JP2008144419A - Structure of manhole - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure of a manhole capable of preventing the manhole from being raised even if the ground therearound is liquefied in an earthquake. <P>SOLUTION: This structure of a manhole comprises a cylindrical manhole and a raising prevention plate. The raising prevention plate projects to the outside of the manhole when viewed from above. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to the structure of manholes and handholes.

When the ground is liquefied due to an earthquake, the vibration causes manholes and handholes (hereinafter collectively referred to as “manholes”, including the description in this specification and claims), and buoyancy acts on the piping. In addition to losing its function as a manhole by insulation, an accident has occurred in which the upper part of the manhole jumps out onto the road surface and becomes a traffic obstacle.
In order to improve such a problem, for example, as shown in FIG. 14, a large concrete block b is formed under the manhole a, and the weight of the block b prevents the manhole a from rising due to liquefaction of the ground. Various configurations have been developed. (See Patent Document 1)
Alternatively, a method for improving the ground so that the ground around the manhole is not liquefied has been proposed. (See Patent Document 2)
Alternatively, a method has been proposed in which liquefied earth and sand are introduced into the manhole to absorb buoyancy. (See Patent Document 3)
JP 2006-194033 A. JP 2006-183244 A. JP 2006-124966 A.

The above-described conventional manhole structure has the following problems.
<1> In a structure in which a counterweight is attached to prevent the manhole from rising, a great deal of labor is required for the installation work of the counterweight, and the amount of excavation is large, which is uneconomical.
<2> In the method of improving the ground around the manhole, ground improvement work is required before and after the manhole is installed, and it takes a long time to cut off the road and is expensive.
<3> The structure in which liquefied earth and sand are introduced into the manhole is unlikely to cause the earth and sand to move instantaneously at the time of an actual earthquake, and the implementation is questionable.

  In order to solve the above-described problems, the manhole structure of the present invention is composed of a cylindrical manhole and a levitation suppression plate, and the levitation suppression plate projects from the manhole in plan view. It is composed.

  Alternatively, the manhole structure of the present invention is configured by a cylindrical manhole and a levitation suppression plate, and in a plan view, a locking projection is projected toward the outside of the manhole, and the levitation suppression plate has a manhole inside. It is a bowl-shaped plate that penetrates a hole having a shape substantially equal to the outer shape, and is configured by disposing a levitation suppression plate on the upper side of the locking projection.

  Or the structure of the manhole of this invention is comprised from a cylindrical manhole and a levitation suppression board, and a levitation suppression board is a board body with a bigger external shape than the outer shape of a manhole, and a levitation suppression board and a manhole are engaging members. It is comprised so that engagement is possible.

Since the structure of the manhole of the present invention is as described above, the following effects can be obtained.
<1> Rather than using the weight of the counterweight, it uses the weight of the clot that is located above the levitation deterrent plate and reaches the ground. Can do.
<2> It does not require long-time work to improve the ground around the manhole, and therefore the impact on traffic can be minimized.
<3> There is no uncertain element that introduces liquefied earth and sand into the manhole, and the manhole can be reliably prevented from rising.
<4> Since it is a simple structure in which a conventional anti-floating plate is simply attached to a known manhole, a conventional commercially available manhole body or a method for constructing a manhole placed on site can be used as it is.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

<1> Manhole.
A hollow cylinder that allows people to enter and exit freely is provided for inspection and repair of underground sewers, electricity and telephone lines, and so on.
The manhole 1 targeted by the present invention is a manhole 1 made of precast concrete, a manhole 1 made of cast-in-place concrete, a manhole 1 made of steel or synthetic resin.
Although the basic shape of the manhole 1 is a hollow cylindrical shape, a horizontal cross section having a square shape, a rectangular shape, an elliptic shape, or the like can also be used.

