含石量和坡度变化对土石混合堆积体的动力响应及失稳的影响

doi:10.3969/j.issn.0253-4967.2020.01.014

摘要/Abstract

摘要：

土石混合堆积体在地震荷载作用下的动力响应是研究其在地震荷载作用下失稳机理的重要指标。文中基于室内振动台模型试验, 研究了含石量和坡度变化对土石混合堆积体动力响应特征的影响。试验结果表明: 峰值加速度(PGA)的放大系数在水平方向随着高程的增加而增大; 坡度越大时水平方向的PGA放大系数越大, 而含石量越大时其对应的水平方向的PGA放大系数越小; 土石混合堆积体的坡脚处竖直方向的PGA放大系数增长明显, 而坡顶竖直方向的PGA放大系数有减弱的趋势; 相同激振强度下, 土石混合堆积体的坡度越大则坡体顶部的永久位移越大, 而含石量越大则对应的坡顶位移越小; 堆积体滑坡振动过程及滑动后, 大粒径颗粒向下运动的速度较快, 使得土石混合堆积体坡脚的堆覆具有非常明显的颗粒分选现象。文中的研究结果对于分析土石混合堆积体的含石量和坡度变化与其在地震荷载作用下的动力响应规律具有实际意义。

关键词: 土石混合堆积体, 含石量, 坡度, 峰值加速度, 动力响应

Abstract:

Soil-rock mixture deposit is an extremely heterogeneous loose rock-soil deposit formed since Quaternary, which is composed of blocks, fine-grained soil and pore with a certain engineering scale and high strength and has a certain stone content. These soil-rock mixtures accumulated on slopes have been completely destroyed and their mechanical strength is very low. They are widely distributed in the mountainous areas of Southwest China, which poses a great threat to the engineering. Earthquakes occur frequently in Southwest China, and the instability of soil-rock mixture deposit under seismic load is one of the important factors causing the damage to this type of deposit. The dynamic response of soil-rock mixture deposit under seismic load is an important index to study its instability mechanism under seismic load.
Based on indoor shaking table model test, the influence of rock content and slope gradient on dynamic response characteristics of soil-rock mixture deposit was studied. In model tests, rock content is 30%, 40% and 50%respectively, and slope gradient varies from 20°, 30° and 40°. Two different seismic loading frequencies and three different excitation strengths were given. The peak acceleration(PGA)amplification coefficients in horizontal and vertical directions of soil-rock mixture deposit were analyzed under the change of rock content and slope gradient. The permanent displacement and deformation law of the top and foot of the slope of soil-rock mixture deposit were analyzed by model test. The experimental results show that the dynamic acceleration response characteristics of the soil-rock mixture deposits at the top and foot of the slope are different under different slope gradients and rock content conditions, and the horizontal PGA amplification coefficients of the soil-rock mixture deposits are also different. With the same seismic frequency and excitation intensity, the horizontal PGA amplification coefficient increases with increased slope gradient, and the rate gets faster. With the increase of stone content, the magnification coefficient of horizontal PGA decreases, and the higher the stone content, the slower the decrease rate of horizontal PGA magnification coefficient. When the slope gradient of soil-rock mixture deposit increases, the corresponding horizontal and vertical PGA amplification coefficients increase with the same seismic frequency and excitation intensity. The amplification coefficients of PGA in the vertical direction are different, but the overall magnification is weaker than that in the horizontal direction. The vertical PGA amplification coefficients of the foot, middle and lower parts of the slope are larger, while the vertical PGA amplification coefficients of the upper and middle parts of the slope tend to decrease. The higher the frequency of seismic wave is, the smaller the vertical PGA amplification coefficient corresponding to the same elevation will be, which indicates that the vertical PGA amplification coefficient is negatively correlated with the elevation. The variation trend of PGA magnification coefficient of soil-rock mixed deposit in vertical direction is different with the change of stone content. Under the same excitation intensity, the larger the slope gradient is, the larger the permanent displacement at the top of the slope will be, and the larger the rock content, the smaller the corresponding displacement at the top of the slope. The permanent displacement of the top of the slope is obviously larger than that of the foot of the slope, which indicates that the magnification effect of the top of the slope is obvious. After the vibration process and sliding of the landslide, the large-sized particles in the soil-rock mixture deposit move downward faster and slip on the surface of the deposit body. There was a very obvious phenomenon of particle sorting in the pile-up at the foot of the landslide body. The results of this study are of practical significance for the analysis of the dynamic response law of soil-rock mixture deposit under seismic load due to the change of rock content and slope gradient.

