土石流發生特性之初步研究

PRELIMINARY STUDY ON THE CHARACTERISTICS OF OCCURRENCE OF DEBRIS FLOW

鄭瑞昌(Ruey-Chang Jeng) ； 江永哲(Yung-Cheh Chiang)

《中華水土保持學報》 17卷2期 (1986/11) Pp. 50-69

https://doi.org/10.29417/JCSWC.198611_17(2).0006

摘要

本省發生土石流災害之規模與頻度，近幾年來屢有增加，如民國71年8.月11.日五股地區之土石流災害，造成重大損失。本研究爲明瞭土石流發生時之性狀，特選定該區採取土石流發生後之土石作爲本研究之材料，從事室內土壤物理性質，土壤力學性質及水槽試驗之測定，獲致下列結論：（一）先端部容積濃度C_d達0.151以上時，可視爲發生土石流流態的一指標，而C_d可以下式求之：C_d = 1.2703-0.9630 R_(SG) 0.68 43 R_(SG)^2-10.7990（1／S）-0.2194C_*-0.1254h／D式中R_(SG)爲土石比例中土所佔的比例；S爲坡度（度）；C_*爲堆積層砂礫容積濃度；h爲逕流水深；D爲堆積層厚。（二）由水槽試驗知：發生土石流的臨界坡度隨著礫石含量之遞增，而有遞減的趨勢。大致而言，在15°以上便會發生土石流。（三）土石流發生時的剪力強度可由快剪試驗求得。而內摩擦角隨礫石含量之增加而呈增高的趨勢。（四）在有地表逕流時，發生土石流的臨界坡度θ_c可以下式求之。tan θ_c = C_*（ρ_g-ρ）/C_*（ρ_g-ρ）+ ρ（1 + h/D）tan φ式中ρ_g爲砂礫密度；ρ爲水密度；ψ爲內摩擦角。

關鍵字

土石流 ； 土石比例 ； 先端部容積濃度 ； 堆積層容積濃度 ； 臨界坡度

並列摘要

In Taiwan, the scale and frequency of debris flow have been increasing for recent years, such as the serious damages of debris flow disaster at Wugu, 11 August 1982. To investigate the characteristics of occurrence of debris flow, the experimental materials were sampled from the watersheds of wugu river in Wugu, Taipei. After the experiments of soil physical, soil mechanics and water flume tests were performed in laboratory, the results were obtained as follows: 1. When the value of the grain concentration volume in the front of debris flow, Cd, was more than 0.151, it was considered to be an index that debris flow had been occurred. And Cd, could estimated by the following regression equation: cd =1.2703 -0.9630 R_(SG)+ 0.6843 R^2_(SG)- 10.7990 (1/S)- 0.2194C_*- 0.1254 h/D where R_(SG) is the ratio of soil and gravel, S is the slope angle (degree), C. is the grain concetration volume in the static debris bed, h is the depth of surface runoff and D is the depth of debris bed. 2. Water flume experiments showed that the critical angle for the occurrence of debris flow would be decreasing with the increasing of gravel content. And the critical angle was about 15 degrees. 3. The shear strength for the occurrence of debris flow could be obtained with quick shear test. The angle of internal friction would be increasing with the increasing of gravel content. 4. When the surface runoff was occurring on the slope, the critical angle for the occurrence of debris flow θ_c, could be derived from the following equation: tanθ_c=C_*(ρ_g-ρ)/C_*(ρ_g-ρ)+ ρ(1+h/D) tanφ where ρ_g and p are the densities of grains and water, respectively, and φ is the angle of internal friction.

並列關鍵字

Debris flow ； Ratio of soil and gravel ； Grain concentration volume in the front of debris flow ； Grain concentration volume in the static debris bed