JP3920471B2 - Frost heave mitigation structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a frost heave mitigating structure that prevents the ground on the back surface of a fixing head from expanding due to frost heaving and the fixing force of anchors, lock bolts, and the like from increasing and leading to breakage.
[0002]
[Prior art]
In general, for so-called earth retaining to prevent collapse of the ground such as excavated slopes, an anchor hole is excavated in the ground, and an uncurtain dong is inserted into the anchor hole, and the end portion is pulled out to the ground surface. Next, a so-called ground anchor method is often used in which a grout material such as cement paste is filled in the anchor hole and hardened, and then the uncurtain dong is tensioned and fixed by taking a reaction force against the earth retaining wall with a jack. ing. As this uncurtain dong, a PC steel rod or a PC strand is usually used.
[0003]
FIG. 4 shows an example of the anchor structure.
As shown in this figure, an anchor hole 2 having a substantially circular cross section is drilled from the ground surface in the ground 1, and a steel bar 3 such as a PC steel bar is inserted into the anchor hole 2.
The lower end side (one end side) of the steel bar 3 is integrally fixed and fixed to the ground 1 by grout or the like. Then, the head side of the steel bar 3 is pulled out to the ground surface through the retaining wall 5 and the bearing plate 6 formed along the surface layer of the ground 1 and is screwed to the steel bar 3. 7 is tensioned and fixed in a state where reaction force is applied to the earth retaining wall 5 via the bearing plate 6.
[0004]
The upper end of the steel bar 3 and the head fixing tool 7 are housed in a storage space 12 formed in a head cap 11 fixed to the upper surface of the bearing plate 6 with mounting screws 10, 10. The storage space 12 is filled with a rust preventive oil 13 to prevent the steel rod 3 from being rusted.
[0005]
[Problems to be solved by the invention]
However, the anchor structure as described above has the following problems.
In a cold region, the surface layer of the ground 1 is frozen and ice crystals expand, so that the ground surface rises, so-called frost heaving occurs.
When this frost heave occurs between the ground 1 and the retaining wall 5, the retaining wall 5 is lifted so that the lower end side of the steel bar 3 fixed to the ground 1 has a bearing plate 6 and a head fixing tool 7. The force pulling to the head side works through.
[0006]
However, since a tension force is applied to the steel bar 3 in advance by the head fixing portion 7, if a tensile force is further applied by the frost heaving, the elastic limit of the steel bar 3 is exceeded and a predetermined effective tension force is applied. However, the steel rod 3 could break between the head fixing part 7 and the bearing plate 6 when the swell due to freezing was large.
[0007]
The present invention has been made in consideration of the above points, and provides a frost heave mitigation structure capable of maintaining effective tension without breaking a steel bar even when the ground is raised by frost heave. The purpose is to do.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention employs the following configuration.
In the frost heave mitigating structure according to claim 1, one end side of the steel rod is fixed to the ground, and the head side is tensioned and fixed by the reaction force applied to the ground by a head fixing tool via a bearing plate, and the support is supported by freezing. A frost heave mitigating structure that alleviates an increase in tension force applied to the steel rod via a pressure plate and a head fixing tool, wherein the steel rod is elastically restored between the head fixing tool and the bearing plate. The elastic member that generates the tension force is interposed in a state having an elastic deformation length corresponding to a movement length when the support plate moves due to frosting of the ground, and on the back side of the support plate, A bottomed cylindrical cylindrical portion that opens to the head side and accommodates the elastic member is provided, and the cylindrical portion is disposed in an anchor hole into which one end side of the steel rod is inserted, and the bottomed cylinder The elastic member between the bottom of the cylindrical portion and the head fixing tool Is interposed, the tension applied to the steel rod during heaving, the elastic member is characterized in that to relieve the increase in該緊tension elastically deformed.
[0009]
Therefore, in the frost heave mitigation structure of the present invention, in a normal state, the head side of the steel bar is tensioned and fixed in a state where the reaction force is applied to the ground by the elastic restoring force of the elastic member. When the bearing plate moves to the head side during frosting, the elastic member is elastically deformed. Accordingly, the steel rod is prevented from being pulled through the head fixing tool by the moving length of the support plate.
Further, in the frost heave mitigating structure of the present invention, since the one end side of the elastic member accommodated in the cylindrical portion is located in the anchor hole, the amount by which the head side of the elastic member protrudes from the ground can be reduced.
[0012]
The frost heave mitigating structure according to claim 2 is the frost heave mitigating structure according to claim 1, wherein a projection for mounting a head cap for storing a rust preventive agent is provided on the head side of the bearing plate from the bearing plate. It is erected and formed integrally with the bearing plate .
[0013]
Therefore, in the frost heave mitigation structure of the present invention, even if frost heave occurs, the head side edge of the steel rod whose one end is fixed to the ground does not move, but the bearing plate moves to the head side by the frost heave thickness. To do. Therefore, the movement length by freezing can be measured by the change in the distance between the head-side edge of the steel bar and the head-side edge of the projection of the bearing plate.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the frost heave mitigating structure of the present invention will be described with reference to FIG. 1 and FIG.
