SurficialFailureofExpansiveSoilCuttingSlopeandItsFlexible ...downloads.hindawi.com/journals/ace/2018/1609608.pdf · Expansive soils, which are regarded as a problem soil, are

Research ArticleSurficial Failure of Expansive Soil Cutting Slope and Its FlexibleSupport Treatment Technology

Jie Xiao12 He-ping Yang1 Jun-hui Zhang 12 and Xian-yuan Tang1

1Engineering Research Center of Catastrophic Prophylaxis and Treatment of Road and Traffic Safety of Ministry of EducationChangsha University of Science and Technology Changsha 410114 China2National Engineering Laboratory of Highway Maintenance Technology Changsha University of Science and TechnologyChangsha 410114 China

Correspondence should be addressed to Jun-hui Zhang zjhseu163com

Received 31 July 2017 Revised 17 November 2017 Accepted 13 December 2017 Published 11 February 2018

Academic Editor Claudio Tamagnini

Copyright copy 2018 Jie Xiao et al-is is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

-e surficial failure of most expansive soil cutting slopes subjected to the repeated wet-dry cycles often occurs during or afterrainfall following a long drought -e reason for this however is still unclear -erefore the laboratory tests were conducted togain the saturated drained shear strength of the natural Nanning expansive soil considering the combined effects of swelling withloading and wet-dry cycles -e findings indicate that the envelope of shear strength which significantly drops close or equal tozero can be well fitted by the generalized power function At the same time the effect of shear strength parameters on the stabilityof the expansive soil cutting slope was investigated-e reasons for the shear strength attenuation of the natural expansive soil andthe surficial failure of the expansive soil cutting slopes were analyzed It is evident that the effective cohesion being small is a vitalfactor influencing the occurrence of surficial failure of an expansion soil slope Moreover an effective flexible support treatmentmeasure was provided

1 Introduction

Expansive soils which are regarded as a problem soil aretypically encountered around the world -e total distri-bution areas of expansive soil are more than one hundredthousand square kilometers in China [1] -ese soils havethree typical properties (ie significant swelling andshrinkage fissures and overconsolidation) due to hydro-philic minerals such as montmorillonite -eir strengthsare particularly sensitive to changes in the surroundingenvironment

-e failure of expansive soil slopes especially surficialfailure is one of the most serious geological disasters thatfrequently occurs during the construction of highwaysrailways and hydraulic engineering projects in expansivesoil areas in China [1] Figure 1 shows a surficial failure of anexpansive soil cutting slope in Nanning-Baise expressway inGuangxi Zhuang Autonomous Region China Numerousresearchers have studied the depth of the surficial failure of

expansive soil slopes by field investigations Liao [1] con-cluded that the surficial failure depths of most expansive soilslopes were in the range of 10 to 30m which was close tothe development depth of fissures [2] Wang et al [3] re-ported that the sliding depth generally ranged from 10 to25m and the reason for the surficial failure of expansive soilslopes may be a drastic reduction in the strength of slopesurface soil It results from the occurrence of swelling-shrinkage cracking and fissures due to the repeated wet-dry cycles -e Yangtze River Scientific Research InstituteandWuhanUniversity found that the atmosphere influencesthe depth of the slope at a ldquocritical depthrdquo of approximately15m by analyzing the measurement results of the suctionmatrix in expansive soil slopes in the field [4]

For an engineering project the shear strength of ex-pansive soils is required to address the stability of expansivesoil slopes A review of the technical literatures revealed thatthe investigation of shear strength behavior of expansivesoils was limited especially with respect to the effect of

HindawiAdvances in Civil EngineeringVolume 2018 Article ID 1609608 13 pageshttpsdoiorg10115520181609608

swelling Dinesh and Chandra [5] reported that the shearstrength of the saturated Indian black cotton soil is reducedwith increasing moisture content Similar research wasconducted by Sun et al [6] and Elkady and Abbas [7] Directshear tests on Egyptian expansive clays by Sherif et al [8]indicated that the undrained shear strength prior to swellingis 3 to 55 times higher than that after swelling Darrag [9]attributed the reduction in the undrained shear strength tothe cohesive reduction in swelling rather than to the frictionangle Al-Mhaidib and Al-Shamrani [10] reported that theshear strength of the expansive shale and bentonite obtainedfrom triaxial testing decreased by 70 to 90 because ofa full swelling Wong [11] investigated the effect of bothswelling and confining stress on the shear strength of anexpansive shale and found that the shear strength of thetested shale decreased with increasing swelling Zhang et al[12] discussed the impact of wet-dry cycles with loading onthe expansive soil strength but did not give specific values forshear strength parameters Other researchers [13ndash15] eval-uated the shear strength envelope of expansive soils andconcluded that the relationship between the effective normalstress and shear strength for expansive clays may be linear orbilinear which depends on the initial void ratio of the testedsamples

-e effective normal stress on the failure plane is verysmall and commonly varies from approximately 10 to 30 kPadue to the surficial nature of slope failures -is stress issignificantly lower than the actual range of stresses at whichspecimens are usually tested for investigating the slopestability of expansive soils -erefore the results of slopestability by applying the shear strength parameters obtainedby universal tests could not be explained nationally since thesaturated peak drained shear strength parameters of theexpansive soil under wet-dry cycles or as the residualdrained shear strength parameters [16 17] were often notlow For example a Nanyang expansive soil cutting slopehad an average slope ratio of 1 2 (V H) and the calculatedfactor of safety was 27 using the universal shear strengthparameters however the surficial failure of the slope oc-curred and even though the slope was flattened to 1 4a sliding failure still happened [1] To explain this phe-nomenon some researchers [1 18] even proposed that thefriction angle and cohesion for calculating the slope stabilityshould be 17 and 114 respectively of those achieved byexperimental results but these selected strength parametersare irrational due to lack of theory basis

In summary little attention has been focused on theshear strength of natural expansive soils influenced byswelling (low stresses) and wet-dry cycles -erefore thepresent paper highlighted the combined effect of swellingwith loading and wet-dry cycles on the saturated drainedshear strength of natural expansive soils -e effect of shearstrength parameters on the stability of expansive soil cuttingslope was discussed -e reasons for the shear strengthattenuation of natural expansive soils and the surficial failureof expansive soil cutting slopes were analyzed Finally aneffective and flexible support treatment measure wasprovided

2 SaturatedDrainedShearStrengthBehaviorofNatural Expansive Soils

21 Testing Soils -e expansive soil used in this study wastaken from a cutting slope at depths ranging from 2 to 3mbelow the ground surface of the Nanning outer ring ex-pressway in the middle of Guangxi Zhuang AutonomousRegion China -e block samples for natural samples werewrapped with a plastic membrane and waxed cloth toprevent moisture loss (ASTM D4220) [19]

