JP5362523B2 - Calculation method to set the step width etc. by calculating the snow pressure resistance such as slope snow pressure and step width on the slope. - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately calculate a small step width in the case of using a small step of a slope also for snowslide prevention and the like or a small step width formed of a snowslide prevention fence by setting a friction coefficient of a slant face, an inclination of the slant face, and an area of a load sphere of a snow layer on the slant face. <P>SOLUTION: The snow layer on the slant face is always made to flow down and deformed by the geothermal melting of snow at the bottom of the snow layer and the consolidation settlement and the gravitating of the snow layer to generate slope snow pressure on the small step and the like, whereby the snow layer accumulated on the small step width is pushed out to be broken and fallen when the small step width is narrow. The small step width La is calculated which secures snow weight accumulated on the small step width corresponding to the slope snow pressure P and resists by a snow pressure resistance force Pa to prevent the breakage and fall of the snow layer on the small step. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a calculation method for securing a step width to prevent avalanches on slopes in snowy regions.

  As shown in Fig. 1, the snow layer on the slope in the snowy region always moves to the valley side due to the melting of snow on the bottom of the snow layer due to geothermal heat, the subsidence of the snow layer, and the gravitational action (creep phenomenon of the snow area). The contour line 1 on the surface is deformed and changed to the snow layer surface 2, and the slope snow pressure P is generated. Due to such factors, the snow layer accumulated in the small step width La section or the like of the flat field is pushed out and the snow plow 3 is generated and collapses, leading to the cause of the avalanche on the slope.

The steps of the slope in the snowy region are set at 1.5m as a standard, depending on the soil texture, slope height, management of the facility, etc. Such a step width of the slope prevents the collapse of the snow layer that accumulates on the slope and leads to avalanche suppression. However, a clear causal relationship has not yet been elucidated. The step width has been set.
▲ 1 ▼ Step width L = 0.8 h method ・ ・ ・ h = Designed snow depth adoption ▲ 2 ▼ Maximum snow depth method ・ ・ ・ Established 30-year reproduction Established maximum snow depth ▲ 3 ▼ In all layer avalanche countermeasures snow study method ... of the small stage width ^"1996-1998, (taking into account the direct higher of Japan, snow Center materials and method surface)"
However, each is a method of setting the step width La mainly based on the snow depth H, and it does not take into account the friction coefficient of the ground surface on the slope and the slope snow pressure, which greatly affects the slip of the snow covered area, and is rational. It was not a typical setting method.

The main method for calculating the slope snow pressure includes the Swiss method and Patent Document 1, but differs from the present invention depending on the following contents.
(1) Although the slope snow pressure SN by the Swiss method is expressed by the following formula, it is difficult to calculate the snow pressure resistance force and the like due to the snow layer in which the slope gradient is deposited in a small step width close to a flat field. In addition, since the slant area snow layer is considered to be the same thickness as it does not deform, we do not consider the collapse of the snow ridge formed on the fence head due to the slant area snow pressure or the like.
^{SN = H 2/2 · K} · N
S · Slope snow pressure K ·· Creep coefficient (K / sin 2θ) Difficult to calculate when slope slope is small N ·· Glide coefficient (2) [Patent Document 1]
“Calculation method of snow load by slope snow pressure acting on protrusion on slope” is a method of calculating slope snow pressure acting on piles buried in slope area snow layer installed on slope. It is difficult to apply to a calculation method in which the snow pressure P and the snow pressure resistance Pa due to the snow layer accumulated in the step width are grasped in a plane, the balance between both snow pressures is confirmed, and the step width is set.
Japanese Patent No. 4358893

  The conventional avalanche prevention fence 4 installation position is generally set on a small mountain side in order to ensure the safety of the foundation work 5 as shown in FIG. 2, and can be handled by the snow weight Wa of the small width La. Use of snow pressure resistance Pa is disabled.

  The effect of suppressing the avalanche of the slanted snow layer on the slope on the slope depends greatly on the field conditions such as the width of the stage, snow depth, snow quality, slope gradient, direction, etc. It is necessary to calculate the slope snow pressure P and the snow pressure resistance Pa of the small steps, and rationally calculate and adjust the small step width La according to the balance of the snow pressures to prevent the fall of the snow layer deposited in the small step width.

  The snow layer on the slope has a soft snow quality with a small density during the snowfall season, and it becomes compacted as time passes and becomes a snow mass. Referring to FIG. 3, the outline of the snow layer is greatly affected by the slope gradient θ and the surface roughness of the snow cover (friction coefficient μ), and the slope snow pressure P on the slope is in the flat field La section with a small step width. The fact that the snow layer is pushed and collapsed to the valley side is caused by the magnitude of the snow pressure resistance Pa due to the small snow layer. Both snow pressures are greatly affected by the slope gradient θ and the friction coefficient μ. However, considering the standardization of the calculation method, the range of the load sphere affecting the slope snow pressure P on the slope is set as L (L = Adjusted by the density of the snow layer of 1.5H to 2.0H), and the range of the load zone that affects the snow pressure resistance Pa of the small step is set as La. Further, the friction coefficient μ is determined as a coefficient within 1.0 based on the unevenness state of the slope, P and Pa per 1 m of the slope extending direction are calculated, the equilibrium state of the snow pressure is confirmed, and the small step width La is calculated.