<2> Levitation restraint plate 2.
On the outer periphery of the manhole 1, a levitating restraint plate 2 is projected in a bowl shape.
The levitation restraint plate 2 is a plate made of concrete, steel, or synthetic resin, and is configured to be positioned in a substantially horizontal direction when the manhole 1 is installed in the ground.
The dimensions of the levitation suppression plate 2 need to be configured to protrude toward the outside of the manhole 1 when viewed as a plan view, that is, in plan view.
For this purpose, for example, the levitation suppression plate 2 employs a bowl-shaped plate body in which a hole having a shape substantially equal to the outer shape of the manhole 1 is opened. (Example of FIGS. 1 and 2)
Alternatively, the levitation suppression plate 2 employs a plate body having an outer shape larger than that of the manhole 1 and having no holes. (Example of FIG. 3)

<3> Attaching the levitation suppression plate 2
Various configurations can be employed to attach the levitation suppression plate 2 to the manhole 1.
For example, (1) when a manhole 1 having a conventional structure is manufactured at a factory or in the field, a levitation restraint plate 2 that protrudes toward the outside of the manhole 1 is formed integrally with the bottom plate of the manhole 1 and in plan view. The method to do can be adopted.
Or (2) When foundation concrete is placed directly under the manhole 1, the suspension prevention plate 2 is formed as an integral structure on the outer periphery of the foundation concrete in a state of protruding toward the outside of the manhole 1 in plan view The method to do can be adopted.
Alternatively, (3) a hook-like plate having a locking projection protruding outwardly on the outer periphery of the cylindrical manhole 1, while the levitation depressing plate 2 penetrates a hole having a shape substantially equal to the outer shape of the manhole 1 It can comprise as a body and can arrange | position the floating suppression board 2 on the upper side of a latching protrusion. (Example of FIGS. 1 and 2)
When viewed in a plan view, the locking protrusion protrudes outward from the outer periphery of the manhole 1, and therefore, the protrusion supports the levitation suppression plate 2 mounted on the upper side thereof.
Alternatively, (4) a locking projection is provided on the outer periphery of the cylindrical manhole 1, and the levitation suppression plate 2 is formed of a plate having a larger outer shape than the outer shape of the manhole 1. It is also possible to provide a locking tool 3 to be engaged and to configure the locking tool 3 and the locking projection so as to be engageable with each other. (Example of FIG. 3)
Alternatively, (5) In the case of the manhole 1 configured by stacking a plurality of short cylinders, there is a possibility that they may be separated from each other due to the vertical movement at the time of an earthquake, but the levitation deterrent plate 2 is arranged at the bottom of the manhole 1, If the levitation deterrent plate 2 and the upper part of the manhole 1 are connected by a locking tool 3 such as a reinforcing bar, a steel bar, an iron plate, a rope, or a carbon fiber belt, the manhole 1 will be restrained from above and below. Not only deterrence but also separation of the short tubes can be deterred.
In that case, the levitation restraint plate 2 may be a flat plate without a hole, and the manhole 1 may be mounted thereon (FIG. 12), but the levitation restraint plate 2 having a configuration in which a through hole is opened may be employed. (Fig. 13)
Further, as shown in FIG. 13, a structure in which the end of a locking tool 3 such as a reinforcing bar, a steel bar, an iron plate, a rope, or a carbon fiber belt is fixed to the floating deterrent plate 2 and the middle is hung around the upper part of the manhole 1. It can also be adopted.

<4> Determination of the shape of the levitation restraint plate 2
The levitation restraint plate 2 provided around the manhole 1 is desirably protruded from the outer peripheral surface of the manhole 1 toward the periphery at least 10% of the outer shape and outer dimension of the manhole 1 in plan view.
The basis for this will be discussed below.

<5> Examination of liquefaction.
The following passage is described in page 421 of the document “New edition of soil and foundation design calculation exercises” (published by the Geotechnical Society of Japan). “Liquefied ground shows behavior similar to mechanical behavior as a liquid. Its unit volume weight is the same as that of saturated sand ground before liquefaction and is about twice the unit volume weight of water. . "
The manhole 1 of the present invention is an application of the above theory to prevent the manhole 1 from rising.

<6> A conventional manhole.
Here, the idea of the present invention is shown by a simplified model.
First, for comparison, consider a conventional simple manhole model as shown in FIG.
The manhole is in a stable state on the supporting ground. This state is expressed as follows.

W1 + W2 + Fa ≧ Ua -------------------------- Equation 1
Where W1 is the weight of the manhole
W2 is the weight of road pavement and earth and sand above the manhole
Fa is the frictional force between the manhole and surrounding soil
Ua is buoyancy due to groundwater received by manholes

<7> A phenomenon during an earthquake.
In the above-described conventional manhole model, when part or all of the surrounding earth and sand is liquefied due to the occurrence of an earthquake, the frictional force between the manhole and the liquid surrounding earth and sand approaches zero. (Fig. 9)
Further, the surrounding earth and sand can be assumed to be a liquid having a unit volume weight that is twice the unit volume weight of water after being liquefied. In other words, buoyancy is doubled.
And it is thought that the manhole begins to float in the state expressed by the following mathematical formula.