Laboratory tests revealed that the soil has an averagenatural moisture content of 203 and an average naturaldensity of 2075mgm3 -e specific gravity Gs of the soil is270 -e particle-size distribution indicated that the soilconsists of 03 sand 561 silt and 436 clay -ereforethis soil could be classified as a silty clay-e liquid limit (LL)and the plasticity index (PI) are 460 and 223 re-spectively -e results of the X-ray diffraction test indicatedthat the predominant clay mineral in the soil is an illite-smectite (58) mixed layer -e free swelling rate (FSR) is62 obtained by free swell tests (T 0124-1993) performedaccording to Test Methods of Soils for Highway Engineering(JTG E40-2007) in China -e specific surface area (SSA) is10553m2g -e other characteristics of soils are seen inTable 1 According to the Specification for the Design ofHighway Subgrades (JTG D30-2004) the potential of theexpansive soil could be classified as medium

22 Preparation of Specimens For the tested natural spec-imens suitable sizes of soil blocks were first cut from theblock samples and were then trimmed into appropriatedimensions for the saturated drained direct shear tests -especimens were circular in shape with an inner diameter of618mm and a thickness of 20mm A sharp-edged cuttingtool with the same dimensions for both inner diameter andthickness was used for the trimming All the cutting andtrimming work was conducted in a humidity-controlledroom -e differences in dry density and moisture con-tent did not exceed 004 gcm3 and 1 for various soilspecimens respectively

23 Wet-Dry Cycle Methods with Loading In a steel watertank a properly sized filter was placed on a porous stoneunder a soil specimen on which another filter under a po-rous stone was placed Since the influence depth effected by

Figure 1 Photo of surficial failure of an expansive soil cut slope

2 Advances in Civil Engineering

atmospheric wet-dry cycles is generally shallow only five-level low stress was applied directly by a given loading asshown in Figure 2 -e other samples were saturated byvacuum saturation method -e vacuum pressure(ie minus101325 kPa) was maintained for 24 h during whichspecimen swelling was not permitted After that distilledwater was slowly added to immerse the specimens to withinapproximately 1 cm of the top of the soil specimen for 72 hUsing this saturation technique saturation degrees ofspecimens can be achieved more than 985 -e saturatedspecimens were dried at 40degC in a hot-air circulator oven for24 h -e loading was not taken into account in the dryingprocess Finally the wet-dry cycle was completed -esecycles were repeated until the prescribed number of cycleswas achieved

24Direct ShearTest -e direct shear apparatus used in thisstudy was manufactured by Nanjing Soil Instrument FactoryTechnology Co Ltd -e shear testing procedure follows T0140-1993 in JTG E40-2007 Test method of soils for highwayengineering which is similar to ASTM D3080 Standard TestMethod for Direct Shear Test of Soils under ConsolidatedDrained Conditions [20] A prescribed normal load wasapplied on the saturated specimen until a vertical de-formation not exceeding 0005mmh occurred making thespecimen completely consolidated -e shearing rate of002mmmin was selected to shear the soil specimen untilthe horizontal displacement reached 6mm in drainedconditions

To reflect the effect of the low normal stress on thedrained shear strength eight normal stresses of 5 15 30 5075 100 200 and 300 kPa were applied For the universaldirect shear tests the minimum normal stress was 50 kPaapplied through a lever loading yoke -erefore the threelow normal stresses of 5 15 and 30 kPa were directly appliedthrough equivalent dead weights

25 Test Results and Analysis

251 Shear Behavior of Saturated Natural Expansive SoilSpecimens Figure 3 shows the relationships between shearstress and horizontal displacement at different vertical stressfor wet-dry cycles with loading (ie 0 2 4 and 8 wet-drycycles)

Except that two stress-displacement curves at verticalstress of 300 kPa at 0 and 2 wet-dry cycles have no peak theothers show a peak For the two stress-displacement curveshaving no peak the maximum shear strength determined isthe stress corresponding to the horizontal displacement of6mm In general the horizontal displacement corre-sponding to the peak value increases with the increase invertical stress for different wet-dry cycles As expected themaximum shear stress decreases with an increase in wet-drycycles -e saturation degrees of specimens after shearstageis slightly greater than that before shear which issimilar to the results achieved by Zhan and Ng [21]

252 Shear Strength Characteristic of Natural ExpansiveSoil Currently different strength functions have beenproposed to describe the nonlinear strength characteristicsfor soils such as the bilinear function [22] trilinear function[23] simple power function [24ndash27] and generalized powerfunction [28] -e generalized power function presented byBaker [28] was utilized to fit the measured data in this studyas follows

τ SNL(σ|A n T) equiv PaAσ

Pa

+ T1113888 1113889

n

(1)

where τ is the shear strength Pa is the atmospheric pressureA n T are nonlinear strength parameters and SNL (σ|A n T)is the nonlinear strength function -is function hassimilar features to the HoekndashBrown nonlinear strengthcriterion for rock mass associated with a Mohr envelope

Table 1 Characteristic index of expansive soil

Proportion of different particle size (mm)Montmorillonite content

Relative content of clayminerals

gt0075 0075ndash0005 lt0005 lt0002 IS I K C030 5614 4356 4229 1178 58 11 20 11

Figure 2 Wet-dry cycle saturation with loading

Advances in Civil Engineering 3

0000 100 200 300 400 500 600 700

20406080

100120140160180200

Shea

r stre

ss (k

Pa)

Horizontal displacement (mm)

5 kPa15 kPa30 kPa50 kPa


(a)

000 100 200 300 400 500 600 700Horizontal displacement (mm)

020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(b)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(c)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(d)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(e)

Figure 3 Results of saturated drained direct shear tests on natural specimens subjected to dierent wet-dry cycles (a) Zero wet-dry cycle(b) Two wet-dry cycles (c) Four wet-dry cycle (d) Six wet-dry cycles (e) Eight wet-dry cycles


erefore it is convenient to analyze the slope stabilityusing the limit equilibrium method Additionally theparameters A n T have clear physical meanings whichcontrol the magnitude of the shear strength the location ofthe envelope on the σ axis and the curvature of the en-velope respectively

From (1) the tangential friction angle φt is determinedas follows

tan ϕt(σ|A n T)[ ] equivdSNL(σ|A n T)

dσ

An

σPa + T( )(1minusn)

(2)

According to (1) and (2) the tangential cohesion in-tercepts ct can be determined as follows

ct PaAσPa+ T( )

n

minus σ

timesAn

σPa + T( )(1minusn)A (1minus n)σ + PaT[ ]


(3)

