Effects of freeze−thaw cycle and dry−wet alternation on slope stability

doi:10.3724/SP.J.1226.2019.00159.

Abstract

Abstract:

The typical loess on high slopes along the BaoLan High-speed Rail, China, was selected as the research object. The influence of the freeze?thaw cycle and dry?wet alternation on the shear-strength parameters of the unsaturated loess was investigated by laboratory experimental methods. Moreover, the temperature field, seepage field, and stability of slopes with different gradients were simulated under the effect of the freeze?thaw cycle and dry?wet alternation by using the geotechnical analysis software Geo-Studio. The research results showed (1) when the freeze?thaw cycle was repeated on the slope, with the frozen depth increasing, the melted depth did the same; besides, the closed loop of isotherms formed on the slope; (2) under the action of dry?wet circulation, the negative pore-water pressure and volumetric water content showed an upward tendency. However, owing to the different slope gradients, rainfall infiltration was not the same. As time went by, the differences of the negative pore-water pressure and volumetric water content between the slopes of different gradients continued to increase; (3) with the freeze?thaw cycle and dry?wet alternation increasing, the slope-safety factor decreased. Especially in the early period, the slope-safety factor changed remarkably. For slopes undergoing freeze?thaw action, the slope-safety factor was negatively correlated with the gradient. However, with regard to slopes undergoing dry?wet alternation, the result became more complex because the slope-safety factor was related to both seepage strength and slope grade. Accordingly, further research is needed to study the effect of seepage strength and slope grade on the stability of loess slopes.

Key words: freeze?thaw action, dry?wet alternation, temperature field, seepage field, slope stability

YaLing Chou,LiYuan Sun,BaoAn Li,XiaoLi Wang. Effects of freeze−thaw cycle and dry−wet alternation on slope stability[J].Sciences in Cold and Arid Regions, 2019, 11(2): 159-172.

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	Cycle number(times)	Shear strength at different vertical pressures (kPa)				Cohesion force (kPa)	Internal friction angle (°)
	Cycle number(times)	100	200	300	400	Cohesion force (kPa)	Internal friction angle (°)
Freeze?thaw cycles	0	108.720	148.584	202.944	279.048	43.488	29.479
	1	77.916	173.952	197.508	262.740	33.522	30.028
	3	81.540	148.584	184.824	262.740	24.462	30.105
	5	83.352	132.276	217.440	255.492	21.744	31.031
Dry?wet cycles	0	108.720	148.584	202.944	279.048	43.488	29.479
	1	86.976	112.344	206.568	224.688	30.804	26.903
	3	86.976	94.224	157.644	228.312	19.932	25.985
	5	79.728	110.532	155.832	230.124	19.932	26.404

Time	Temperature	Time	Temperature
00:00	?9 °C	12:00	3 °C
02:00	?8 °C	14:00	5 °C
04:00	?7°C	16:00	3 °C
06:00	?6 °C	18:00	0 °C
08:00	?3 °C	20:00	?6 °C
10:00	1 °C	22:00	?7 °C

Month	Diurnal minimum temperature (°C)	Daily mean temperature (°C)	Monthly precipitation (mm)
1	?10.2	?5.3	1.4
2	?6.0	?1.0	2.6
3	?0.2	5.4	9.2
4	6.0	12.1	14.7
5	10.7	17.0	33.2
6	14.2	20.4	44.0
7	16.6	22.4	67.0
8	15.6	21.1	73.2
9	11.4	16.3	40.8
10	2.9	9.8	21.3
11	?2.2	2.5	2.8
12	?8.4	?3.9	0.9

Condition	Evaporation
Potential evaporation strength (m/h)	0.00011
Duration (h)	12
Total potential evaporation (m)	0.00132

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