JP2824495B2 - Liquefaction prevention method for sand ground - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is easy to handle during an earthquake,
Also, the present invention relates to a construction method capable of preventing liquefaction of sand ground at low cost.

[Prior Art] Generally, sand ground near saturation may be liquefied during an earthquake. Therefore, when a structure is constructed on such sand ground, the ground is improved by various ground improvement methods. There is a need. As typical soil improvement methods, compaction, chemical injection, cement mixing, etc. are known.However, since these methods completely improve the entire ground, the construction period is long and costs are long. There are many problems such as extremely expensive ones. Usually, the following methods (a) and (b) are mainly used as low vibration, low noise sand liquefaction prevention methods that can be constructed in urban areas. ing.

(A) Groundwater level lowering method In this method, a water blocking wall that reaches an impermeable layer is formed in the ground around the structure, and a pumping well consisting of deep wells and well points is provided inside the water blocking wall. There is a feature. By always operating the pumping well, the original groundwater level can be lowered, and liquefaction of the sand ground can be prevented.

(B) Gravel drain method In this method, a large number of gravel (gravel) piles are installed in the ground around the structure, and the gravel pile shortens the drainage path of the horizontal liquefied layer to increase the drainage effect. It is characterized by reducing the rise in pore water pressure during an earthquake in sandy ground. Therefore, pore water pressure can be dissipated at an early stage, and liquefaction of sand ground can be prevented.

[Problems to be Solved by the Invention] In the groundwater level lowering method (a), it is necessary to keep the submersible pump operating at all times to keep pumping groundwater, and equipment for pumping is indispensable. This causes problems such as high equipment costs and running costs, and environmental problems such as ground subsidence caused by a decrease in groundwater level.

In the gravel drain method (b), the drainage performance greatly differs depending on the position of the drain, the gap between the drainage and the like, and it is difficult to obtain a reliable drainage effect, and the effect of preventing liquefaction of the sand ground is unclear. There are also problems such as high construction costs.

The present invention has been made in view of the above-mentioned circumstances, does not require ground improvement, can be installed on individual structures, does not require large-scale facilities for pumping treatment, and It is an object of the present invention to provide a construction method capable of obtaining a reliable drainage effect, preventing liquefaction of sand ground at an easy handling and at low cost.

[Means for Solving the Problems] In order to solve the above problems, the present invention employs the following sand ground liquefaction prevention method. That is, this is a construction method in which liquefaction is prevented by pumping pore water in sandy ground by a water collecting device provided on the foundation of the structure.

The water collecting device is a water-stopping base slab having a hollow portion therein, which constitutes a foundation of a structure, a water collecting hole provided in a bottom portion of the base slab, and embedded in a hollow portion of the base slab. And a control device for controlling the pressurizing and depressurizing device connected to the pressurizing and depressurizing bag.

When an earthquake occurs, the control device operates the pressurizing / depressurizing device to contract the pressurizing / depressurizing bag, and pumps pore water in the sandy ground into the hollow portion. When the earthquake has subsided, the control device operates the pressurizing / depressurizing device to expand the pressurizing / depressurizing bag, and returns the pumped pore water to the sandy ground.

[Operation] In the method for preventing liquefaction of sand ground according to the present invention, when an earthquake occurs, the pressurizing and depressurizing device is actuated by the control device to shrink the pressurizing and depressurizing bag, and pore water in the sandy ground is removed. Is pumped into the hollow part to reduce the pore water pressure. Since the vertical effective stress in the ground increases due to the decrease in pore water pressure, the sand ground hardly liquefies. In addition, since water continues to be collected during an earthquake, excess water pressure generated during the earthquake is also dissipated, and a rise in pore water pressure during the earthquake can be suppressed.

Also, when the earthquake subsides, the control device operates the pressurizing / depressurizing device to expand the pressurizing / depressurizing bag, and returns the pore water pumped into the hollow portion to the sandy ground, thereby lowering the groundwater level. Avoid decline and prevent land subsidence.

[Embodiment] A method for preventing liquefaction of a sand ground, which is an embodiment of the present invention, will be described in detail with reference to Figs.

This embodiment is a method for preventing liquefaction performed when constructing a structure 2 on a sandy ground 1 where liquefaction is expected, and a foundation 3 of the structure 2 is made of a material having a water stopping property. The foundation slab 5 is formed on a pile driving foundation 4 buried vertically in a sand ground 1. Foundation 3
Is provided with a water collecting device 6, and the foundation slab 5 is constructed below the original groundwater level 7 in the sandy ground 1.

