JP3486572B2 - Ground reinforcement composite method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground improvement method which is optimal for supporting the landfill ground and countermeasures against liquefaction. 2. Description of the Related Art Conventionally, as a method of improving a landfill ground, there have been many examples in which a large number of sand piles compacted on a sand ground are formed to take measures against liquefaction of the ground, and a sand drain pile, There is an example of using a sand mat and embankment in combination to achieve ground support and settlement measures. In addition, as a technology for compacting the upper layer of the ground, a heavy sui, which is extremely heavy at 8 to 40 tons, is dropped from a high place of 10 to 30 m, and the impact force of the order of 1,000 tons given to the ground surface by this is obtained. By utilizing the ground vibration of several G generated at that time, a dynamic consolidation method of compacting the ground to a deep part or a vibration force of several tens to one hundred and several tens tons on top of a tamper plate, acceleration several g, several tens of H
There is a vibration compaction method in which a large-capacity vibrator having a frequency of z is mounted, and the operation of the vibrator is transmitted to the ground via a plate to compact the ground. [0003] In the above construction method, a deep well pipe is installed on the ground, and a sand pile having a cross-sectional shape having no direction is installed at a depth similar to the depth well pipe, and groundwater is pumped up.
There is also known a combined construction method that reduces the pore water pressure in each underground layer, increases the effective stress required for consolidation as pore water escapes, and obtains the same effect as continuously loading small loads in embankment loading method . [0004] However, in recent years,
New lessons for improved ground, including lessons learned from the Great Hanshin-Awaji Earthquake, the need to create a ground that can withstand greater seismic force, and the need for further resource conservation and cost reductions due to growing global environmental issues. There is. [0005] Accordingly, an object of the present invention is optimal for supporting force of landfill ground and countermeasures against liquefaction, and preloading (filling).
It is an object of the present invention to provide a ground reinforcement composite construction method that can contribute to resource saving by reducing the amount. [0006] Under such circumstances, the present inventors have conducted intensive studies and as a result, have paid attention to unsaturation of the ground where the groundwater level of the sand pile formation ground has been lowered by a pumping well. If this unsaturated soil is compacted by the dynamic compaction method or the vibration compaction method, the pore water in the area where the viscous soil is predominant is pushed out by sand seam (thin sand layer) or sand pile and drained by gravity. The present inventors have found that the gap in the sandy soil portion is crushed and densified, and that an extremely high quality ground can be formed, and the present invention has been completed. That is, the present invention is, sand
Sand pile formation process to stabilize the ground by creating a large number of sand piles in the landfill where seams are interposed , and soil desaturation process to excavate pumping wells in the sand pile formation ground and pump groundwater to desaturate the ground The soil consolidation process is characterized by performing a soil compaction process in which the unsaturated soil is further compacted by impact or vibration such as dynamic compaction or vibration compaction to obtain a high density ground in this order. To provide. By adopting such a configuration, the following operation is achieved. In other words, the landfill has many sand seams. The water pressure in the sand seam is higher than the hydrostatic pressure and is non-uniform because the landfill itself is in the process of consolidation due to its own weight. Placing a sand pile on such a landfill has the effect of connecting a myriad of sand seams in the ground in the vertical direction. By this effect, the hydraulic state of the ground changes from the pressure-receiving state to a state close to the hydrostatic pressure, and the state can be shifted to a stable state where there is no place where the water pressure is abnormally high. Further, in the landfill, the groundwater communicates with the ground and shifts to the hydrostatic pressure state, thereby easily lowering the groundwater level due to the pumping well. For example, a heavy switch, which is very heavy, for example, 8 to 40 tons, is dropped from a height of 10 to 30 m on such ground, and the impact force of the order of 1,000 tons given to the ground surface by this, and the number generated at that time, If the ground vibration that extends to G is given, the pore water in the area where the viscous soil is predominant is pushed out by sand seam (thin layer of sand) or sand pile and drained by gravity,
In addition, the gap (air) in the sandy soil part is crushed and densified, so that extremely high quality ground that can not be achieved with sand piles and preload can be created, and the amount of preload used in the conventional method can be reduced. It also contributes to resource saving. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The ground to which the ground strengthening composite method of the present invention is applied is not particularly limited as long as it is a landfill ground. For example, a sandy ground, a cohesive soil, and a cohesive soil may be used. The ground in which the sandy soil is in an alternate layer is mentioned. Next, a ground strengthening composite construction method according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a view for explaining the ground reinforcement composite construction method of the present embodiment. FIG. 1 (A) is a schematic view of a first step showing a sand pile formation step, and FIG. 1 (B) is a view showing a ground desaturation step. FIG. 1 (C) is a schematic diagram of a third step showing a ground compaction step by a dynamic compaction method or a vibration compaction method. FIG.
