the effect of pressure-grouted soil nail

8/16/2019 The Effect of Pressure-grouted Soil Nail

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The effect of pressure-grouted soil nails on the stability of weathered soil

slopes

Yongmin Kim a, Sungjune Lee b, Sangseom Jeong a, Jaehong Kim c,⇑

a Department of Civil Engineering, Yonsei University, Seoul 120-749, Republic of Koreab Department of Civil Engineering, Cheongju University, Cheongju 360-764, Republic of Koreac Department of Civil Engineering, Chonbuk National University, Jeonju 561-756, Republic of Korea

a r t i c l e i n f o

Article history:

Received 17 July 2012

Received in revised form12 November 2012

Accepted 6 December 2012

Available online 16 January 2013

Keywords:

Pressure-grouted soil nail

Pullout resistance

Shear strength reduction method

Stability of reinforced slope

3D finite element analysis

a b s t r a c t

Pressure-grouted soil nails have been increasingly used for stabilizing slopes. The pullout resistance of a

soil nail is the main factor for reinforcing the slope stability. In this study, a two-dimensional axisymmet-

ric finite element model is developed to simulate thepullout behavior of a pressure-grouted soil nail. This

model is verified with field pullout tests result of a pressure-grouted soil nails by comparing with gravity-

grouted soil nails. Based on the analysis, a three-dimensional finite element model is proposed for stabil-

ity analysis of a slope reinforced with pressure-grouted soil nails using the shear strength reduction

method. A series of numerical slope stability analyses for a slope composed of weathered soil are per-

formed to investigate the effects of grouting pressure on the slope stability and the behavior of the soil

nails. Special attention is given to the installation effect of a pressure-grouted soil nails. It is found from

the result of this study that the pressure-grouted soil nails increase the safety factor by fifty percent in a

slope by increasing the stiffness of the nailed slope system. Numerical analysis results confirm the fact

that the pullout resistance of a soil nail is themain factor for stabilizing slopes rather than the shear resis-

tance of the soil nail.

2012 Elsevier Ltd. All rights reserved.

1. Introduction

Soil nails have been commonly used for slope stabilization by

enhancing the shear resistance of soil and/or the pullout resistance

at the interface between the grout and adjacent soil mass because

of their low construction cost and simple installation procedure

[4,18]. Although most of soil nails are installed without pressure

(gravity-grouted soil nails), pressure-grouted soil nails installed

with a high grouting pressure (300–1000 kPa) have been increas-

ingly used to improve slope stability in South Korea and other

places in the world. While pressure-grouted soil nail construction

requires additional equipment (such as a pump to place grout un-

der constant pressure and a packer system to attain the groutingpressure) and higher construction quality control than conven-

tional soil nails, the pressure-grouted soil nail has many advanta-

ges compared with the conventional gravity-grouted soil nail

such as: (1) enhancement of grouting formation in a borehole;

(2) increase in diameter of a soil nail; (3) increase in shear strength

at the interface between the soil nail and the surrounding soil; and

(4) reduction of the number of reinforcing soil nails [19].

The pullout resistance of a pressure-grouted soil nail is the main

factor for designing a slope reinforced with soil nails rather than

shear resistance of the soil nails to resist the ground movement

along the slope failure surface. Thus, many researchers have stud-

ied the pullout behavior of pressure-grouted soil nails through lab-

oratory or field tests. Main influencing factors on the fundamental

mechanism of the pullout behavior of a soil nail were investigated

through laboratory model pullout tests [5,6,9,14,15,25,28–30]. The

pullout resistance of pressure-grouted soil nails was obtained from

field pullout tests [17–19]. A numerical analysis method was also

developed to investigate the effects of grouting pressure on the

pullout resistance of a pressure-grouted soil nail [26]. However,

while these previous studies were mainly focused on the pullout

resistance of a pressure-grouted soil nail itself, few studies have

been performed on the reinforcing effects of pressure-grouted soilnails for slope stability.

Some researchers performed numerical analyses for reinforced

soil structures with gravity-grouted soil nails [21,23,24]. However,

no information of numerical studies on reinforced slope with pres-

sure-grouted soil nails is available.

In order to investigate the reinforcing effects of pressure-grout-

ed soil nails for slope stability, a new numerical method for slope

stability analysis is developed. Special attention is given to the

installation effect of a pressure-grouted soil nails using finite ele-

ment (FE) analysis. Results of field pullout tests on pressure-grout-

ed soil nails are compared with the analysis results for verification

purpose. A series of numerical analyses for a slope without soil

0266-352X/$ - see front matter 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.compgeo.2012.12.003

⇑ Corresponding author.

E-mail addresses: [email protected] (S. Jeong), [email protected] (J. Kim).

Computers and Geotechnics 49 (2013) 253–263

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ment (thickness of 4 mm) to simulate the thin localized shear zone

[3,7,10,16,20].