W1 + W2 + Fb <Ub -------------------------- Equation 2

here
W1 is the same as equation 1.
W2 is the same as Formula 1. Fb is the frictional force between the manhole and surrounding soil: Fb ≒ 0
Ub is the buoyancy due to the liquefied earth and sand that the manhole receives: Ub ≒ Ua × 2

As can be seen from the above, in the case of a manhole having a conventional shape, the liquefaction phenomenon brings the peripheral frictional force close to zero and the buoyancy is nearly doubled, so that the manhole rises and the manhole jumps out to the ground surface. A condition occurs.

<8> In the case of the manhole 1 of the present invention.
A simple model when the manhole 1 equipped with the deterrent plate of the present invention is in the liquefied surrounding earth and sand at the time of an earthquake will be examined with reference to FIG.
The state where the manhole 1 is prevented from being lifted by the earth and sand above the levitation restraining plate 2 can be expressed by the following mathematical formula.

W1 + W2 + W3 + Fb ≧ Ub -------------------- Equation 3

Where W1 is the same as Equation 2.
W2 is the same as equation 2.
W3 is the weight of sediment above the deterrent plate
Fb is the same as equation 2
Ub is the same as equation 2

In other words, the deterrence plate 2 of the present invention is an invention that focuses on the fact that the deterrence plate 2 does not rise due to the resistance of earth and sand in the liquefied earth and sand so that the parachute does not fall due to the resistance of air in the air. The resistance is the weight of the liquefied earth and sand.

<9> Calculation example.
An example of calculation using general numerical values in a simple model as shown in FIG.

V1: Manhole volume
V2: Manhole interior space
γc: Unit volume weight of concrete: 25kN / m3
γ1: Unit volume weight of surrounding earth and sand: 20kN / m3
γ2: earth and sand above the manhole and other unit volume weight: 20kN / m3

V1 = 1.0 × 1.0 × 3.14 × 3.0 = 9.42 m3
V2 = 0.8 x 0.8 x 3.14 x 2.6 = 5.22 m3

W1 = (V1-V2) × γc = (9.42-5.22) × 25kN / m3 = 105kN
W2 = 1.0 × 1.0 × 3.14 × 1.0 × 20 = 62.8 kN
W3 = (1.2 × 1.2-1.0 × 1.0) 3.14 × 3.6 × 20 = 99.5 kN

Ua = V1 x unit volume weight of water = 9.42 x 10 = 94.2 kN
Ub = V1 × γ2 = 9.42 × 20 = 188.4 kN

<10> The manhole 1 of the present invention in normal times.
Here, the relational expression when the simple model of FIG. 4 is in the normal state is as follows, and it can be said that it is in a stable state even if the peripheral frictional force Fa is ignored.

W1 + W2 + Fa ≧ Ua ----------------------------- Equation 1
105kN + 62.8kN + α> 94.2kN

<11> The manhole 1 of the present invention at the time of an earthquake.
Next, in the state where the manhole 1 of the present invention is in the liquefied earth and sand at the time of the earthquake, the peripheral friction force Fb cannot be expected as in the following formula, so it becomes zero and the buoyancy is doubled.
In this state, the buoyancy on the right side is larger than that on the left side, and the manhole is unstable and levitates.

W1 + W2 + Fb <Ub ----------------------------- Equation 2
105kN + 62.8kN + 0 <188.4kN

However, when the restraint plate 2 of 10% or more of the outer shape of the manhole 1 is mounted around the manhole 1 of the present invention, the weight of the manhole 1 on the left side and the upper earth and sand is larger than the buoyancy on the right side in the following formula. Therefore, the manhole 1 does not rise.