In these drawings, the same components as those in FIG. 4 shown as the conventional example are denoted by the same reference numerals, and the description thereof will be simplified.
As shown in FIG. 1, a bearing plate 18 that supports the tension of the steel bar 3 is disposed on the surface of the earth retaining wall 5. On the back side of the pressure bearing plate 18, a bottomed cylindrical cylindrical portion 25 that opens to the head side is provided so as to be positioned in the anchor hole 2. A through hole 29 through which the steel rod 3 passes is formed in the bottom portion 28 of the cylindrical portion 25.
[0015]
Further, on the head side of the bearing plate 18, a protrusion 30 having a male screw formed on the outer periphery is provided upright. A head cap 21 is screwed to the projecting portion 30 with an O-ring 32 between the head pressure plate 18 and the pressure plate 18. Inside the head cap 21, a storage space 31 in which a rust preventive agent that rusts the steel bar 3 is stored is formed so as to store the head side of the steel bar 3.
[0016]
A head fixing tool 7 is screwed to the head side of the steel bar 3, and a collar 19 is disposed at the lower end of the head fixing tool 7. The collar 19 is formed with an insertion hole 22 through which the steel bar 3 is inserted and a step portion 23 that opens toward the back side.
A coil spring (elastic member) 20 is interposed between the head fixing tool 7 and the bearing plate 18 via a collar 19.
[0017]
The coil spring 20 is accommodated in the cylindrical portion 25 of the bearing plate 18 with the head side engaged with the step portion 23 of the collar 19 and the back side engaged with the bottom portion 28 of the cylindrical portion 25 of the bearing plate 18 in a compressed state. The spring constant of the coil spring 20 is set so that the effective tension of the steel bar 3 can be output and is sufficiently small with respect to the tensile strength of the steel bar 3.
[0018]
That is, when the cross-sectional area of the steel rod 3 is A, the free length is L, and the Young's modulus is E, the relationship between the tensile load P and the elongation λ is expressed by the following equation.
P = λ × (A × E / L) (1)
(A × E / L) in this equation corresponds to a spring constant, and the spring constant of the coil spring 20 is set sufficiently smaller than the value calculated by (A × E / L) of the steel rod 3. Yes.
The coil spring 20 is transmitted to the steel rod 3 with a predetermined design force when the frost heave is not generated and when the frost heave occurs and the coil spring 20 is bent by a predetermined amount. Thus, the spring constant and the compression amount are set.
[0019]
The operation of the frost heave mitigating structure having the above configuration will be described below.
As shown in FIG. 2, when a frozen portion 1a having a thickness L1, for example, is generated on the surface layer of the ground 1 due to freezing, the earth retaining wall 5, the bearing plate 18 and the head cap 21 also move to the head side following this. To do.
Thereby, although the bottom part 28 of the bearing plate 18 also moves to the head side, the steel bar 3 fixed to the ground 1 where the lower end side is not frosted does not move. Accordingly, the collar 19 and the bottom portion 28 approach the length L1, and the coil spring 20 is elastically deformed and compressed by the length L1.
[0020]
This compression increases the elastic restoring force of the coil spring 20 by an amount obtained by multiplying the spring constant by the length L1, and the steel rod 3 is subjected to a load in a direction in which the tension force increases via the collar 19 and the head fixing device 7. Join.
In other words, a predetermined design force during freezing is transmitted to the steel rod 3 on which the design force has always been applied before freezing. However, since the spring constant of the coil spring 20 is sufficiently smaller than that of the steel bar 3, this load can be suppressed within a sufficiently small elastic range with respect to the tensile strength of the steel bar 3.
[0021]
On the other hand, as shown in FIG. 2, the distance between the head side edge of the steel rod 3 before freezing and the head side edge of the protrusion 30 is a length L3. The distance between the part side edge and the head side edge of the protrusion 30 changes to the length L2.
Therefore, by measuring the lengths L2 and L3 and calculating the difference between them, the moving length of the bearing plate 18, that is, the thickness L1 of the frozen portion 1a can be obtained. By multiplying the spring constant of the spring 20 by the thickness L1, the load applied to the steel bar 3 by freezing can also be obtained.
[0022]
In the frost heave mitigation structure of the present embodiment, the coil spring 20 can tension and fix the steel bar 3 by its elastic restoring force, and even if the bearing plate 18 moves by the length L1 due to frost heave, the coil spring 20 This movement is not transmitted to the steel rod 3 because it is elastically deformed to absorb this movement amount.
