Study on Dam Slope Stability Under the Condition of Rainfall

7/31/2019 Study on Dam Slope Stability Under the Condition of Rainfall

1/6

INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 1, ISSUE 5, JUNE 2012 ISSN 2277-8616

39IJSTR2012www.ijstr.org

Study On Dam Slope Stability Under TheCondition of Rainfall

Prof. Sun Keming, PhD Student: Moj Raj Bagale

Abstract: Analyze the static simulation of the dam by using the strength reduction principle, get the stress, strain and displacement distribution rule andthe corresponding safety factor in the water level change and rainfall infiltration are two working conditions of the reservoirs retaining dam bodyrespectively, get the displacement of the slip plane when the unstable failure happens on the dam, the influence of the reservoirs water level on thedams safety factor, and the influence of the rainfall infiltration on the dams stability; Based on fluid-solid interaction mechanics theory, a coupledmathematical model for describing the slope stability of dam under the condition of rainfall was developed. The model is used to evaluate the safety ofthe slope. The model simulates the effect of the slope gradient ratio and the slope angle on the slope stability under the different conditions of rainfall inthe return periods. Results show that slope safety factor in the different rainfall Conditions decreases with the increase in rainfall of time. Credibleprovided for designing and appraising stability of the dam, based on the assessment of the effect of slope gradient ratio on the slope stability in thedifferent rainfall conditions of the return periods.

Key words: slope stability; coupled mathematical model; numerical simulation, static simulation; fluid-solid interaction ;rainfall infiltration ;slope stability;

1 IntroductionThe dam slope instability often occurred, which has caused

the problem of dam leakage and endanger the environmentseriously. One important aspect to the slope stabilityresearch is rainfall infiltration effect towards the slopestability. Water increase the soil moisture content, furtherlarger soil force density and finally causes the shear stressof the slip plane increased under the rainfall condition.Meanwhile, rainfall can change mechanical properties ofslope soil, which decrease the soil cohesion, further matrixsuction and finally shear strength. The two adverse factorsof slope soil deadweight increase and strength decreaseinfluence the slope stability simultaneously under thecondition of rainfall, which could produce slope landslide asthe factors reached a level. Therefore, the study on rainfallinfiltration and landslide has the important meaning .The

effect of rain condition (rainfall intensity and duration), initialcondition and permeability anisotropy of soil on thetemporal status infiltration field and slope stability areinvestigated.

2 Mathematical Models;2.1 Fluid-solid Coupling equations of unsaturatedsoil water flow1) Stress equilibrium equations (without body force)From the Terzaghi effective stress theory, equation (1) can

be

op ijfjij ,'

1

2) Constitutive model under the unsaturated mediacondition

)1(', fji pH

G 2

Among it, G=E (1-v)/(1+v)(1-2v),H= E/1-2v

Where E is elastic modulus, v is Poisson ratio, isvolumetric strain. The solid particles flow along with watewhen there is seepage action in porous medium; it meansthat fluid have certain seepage velocity, so do the solidparticles, where V is fluid velocity relative to solid particlesvelocity.

f

f

qS

V ..

13

Where is porosity; fS is saturation; fq is Darcy

velocity, the equation is as follows;

)()(

gppKK

qff

f

rf

f 4

Where k is absolute permeability tensor of porous medium

f is fluid density

Liquid K rf relative permeability, the equation is asfollows:

r

r

dyyy

y

dyyy

y

Ks

rf'

2

'

2

5

mn

s

aeC

/ln6

Among them n, m are constants; s is moisture contenunder saturation condition Liquid equilibrium equation;

_______________________

Professor: Sun Keming,PhD Student: Moj Raj Bagale,

Department of Engineering and Mechanics:Liaoning Technical University, Fuxin , Liaoning Province,China.
http://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e4%bd%8d%e5%8f%98%e5%8c%96&tjType=sentence&style=&t=water+level+changehttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8%e5%85%a5%e6%b8%97&tjType=sentence&style=&t=rainfall+infiltrationhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%8b%a6%e6%b0%b4%e5%9d%9d&tjType=sentence&style=&t=retaining+damhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%bb%91%e7%a7%bb%e9%9d%a2&tjType=sentence&style=&t=slip+planehttp://dict.cnki.net/dict_result.aspx?searchword=%e5%a4%b1%e7%a8%b3%e7%a0%b4%e5%9d%8f&tjType=sentence&style=&t=unstable+failurehttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8%e5%85%a5%e6%b8%97&tjType=sentence&style=&t=rainfall+infiltrationhttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8%e5%85%a5%e6%b8%97&tjType=sentence&style=&t=rainfall+infiltrationhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e5%a4%b1%e7%a8%b3%e7%a0%b4%e5%9d%8f&tjType=sentence&style=&t=unstable+failurehttp://dict.cnki.net/dict_result.aspx?searchword=%e6%bb%91%e7%a7%bb%e9%9d%a2&tjType=sentence&style=&t=slip+planehttp://dict.cnki.net/dict_result.aspx?searchword=%e6%8b%a6%e6%b0%b4%e5%9d%9d&tjType=sentence&style=&t=retaining+damhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8%e5%85%a5%e6%b8%97&tjType=sentence&style=&t=rainfall+infiltrationhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e4%bd%8d%e5%8f%98%e5%8c%96&tjType=sentence&style=&t=water+level+change


2/6



0...

rf

ffV

t

S

7Solid equilibrium equation;

0..1.1

sss V

t8

Fluid-solid Coupling equations under unsaturated conditioncan be given by simultaneous equations including equation(1), (2),(3),(4)and (7).