Inside the base slab 5, a plurality of hollow portions 8, 8,... Defined by partition walls 5a are formed. A plurality of water collecting holes 10 communicating the hollow portion 8 and the sand ground 1 are formed in the bottom 9 of the base slab 5, and the water pressure in the sand ground 1 is sensed around these water collecting holes 10. A plurality of pressure sensors 11 are provided. Further, a filter medium 12 is attached to the water collecting hole 10. The filter medium 12 is composed of a three-layer filter in which the lower layer is the coarsest and the upper layer is the finest. The filter medium 12 blocks fine sand from entering the hollow portion 8 and allows only water to permeate. A pressurizing / depressurizing bag 13 is embedded in the hollow portion 8.

The pressurizing / depressurizing bag 13 is made of, for example, a high pressure-resistant rubber that can withstand a pressure equal to or higher than the maximum water pressure in the sand ground 1.
Usually, the inside is filled with air compressed at a pressure slightly higher than the water pressure in the sand ground 1. A tube 14 extending vertically upward is attached to the pressurizing / depressurizing bag 13, and an upper end 14a of the tube 14 is attached to a pressurizing / depressurizing device 16 via a valve 15.

The pressurizing device 16 is installed on the upper surface 17 of the base slab 5,
The inside of the pressurizing / depressurizing bag 13 is expanded or contracted by pressurizing or depressurizing the air to thereby increase or decrease the pressure inside the pressurizing / depressurizing bag 13. A pipe 14 is attached to one end of the pressurizing / depressurizing device 16 via a valve 15, and a pipe 19 is connected to the other end via a valve 18.
Is attached. The tube 19 extends vertically upward, and a tip portion 19a thereof penetrates the wall body 20 and protrudes outward in the horizontal direction. A control device 21 is provided on the upper surface 17 of the base slab 5.

The control device 21 sends an appropriate output to the pressurizing and depressurizing device 16 based on the signal generated by the pressure sensor 11, and operates the pressurizing and depressurizing device 16, so that the built-in computer can always keep the optimum management state. Things.

A plurality of the water collecting devices 6 configured as described above are installed on the foundation 3 of the structure 2 as shown in FIG. The foundation 3 is divided into a plurality of sections 22, 22, ... by partition walls 5a, 5a, ... and partition walls 5b, 5b, ... provided in the vertical and horizontal directions.
A plurality of locations suitable for preventing liquefaction of the sand ground 1 are selected from 2, 22, ..., and one or two control devices 21 are installed. A water collecting hole 10 is formed in a bottom portion 9 below each control device 21. The number of the water collecting devices 6 and the water collecting holes 10 may be any number as long as the water can be pumped to such an extent that the rise of the pore water pressure due to the liquefaction of the sand ground 1 can be stopped, and is not limited to the above structure. Absent. Further, the pressurizing / depressurizing bag 13 does not need to be limited to one, and a plurality of the pressurizing / depressurizing bags 13 may be combined and used as one pressurizing / depressurizing bag.

Next, the operation and the like of the above construction method will be described. During a calm period, the pressure sensor 11 installed on the bottom 9 senses the water pressure in the sand ground 1 and sends a signal to the control device 21. Control device
21 sends an appropriate output to the pressurizing and depressurizing device 16 based on this signal, and operates the pressurizing and depressurizing device 16. The pressurizing / depressurizing device 16 adjusts the pressure of the air inside the pressurizing / depressurizing bag 13 to be slightly higher than the above water pressure.

When an earthquake occurs and the water pressure in the sand ground 1 rises sharply, the pressure sensor 11 senses this rise in water pressure and sends a signal to the control device 21. The control device 21 sends an appropriate output to the pressurizing / depressurizing device 16 based on this signal to operate the pressurizing / depressurizing device 16 to bleed air from the pressurizing / depressurizing bag 13 and to contract the pressurizing / depressurizing bag 13. The pore water in the sandy ground 1 whose water pressure has risen passes through the filter medium 12 of the water collecting hole 10 and enters the gap between the hollow portion 8 and the bag 13 for pressurization and decompression. Also, during the occurrence of the earthquake, the pressurizing / depressurizing bag body 13 is kept contracting to keep the pore water pumped.

Further, when the water pressure in the sandy ground 1 decreases after the earthquake has subsided, the pressure sensor 11 senses the decrease in the water pressure, and the control device 21
Send a signal to The control device 21 sends an appropriate output to the pressurizing / depressurizing device 16 based on the signal, activates the pressurizing / depressurizing device 16, sends air into the pressurizing / depressurizing bag 13, and inflates the pressurizing / depressurizing bag 13. The pore water that has entered the gap between the hollow portion 8 and the pressurizing / depressurizing bag 13 is discharged into the sand ground 1 through the filter medium 12 of the water collecting hole 10 as the pressurizing / depressurizing bag 13 expands. Becomes

Each time an earthquake occurs, the above operation is repeated, and pore water in the sand ground 1 is pumped and drained to prevent liquefaction of the sand ground.