Key words: soil-rock mixture deposit, stone content, slope gradient, peak ground acceleration, dynamic response

中图分类号:

P694

韩培锋, 樊晓一, 田述军, 文华, 张友谊. 含石量和坡度变化对土石混合堆积体的动力响应及失稳的影响[J]. 地震地质, 2020, 42(1): 212-225.

HAN Pei-feng, FAN Xiao-yi, TIAN Shu-jun, WEN Hua, ZHANG You-yi. STUDY ON DYNAMIC RESPONSE AND INSTABILITY OF SOIL-ROCK MIXTURE DEPOSIT WITH DIFFERENT STONE CONTENTS AND SLOPE GRADIENTS[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(1): 212-225.

图/表 17

图 1 堆积体模型试验振动台装置图

Fig. 1 Shaking table device diagram for model test of soil-rock mixture deposit.

表1 模型试验相似常数

Table1 Similarity coefficients of model test

物理量	相似关系	相似比
长度l	C_l	Λ
位移u	C_u=C_l	Λ
速度v	C_v =(C_lC_a)^-1/2	λ^-1/2
加速度a	C_a	1
黏聚力c	C_v=C_l C_ρC_a	Λ
内摩擦角φ	C_c	1
振动频率f	C_f=(C_a /C_l)^1/2	λ^-1/2
时间t	C_t =(C_l/C_a)^1/2	λ^1/2
密度ρ	C_ρ	1

图 2 土石混合堆积体模型图(单位: mm)

Fig. 2 Model of soil-rock mixture deposit(unit: mm).

图 3 土石混合堆积体实物模型图

Fig. 3 Physical model chart of soil-rock mixture deposit.

图 4 地震波时程图

Fig. 4 Seismic time-history curve.

图 5 不同坡度的堆积体水平方向的加速度响应 a 含石量30%, 15Hz; b 含石量30%, 20Hz; c 含石量40%, 15Hz; d 含石量40%, 20Hz

Fig. 5 Acceleration response of deposit with different slope gradients in horizontal direction.

图 6 不同含石量的堆积体水平方向加速度响应 a 坡度30°, 15Hz; b 坡度30°, 20Hz; c 坡度40°, 15Hz; d 坡度40°, 20Hz

Fig. 6 Acceleration response of deposit with different stone contents in horizontal direction.

图 7 不同坡度的堆积体坡顶水平方向加速度响应a 15Hz; b 20Hz

Fig. 7 The horizontal acceleration response of the top of deposit with different slope gradients.

图 8 不同含石量的堆积体坡顶水平方向的加速度响应a 15Hz; b 20Hz

Fig. 8 The horizontal acceleration response of the top of deposit with different stone contents.

图 9 不同坡度的堆积体竖直方向的加速度响应a 15Hz; b 20Hz

Fig. 9 The vertical acceleration response of deposit with different slope gradients.

图 10 不同含石量的堆积体竖直方向的加速度响应a 15Hz; b 20Hz

Fig. 10 The vertical acceleration response of deposit with different stone contents.

图 11 不同坡度的堆积体坡顶竖直方向的加速度响应 a 含石量30%, 15Hz; b 含石量30%, 20Hz; c 含石量40%, 15Hz; d 含石量40%, 20Hz

Fig. 11 The vertical acceleration response of the top of deposit with different slope gradients.

图 12 不同含石量的堆积体坡顶竖直方向的加速度响应a 坡度30°, 15Hz; b 坡度30°, 20Hz; c 坡度40°, 15Hz; d 坡度40°, 20Hz

Fig. 12 The vertical acceleration response of the top of deposit with different stone contents.

图 13 坡度变化下堆积体不同部位的永久位移变化曲线 a 含石量30%, 坡顶; b 含石量40%, 坡顶; c 含石量30%, 坡脚; d 含石量40%, 坡脚

Fig. 13 Permanent displacement curves of different parts of deposit with different slope gradients.

图 14 含石量变化下堆积体不同部位的永久位移变化曲线 a 坡度30°, 坡顶; b 坡度40°, 坡顶; c 坡度30°, 坡脚; d 坡度40°, 坡脚

Fig. 14 Permanent displacement curves of different parts of deposit with different stone contents.

图 15 土石混合堆积体失稳破坏过程中不同时刻的模型 a t=95s; b t=103s

Fig. 15 Modeling diagrams of soil-rock mixture deposit at different times during instability and failure process.

图 16 物理模型坡脚处的颗粒分选现象

Fig. 16 Phenomenon chart of particle-size sorting at slope foot of physical model.

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