  The small steps on the slopes in the snowy area are also used as avalanche prevention facilities, but it was found that the slipping condition of the sloping snow layer and the suppression effect by the steps greatly depended on the slope gradient θ and friction coefficient μ, etc. Calculate the snow pressure P and the snow pressure resistance Pa of the small step, check the equilibrium state of the snow pressure and rationally calculate the small step width La, and prevent the snow layer of the small step from being pushed to the valley side and collapsing. Became possible. As shown in FIG. 3, it has become possible to plan the slope by calculating the small step width La from the beginning with the snow depth, slope gradient θ, and slope friction coefficient μ.

  In addition, when the existing small step width La is insufficient as shown in FIG. 4 or FIG. 8, the wide width Lb of the small step width is planned by the avalanche prevention fence 4 or the overhanging work 7 to rationalize the overall target step width Lc. It became possible to set to. Furthermore, as shown in FIG. 5, the height h3 of the avalanche prevention fence 4 has been set so far by the slant area snow layer H. According to the present invention, it is possible to rationally calculate the height h3 of the avalanche prevention fence 4 by setting the influence range L of the load range of the snow layer on the slope and checking Lc by the step widths La and Lb.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

FIG. 3 shows a method for calculating the step width La of the slope at the place where the slope planning is newly planned.
It should be noted that the snow depth H increases with the rise of the snow layer from the slope A point, but this is offset by the fact that both the slope and the stepped part rise. Calculate with H. Further, the friction coefficient μ is set with reference to the shear strength (0.1 to 0.5 t / m ² ) of the snow layer at the site where the friction coefficient is large.
(1) Calculation of slope snow pressure P Slope area snow depth H = 2.0 m, slope slope θ = 40 degrees, friction coefficient μ = 0.25, load range (m) L1 = L cos θ (L = 1.5H ) Unit weight (density) of snow layer σ = 0.35, snow weight in load range (t / m) W = L1 · H · σ
Slope snow pressure P = W (sin θ−μ · cos θ) = 0.726 (t / m)
(2) Calculation of the step width La Snow depth H = 2.0 m, slope gradient θ1 = 0 degree, friction coefficient μa = 0.35 (considering drainage grooves, etc.), unit weight (density) of the snow layer σ = 0. 35, Snow cover weight of tread width La (t / m) Wa = La · H · σ
Snow pressure resistance (t / m) of the step width is calculated as P <Pa Pa> 0.726 (t / m)
From Pa = Wa (sin θ1-μa · cos θ1) = 0.726 (t / m), La = 2.96 m
Based on the above calculation, the step width is set to (La≈3.0 m) to prevent avalanche on the slope.

Fig. 4 shows that the existing step width La (assuming La = 1.5 m) is narrow, so there is concern about the collapse of the snowfall due to the occurrence of extrusion due to the slope snow pressure P, so the avalanche prevention fence 4 calculates the widening of Lb FIG. 6 is a plan cross-sectional view for preventing avalanche by forming the entire small step width Lc.
(1) Calculation of widening small step width Lb and snow pressure resistance Pb If the on-site conditions are the same as in FIG. 3 described above, the snow pressure relationship is (Pa + Pb = 0.726 t / m), and the small step width relationship is (Lc = La + Lb). = 3.0 m).
Widening small step width Lb = Lc−La = 1.5 m (existing small step width La “assuming La = 1.5 m”)
Snow pressure resistance Pb = 0.726 / Lc · Lb = 0.363 (t / m)
(2) Calculation of Anchor Tensile Force Tb Calculation of stress against snow pressure acting on the avalanche prevention fence 4 and the like will be described below. Since the slope width of the slope in FIG. 4 is set to Lb = 1.5 m, the foundation work 5 of the avalanche prevention fence 4 has (Wb = snow load in the Lb section) and (the side pressure S due to the snow pressure resistance Pb). The anchor tension force Tb is generated in the anchor 6 through the foundation work 5. In calculating the anchor tensile force Tb, the friction resistance force R and the design anchor force Tb can be calculated by the following formula to ensure the safety of the avalanche prevention fence 4. The following is specified as calculation data for the cross-sectional structure in which the avalanche prevention fence 4, the foundation work 5, and the anchor work 6 are combined. In designing, since the slope snow pressure and the like are calculated per meter, the anchor force Tb varies depending on the anchor interval.
R> S S = (Pb · cos θ) + (Wb + PCFW) · sin θ
Pb = Wb (sin θ−μcos θ)
R = μ1 · (S · cos θ · Tb)
Where S: lateral pressure acting on avalanche prevention fence 4 μ1: friction coefficient between ground and foundation work μ1 = tanφ
φ: Internal friction angle of the earth and sand on the slope θ: Slope gradient PCFW: Weight of the frame base Tb: Design anchor force (design anchor force in the vertical direction of the slope)

  FIG. 5 is a cross-sectional view in which the avalanche prevention fence 4 is independently planned without a step or the like on the slope. So far, the height h3 of the avalanche prevention fence 4 has been set mainly with the same snow depth H, but there is a risk of collapse due to the occurrence of a snow leopard 3 etc. as clearly shown in FIG. It is necessary to calculate the slope snow pressure P and calculate the step width Lb to cope with it. In addition, when the avalanche prevention fence 4 is planned independently, h2 <h3 when compared with h2 in FIG. 4 even with the same slope gradient and friction coefficient as in FIG. 4, and the step and the avalanche prevention fence 4 are integrated. A simple cross-sectional structure is economical and effective.