W1 + W2 + W3 + Fb ≧ Ub ----------------- Equation 3
105kN + 62.8kN + 99.5kN + 0> 188.4kN

<12> Evaluation of the present invention.
Actually, the size and shape of the manhole 1 vary, and the depth at which the manhole 1 is installed also varies. The soil quality of the surrounding earth and sand is not constant.
At present, the degree of viscosity and fluidity of liquefied earth and sand is unknown, but the water inside the liquefied earth and sand tends to rise, and the earth and sand whose specific gravity is higher than water tends to sink.
And even liquefied soil is surely heavy.
Although there are some unclear points like this, by planning the area of the deterrent plate 2 with a margin, not only can the jump out of the liquefied earth and sand to the surface of the manhole 1 and exposure can be prevented, Even after liquefaction, the depth and position can be kept practical.
From the above model, it can be assumed that the effect of resisting lifting appears by installing the deterrent plate 2 having a width of 10% or more of the outer shape of the manhole 1 outside the manhole 1 housing.

<13> Other evaluations.
In the case of installing the floating restraint plate 2 having a planar shape different from the planar shape of the manhole 1, for example, when the planar shape of the manhole 1 is circular and the floating restraint plate 2 is a polygonal flat plate, The total area of 2 is preferably 0.44 times or more the flat area of the manhole 1.
Moreover, even when the area where the levitation suppression plate 2 protrudes from the outer periphery of the manhole 1 is small, the suppression effect can be expected.
However, in order to ensure that the manhole 1 does not tilt and can be used in an earthquake, maintain an area of 44% or more on the outer periphery of the manhole 1 in plan view, and back and forth around the center of gravity of the manhole 1 It is preferable to perform area distribution with a good balance between left and right.

<14> Model experiment.
A laboratory experiment by the inventors of the present invention will be described.
Since manholes vary in depth and shape, they can be put into practical use by classifying them into several types according to depth and shape, and by determining the width and area of the deterrent plate through full-scale experiments. The experiment was conducted as a manhole.
First, two milk bottles having a diameter of about 5 cm were prepared, and one of them was provided with a thin plate as a levitation restraint plate 2 on the outside of the entire circumference with a width of 1 cm.
The other one was used as a comparative example, and the levitation restraint plate 2 was not attached in a milk bottle of the same standard.
Then, a sand layer having a thickness of about 10 cm was formed on the bottom of a large plastic bucket, and the two milk bottles were installed on the sand layer. (Fig. 4)
After that, the area around the milk bottle was filled with sand and solidified. (Fig. 5)
Next, water was sprinkled so that the sand approached water saturation, and then the bucket was vibrated rapidly.
The milk bottle of the comparative example in which the anti-floating plate 2 was not attached started to rise easily according to the time when the vibration was applied. (Fig. 6)
And about 20 seconds later, the whole jumped out to the surface of the sand layer and rolled over. (Figure 7 right)
On the other hand, the milk bottle with the levitation restraint plate 2 attached to the periphery did not move at all and did not rise even when sand liquefaction started. (Figure 7 left)
And even if it tried to raise after stopping a vibration, the sand layer on the levitation suppression board 2 was in the state where it was tightened, and the resistance of raising became large.
Thus, it was proved by the model that the manhole 1 of the present invention is stable against liquefaction.

The perspective view of the Example of the structure of the manhole of this invention. The side view of the Example of FIG. The side view of another Example. Explanatory drawing of model experiment. Explanatory drawing of model experiment. Explanatory drawing of model experiment. Explanatory drawing of model experiment. Explanatory drawing of the model of the conventional manhole. Explanatory drawing at the time of the earthquake of the conventional manhole model. Explanatory drawing of the model of this invention. The dimension drawing of the Example of the manhole of this invention. The side view of another Example. The side view of another Example. Explanatory drawing of the conventional manhole.

Explanation of symbols

1: Manhole 2: Levitation restraint plate 3: Locking tool

Claims (4)

Consists of a cylindrical manhole and levitation deterrent plate,
In plan view, it was constructed by projecting a levitation suppression plate toward the outside of the manhole.
Manhole structure
Consists of a cylindrical manhole and levitation deterrent plate,
In plan view, projecting the locking protrusion toward the outside of the manhole,
The levitation deterrent plate is a bowl-shaped plate that penetrates a hole having a shape substantially equal to the outer shape of the manhole on the inside,
Constructed by placing a levitation deterrent plate above the locking projection,
Manhole structure.
Consists of a cylindrical manhole and levitation deterrent plate,
The levitation deterrent plate is a plate with a larger outer shape than the manhole.
The levitation suppression plate and the manhole are configured to be engageable by an engagement member.
Manhole structure.
The levitation deterrent plate
In plan view, at least 10% of the outer dimensions of the manhole are projected toward the outside of the manhole.
The manhole structure according to claim 1.

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