雪氷チーム

Snow and Ice Reserch Team

雪崩予防柵の合理的設計手法に関する研究
Rational Design Method for Avalanche Snow Bridges
現在の雪崩予防柵の設計手法では、積雪深が小さくなるほど雪崩予防柵の斜面方向の設置間隔である列間斜距離が短くなります。そのため、雪の少ない地域で雪崩予防柵の設置基数が増えるという矛盾が生じています。
このため寒地土木研究所では、雪崩予防柵の列間斜距離の合理的な設計手法を検討し、柵の列間を広げる考え方を提案しました。

Hs
予防柵

tanθ-μ×Hs

Hs：設計積雪深Bridge

列間距離：L

Distance between
the rows of bridges

The slopeward distance between rows of avalanche snow bridges as calculated byusing the current design method involves a counterintuitive result: The design▲雪崩予防柵の設置例
distance decreases with decreases in snow depth. Because of this, snow bridges
Avalanche snow bridges
installed in areas with moderate snow depth now outnumber those installed in areas
installed on a slopewith great snow depth.
The Civil Engineering Research Institute for Cold Region is proposing that the slopeward distance
between rows of avalanche snow bridges can be increased through the use of a rational design method.

2・tanθL=

Design snow depth

θ：傾斜角Gradient slope

μ：底面での摩擦係数

列間斜距離
Slopeward distance between rows

Friction modulus at the bottom▲現行の設計要領による積雪深（Hs）と列間斜距離（L）の関係
Snow depth (Hs) and slopeward distance between
rows (L) based on the current design guideline

雪崩予防柵の列間斜距離に関する現地試験

Field experiment on slopeward distance between rows of avalanche snow bridges

雪崩予防柵の列間斜距離の合理的な設計手法を検討するため、柵の列間斜距離を変えた実物大の雪崩予防柵を用いた現地試験を行いました。試験の結果、柵の列間斜距離を長くすると、斜面積雪の移動速度（グライド速度）が大きくなり、また柵に作用する雪圧も大きくなる等の傾向を把握しました。

20m

15m

Toward developing a rational method for determining the maximum slopeward distance
between rows of snow bridges, field experiments were conducted in which sets of snow
bridges were installed with several different slopeward distances. It was found that when thedistance between the rows was greater, the glide speed (moving speed) of snow on the slope
was greater, as was the pressure of the snow acting on the snow bridge.

15m

10m
柵高2.5m

柵高2.5m

柵高1.0mHeight ofsnow bridge:
2.5m

Height ofsnow bridge:
2.5m

Height ofsnow bridge:
1.0m

試験実施箇所
Experiment site

▲現地試験の状況

雪圧計測機器Snow pressure measurement devices▲斜面積雪の移動状況の観察

Field experiment conditions▲雪圧の測定方法

Snow movement observed on the slope

Measurement of snow pressure on the snow bridge

雪崩予防柵の合理的な設計手法の検討
Rational design method for avalanche snow bridges

雪崩予防柵の列間斜距離を現行の設計より長くした場合の雪圧は、現行の設計雪圧とは異なる理論雪圧によって与えられます。列間斜距離を広げることによる雪圧の増加と雪の破壊強度との比較検討によると、雪崩予防柵の列間斜距離を拡張できる範囲は、積雪深が小さいほど、また斜面勾配が小さいほど大きくなるという結果が得られました。

雪圧 S (kN/m)Snow pressure S (kN/m)

Hs 2
S = ρg
KN2

測定値
Measured value
理論値（現行設計）
Theoretical value(current design)
理論値（右式）
Theoretical value(given by the equationon the upper right)

第２回断面観測（4/26）
Second cross-section observation (Apr. 26)

45

S = ρgHs cos θ (sin θ − µ cos θ)L
S：雪圧
L：列間斜距離
ρ：雪の密度g：重力加速度
Hs：設計積雪深
K：クリープ係数
N：グライド係数
θ：斜面勾配
μ：雪と地面の摩擦係数

3525

155

積雪深= 2mの場合
With 2m snow depth

列間斜距離に比例する理論雪圧
Theoretical snow pressure proportional toslopeward distance between rows

Snow pressure
Slopeward distance between rows
Snow density
Gravitational acceleration
Design snow depth
Creep coefficient
Glide coefficient
Slope gradient
Coefficient of friction
between snow and ground

列間斜距離の現行の設計値Current design value for the slopeward
distance between rows
510152025

列間斜距離 L (m)Slopeward distance between rows L (m)

列間斜距離L（m）
Slopeward distance between rows L (m)

現行の設計雪圧
Current design snow pressure

For the snow bridges installed with a greater slopeward interval than that of the current design,
the snow pressure differs from the theoretical snow pressure of the current design guideline.
Based on the relationship between the snow pressure, which increases with increases inslopeward installation interval, and the fracture strength of snow, it was found that themaximum permissible interval could be increased for cases of smaller snow depth and slope
gradient.

現行の列間斜距離の設計値
Current design value for slopeward
distance between rows

70

積雪深= 3mの場合
With 3m snow depth60

圧縮破壊強度から求めた列間斜距離の上限値
Maximum slopeward distance between rows obtained based on compressive fracture strength50

列間斜距離（L）の上限条件
Conditions under which the slopeward distance between rows (L) is the greatest

40

雪の圧縮破壊強度

30

L<可能性
Possible range for slopeward
distance increase between rows

100

Snow pressure

列間斜距離拡張の20Snow compressive fracture strength
σ=ρg (sin θ − µ cosθ)
雪圧σ： 雪の圧縮破壊強度

Snow compressive fracture strength

30354045

斜面勾配θ（°）
Slope gradient θ (°)▲雪圧の測定値と設計値の比較

Measured and theoretical values of snow pressure

安全・快適

北の道

Safe, pleasant driving on Northern Roads▲斜面勾配と列間斜距離（L）の関係

Relationship between slope gradient and slopeward distance between rows (L)

独立行政法人土木研究所 寒地土木研究所

Incorporated Administrative Agency Public Works Research Institute Civil Engineering Research Institute for Cold Region