01

1...tSt

pApKK

f

f

f

f

9

ff

s

f

f

ff

f

f

S

KK

SGSA ,1

1

2.1

From them, f is fluid compressibility and s is solidskeleton compressibility3] Slope safety factor equation

sFW

WC

W

NC

sin

tancos

sin

tan

10

Where is minimum interface friction angle in multi-layer

covers system; is the slope angle, W is the total gravityof typical covering soil slices; N is the effective normal

stress

2.2 Definite conditionsThe mechanism process of water movement of unsaturatedearth fill dam under the condition of rainfall can be solvedby equation (9), and the definite condition was given tosolve the mathematical model.1) Initial condition;

P(x,y,t)|0t = 0p 11

00|,, ttyx 12

P(x,y,t)| 11p

13

cos|.

2,1 tRtR

npK 14 among them: R (t) is

rainfall intensity; is the angle of the dam slope andhorizontal plane .

[3].Consider the rainfall on dam slopestability influence analysis;The natural conditions of the dam slope stability have along and huge impact, the rainfall on dam slope stability fora detailed analysis. Because of this case of elastic-plasticmodel of iterative calculation is very complex, so take theelastic model, and not by strength reduction method, and

the use of rigid body limit equilibrium method. Internafriction angle is 35, cohesive force of size is 20Mpa. In thiscase, it is also divided into two situations are analyzed andcompared, in order to get more accurate result and theconclusion. A case is in the natural conditions of the damslope stability analysis; the other is for dam slope stabilityconsidering rainfall effect. The rainfall intensity is 0.2mm / h(a) Under natural conditions for the slope stability analysis

of the dam; The finite element calculation in reductioncoefficient is 1.349 which is not convergence; this is innatural conditions of the dam safety coefficient. Combinedwith strain cloud of maximum principal figure 55, straindistribution figure56, and the maximum principal stressdistribution analysis figure 59, see the feet of slope, themost vulnerable to yield skeleton of the dam anddeformation and failure, because in the slope toe sizechange dramatically, will lead to stress concentration, sothe most dangerous.

Fig. 1. Diagram of penetrating velocity

Fig. 2.Diagram of pore water pressure distribution

Fig.3 Diagram of saturation line


3/6



Fig.4 Diagram of saturation

Fig.5. Diagram of displacement

Fig.6. Levels displacement diagram

Fig.7 Vertical displacement diagram

Fig.8 Diagram of plain strain

Fig.9 Max principal strain distribution

Fig.10Min principal strain distribution

Fig.11 Diagram of mises stress distribution


4/6



Fig.12 Max principal stress distribution

Fig.13 Min principal stress distribution

(b) After the rain of slope stability analysis of the dam

Fig.14 Diagram of penetrating velocity

Fig.15Diagram of Pore water pressure distribution

Fig.16 Diagram of Pore water pressure distribution

Fig.17 Diagram of saturation line

Fig.18 Diagram of displacement

Fig.19 Levels displacement diagram


5/6



Fig.20 Vertical displacement diagram

Fig.21 Diagram of plain strain

Fig.22Max principal strain distribution

Fig.23 Diagram of mises stress distribution

Fig.24 Max principal stress distribution

Fig.25 Min principal stress distribution

In the reduction coefficient is 1.268, the iterative calculationis no longer convergence, therefore, under the effect orainfall the slope safety coefficient of the dam is1.268Considering the situation of the rainfall, need above the

water of the boundary loading conditions of rainfalinfiltration, is based on the form of the pore pressure loaddifferent from before boundary conditions to add porepressure, here to force load directly loading. From the figure11 to figure 13 and figure 23 to figure 25 shows the all kindsof stress distribution, consider rainfall, due to increased theload, so the internal stress field of dam body changesCorresponding figure 1 to figure 4 and figure 13 to figure 16can see, rainfall makes the flow velocity of the water insidethe dam has increased dramatically, the current watedistribution area greatly increase; Internal degree osaturation distribution of the dam is quite changed; Thepore pressure distribution has been changed obviously; Ocourse, infiltrating the position of the line also have

outstanding change. This shows that rainfall makes damseepage field of internal generate a large changes. So theconclusion is: the internal stress field of dam body changeson the seepage field has very big effect. From figure 18 tofigure 20 can be seen, in the slope feet by the largestamount displacement, and explains the instability. Againfrom strain analysis, as shown in figure 21 and figure 22 slope feet strain is also the biggest, this and the analysis othe above conclusion is consistent. But the example thedisplacement figure 4 and strain cloud figure 8 contrastscan be seen, the skeleton of the deformation of the damlocation, size and distribution has change greatly, andvisible rainfall for the stability of the dam body has very big


6/6


44IJSTR2012www ijstr org

effect. So, for slope problems of the research, naturalcondition is very important factors. Comprehensive analysisof the various examples above, we can draw theconclusion: the internal stress field of dam seepage fieldand the stability of the slope are on the dam has a greatinfluence, and both influence each other, interaction,coupling relationship.