Is a schematic diagram showing a cross section of the ground before the present ground strengthening composite method is applied, FIG. 3 is a schematic diagram showing a cross section of the ground after the first process is performed, and FIG. 4 is a process in which the second process is performed. FIG. 5 is a schematic diagram showing a cross section of the ground, FIG. 5 is a schematic diagram showing a cross section of the ground showing the occurrence of perched water in which the cohesive soil of the ground where the third step is performed is excellent, and FIG. 6 (A) is an X part in FIG. Enlarged view of (B) and (C)
FIG. 7 is an enlarged view of a portion X showing a situation in which pore water is squeezed out as compaction proceeds, and FIG. 7 is a schematic diagram of a vibration compaction device used in the third step. In FIG. 1 (A), the first step is performed by a known sand pile forming method, in which a large number of sand piles 3 compacted by a sand pile forming apparatus 1 are formed on a landfill ground 2. Countless sand seams (not shown) interposed in the ground are connected in the vertical direction to reduce the pressure of the ground. As the sand pile 3, for example, a drain body such as a sand drain pile and a compacted sand pile is used. In addition, the sand pile diameter and the sand pile length are not particularly limited as long as the soil can be unpressurized. For example, the sand pile diameter is about 1 m or more in circumference, and the sand pile length is the same as the pumping well described later. It is of the same length. The ground to which the first step of the present invention is applied has a large number of sand seams 10a to 10d interposed therebetween, as shown in FIG. This sand seam 10a, 10b, 10
The water pressures p ₁ , p ₂ , p ₃ , and p ₄ in c and 10d are higher than the hydrostatic pressure because they are in the process of consolidation due to the weight of the landfill ground itself, and p ₃ <p ₄ <p ₁ <p ₂ . It is uneven. In the first step, a large number of sand piles 3 having no direction in the cross section are cast on the ground 2, and as shown in FIG. 3, there are countless sand seams 10a to 10 existing in the ground.
d will be connected in the vertical direction. Therefore, passage of groundwater are formed in the horizontal and vertical directions, hydraulic state of the ground _{is, p 1 = p 2 = p} 3 = p 4 from the pressure state
Changes to a state close to the hydrostatic pressure, and a stable state without an abnormally high hydraulic pressure portion. In the ground after the first step, part of the groundwater flows upward through the sand pile 3 and is drained.
Further, the ground moves to the hydrostatic pressure state through the communication of the groundwater, so that the groundwater level can be easily lowered by the pumping well in the second step described later. After the completion of the first step, the procedure moves to the second step. In the second step, as shown in FIG. 1 (B), a pumping well 4 is dug in a sand pile formation ground 2 and groundwater is pumped up by a pump 5 to lower the groundwater level 6 to desaturate the ground. is there.
The pumping well may be, for example, a well-collected deep well pipe installed by a known method. As a full-water collecting type deep well pipe, a porous concrete pipe that is unlikely to be clogged and that can be easily constructed, and can be expected to have a certain level of strength, and is made of steel, which is easily available for material processing, has a slit hole on the entire surface. And
Alternatively, a casing in which the slit hole is protected by a wire mesh or the like is surrounded by sand, crushed stone, or the like as a filter material. The pumping well 4 may be installed at any place where the groundwater in the ground to be reinforced is lowered, and may be between the sand piles 3 or in the sand piles 3. By providing the pumping well 4, the groundwater collects at the pumping well through the sand pile and the sand seam, and the groundwater level is lowered around the pumping well by pumping the groundwater. Accordingly, voids (air) due to such groundwater drainage remain in the sand piles and sand seams, and become unsaturated. However, as shown in FIG. 4, in the portion 12 where the cohesive soil is dominant, a part of the groundwater is left as permeate water 13 which is taken into the portion where the cohesive soil is dominant, but there is a place where the sand pile or the sand Since the seam has a negative pressure, a force acts to draw pore water from the viscous soil portion. After the completion of the second step, the process proceeds to the third step. The third step is, as shown in FIGS. 1C and 5, a soil compaction step in which the unsaturated ground 2 is further compacted by a dynamic compaction method or a vibration compaction method to obtain a high-density ground. . The compaction by the dynamic compaction method may be performed by a known method. For example, as shown in FIG. 1 (C), a heavy switch 8 having a very heavy weight of 8 to 40 tons suspended by a crane truck 7 is used.
Drop it from a height of 0 to 30 m, and the ground surface 2
A method is used in which the gap 9 interposed in the ground 2 is crushed and deepened by utilizing the impact force of the order of 1,000 tons given to 1 and the ground vibration of several G generated at that time. The vibration compaction method is disclosed in Patent No. 267.
