JPH03275814A - Method for coping with liquefaction of embedded structure - Google Patents

Abstract

PURPOSE:To improve safety by a method wherein a liquefaction suppressing pile to dissipate an excessive gap water pressure generated around a building during earthquake is built on the under surface of an embedded building built in a ground, and a drainage passage connected to the liquefaction suppressing pile is built. CONSTITUTION:In building of an embedded structure, e.g. an underground multi- purpose duct 1, built in a ground or a half-underground place, after a sheathing sheet pile is driven, a liquefaction suppressing pile 2 to which a drainage function is added is driven, a bottom is levelled by using crushed stones 3, and building is carried out by using cast-in-place concrete. A distributing member 23 of the pile 2 is formed down to a position in crushed stones 3, a drainage material 6 is caused to rise along a side wall 1b of the groove 1 and connected to a blind culvert 8 in a crushed stone mat 7 for drainage. The rise of a gap water pressure during earthquake is suppressed by drainage of underground water to prevent floating of the groove 1, resulting in improvement of safety.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a method for reducing the cross-sectional width of lifelines such as power transmission lines, gas pipes, and water pipes when burying them underground. This paper relates to liquefaction countermeasure construction methods for large-scale underground structures or semi-underground structures such as large public ditches or moat roads.

[Conventional technology]

Liquefaction prevention methods for ground that is likely to liquefy (hereinafter simply referred to as liquefaction ground) include the ground compaction method, which has been widely used in the past, and the crushed stone drain method (Japanese Patent Application Laid-open No. 100919/1983, Utsukai Showa 56-116434
(see Publication No.), and is applied to ground where liquefaction is expected to occur. Furthermore, pressure-resistant resin pipes with filters installed around the pipe have been used for the past to collect and drain pore water in the ground and as a countermeasure against liquefaction. Also,
In recent years, in order to drain excess pore water in the ground during earthquakes, many holes are drilled in piles made of steel pipes, etc., and water-permeable filters are installed in the holes to prevent dirt from entering. Hollow perforated piles (see JP-A-61-146910), porous concrete piles (see JP-A-61-83711), etc. have been developed, which are expected to improve the strength and rigidity of piles in addition to their effectiveness. In addition, there are also those with a vertical drainage pipe attached (see Japanese Patent Application Laid-open No. 146315/1983).

By the way, the following measures have been conventionally considered or used to prevent liquefaction for buried structures such as public ditches.

(1) Sheet pile enclosure system As shown in Figure 7, by surrounding the sides of the common trench 1 with sheet piles 31, the excess pore water pressure that rises in the event of an earthquake on the outside is prevented from being transmitted to the bottom of the common trench 1. This method has the effect of suppressing the generation of pressure and suppressing liquefaction of the ground 5 within the sheet pile enclosure by restraining it with the sheet piles 31. Therefore, it is effective as a countermeasure against liquefaction when the cross-sectional width of the common groove 1 is small.

(2) Pile support system As shown in Figure 8, the piles 32 support the dead weight of the common ditch 1 and the overload on the common ditch 2, and the piles 32 resist pulling out against the uplift force generated during ground liquefaction. This is a method to counter this.

(3) Ground improvement method The ground around the common ditch will be improved using various ground improvement methods.

For example, JP-A-63-107610 discloses a liquefaction countermeasure construction method in which crushed stone drain piles are intermittently placed around a pipeline buried in liquefied ground along the longitudinal direction of the pipeline. Disclosed.

In addition, research on the effect of liquefaction countermeasures depending on the width of the moat road when crushed stone drains are applied to the moat road (Taniguchi et al.; Analysis of the gravel drain construction method as a liquefaction countermeasure for the moat road, 22nd Soil Engineering Research Presentation Association (Niigata)
, June 1988), and research on the effect of the deep mixing method on preventing liquefaction of moat roads during liquefaction (Koga, Koseki, et al.: Model vibration experiment regarding liquefaction countermeasures for moat roads using deep mixing method). Part 2) - Discussion on dynamic external forces - 23rd Soil Engineering Research Presentation (Miyazaki), 1988
(see June 2013).