2.2. Numerical procedure for simulating pressure-grouted soil nail

installation

The installation procedure of a pressure-grouted soil nail is sim-

ulated in the model described above to investigate the effects of

grouting pressure on its pullout behavior. In this study, seven steps

are applied to simulate the installation procedure of the pressure-

grouted soil nail (Fig. 2):

Step 1: The 2D axisymmetric FE mesh including the soil nail is

generated with boundary conditions. Initial ground stresses

are applied to the FE model (Fig. 2a).

Step 2: The elements of the nail are removed to simulate the

procedure of drilling a borehole (Fig. 2b).

Step 3: The grouting pressure is applied to the borehole surface

for the bonded zone while the borehole surface for the

unbounded zone is fixed against displacements (Fig. 2c).

Step 4: The grouting pressure acting on the borehole surface is

removed and replaced by fixed boundary condition to lock the

stresses and displacement generated by the grouting pressure

in the elements surrounding the borehole (Fig. 2d).

Step 5: The soil nail elements are added in the borehole with the

model properties of the soil nail. The fixed boundary conditions

employed by previous step are not changed (Fig. 2d).

Step 6 : The fixed boundary conditions for the borehole surface

are removed. This process causes the locked-in stresses and dis-

placement to be released and transmitted to the soil nail ele-

ments (Fig. 2e).

Step 7 : The pullout test process is simulated in this step (Fig. 2f).

On the other hand, the analysis procedure described above

excluding the pressure grouting simulation steps (step 3 and step

4) is used for the analysis of a gravity-grouted soil nail.

2.3. Pullout behavior of pressure-grouted soil nails in weathered soil

The FE analysis model described above is verified with the re-

sults from the field pullout tests performed in two test sites in

South Korea (Pusan and Gyeonggi case). The analysis results are

compared with those from the tests to investigate the pullout

behavior of the pressure-grouted soil nails.

nail

soil

gravity

initial ground stress

remove

nail element

grouting pressure

fixed boundary

(a) Step 1 (b) Step 2 (c) Step 3-4

fixed boundary

add nail element

remove

fixed boundary

pullout

(d) Step 5 (e) Step 6 (f) Step 7

Fig. 2. Numerical analysis procedure for simulating construction process and pullout test for a pressure-grouted soil nail: (a) step 1, (b) step 2, (c) steps 3–4, (d) step 5, (e)step 6, and (f) step 7.

Y. Kim et al. / Computers and Geotechnics 49 (2013) 253–263 255


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2.3.1. Pusan case

Four instrumented pressure-grouted soil nails and three instru-

mented gravity-grouted soil nails were installed in the moderately

to completely weathered soil [19]. Fig. 3 shows information about

the soil and soil nails of Pusan case. All tested soil nails have a

diameter of 105 mm and a total length of 3 m including the unb-

onded length of 1 m and the bonded length of 2 m. The tested soil

nails were constructed with placing a deformed steel bar (30 mm

in diameter) in the middle of a borehole and then with placing neat

cement grout (water-to-cement ratio of 0.42) under the grouting

pressure of 500 kPa. Material properties of the equivalent soil nail

and weathered soil used for FE analysis are summarized in Tables 1and 2, where the following parameters are listed: diameter (D),

cross-sectional area ( A), elastic modulus (E ), Poisson’s ratio (m), fric-tion angle (/), dilatancy angle (w), cohesion (c ), unit weight (c).

Fig. 4 shows a comparison of load–displacement relationships

determined from the pullout tests and those from the numerical

analysis for the pressure-grouted and gravity-grouted soil nails.

Each average load–displacement relationship for the four pres-

sure-grouted soil nails and three gravity-grouted soil nails is used

in these comparisons. Although the FE analysis results show stiffer

pull-out behavior than the measured, a reasonably good agreement

of load–displacement relationships (especially ultimate pull-out

resistances) is obtained between the numerical analysis results

and pullout test results for both types of soil nails.

As expected, the pressure-grouted soil nail shows around 36%

higher pullout load than the gravity-grouted soil nail.

2.3.2. Gyeonggi case

The load transfer characteristics of two instrumented pressure-

grouted soil nails installed in weathered soil are compared with

those predicted by the proposed numerical analysis. Information

about the soil and soil nails of Gyeonggi case are shown in Fig. 5.

The test pressure-grouted soil nails of PNG1 and PNG2 have length

of 3 m and 4 m, respectively. Both of them have a same unbonded

length of 1 m. These soil nails were constructed with same instal-lation procedure of the pressure-grouted soil nails in Pusan case as

described above. Material properties of the weathered soil and soil

nails used for FE analysis are summarized in Table 3.

Fig. 6 illustrates comparisons of predicted and measured load–

displacement relationships for the two pressure-grouted soil nails.

Stiffer field load–displacement relationships compared with those

from numerical analyses are observed in this case but opposite re-

sults were shown in the previous Pusan case. This indicates the

limitation of the numerical analysis method used in this study.