Figure 4 shows the shear strength of natural specimenssubjected to dierent wet-dry cycles with loading obtainedby the results of Figure 3 Table 2 lists the tting parametersand intercept of the nonlinear tting curve For comparisonit also presents the eective cohesion cprime and eective frictionangle φprime determined by universal high testing normal stressranges of 75ndash300 kPa It can be seen from Figure 4 that theshear strength envelope curve is well tted by the generalizedpower function mentioned above e universal saturateddrained shear strength becomes fundamentally stable whensubjected to four wet-dry cycles and the eective cohesionand friction angle are approximately 200 kPa and 280degrespectively However it is clear that the intercept at lownormal stresses is not stable when subjected to four wet-drycycles It gradually decreases from 267 kPa to 0 kPa whenthe numbers of wet-dry cycles increase from 0 to 8 isindicates that the eect of wet-dry cycles with loading on thesaturated drained shear strength of the natural expansive soilat low normal stresses is more signicant than that at highstresses Day [29] suggested that the disproportional swellingof the compacted clay at low eective stresses was the reasonfor the nonlinear shear strength curve However for natural

020406080

100120140160180200220240260

8 cycles

0 cycles with loading2 cycles with loading4 cycles with loading6 cycles with loading8 cycles with loading

0 cycles

Dra

ined

shea

r str

engt

h (k

Pa)

Normal stress (kPa)

2 cycles

6 cycles4 cycles

0 50 100 150 200 250 300 350

Figure 4 Shear strength variations under wet-dry cycles with loading

Table 2 Shear strength parameters of natural expansive soils under wet-dry cycles with loading

Number of wet-dry cyclesNonlinear tting parameters

e intercept of nonlinear tting curve (kPa)

Mohr strengthparameters(75ndash300 kPa)

A T n Adj R2 cprime (kPa) φprime (deg) R2

0 05665 04617 09889 09956 267 304 285 09972 06111 02535 09495 09906 168 237 286 09864 06900 00724 08731 09898 71 216 284 09886 07074 00094 08417 09953 14 193 281 09948 07176 00000 08444 09904 00 208 282 0985


expansive soils the eect of wet-dry cycles with loadingshould be also taken into account

253 Discussion on Shear Strength Attenuation of NaturalExpansive Soil e increase in water content and water lmthickness of clay particles in soils will decrease the strengthof soils Overburden pressures signicantly incentuence theamount of water absorbed by the soils and hence smalleroverburden pressures lead to higher soil water absorptioncapacitieserefore it is evident that the water lm betweenthe clay particles subjected to lower overburden pressureswill be thicker and the dry densities will be lower When thesoil absorbs water in dry conditions most of the gases insoils could be discharged in the form of bubbles isprocess may aect the action on the soil skeleton resultingin microcracks in some weak bonding positions of clayparticles In addition cementation substances in the soilmay also be dissolved or softened and the softened ce-mentation substances and water lm play lubricating rolesin the soil leading to a reduction in the friction resistancebetween clayey clay particles ese will destroy thebonding between soil structures and allow the slidingbetween clay particles On the osmotic swelling stage thesmectite lattice spacing of the soils may increase due to thehydration It results in the soils further dispersing into neparticles Each ne particle could further absorb watermolecules and hydration cations to form thicker hydratelms Furthermore the diusion of the double layer re-pulsion should cause a lattice layer separation to seriouslydisperse into very thin sheets resulting in a signicantdecrease in strength

During the process of repeated wet and dry cycles theoccurrence of a large number of macro- and microcrackswhich gradually decreases from the surface of the slope tothe interior of the active zone in-situ destroys the integrity

identity and continuity of the soil mass Alternatively thecontinuous accumulation of the plastic strain will causelosses in cohesion of shear strength resulting from thebonding of clay particles e cementation eect caused bythe iron and manganese oxides existing in the naturalsamples may be destroyed resulting in a loose structure Inaddition the natural original structure or the bonding of thesoil might be irreversibly broken down by wet-dry cycles[30] especially for the soils in the surcial layer of the slope

erefore it should be noted that the expansive soil hasa remarkable swelling characteristic being dierent from thecommon soils the shear strength of which should accountfor the eect of wet and dry cycles as well as the eect ofoverburden pressures Surface soil in shallower expansivesoil slopes has more severe attenuation of shear strength

3 Surficial Stability Analysis of Expansive SoilCutting Slope

31 Eect of Routine Shear Strength Parameter on ExpansiveSoil Cutting Slope Stability To investigate the eect of shearstrength parameters on the expansive soil slope stabilitya series of limit equilibrium analyses were carried out usingSlopeW [31] It is well known that the surface expansive soilwith loose structures and a large number of micro- andmacrossures due to wet-dry cycles can be close to orapproaching fully saturation condition during or aftera long-term rainfall is highly unfavorable conditionshould be considered to analyze the slope stability in generalerefore it was taken into account in this study

A homogeneous slope was assumed for this limitequilibrium analysis with a height of 60m and a slope ratioof 1 15 (V H) e side and bottom boundaries were nocentow boundaries e others were centux boundaries to modelthe inltration phases of rainfall and constant water pres-sure was prescribed to simulate the eld situations

15

Elev

atio

n (m

)

Distance (m)

1413121110

9876543210

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

20

40

60

80

Figure 5 Slope calculation model


(ie runo) It should be noted that the slope was notprescribed by layers with dierent saturated permeabilitycoebrvbarcients according to the eect of wet-dry cycles becausethe fully saturation condition was focused on in this studye initial ground water table was horizontal at the elevationof 10m A saturated steady seepage centow state calculated isshown in Figure 5 e physical and mechanical propertiesof expansive soil assumed in the dierent analyses are in-dicated in Table 3

Figures 6 and 7 show the factors of safety calculatedusing the simplied Bishop method with dierent eectivecohesions and eective friction angles respectively edashed line for the factor of safety of 10 gives the range of

shear strength parameters for the slope in the limit equi-librium state For the saturated steady seepage state thefactor of safety increases nonlinearly with eective cohesionsless than 5 kPa for a given eective friction angle and thenincreases linearly nearly On the contrary the factor of safetyincreases linearly with increasing eective friction angle fora given eective cohesion

In the limit equilibrium state the eective cohesion andthe eective friction angle obtained respectively are ap-proximately (70 kPa 24deg) (82 kPa 21deg) (93 kPa 18deg)(106 kPa 15deg) (122 kPa 12deg) and (138 kPa 9deg) e factor ofsafety increases from 034 to 148 with the eective cohesionchanging from 0 to 15 kPa for the eective friction angle of

Table 3 Physical and mechanical properties of expansive soil

Unit weight (kN) Saturated permeability coebrvbarcient (ms) Eective friction angle (deg) Eective cohesion (kPa)Soil properties 20 23eminus7 9 12 15 18 21 24 0 1 2 3 5 75 10 15 20 25 30

00

05

10

15

20

25

Fact

or o

f saf

ety

91215

182124

0 5 10 15 20 25 30 35Effective cohesion cprime (kPa)

Figure 6 Relationship between factor of safety and eective co-hesion cprime

00

05

10

15

20

25

Fact

or o

f saf

ety

Effective friction angle φprime (deg)