(4) Combination method A method that combines the sheet pile enclosure method (1) and the ground improvement method (3), or a method that combines the pile support method (2) and the ground improvement method (3).

[Problem to be solved by the invention]

The conventional liquefaction countermeasures for buried structures described above have the following problems.

(1) Sheet pile enclosure method If you simply provide a sheet pile enclosure, the weight of the buried structure such as a public ditch and its overload, as well as the weight of the backfill soil between the sheet pile and the buried structure, will be lower than the underside of the buried structure (the sheet pile enclosure). )
Acts as overburden pressure on the ground. Therefore, if the cross-sectional width of the buried structure is large, the ground restraint effect by sheet piles will not work effectively during an earthquake, the ground beneath the buried structure will liquefy, and the uplift force will be greater than the sum of its own weight and overburden load. , floating cannot be prevented.

As shown in FIG. 7, even when the sheet piles are connected to each other on the top surface of the buried structure, pull-out resistance is required at the part where the sheet piles are embedded deeper than the liquefaction layer, and the embedded length may become long.

Furthermore, the surface of the sheet pile and the surface of the buried structure (mainly the side surface) tend to form streamlines, and there is a risk of sand blowing in the ground directly above the side surface of the sheet pile and the buried structure.

(2) Pile support method Excess pore water pressure is inevitably transmitted from the liquefied ground around the buried structure to the ground below it.

Since this method uses the resistance to pull out the piles, the number of piles increases as the scale of buried structures such as public ditches increases.

In addition, the sides of buried structures and piles tend to form streamlines, which tends to generate sand blowing from the surrounding areas.

(3) Ground improvement method As the scale of the buried structure increases, the area to be improved increases, and the construction period becomes longer than in the above two methods.

In addition, for example, in liquefied ground that causes horizontal movement overall, in the case of a sheet pile enclosure method or a pile support method, the strength and rigidity of the members may prevent the occurrence of shear planes on the drying surface of the buried structure. Although it can be prevented, there is no clear guarantee in this regard with ground improvement. In other words, in order to improve the ground around buried structures, liquefaction in the improved area is suppressed, but if excessive pore water pressure is transmitted to the bottom of buried structures such as public ditches for some reason, the acting uplift pressure will be lower than the improved area. There is a risk that the buried structure will float to the surface. With crushed stone drains, which are considered to be one of the ground improvement methods, the above-mentioned phenomenon is thought to be less likely to occur since the drainage effect can be expected, but the possibility still exists.

(4) Combination method of (1) or (2) and (3) For example, there are cases where ground improvement is performed by injecting chemicals into the underside of a common ditch within a sheet pile enclosure, but this increases the construction cost.

The present invention aims to solve the problems in the prior art as described above. In other words, when installing underground or semi-underground structures such as large-scale public ditches or ditched roads in liquefied ground, it suppresses the rise in excessive pore water pressure in the surrounding ground and improves the safety of the buried structures against earthquakes. The purpose of this project is to prevent sand blowing and liquefaction in the ground surrounding structures, and to improve the construction efficiency and economic efficiency of these buried structures.

[Means to solve the problem]

The method for preventing liquefaction of buried structures of the present invention is to prevent liquefaction from occurring on the underside of buried structures built underground or semi-underground, such as public ditches or dug roads, during earthquakes. By installing liquefaction prevention piles of the required length that have a drainage function to dissipate excess pore water pressure, and by forming drainage channels continuous with these piles and draining underground water,
In addition to supporting the buried structure with liquefaction prevention piles, it suppresses the rise in pore water pressure around and under the buried structure, thereby preventing liquefaction.