What is necessary is just to carry out by the method of 3209 gazette, for example, the vibration compaction apparatus as shown in FIG. 7 is used. In FIG.
Reference numeral 21 denotes a tamper plate, and reference numeral 22 denotes a grounding surface of the tamper plate, and a vibrator 19 is mounted via a mounting portion 20 at a substantially central position on an upper surface thereof. Reference numeral 18 denotes a shock absorber inserted between the entire vibro tamper and the suspension wire 17, and reference numeral 23 denotes a shock absorber attached to a lateral surface of the vibro tamper 22. This vibrator 19 is of a biaxial or 4-axial eccentric weight type, with a vibrating force of several tens to one hundred and several tens tons, a vibration frequency of several tens Hz, a virtual amplitude of 15 to 25 mm, and a virtual acceleration of 5 to 10 g. Those having a capacity of the order of magnitude are used. When the vibration compaction device 25 places the grounding surface 22 of the plate 21 on the compaction construction ground and drives the vibrator 19 by an electric motor, a vertical vibration is generated, and the acceleration thereof is reduced by the tamper plate 21. And presses the ground and soil through the base plate, thereby compacting the ground in the area in contact with the plate 21 downward. The shock absorbers 18 and 23 attached to each wire are:
In this case, even if the wire is tensioned to move the tamper while the exciter is in operation, the vibration is absorbed thereby, and the vibration is not transmitted directly to the device through the wire. In the third step, the heavy switch 8 of the dynamic compaction method is used.
5 or the large vibration force of the tamper plate 21 is applied to the ground, as shown in FIGS. It is extruded into the pile 3 and the sand seam 10 as pore water 16 (FIG. 6B), and the pore water 16 is drained downward by gravity (FIG. 6C), and as shown in FIG. The gap (air) 9 in the sandy soil portion can be crushed and the density can be increased, so that a high-density ground that cannot be achieved by sand pile driving or preloading can be formed. In the first step of the present invention, if sand piles are laid in the landfill ground, there is an effect of connecting a myriad of sand seams existing in the ground in the vertical direction. From the state to a state close to the hydrostatic pressure, It is possible to shift to a stable state where there is no place where the pressure is abnormally high, and the landfill ground shifts to a state where the groundwater communicates, so that the lowering of the groundwater level due to the installation of the pumping well in the second step is easy. An extremely heavy heavy water switch of the third step is dropped from a high place on the ground that has been unsaturated due to the lowering of the groundwater level, or the tamplate is vibrated by a large-capacity vibrator, and a thousand tons are applied to the ground surface. If you give an impact force on the order of
Pore water in areas where cohesive soil is predominant is extruded into sand seams and sand piles and drained by gravity, and gaps (air) in sandy soil areas are crushed and densified, making it extremely difficult to achieve with sand piles and preloading. High quality ground can be created, and the amount of preload used in the conventional method can be reduced, thereby contributing to resource saving.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining a ground reinforcement composite construction method of the present embodiment, wherein (A) is a sand pile forming step, (B) is a ground desaturation step, and (C) is It is a schematic diagram which shows a dynamic compaction method. FIG. 2 is a schematic diagram showing a cross section of the ground before the ground reinforcement composite method of the present embodiment is applied. FIG. 3 is a schematic view showing a cross section of the ground after the first step is performed. FIG. 4 is a schematic view showing a cross section of the ground after the second step is performed. FIG. 5 is a schematic diagram of a section of the ground showing the occurrence of perched water in which the clayey soil of the ground where the third step is performed is excellent. 6A is an enlarged view of a portion X in FIG. 5, and FIGS. 6B and 6C are enlarged views of a portion X showing a situation where pore water is squeezed out as compaction proceeds. FIG. 7 is a schematic view of a vibration compaction device used in a third step. [Description of Signs] 1 Sand pile creation device 2 Ground 3 Sand pile 4 Pumping well 5 Pump pump 6 Groundwater level 7 Crane truck 8 Hammer 9 Gap (air) 10, 10a-10d Sand seam 12 Cohesive soil 13 Cohesive soil is predominant Permeated water 16 taken into the damaged part Pore water 17 Hanging wires 18 and 23 Buffer 19 Vibrator 21 Tamper plate 25 Vibration compaction device

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Claims (1)

(57) [Claims] [Claim 1] A sand pile formation process for stabilizing the ground by forming a large number of sand piles in a landfill where sand seams are interposed .
A soil desaturation process in which a pumping well is dug in a sand pile formation ground to pump up groundwater to desaturate the ground, and the unsaturated ground is further compacted by impact or vibration such as dynamic compaction method or vibration compaction method A ground strengthening composite method characterized by performing a ground compaction process for obtaining a high density ground in this order.