02510

7515251

3

2030

5 10 15 20 25 30

Figure 7 Relationship between factor of safety and eectivefriction angle φprime

00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)

Effective cohesion cprime (kPa)0 10 20 30 40

91215

182124

Figure 8 Relationship between the maximum sliding verticaldepth and eective cohesion cprime

00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)

Effective friction angle φprime (deg)0 5 10 15 20 25 30

02510

751525

13

2030

Figure 9 Relationship between the maximum sliding verticaldepth and eective friction angle φprime


24deg However the factor of safety only increases from 079 to118 as the eective friction angle increases from 9deg to 24degrespectively for the eective cohesion of 10 kPa esendings indicate that the variations in the eective cohesionhave a greater impact on the factor of safety than changes inthe eective friction angle When the eective cohesionexceeds 15 kPa the factor of safety is greater than 10

Figures 8 and 9 show themaximum sliding vertical depthfor dierent eective cohesions and eective friction anglesrespectively From Figures 8 and 9 it can be seen that themaximum sliding vertical depth increases sharply from012m to more than 148m when the eective cohesionvaried from 0 kPa to 1 kPa for the eective friction angle inthe range of 9deg and 24deg Furthermore when the maximumsliding vertical depths are 20m and 30m the corre-sponding eective cohesions are less than 4 kPa and 75 kParespectively is indicates that the maximum sliding ver-tical depth increases considerably with increasing eectivecohesion for a given eective friction angle e eect ofeective friction on the maximum sliding vertical depthincreases with increasing the eective cohesion (as seen inFigure 9) However the variations in the maximum slidingvertical depth with increasing the eective friction are notremarkable than that with increasing the eective cohesionerefore the eective cohesion which is small is a vitalfactor to the occurrence of the surcial failure of the ex-pansion soil slope Day [32] also proposed that the factor ofsafety for the surcial stability is highly dependent on theeective cohesion

32Eect ofNonlinearShearStrengthParameter onExpansiveSoilCutting Slope Stability ere is a built-in universal data-point strength function in SlopeW to describe the nonlinearshear strength envelope of the materials (soils or rocks) ina stability analysis using the limit equilibrium method Foreach slice SlopeW rst computes the eective normal stressat the slice base and then calculates the slope (tangent) of thenonlinear curve at the slice base eective normal stress as tobe φprime for that slice e tangent is projected to the origin axisto compute an intercept as to be cprime Consequently each slicehas a cprime and φprime corresponding to the slice base eectivenormal stress (as seen in Figure 10)

Based on the same slope calculation model andboundary conditions as seen in Figure 5 the measurednonlinear shear strength data of no wet-dry cycles withloading and eight wet-dry cycles with loading were in-troduced in SlopeWe factor of safety calculated and themaximum sliding depth obtained are shown in Figures 11and 12 respectively

e factor of safety calculated using the nonlinear shearstrength of a natural expansive soil cutting slope withoutwet-dry cycles is 232 and the maximum vertical slidingdepth is 438m e results clearly indicate that the newlyexcavated expansive soil slope without original structuralssures is stable even in a full saturation condition Howeverthe factor of safety reduces considerably to 094 when theexpansive soils are subjected to eight wet-dry cycles withloading and the maximum vertical sliding depth is only

111m is result is fundamentally in agreement with theresults observed in-situ [1] It illustrates that a surcialfailure of the expansive soil slope will occur when it is closeto the saturation condition during or after long-termcontinuous rainfall due to the shear strength of surfacesoils of slope continuously decreasing after subjected to therepeated wet-dry cycles

00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime

Figure 10 General data-point shear-normal function

232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m

Figure 11 Factor of safety and the maximum vertical sliding depth(no wet-dry cycles with loading)

094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

Figure 12 Factor of safety and the maximum vertical sliding depth(after eight wet-dry cycles with loading)


33 Discussion on Surficial Failure of Expansive Soil CuttingSlope -e previous research has shown that the strengthreduces due to swelling of expansive soils after absorbingwater and this potential is controlled by the overburdenpressure -erefore to a large extent the shear strengthrelates to the overburden pressure Studies of dams filledwith expansion soils have indicated that the shear strengthparameters should be different due to gravity stress variationin different depths [33] research also shows that the ex-pansive soil in the middle of the dam which was subjected to200 kPa pressure can also maintain a high shear strength(cprime80 kPa φprime11deg) but the strength is almost close tozero near the surface of slope in the absence of effectiveprotections -erefore the shear strength parameter ofexpansive soil selected to analyze the slope stability shouldvary according to different locations Otherwise it will resultin a wrong analysis result for a surficial failure of expansivesoil cutting slopes For the surficial failure of expansive soilslopes the back-calculated effective cohesion ranges mostlybetween 2 and 4 kPa -is is far less than the traditionalshear test results [33] and is basically in agreement withthe nonlinear shear strength parameters considering thecombined effects of the wet-dry cycle and low normalstress

Generally a newly excavated expansive soil slope thatis free of wet-dry cycles is stable because there are noshrinkage cracks except for only a small number ofunloading cracks or fissures hence the strength of moreintact slope soil does not attenuate even if the saturatedshear strength is also high Moreover the permeabilitycoefficient of the surface soil is very small and it can beconsidered impermeable -erefore the influence ofrainfall on the surface soil is very limited and it is stillnot saturated leading to a stable slope When treatmentmeasures are not timely or invalid numerous macro-and microshrinkage cracks will occur on the slopesurface soil after the wet-dry cycles undermining theintegrity of the slope (as seen in Figure 13) -is will leadto the development of an extensive network of cracks andfissures which provides a convenient channel for therainfall readily infiltrating into the surface slope andincreases the permeability of surface regolith soil -en

the near surface soil will be more permeable than thedeeper soil It will lead to the deeper soil being lessweathered and thus the intact expansive soil or claystonehas a lower permeability [29 34] As the number of wetand dry cycles increase the affected depth will increasecontinuously until it reaches a stable depth During thewet-dry cycle the shear strength of the surface soilcontinues to attenuate -ere is a greater decrease instrength near the slope surface even being close to orapproaching zero -is process will vary and depends onthe weather and other environmental conditions-erefore the failure time can vary from several monthsto several years [35] -is finding reveals why an ex-pansive soil slope is usually stable during excavation orafter excavation for a short time

-erefore there might be three important factorsresulting in a surficial failure of an expansive soil sloperemarkable degreasing shear strength of surface soil sub-jected to wet-dry cycles increasing permeability coefficientof surface soil and continuous or heavy rainfall after a longdrought