As a drainage channel, for example, the bottom of a buried structure such as a public ditch or a dug road is shaped with crushed stone, and this is connected to the upper end of the liquefaction prevention pile as a drainage layer, and the bottom is connected to this drainage layer. Possible routes include attaching a drainage material to the outer surface of the side wall of the buried structure and communicating it with a drainage layer such as a crushed stone mat for drainage near the top of the buried structure, or direct drainage to the ground. In addition, it is possible to connect the liquefaction prevention pile with the inside of a common trench as an underground structure using a drainage pipe, and drain water from the inside of the common trench, or by installing piping inside the side wall of the buried structure. It is also possible to route the groundwater induced into the soil-deterrent pile through the buried structure to the upper drainage layer or other drainage equipment.

〔Example〕

Next, the illustrated embodiment will be described.

FIGS. 5 and 6 show examples of liquefaction prevention piles used in the present invention.

The liquefaction prevention pile 2a shown in FIG. 5 has a large number of openings 21 in a predetermined section of the steel pipe, that is, in the thickness direction of the liquefied ground.
Filter 2 to prevent dirt from entering the opening 21
2, and the inside of the steel pipe is used as a drainage space.

The liquefaction prevention pile 2b shown in FIG. 6 has a drainage member 23 provided in a predetermined section in the longitudinal direction on the outer surface of the steel pipe. A filter 25 is provided to prevent this.

The above are examples of liquefaction prevention piles, and the liquefaction prevention piles used in the present invention have a supporting function as a pile and a material that dissipates excess pore water pressure generated in the ground during an earthquake. Any type is acceptable as long as it has a drainage function.

FIG. 1 shows an outline of the case where the present invention is applied to a common ditch work, and shows a state in which a common ditch 1 is supported by liquefaction prevention piles 2. In this figure, the drainage route from the liquefaction prevention pile 2 due to the increase in excess pore water pressure during an earthquake is omitted. During construction, after constructing earth retaining sheet piles (not shown), liquefaction prevention piles 2 with drainage functions are driven, and crushed stone (
Shape the bottom surface of the common ditch 1 using Kurite stone 3 and construct the common ditch 1 using cast-in-place concrete. The retaining sheet piles will be removed after construction. The head of the liquefaction prevention pile 2 and the common groove J are rigidly connected, and the structure is such that the common groove 1 and its overload are supported by the liquefaction prevention pile 2. In the figure, 4 indicates the liquefied ground around the common ditch 1, and 5 indicates the liquefied ground on the lower surface of the common ditch 1.

The embodiment shown in Fig. 2 shows an example of a specific drainage route, and includes the drainage member 23 of the liquefaction prevention pile 2 (in the case where the inside of the steel pipe is used as the drainage space, the opening 21 near the head of the pile).
into the crushed stone 3, and a drainage material 6 made of resin etc.
is raised from its upper surface along the side wall 1b (only one side is shown) of the common ditch 1, and is connected to a blind culvert 8 provided within the crushed stone pine door for drainage. By forming such a drainage channel, it is possible to suppress an increase in pore water pressure during an earthquake by draining underground water.

Furthermore, because the common ditch 1 and its overload are completely supported by piles, the excess pore water pressure generated in the liquefied ground 5 on the bottom surface of the common ditch 1 during an earthquake shows a value near zero at the bottom of the common ditch 1. , the floating of the common ditch 1 is prevented and no subsidence occurs.

The pitch of the liquefaction prevention piles 2 in the direction perpendicular to the plane of the paper is such that the excess pore water pressure dissipation effect of a single liquefaction prevention pile 2 overlaps with that of the adjacent liquefaction prevention pile 2, so that the pitch of the common ditch 1 is It is possible to prevent large excess pore water pressure generated in the outer liquefied ground 4 from being transmitted to the liquefied ground 5 on the lower surface of the common ditch 1.

The embodiment shown in FIG. 3 shows another example of the drainage route, in which the drainage member 23 of the liquefaction prevention pile 2 is embedded up to the bottom plate 1a of the common ditch 1, and a flexible resin vibrator 9 is used to make the drain inside the common ditch 1. It is piped to the

This eliminates the need for drainage measures such as crushed stone pine doors for drainage on the upper surface of the common ditch 1 in the embodiment shown in FIG. In the method of this embodiment, it is difficult to prevent the formation of water channels on the surface of the side wall 1b of the common trench 1, and there is a risk of sand blowing occurring on the ground directly above the side wall of the common trench 1 during an earthquake, but the speed of water flow is extremely fast.