Therefore, the tension force applied to the steel bar 3 is not greatly increased due to the tension of the steel bar 3, but greatly reduced by the elastic deformation of the coil spring 20 that is several tenths smaller than this. Therefore, it is possible to prevent the tension force from exceeding the elastic limit so that the predetermined effective tension force cannot be maintained or the steel bar 3 itself is broken. In addition, as described above, even when a load due to elastic deformation of the coil spring 20 is applied to the steel bar 3 during frosting, the load is a predetermined design force during frosting, so the steel bar 3 maintains an appropriate effective tension. be able to.
[0023]
Further, in the frost heave mitigation structure of the present embodiment, it occurs on the back side of the retaining wall 5 only by measuring the distance between the head side edge of the steel bar 3 and the head side edge of the protrusion 30. Therefore, it is possible to easily confirm the presence or absence of freezing that cannot be normally observed, the thickness of freezing, and the load applied to the steel rod 3 by freezing.
Furthermore, in the frost heave mitigating structure of the present embodiment, since the cylindrical portion 25 of the bearing plate 18 that houses the coil spring 20 is disposed in the anchor hole, the length of the steel rod 3 protruding to the ground surface can be shortened. And appearance is improved. In addition, in this structure, since the steel bar 3, the head fixing tool 7 and the coil spring 20 are built in the head cap 21 and immersed in the rust preventive agent, they can be rust-prevented for a long period of time. Accidents caused by can also be prevented for a long time.
[0024]
In the above-described embodiment, the elastic member is a coil spring. However, the elastic member is not limited to this and may be an elastic member such as a disc spring or urethane rubber. Moreover, as a steel bar, as shown in FIG. 3, a PC steel bar, a deformed PC steel bar, a deformed round steel formed with a screw, or a structure using a lock bolt may be used.
[0025]
【The invention's effect】
As described above, the frost heave mitigating structure according to claim 1 is provided with an elastic member for generating a tension force on the steel rod by elastic restoring force between the head fixing tool and the bearing plate, The elastic member is elastically deformed by the tension force applied to the rod, thereby reducing the increase in tension force.
As a result, in this frost heave mitigation structure, it is possible to maintain the effective tension of the steel rod even in the cold region where freezing of the natural ground occurs, and to prevent the steel rod from being broken due to frost heave. An effect is obtained.
[0026]
Also, on the back side of the pressure bearing plate, a bottomed cylindrical cylindrical portion that opens to the head side and accommodates the elastic member is provided, and one end side of the steel rod is inserted into the cylindrical portion. It is arranged in the anchor hole, and the elastic member is interposed between the bottom portion of the bottomed cylindrical cylindrical portion and the head fixing tool . The length of the steel bar protruding to the ground surface can also be shortened, and the effect of improving the appearance can be obtained.
[0027]
In the frost heave mitigating structure according to claim 2 , a protrusion for mounting a head cap for storing a rust preventive agent is provided on the head side of the bearing plate so as to stand upright from the bearing plate and integrated with the bearing plate. It is the structure formed in .
Thus, in this frost heave relaxed structure, steel rod, since the elastic member or the like can be prolonged rust, Ru can prevent long-term also accidents caused by frost heaving.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of the present invention, in which a coil spring is interposed between a pressure bearing plate and a head fixing tool.
FIG. 2 is a view showing an embodiment of the present invention, and is a cross-sectional view in which a coil spring is elastically deformed by freezing.
FIG. 3 is a diagram showing an embodiment of the present invention, and is a cross-sectional view in which a deformed round steel is used as a steel bar.
FIG. 4 is a cross-sectional view showing an example of a frost heave mitigation structure according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ground 2 Anchor hole 3 Steel rod 7 Head fixing tool 18 Bearing plate 20 Coil spring (elastic member)
21 Head cap 25 Cylindrical portion 30 Projection

Claims (2)

One end side of the steel rod is fixed to the ground, and the head side is tensioned and fixed by the reaction force applied to the ground by the head fixing tool via the supporting pressure plate, and the above-mentioned via the supporting pressure plate and the head fixing tool by freezing A frost heave mitigation structure that alleviates an increase in tension applied to a steel bar,
An elastic member that generates the tension force on the steel rod by an elastic restoring force between the head fixing device and the bearing pressure plate corresponds to a moving length when the bearing plate moves at least due to freezing of the ground. Is inserted in a state having an elastic deformation length to
On the back side of the bearing plate, a bottomed cylindrical cylindrical portion that opens to the head side and accommodates the elastic member is provided, and the cylindrical portion is an anchor hole into which one end side of the steel rod is inserted. The elastic member is interposed between the bottom of the bottomed cylindrical cylindrical portion and the head fixing tool,
A frost heave mitigating structure, wherein the elastic member is elastically deformed to relieve the tension force applied to the steel rod during frosting, and the increase in the tension force is alleviated. In the frost heave mitigation structure according to claim 1,
On the head side of the bearing plate, a protrusion for mounting a head cap for storing a rust preventive agent is provided upright from the bearing plate and integrally formed with the bearing plate. Freezing-up mitigation structure.

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