4 Flexible Support Treatment Measure forExpansive Soil Cutting Slope

41 Design and Construction of Geogrid Reinforced FlexibleSupport Structure For a project the technical measuresused to treat expansive soil cutting slopes can be categorizedas rigid and flexible treatment techniques Common rigidtreatment structures include a self-weight retaining wallantislide piles or a schistous slope wall For these structuresthe shear fracture or extrusion failure often occurs due to theswelling deformation of expansive soil slopes after wetting Itwill result in a large swelling force exceeding the resistance ofthe rigid structure -erefore according to the character-istics of the surficial failure of expansive soil cutting slopesflexible techniques using geotextiles are more suitable forcutting slopes in expansive soil areas -is is because thata flexible structure allows a limited deformation of the slopesurface and can adsorb the energy produced by the swellingand horizontal slope deformation And then a new balancefor an expansive soil cutting slope will be reached

A typical design diagram of the expansive soil cuttingslope treated by the geogrid reinforced flexible supportstructures is shown in Figure 14

-e construction of the geogrid reinforced flexiblestructure can be described as follows [37 38]

(1) -e designed cutting slope is overexcavated toa designed width which depends on the depth ob-viously affected by the atmosphere and exceeds 35min general

(2) -e geogrid is placed and the fill layer is thenbackfilled and compacted layer by layer witha thickness of 50 cm for each layer

(3) -e layer with the geogrid is back-enveloped witha 1m lap length and the next geogrid is placed on thelayer

Figure 13 Slaking of expansive clay soil due to swelling [36]


(4) e upper and lower geogrid layers are connectedwith connecting rods and then the ll is backlledand compacted with a new layer

(5) Steps 3 and 4 are repeated to the designed height andthe slope of the geogrid reinforced structure is ad-justed to 1 15 (V H)

(6) During the process of construction drainage facil-ities are constructed in the back and the subbase ofthe geogrid reinforced structure

(7) When the geogrid reinforced structure is completeda moisture barrier is constructed at the top of the slope

e working mechanism of the geogrid reinforcedcentexible structure can be summarized as follows

(1) e friction and interlocking between the geogridand the ller along with the enveloping and con-necting of the layers of the geogrid can reinforce thelayers as a whole to stabilize the reinforced structure

(2) e swelling stress in the slope will be releasedthrough the deformation of the slope surface whichis permitted to a certain degree Moreover the largedead weight of the structure is benecial to restrainthe deformation [12]

(3) e structure covering the face of a freshly cuttingslope has a slope of 1 15 and a thickness exceeding35m which prevents or considerably reduces theattenuation of shear strength due to the noticeabledecrease in the eect of weathering (ie the wet-drycycles) At the same time the self-weight of thereinforced structure can increase the strength of theslope soil as discussed above

42 Stability Analysis of Expansive Soil Cutting Slope Treatedby Geogrid Reinforced Flexible Structure e comparison offactor of safety of expansive soil cutting slope treated bygeogrid reinforced centexible structure or not are only focusedin this paper e slope calculation model and boundaryconditions are assumed as the same as seen in Figure 5 emeasured nonlinear shear strength data of eight wet-drycycles with loading were introduced in SlopeWe geogridreinforced spacing and length were 05m and 35m re-spectively e interface apparent cohesion and apparentfriction between geogrid and expansive soil were 81 kPa and69deg [39] respectively e geogrid layouts and the calculatedfactor of safety of slope treated by the geogrid reinforcedcentexible structure are shown in Figure 15

200

350Back fill with planting soil

75100 30350

Geomembrane

Natural expansive soil cut slope

Geogrid

Back fill with crash stone

Back fill with crash stone soil

Back fill with planting soil

Expansive soil filler

3 3Pavement

Infiltration ditch

Infiltration ditchSide ditch

3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30

Figure 14 A typical design diagram of geogrid reinforced centexible support structure (unit centimeter)

00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177

Figure 15 Factor of safety of geogrid reinforced slope


From Figure 15 it can be seen that the position of themost dangerous sliding surface was moved from shallow(111m vertical depth as seen in Figure 12) to the rear of thegeogrid (about 233m vertical depth) -e safety factor ofslope treated by the geogrid reinforced flexible structure was177 It is much greater than safety factor of 094 for naturalslope as seen in Figure 12-erefore the effect of the geogridreinforced flexible structure on the stability of expansiveslopes is significant It can notably improve the stability ofslope

43 Application of Geogrid Reinforced Flexible Structure toTreat Cutting Slopes in Practice According to the workingmechanism for the flexible structure to treat cutting slopesmentioned above fourteen expansive soil failure cuttingslopes located in Nanning to Youyi Guan expressway weretreated using the geogrid reinforced flexible support in 2003which are stable till now after about fourteen years ofseasonal wet-dry cycles and several typhoon rainstorms(Figure 16(a)) It also can be seen from Figure 16(a) that thetreated expansive soil cutting slope is environment friendlyAfter that this technique was applied to treat six ex-pansive soil cutting slopes from Baise to Longlin ex-pressway from 2008 to 2009 (Figure 16(b)) cutting slopesof 12 km (K9 + 600simK10 + 800) of Beijing west sixth ringexpressway in 2010 (Figure 16(c)) and eighteen expansivesoil cutting slopes of the Nanning outer ring expresswayfrom 2010 to 2012 (Figure 16(d)) All these cutting slopesare still in good operational condition and environmentfriendly

5 Conclusions

Based on the laboratory tests on natural Nanning expansivesoil the stability of expansive soil cutting slope was ana-lyzed and the application of flexible support treatmentmeasure was described and the following conclusions canbe drawn

(1) -e shear strength envelope of natural Nanningexpansive soil subjected to repeated wet-dry cycleswith loading is nonlinear and can be well fitted bya generalized power function -e occurrence of thesurficial failure of expansive soil cutting slopes is verydifferent from general clays -is is because the shearstrength of the expansive soil decreases significantlydue to the effect of wet-dry cycles -is decrease inthe effective cohesion especially is considerable andit can even be close to or equals zero

(2) When analyzing the stability of expansive soil cuttingslopes the selection of shear strength parametersmust consider the combined effects of wet-dry cyclesand low stress -e results of slope stability achievedusing nonlinear shear strength parameters are ba-sically consistent with the actual conditions in-dicating that the method is reasonable and reliable-e application of practical engineering methods fortreatment expansive soil cutting slopes proves thatthe geogrid flexible support treatment measure iseffective and environment friendly

Conflicts of Interest

-e authors declare that they have no conflicts of interest

Acknowledgments

-is work was supported by the National Key Research andDevelopment Program of China (2017YFC0805300) theNational Natural Science Foundation of China (51478054

(a)

(b)

(c)

(d)

