天然谷 meaning in Chinese

gouffre

It is testified that the landfall happens because of the increase in shearing stress and tensile stress . the mechanism and main prevention - cure measure of cutting the top of loess slope according to its nature gradient for the landfall are quantitatively reformed and simulated
模拟再现了陕北宅基边坡伤亡性黄土崩塌的形成机制，验证了治理此类崩塌的有效措施?建成的宅基边坡谷缘坡度不得大于天然谷缘坡度。