The embodiment shown in FIG. 4 shows a case in which a drainage path is provided within the side wall lb of the common ditch 1, as an example in which the common ditch 1 itself has a drainage function. In this example, piping 10 is installed inside the side wall 1b of the common ditch 1 to secure a drainage route from the liquefaction prevention pile 2, and on the top surface of the common ditch 1 there is a crushed stone pine door for drainage similar to the embodiment shown in FIG. Drainage measures are taken with 8 blind culverts.

In addition, a pipe 11 with a filter extending into the pipe 1o is provided on the side of the common ditch 1 with an appropriate pinch to prevent liquefaction of the surrounding liquefied ground 4.

In the embodiments shown in FIGS. 3 and 4 as well, the liquefaction prevention piles 2 function sufficiently against the uplift force acting on the common ditch 1 during an earthquake, and the safety against floating is greatly improved.

Although the common ditch 1 in the embodiments described above is made of cast-in-place concrete, there is no problem when using a common ditch made of precast concrete. For example, mortar or concrete may be placed between the liquefaction prevention pile and the common ditch. This can be sufficiently handled by using a filling structure. Furthermore, these liquefaction countermeasures are not limited to public ditches, but can be similarly applied as liquefaction countermeasures for moat roads.

Furthermore, in the case where the liquefied ground is sloped or the entire liquefied ground moves laterally due to sand blowing, etc., this invention prevents this by suppressing the decline in the strength and rigidity of the steel material and the strength of the surrounding ground. It is extremely effective as a countermeasure against liquefaction in that it not only prevents buried structures such as public ditches from floating up, but also prevents ground deformation.

〔Effect of the invention〕

■ By using liquefaction prevention piles that have a drainage function to dissipate excess pore water pressure as support piles for buried structures such as public ditches, liquefaction of the ground around and under the buried structures can be prevented in the event of an earthquake. Deterred.

■ The existence of liquefaction prevention piles and drainage channels connected to them solves the problem of water channels forming on the surface of buried structures or piles, making it possible to prevent the occurrence of sand blowing around buried structures.

■ In addition to the strength and rigidity of the shaft itself, by suppressing the strength reduction of the surrounding ground, horizontal resistance of the ground can be expected, making it suitable for buried structures even in liquefied ground that can be significantly deformed (particularly lateral fluid movement). The integrity of objects and the surrounding ground can be maintained.

■ Liquefaction prevention piles function well as piles against the uplift force generated on the underside of buried structures due to excess pore water pressure, and can prevent buried structures from floating up.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view showing an outline of the present invention, Figs.
5 and 6 are perspective views showing an example of liquefaction prevention piles used in the invention, respectively.
FIG. 8 and FIG. 8 are vertical sectional views showing a conventional example. 1... Common ditch, 2... Liquefaction prevention pile, 3... Crushed stone, 4゜5... Liquefied ground, 6... Drainage material, 7...
Crushed stone mat for drainage, 8... Blind culvert, 9... Resin pipe, IO... Piping, Engineering 1... Piping with filter

Claims (3)

[Claims] (1) Required length for the lower surface of a buried structure built underground or semi-underground to have a drainage function to dissipate excess pore water pressure that occurs around the buried structure and in the ground beneath it during an earthquake. A liquefaction countermeasure construction method for a buried structure, characterized by providing a liquefaction prevention pile and a drainage channel continuous with the liquefaction prevention pile. (2) The liquefaction countermeasure construction method for a buried structure according to claim 1, wherein a drainage channel continuous with the liquefaction prevention pile is provided within the buried structure. (3) The method for preventing liquefaction of a buried structure according to claim 2, wherein the buried structure is a common ditch, and a drainage channel continuous with the liquefaction prevention pile is provided in the common ditch.