Figure 16 Photos of expansive soil cut slope treated by geogridreinforced flexible support measures (a) Nanning to Youyi Guanexpressway (a ramp slope 350m long and 20m high) (b) Baise toLonglin expressway (a slope 160m long and 87m high) (c) Beijingwest sixth ring expressway (a slope 12 km long and 223m high)(d) Nanning outer ring expressway (a slope 246m long and 92mhigh)


and 51608053) Natural Science Foundation of HunanProvince (2017JJ3335) Key Project of Education De-partment of Hunan Province (17A008) Open Fund of StateEngineering Laboratory of Highway Maintenance Tech-nology (Changsha University of Science amp Technology)(kfj150103) Open Fund of Engineering Research Center ofCatastrophic Prophylaxis and Treatment of Road amp TrafficSafety of Ministry of Education (Changsha University ofScience amp Technology) (kfj20160401) Jiangxi Communi-cations Department Program (2013C0011) and the ScientificResearch Fund of Hunan Provincial Education Department(15C0043)

References

[1] S W Liao Expansive Soil and Railway Engineering ChinaRailway Publishing House Beijing China 1984

[2] D K McCook ldquoDiscussion of modeling for analyses of fullysoftened leveesrdquo in Proceedings of the 32nd Annual USSDConference Innovative Dam and Levee Design and Con-struction for Sustainable Water Management New OrleansLA USA April 2012

[3] W S Wang Y L Xie and J L Liang ldquoClassification ofexpansive clay slope on road cuttingrdquo Journal of ChangrsquoanUniversity vol 25 no 1 pp 20ndash24 2005

[4] ZWang BW Gong and C G Bao ldquoMeasurement of matrixsuction of expansive soil slope in Northern Hubeirdquo ChineseJournal of Geotechnical Engineering vol 23 no 1 pp 64ndash67 2001

[5] M Dinesh and S Chandra ldquoFrictional resistance of boredpiles in expansive claysrdquo Geotechnique vol 11 no 4pp 294ndash301 1961

[6] D A Sun W J Sun and L Xiang ldquoEffect of degree ofsaturation on mechanical behaviour of unsaturated soils andits elastoplastic simulationrdquo Computers and Geotechnicsvol 37 no 5 pp 678ndash688 2010

[7] T Elkady and M Abbas ldquoShear strength behavior of highlyexpansive soilrdquo in Proceedings of the GeoCongress 2012pp 2532ndash2541 Oakland CA USA March 2012

[8] M M Sherif O Mazen and N S Gergis ldquoBehaviour ofexpansive soil during shearrdquo in Proceedings of the First Na-tional Conference on the Science and Technology of Buildingspp 557ndash562 Khartoum Sudan 1984

[9] A A Darrag Effect of Swelling on the Shear Strength ofEgyptian Expansive Soils MSc thesis Cairo University CairoEgypt 1984

[10] A I Al-Mhaidib and M A Al-Shamrani ldquoInfluence of swellon shear strength of expansive soilsrdquo in Proceedings of theGeoShanghai Conference Advances in Unsaturated SoilsSeepage and Environmental Geotechnics vol 148 pp 160ndash165 Geotechnical Special Publication 2006

[11] R C K Wong ldquoSwelling and softening behaviour of La Bicheshalerdquo Canadian Geotechnical Journal vol 35 no 2pp 206ndash221 1998

[12] R Zhang H P Yang and J L Zheng ldquo-e effect of verticalpressure on the deformation and strength of expansive soil duringcyclic wetting and dryingrdquo in Proceedings of the Unsaturated Soils2006 pp 894ndash905 Carefree AZ USA April 2006

[13] B N Shanker and S Krishna ldquoLaboratory studies on shearstrength of expansive claysrdquo in Proceedings of Indian Geo-technical Conference vol 1 pp 155ndash158 VishakhaptnamIndia December 1989

[14] B N Shanker V Saikrishna and G N Reddy ldquoEffect ofdrainage conditions on shear strength of swollen expansive

soilsrdquo in Proceedings of the Indian Geotechnical Conferencepp 247ndash249 Bombay India December 1990

[15] R K Katti D R Katti and A R Katti Behaviour of SaturatedExpansive Soils and Control Methods A A Balkema Rot-terdam Netherlands 2002

[16] H P Yang J Xiao S Wang and W R Zuo ldquoStudy on thedetermination of residual shear strength for expansive soilrdquo inProceedings of the Recent Advancement in Soil Behavior in SituTest Methods Pile Foundations and Tunneling vol 192pp 49ndash54 Geotechnical Special Publication ChangshaHunan China August 2009

[17] B Tiwari T L Brandon H Marui and G R TuladharldquoComparison of residual shear strengths from back analysisand ring shear tests on undisturbed and remolded specimensrdquoJournal of Geotechnical and Geoenvironmental Engineeringvol 131 no 9 pp 1071ndash1079 2014

[18] J H Zhang Q P Jiang Y Q Zhang L L Dai and H X WuldquoNondestructive measurement of water content and moisturemigration of unsaturated red clays in South Chinardquo Advancesin Materials Science and Engineering vol 2015 Article ID542538 7 pages 2015

[19] ASTM Standard Test Method D 4220 Standard Practices forPreserving and Transporting Soil Samples Annual Book ofASTM Standards ASTM International vol 0408 WestConshohocken PA USA 2000

[20] ASTM Standard Test Method D 3080 Standard TestMethod for Direct Shear Test of Soils under ConsolidatedDrained Conditions vol 0408 Annual Book of ASTMStandards ASTM International West Conshohocken PAUSA 2000

[21] L T Zhan and CWW Ng ldquoShear strength characteristics ofan unsaturated expansive clayrdquo Canadian GeotechnicalJournal vol 43 pp 751ndash763 2006

[22] G Lefebvre ldquoStrength and slope stability in Canadian soft claydepositsrdquo Canadian Geotechnical Journal vol 18 no 3pp 420ndash442 1981

[23] B B F De Mello ldquoReflections on design decisions of practicalsignificance to embankment dams-17th Rankine LecturerdquoGeotechnique vol 27 no 3 pp 281ndash354 1977

[24] J A Charles and K S Watts ldquo-e influence of confiningpressure on the shear strength of compacted rockfillrdquoGeotechnique vol 30 no 4 pp 353ndash367 1980

[25] M Maksimovic ldquoNonlinear failure envelope for soilsrdquoJournal of Geotechnical Engineering vol 115 no 4 pp 581ndash5861989

[26] J Perry ldquoA technique for defining non-linear shear strengthenvelopes and their incorporation in a slope stability methodof analysisrdquo Quarterly Journal of Engineering Geology andHydrogeology vol 27 no 3 pp 231ndash241 1994

[27] P V Lade ldquo-e mechanics of surficial failure in soil slopesrdquoEngineering Geology vol 114 pp 57ndash64 2010

[28] R Baker ldquoNonlinear Mohr envelopes based on triaxial datardquoJournal of Geotechnical and Geoenvironmental Engineeringvol 130 pp 498ndash506 2004

[29] R W Day ldquoDiscussion on slope failures in Tertiary expansiveOC claysrdquo Journal of Geotechnical and GeoenvironmentalEngineering vol 125 pp 427ndash431 1999