As described above in detail, according to the above-described embodiment, the water collecting device 6 includes the water-stopping base slab 5 having the hollow portion 8 therein and the water collecting portion formed on the bottom portion 9 of the base slab 5. Hole 10
And a pressurizing / depressurizing bag 13 buried in the hollow portion 8, a pressurizing / depressurizing device 16 connected to the pressurizing / depressurizing bag 13, and a controller 21 for controlling the pressurizing / depressurizing device 16. It can be installed on any structure, it is easy to handle without requiring large facilities for water pumping treatment, the cost of equipment and running can be kept low, pumping pore water in sandy ground,
The drainage effect is surely obtained.

When an earthquake occurs, the pressurizing / depressurizing device 16
Since the pore water in the sand ground 1 is pumped into the hollow part 8 by contracting the pores 13, the pore water pressure in the sand ground 1 can be reduced. Liquefaction of the sand ground 1 can be prevented. Further, during the occurrence of the earthquake, the pressurizing / depressurizing bag 13 is continuously contracted to keep the pore water in a pumped state, so that the pore water pressure in the sandy ground 1 remains low, and the The excess water pressure dissipates and the rise in pore water pressure during an earthquake can be suppressed.

Further, when the earthquake subsides, the pressurized / depressurized bag body 13 is expanded to drain the pumped pore water into the sand ground 1, so that the pore water pressure in the sand ground 1 can be returned to the original, and the pore water pressure can be reduced. The drop in groundwater level caused by the drop can be avoided, and the progress of land subsidence can be prevented.

As described in detail above, according to the sand ground liquefaction prevention method of this embodiment, by installing on individual structures,
The pore water in the sand ground can be reliably pumped and drained, and liquefaction of the sand ground can be prevented easily and at low cost.

[Effects of the Invention] As described above in detail, according to the present invention, the water collecting device includes a water-blocking base slab having a hollow part inside the base of the structure, and a low plate of the base slab. Water collecting holes provided in the section, a pressurizing / depressurizing bag buried in the hollow portion of the base slab, a pressurizing / depressurizing device connected to the pressurizing / depressurizing bag, and a control device for controlling the pressurizing / depressurizing device. , So that it can be installed on individual structures and is easy to handle without requiring large-scale facilities for pumping treatment.
Equipment and running costs can be kept low,
The pumping and draining effects of pore water in the sandy ground can be reliably obtained.

Also, when an earthquake occurs, the pressurizing / depressurizing device shrinks the pressurizing / depressurizing bag to pump pore water in the sandy ground into the hollow part, so that the pore water pressure in the sandy ground can be reduced. The effective vertical stress in the ground increases, and liquefaction of the sand ground can be prevented. Also, during the occurrence of the earthquake, the pressurizing and depressurizing bag is kept contracting to keep the pore water pumped up, so that the pore water pressure in the sandy ground remains low, and the excess water generated during the earthquake The water pressure also dissipates, and the rise in pore water pressure during an earthquake can be suppressed.

Also, when the earthquake subsides, the pressurizing / depressurizing device inflates the pressurizing / depressurizing bag and returns the pumped pore water back to the sandy ground, so that the pore water pressure in the sandy ground can be restored and the pore pressure The drop in groundwater level caused by the drop can be avoided, and the progress of land subsidence can be prevented.

As described above, various points are improved, and excellent effects can be expected.

[Brief description of the drawings]

1 to 3 are views showing a method for preventing liquefaction of a sand ground according to an embodiment of the present invention. FIG. 1 is a partial sectional view of a water collecting device, and FIG. FIG. 3 is a schematic side view showing a state provided on the foundation of the structure, and FIG. 3 is a schematic side view showing a position of a water collecting device provided on the foundation of the structure. DESCRIPTION OF SYMBOLS 1 ... Sand ground, 2 ... Structure, 3 ... Foundation, 4 ... Pile driving foundation, 5 ... Foundation slab, 6 ... Water collecting device, 8 ... Hollow part, 9 ... Bottom part, 10 …… water collecting hole, 11 …… Pressure sensor, 12 …… Filter medium, 13 …… Pressure / decompression bag, 14,19 …… Tube, 15,18 …… Valve, 16 …… Pressure / decompression device, 20 …… Wall, 21 ... Control device.

Claims (1)

(57) [Claims] 1. A method for preventing liquefaction by pumping pore water in sandy ground by a water collecting device provided on a foundation of a structure. A base slab having a water-blocking property and having a hollow portion therein, a water collecting hole provided in a bottom portion of the base slab, a pressurizing / depressurizing bag buried in the hollow portion of the base slab, A pressurizing and depressurizing device connected to the bag, and a control device for controlling the pressurizing and depressurizing device, when an earthquake occurs, the pressurizing and depressurizing device is operated by the control device to contract the pressurizing and depressurizing bag, The pore water in the sand ground is pumped into the hollow part, and at the time when the earthquake has subsided, the control device operates the pressurizing / depressurizing device to expand the pressurizing / depressurizing bag, and the pumped pore water is poured into the sandy ground. A method for preventing liquefaction of sand ground, characterized by returning.