (3) spirally joined around the body (2) The projecting length of the blade (3) is in the range of 1/5 to 1/20 of the maximum diameter of the body (2), while rotating the screw drill (1) upright. Pierce the ground surface, squeeze the blade (3) of the scree drill (1) into the ground (5), and submerge the screw drill (1) to a predetermined depth with the propulsive force of the blade (3) (6) when you form, reforming zone moisture is squeezed by liquidity decreased around the foundation radially press and while seeking the hole (5) of the screw drill (1) (6) by the fuselage (2) After forming (13), in order to prevent the reforming zone (13) from collapsing, the fuselage (2) The screw drill (1) is removed from the ground (5) while air is fed into the hole (6) from the tip, and the aggregate (7) is packed into the hole (6) formed in the center of the modified region (13). The improvement method of the ground characterized by constructing a reinforcement layer (8) by and supporting a structure (11) by this reinforcement layer (8).

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