[30] L T Zhan R Chen and C W W Ng ldquoWetting-inducedsoftening behavior of an unsaturated expansive clayrdquoLandslides vol 11 pp 1051ndash1061 2014

[31] Geo-Slope International Ltd Stability Modeling with SlopeW2007 Version an Engineering Methodology Calgary ABCanada 3rd edition 2008


[32] R W Day ldquoSurficial stability of compacted clay case studyrdquoJournal of Geotechnical Engineering vol 120 no 11pp 1980ndash1990 1994

[33] T H Liu Problems Related to Expansive Soil in EngineeringConstructions China Architecture and Building Press BeijingChina 1997

[34] A E Templeton G L Sills and L A Cooley ldquoLong termfailure in compacted clay slopesrdquo in Proceedings InternationalConference on Case Histories in Geotechnical Engineeringvol 2 pp 749ndash754 University of Missouri at Rolla St LouisMO USA June 1993

[35] Z J Zhang M J Tao and M Morvant ldquoCohesive slopesurface failure and evaluationrdquo Journal Geotechnical and Geo-environmental Engineering vol 131 no 7 pp 898ndash906 2005

[36] J A ROrtigao T R R Loures CNogueira andL SAlves ldquoSlopefailures in Tertiary expansive OC claysrdquo Journal of Geotechnicaland Geoenvironmental Engineering vol 123 pp 812ndash817 1997

[37] H P Yang J L Zheng and R Zhang ldquoAddressing expansivesoilsrdquo Civil Engineering vol 77 no 3 pp 62ndash69 2007

[38] J L Zheng R Zhang and H P Yang ldquoHighway subgradeconstruction in expansive soil areasrdquo Journal of Materials inCivil Engineering vol 21 no 4 pp 154ndash162 2009

[39] H P Yang L Wan and J L Zheng ldquoDevelopment andapplication of large scale numerical control pullout testsystemrdquo Chinese Journal of Geotechnical Engineering vol 29no 7 pp 1080ndash1084 2007


International Journal of

AerospaceEngineeringHindawiwwwhindawicom Volume 2018

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Hindawiwwwhindawicom

Volume 2018

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

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Modelling ampSimulationin EngineeringHindawiwwwhindawicom Volume 2018


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Navigation and Observation


Hindawi

wwwhindawicom Volume 2018

Advances in

Multimedia

Submit your manuscripts atwwwhindawicom

swelling Dinesh and Chandra [5] reported that the shearstrength of the saturated Indian black cotton soil is reducedwith increasing moisture content Similar research wasconducted by Sun et al [6] and Elkady and Abbas [7] Directshear tests on Egyptian expansive clays by Sherif et al [8]indicated that the undrained shear strength prior to swellingis 3 to 55 times higher than that after swelling Darrag [9]attributed the reduction in the undrained shear strength tothe cohesive reduction in swelling rather than to the frictionangle Al-Mhaidib and Al-Shamrani [10] reported that theshear strength of the expansive shale and bentonite obtainedfrom triaxial testing decreased by 70 to 90 because ofa full swelling Wong [11] investigated the effect of bothswelling and confining stress on the shear strength of anexpansive shale and found that the shear strength of thetested shale decreased with increasing swelling Zhang et al[12] discussed the impact of wet-dry cycles with loading onthe expansive soil strength but did not give specific values forshear strength parameters Other researchers [13ndash15] eval-uated the shear strength envelope of expansive soils andconcluded that the relationship between the effective normalstress and shear strength for expansive clays may be linear orbilinear which depends on the initial void ratio of the testedsamples

-e effective normal stress on the failure plane is verysmall and commonly varies from approximately 10 to 30 kPadue to the surficial nature of slope failures -is stress issignificantly lower than the actual range of stresses at whichspecimens are usually tested for investigating the slopestability of expansive soils -erefore the results of slopestability by applying the shear strength parameters obtainedby universal tests could not be explained nationally since thesaturated peak drained shear strength parameters of theexpansive soil under wet-dry cycles or as the residualdrained shear strength parameters [16 17] were often notlow For example a Nanyang expansive soil cutting slopehad an average slope ratio of 1 2 (V H) and the calculatedfactor of safety was 27 using the universal shear strengthparameters however the surficial failure of the slope oc-curred and even though the slope was flattened to 1 4a sliding failure still happened [1] To explain this phe-nomenon some researchers [1 18] even proposed that thefriction angle and cohesion for calculating the slope stabilityshould be 17 and 114 respectively of those achieved byexperimental results but these selected strength parametersare irrational due to lack of theory basis

In summary little attention has been focused on theshear strength of natural expansive soils influenced byswelling (low stresses) and wet-dry cycles -erefore thepresent paper highlighted the combined effect of swellingwith loading and wet-dry cycles on the saturated drainedshear strength of natural expansive soils -e effect of shearstrength parameters on the stability of expansive soil cuttingslope was discussed -e reasons for the shear strengthattenuation of natural expansive soils and the surficial failureof expansive soil cutting slopes were analyzed Finally aneffective and flexible support treatment measure wasprovided

2 SaturatedDrainedShearStrengthBehaviorofNatural Expansive Soils

21 Testing Soils -e expansive soil used in this study wastaken from a cutting slope at depths ranging from 2 to 3mbelow the ground surface of the Nanning outer ring ex-pressway in the middle of Guangxi Zhuang AutonomousRegion China -e block samples for natural samples werewrapped with a plastic membrane and waxed cloth toprevent moisture loss (ASTM D4220) [19]

Laboratory tests revealed that the soil has an averagenatural moisture content of 203 and an average naturaldensity of 2075mgm3 -e specific gravity Gs of the soil is270 -e particle-size distribution indicated that the soilconsists of 03 sand 561 silt and 436 clay -ereforethis soil could be classified as a silty clay-e liquid limit (LL)and the plasticity index (PI) are 460 and 223 re-spectively -e results of the X-ray diffraction test indicatedthat the predominant clay mineral in the soil is an illite-smectite (58) mixed layer -e free swelling rate (FSR) is62 obtained by free swell tests (T 0124-1993) performedaccording to Test Methods of Soils for Highway Engineering(JTG E40-2007) in China -e specific surface area (SSA) is10553m2g -e other characteristics of soils are seen inTable 1 According to the Specification for the Design ofHighway Subgrades (JTG D30-2004) the potential of theexpansive soil could be classified as medium

22 Preparation of Specimens For the tested natural spec-imens suitable sizes of soil blocks were first cut from theblock samples and were then trimmed into appropriatedimensions for the saturated drained direct shear tests -especimens were circular in shape with an inner diameter of618mm and a thickness of 20mm A sharp-edged cuttingtool with the same dimensions for both inner diameter andthickness was used for the trimming All the cutting andtrimming work was conducted in a humidity-controlledroom -e differences in dry density and moisture con-tent did not exceed 004 gcm3 and 1 for various soilspecimens respectively