[4] ConclusionThis paper researches the static and dynamic simulationanalysis of the cracks. Analyze the static simulation of thedam by using the strength reduction principle, get thestress, strain and displacement distribution rule and thecorresponding safety factor in the water level change andrainfall infiltration two working conditions of the reservoirsretaining dam body, the rules are shown as follows: Therainfall has a great influence on the slope stability of thedam. The rainfall impact will cause the great change of theseepage field and the stress field, influences the stress andstrain distribution of the dam, and changes the situation ofthe dam skeletons deformation, finally causes the instablefailure of the dam. Based on underground water seepage

theory, a fluid-solid coupled mathematical model fordescribing permeation process under unsaturated conditionis established, which calculates the safety factor of the damslope under the condition of rainfall in the paper. Then, thecurves which describe the relationship between slopegradient ratio, slope angle and rainfall duration (24 hours)are given in the different return periods of rainfall. Theresults of numerical calculation show that safety factordecreases along with rainfall duration increasing in thedifferent return periods of rainfall. When the slope isreduced, slope safety factors reduce slowly in the range ofallowable value. Safety factors of slope decrease obviouslyas the slope is increased. Therefore, the theoretical basis ismore credible provided for designing and appraising

stability of the dam in the paper.

[5] AcknowledgmentFirstly,I like to give thanks Chinese government ofproviding unique opportunity of three years scholarship formy doctoral degree and secondly, I like to give thanks toLiaoning technical university ,Fuxin, Lliaoning ProvinceChina for providing exciting environment for my researchwork.Lastly I like to thanks for dedicated and committedprofessor sun keming for his valuable and precious time forwriting my paper. I could write this paper after hiscontinuous guideline and many meetings with him.

[5]REFERENCES[1] Chen Yunmin, Wang Lizhong etc Study on SlopeStability of the Municipal Solid Waste

[2] Fredlund, D.G.and H.Rahardjo. Soil Mechanics forUnsaturated Soils [M].

[3]AmericanSocietyofCivilEngineers.1993:241-270.

[4] Chen Minhua, Zhou Fujian, Huang Yanhe, LuChenlong, Lin Fuxing.Effects of Slope Length andGradeon Soil and Water Loss[J].

[5]Soil and Water Conservation Journal, 1995, 9(1):3136.

[6] Kaehanov L M Time of the rapture process under creepconditions [J]. TVZ Akad Nank S S R Otd Tech. Nuak.l958,8

[7]Rabonov Y N. Creep rapture[C] Proc12,Ienter Congress

[8]Appl Mech Stanford, Springer, Berlin 1969.

[9] Lemaitre J Application of damage concepts to predictcreep-fatigue failure[C]. JEngMatTech, ASME, 1979101:202-209

[10] Leckie F A,Hayhurst D R.Creepruptureofstructure[C].Proc.R.Soc.A340,1974

[11] Hult J.Damage induced tensileinstability[C].Trans.3rdAMIRT, London, 1974.

[12] Kajcionovic D. Continuum damage theory of brittlematerials [J].J. Appl. Mech. 1981 (48):809-824.
http://dict.cnki.net/dict_result.aspx?searchword=%e5%8a%a8%e6%80%81%e6%a8%a1%e6%8b%9f&tjType=sentence&style=&t=dynamic+simulationhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e4%bd%8d%e5%8f%98%e5%8c%96&tjType=sentence&style=&t=water+level+changehttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8%e5%85%a5%e6%b8%97&tjType=sentence&style=&t=rainfall+infiltrationhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%8b%a6%e6%b0%b4%e5%9d%9d&tjType=sentence&style=&t=retaining+damhttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8&tjType=sentence&style=&t=rainfallhttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8&tjType=sentence&style=&t=rainfallhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%8b%a6%e6%b0%b4%e5%9d%9d&tjType=sentence&style=&t=retaining+damhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e5%ba%93&tjType=sentence&style=&t=reservoirhttp://dict.cnki.net/dict_result.aspx?searchword=%e9%99%8d%e9%9b%a8%e5%85%a5%e6%b8%97&tjType=sentence&style=&t=rainfall+infiltrationhttp://dict.cnki.net/dict_result.aspx?searchword=%e6%b0%b4%e4%bd%8d%e5%8f%98%e5%8c%96&tjType=sentence&style=&t=water+level+changehttp://dict.cnki.net/dict_result.aspx?searchword=%e5%8a%a8%e6%80%81%e6%a8%a1%e6%8b%9f&tjType=sentence&style=&t=dynamic+simulation

Documents

Study on Dam Slope Stability Under the Condition of Rainfall