FIG. 6 is a cross-sectional view of the entire slope planned by combining the steps and the avalanche prevention fence 4. FIG. 7 is a front view of the avalanche prevention fence 4 for embodying the present invention, showing the continuous avalanche prevention fence 4 as seen from the bottom of the slope. The shape of the avalanche prevention fence 4 is clearly indicated in terms of continuity in consideration of falling rocks at the site and the phenomenon of falling through the snow layer between the fence and the fence. The length of about 4 m to 6 m may be used. The wire rope etc. in the middle part may be steel, and the wire mesh is installed according to the falling rock situation at the site.
FIG. 8 is also a cross-sectional structure diagram in which the width of the step is widened by overhanging with a protective wall or the like for embodying the present invention.

A cross-sectional view of the avalanche occurrence on a road slope. The enlarged sectional view showing the situation where the snow pressure resistance Pa due to the weight of the snow layer of the step is not utilized because the avalanche prevention fence is installed in the immediate vicinity of the step terrace. The expanded sectional view in the case of calculating the step width by this invention. The expanded sectional view of the state which installed the avalanche prevention fence under the step by the idea of this invention, and aimed at effective utilization of the step width. The expanded sectional view which calculates the step width in the case of aiming at an avalanche countermeasure only with an avalanche prevention fence. A cross-sectional view of the entire avalanche prevention fence combined with an avalanche prevention fence. The front view seen from the slope of the avalanche prevention fence specifically expressed by this invention. An example of the widening method of the small step specifically expressed by the present invention.

1 ... Snow surface of the snow layer assuming that snow has accumulated on the slope at the same thickness 2 .... Snow surface of the snow layer 3 showing the deformation of the slant area snow layer due to geothermal melting and subsidence 3.・ ・ ・ Snow traps, etc. that have a risk of collapsing 4． ・ ・ ・ Avalanche prevention fences.
4 (1) ... Stand 4 of the same fence made of steel material 4 (2) ... Secret 4 of the same fence made of steel material 4 (3) ... Side material 4 of the same fence made of wire rope or steel material 4 (4)・ ・ ・ Mesh 4 of the same fence ▲ 5 ▼ ・ ・ ・ Patent 5 of the fence ・ ・ ・ ・ Basic foundation 6 of the fence ・ ・ ・ ・ ・ ・ Anchor 7 of the fence ・ ・ ・ ・ ・ ・ Protection wall 7 ▲ 1 ▼ ・·························· Intersection D between Hoshijiri and Kokoro flats ··· Road width H ··· Snow depth H1 assuming that snow is deposited on the slope at an equal thickness Spare height h1 of the fence height: fence height h2 when the avalanche prevention fence is installed in the immediate vicinity of the mountain side of the small step ... fence height h3 when the avalanche prevention fence is installed in the immediate vicinity of the small step valley side ····················· When the avalanche deterrent fence is installed alone, the fence height L ··· The affected range L1 ··· L of the slope snow pressure P from the intersection A on the slope is leveled by correcting the slope Case load range Range of influence La ... Step width Lb ... Step width Lc formed by an avalanche prevention fence ... Step width P combined with step width La and Lb ... Snow pressure Pa of slope in the L section ...・ Snow pressure resistance force Pb in the step width La section ・ ・ ・ Snow pressure resistance force R in the Lb section due to the avalanche prevention fence, etc. ・ ・ ・ Resistive shear force S required by the foundation work ・ ・ ・ ・ Basics from the avalanche prevention fence Snow pressure Tb transmitted to the work ... Anchor pulling force θ to secure shear force R ··· Slope gradient

Claims (4)

  A calculation method for setting the step width based on the slope snow pressure on the slope. When the snow depth is H, the slope is divided into a slope L section and a section width La section at the intersection A of the slope and the step. Set the range of influence of the load area depending on the weight of the snow cover, calculate the snow pressure P of the slope and the snow pressure resistance Pa of the step from the coefficient of friction and slope of each slope, and the snow layer of the step is on the valley side A method for calculating the step width to prevent the material from being pushed out and collapsing.   The method of calculating the small step width Lb for widening the small step width La when the existing small step width La is calculated from the snow accumulation depth H and the slope gradient θ and the slope snow pressure is P> Pa in claim 1.   An avalanche prevention facility that secures the small step width Lb calculated by the calculation method according to claim 2 by a combination of an avalanche prevention fence, a foundation work, and an anchor, and prevents a snow layer from collapsing.   An avalanche prevention facility that secures the step width Lb calculated by the calculation method according to claim 2 by a protective wall and prevents the fall of a snow layer.

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