23 Wet-Dry Cycle Methods with Loading In a steel watertank a properly sized filter was placed on a porous stoneunder a soil specimen on which another filter under a po-rous stone was placed Since the influence depth effected by

Figure 1 Photo of surficial failure of an expansive soil cut slope










Pa

+ T1113888 1113889

n

(1)








0000 100 200 300 400 500 600 700

20406080

100120140160180200

Shea

r stre

ss (k

Pa)




(a)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(b)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(c)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(d)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(e)






dσ

An


(2)


ct PaAσPa+ T( )

n

minus σ

timesAn



(3)


020406080

100120140160180200220240260

8 cycles


0 cycles

Dra

ined

shea

r str

engt

h (k

Pa)

Normal stress (kPa)

2 cycles

6 cycles4 cycles

0 50 100 150 200 250 300 350







0 05665 04617 09889 09956 267 304 285 09972 06111 02535 09495 09906 168 237 286 09864 06900 00724 08731 09898 71 216 284 09886 07074 00094 08417 09953 14 193 281 09948 07176 00000 08444 09904 00 208 282 0985










15

Elev

atio

n (m

)

Distance (m)

1413121110

9876543210

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

20

40

60

80









00

05

10

15

20

25

Fact

or o

f saf

ety

91215

182124



00

05

10

15

20

25

Fact

or o

f saf

ety


02510

7515251

3

2030

5 10 15 20 25 30


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


91215

182124


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


02510

751525

13

2030









00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime


232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m


094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia










Pa

+ T1113888 1113889

n

(1)








0000 100 200 300 400 500 600 700

20406080

100120140160180200

Shea

r stre

ss (k

Pa)




(a)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(b)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(c)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(d)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(e)






dσ

An


(2)


ct PaAσPa+ T( )

n

minus σ

timesAn



(3)


020406080

100120140160180200220240260

8 cycles


0 cycles

Dra

ined

shea

r str

engt

h (k

Pa)

Normal stress (kPa)

2 cycles

6 cycles4 cycles

0 50 100 150 200 250 300 350







0 05665 04617 09889 09956 267 304 285 09972 06111 02535 09495 09906 168 237 286 09864 06900 00724 08731 09898 71 216 284 09886 07074 00094 08417 09953 14 193 281 09948 07176 00000 08444 09904 00 208 282 0985










15

Elev

atio

n (m

)

Distance (m)

1413121110

9876543210

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

20

40

60

80









00

05

10

15

20

25

Fact

or o

f saf

ety

91215

182124



00

05

10

15

20

25

Fact

or o

f saf

ety


02510

7515251

3

2030

5 10 15 20 25 30


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


91215

182124


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


02510

751525

13

2030









00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime


232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m


094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


0000 100 200 300 400 500 600 700

20406080

100120140160180200

Shea

r stre

ss (k

Pa)




(a)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(b)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(c)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(d)


020406080

100120140160180200

Shea

r stre

ss (k

Pa)



(e)






dσ

An


(2)


ct PaAσPa+ T( )

n

minus σ

timesAn



(3)


020406080

100120140160180200220240260

8 cycles


0 cycles

Dra

ined

shea

r str

engt

h (k

Pa)

Normal stress (kPa)

2 cycles

6 cycles4 cycles

0 50 100 150 200 250 300 350







0 05665 04617 09889 09956 267 304 285 09972 06111 02535 09495 09906 168 237 286 09864 06900 00724 08731 09898 71 216 284 09886 07074 00094 08417 09953 14 193 281 09948 07176 00000 08444 09904 00 208 282 0985










15

Elev

atio

n (m

)

Distance (m)

1413121110

9876543210

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

20

40

60

80









00

05

10

15

20

25

Fact

or o

f saf

ety

91215

182124



00

05

10

15

20

25

Fact

or o

f saf

ety


02510

7515251

3

2030

5 10 15 20 25 30


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


91215

182124


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


02510

751525

13

2030









00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime


232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m


094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia





dσ

An


(2)


ct PaAσPa+ T( )

n

minus σ

timesAn



(3)


020406080

100120140160180200220240260

8 cycles


0 cycles

Dra

ined

shea

r str

engt

h (k

Pa)

Normal stress (kPa)

2 cycles

6 cycles4 cycles

0 50 100 150 200 250 300 350







0 05665 04617 09889 09956 267 304 285 09972 06111 02535 09495 09906 168 237 286 09864 06900 00724 08731 09898 71 216 284 09886 07074 00094 08417 09953 14 193 281 09948 07176 00000 08444 09904 00 208 282 0985










15

Elev

atio

n (m

)

Distance (m)

1413121110

9876543210

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

20

40

60

80









00

05

10

15

20

25

Fact

or o

f saf

ety

91215

182124



00

05

10

15

20

25

Fact

or o

f saf

ety


02510

7515251

3

2030

5 10 15 20 25 30


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


91215

182124


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


02510

751525

13

2030









00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime


232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m


094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia










15

Elev

atio

n (m

)

Distance (m)

1413121110

9876543210

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

20

40

60

80









00

05

10

15

20

25

Fact

or o

f saf

ety

91215

182124



00

05

10

15

20

25

Fact

or o

f saf

ety


02510

7515251

3

2030

5 10 15 20 25 30


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


91215

182124


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


02510

751525

13

2030









00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime


232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m


094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia








00

05

10

15

20

25

Fact

or o

f saf

ety

91215

182124



00

05

10

15

20

25

Fact

or o

f saf

ety


02510

7515251

3

2030

5 10 15 20 25 30


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


91215

182124


00

10

20

30

40

50

60

70

80

Max

imum

slid

ing

dept

h (m

)


02510

751525

13

2030









00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime


232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m


094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia








00

5

10

15

20

25

20 40 60 80 100

Cprime

Shea

r stre

ss (k

Pa)

Normal stress (kPa)

ϕprime


232

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 438 m


094

Distance (m)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Elev

atio

n (m

)

0123456789

101112131415

Dv = 111 m

























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia
























200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia











200


75100 30350

Geomembrane


Geogrid





3 3Pavement

Infiltration ditch


3

5050

50150

44 50 5060

hlt10

00 50

1 20

30

1 15

30


00123456789

101112131415

5 10 15 20 25Distance (m)

Elev

atio

n (m

)

Dv = 233 m 177





5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




5 Conclusions






Acknowledgments


(a)

(b)

(c)

(d)




References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia



References













































RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia













RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia




RoboticsJournal of




VLSI Design



Shock and Vibration







Journal of



Volume 2018



Volume 2018


Journal of




SensorsJournal of



RotatingMachinery





Propagation






Hindawi


Advances in

Multimedia


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