The complicated pullout behavior of a pressure-grouted soil nail,

which depends on types of soil, geometry of the irregular expanded

105mm

Weathered Soil

Pressure-Grouted

Soil Nails

Gravity-Grouted

Soil Nails

Steel bar

105mm

U n b o n d e d

L e

n g t h = 1 m

B o n d e d

L e n g t h = 2 m

L e n g t h = 3 m

Fig. 3. Information about the soil and test soil nails (Pusan case).

Table 1

Equivalent material properties of the soil nail used in numerical analysis.

Material properties

Diameter D (m) Area, A (m2) Unit weight, c (kN/m3) Elastic modulus , E (MPa) Poisson’s ratio, m

Steel bar Original property 0.029 0.00066 77.0 210,000 0.2

Grout 0.076 0.008 24.0 23,000 0.3

Soil nail Equivalent property – 28 37,250 0.29

Table 2

Material properties of the weathered soil and soil nail (Pusan case).

Material properties

Elastic modulus, E (MPa) Poisson’s ratio, m Friction angle, / () Dilatancy angle, w () Cohesion, c (kPa) Unit weight, c (kN/m3)

Weathered soil 33.32 0.34 31 10.5 15.88 16.66

0 10 20 30 40 50

Vertical displacement, mm

0

50

100

150

200

250

P u l l o u t l o a

d ,

k N

Pressure-GroutedThis study(FEM)

Measured(average)

Gravity-GroutedThis study(FEM)

Measured(average)

Fig. 4. Comparisons of predicted and measured load–displacement relationships

(Pusan case).

256 Y. Kim et al. / Computers and Geotechnics 49 (2013) 253–263


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soil nail, types of grouting, cannot be simply simulated through the

numerical method in an idealized condition. Although the pro-

posed numerical analysis method has such limitation, the general

trend of the measured pullout behavior of the soil nails (especially

for the ultimate pullout resistance) is fairly well predicted. Stiffer

load–displacement relationship and lower pullout load for the

shorter pressure-grouted soil nail of PNG1 than the longer one of

PNG2 are obtained from the comparisons as shown in Fig. 6.

3. Slope stability analysis for a reinforced slope with pressure-

grouted soil nails

A 3D FE model for the slope stability analysis of a slope rein-

forced with pressure-grouted soil nails is proposed to obtain the

safety factor of the reinforced slope and to investigate their rein-

forcing effects on the slope stability. The numerical technique for

simulating pullout behavior of soil nails described in previous sec-

tion is implemented in this 3D FE model. The shear strength reduc-

tion method is used for the slope stability analysis to obtain the

safety factor of a slope.

3.1. 3D FE model of a reinforce slope with pressure-grouted soil nails

A 3D FE model to simulate the slope stability analysis for a rein-

forced slope reinforced with pressure-grouted soil nails using ABA-

QUS is developed in this study. The 3D FE mesh used in analysis is

shown in Fig. 7. The slope composed of weathered soil has an angle

of 60 to the horizontal plane, a slope height of 10 m, and a slope

width of 3 m. The soil nails installed vertically to the slope surface

has a diameter of 105 mm and a total length of 12 m with an unb-

onded length of 3 m and a bonded length of 9 m. A 5.0 mm thick

thin layer of material surrounding the nail is used to simulate

the thin localized shear zone. The plates of 2.0 2.0 0.5 m con-

nected to the head of the soil nails are placed on the slope surface

to help the soil nails mobilize their pullout resistance fully. The

geometry and the boundary conditions applied to the 3D FE model

(Fig. 7) are selected considering the pressure grouting effects and

slope stability analysis. An 8-node linear brick element with re-

duced integration is used for modeling the 3D FE model.

The soil nails and plates are modeled as linear elastic solids. The

Mohr–Coulomb model with non-associated flow rule is used for

the weathered soil. The material properties used in the 3D FE mod-

el are summarized in Table 4.

3.2. Shear strength reduction method

To calculate the safety factor of a slope defined in the shear

strength reduction method which was proposed as early as 1975

by Zienkiewicz et al. [32], a series of slope stability analyses are

performed with the reduced shear strength parameters c 0trial and

/0trial defined as follows:

c 0trial ¼ 1

F trial c 0 ð2Þ

u0trial ¼ arctan 1

F

trial tan/0

ð3Þ

where c 0 and/0 are real shear strength parameters and F trial is a trial

safety factor.

The essence of the finite element method with shear strength

reduction method is the reduction of the soil shear strength

parameters until the slope fails. Usually, initial F trial is setto be suf-

ficiently small so as to guarantee that the systemis stable. Then the

value of F trial is increased by F inc values until the slope fails. After

Pressure-Grouted

Soil Nails

105mm

105mm

U n b o n d e d

L e n g t h = 1 m

B o n d e d

L e n g t h = 2 m

U n b o n d e d

L e n g t h = 1 m

B o n d e d

L e n g t h = 3 m

PNG

1

PNG2

Weathered Soil

Fig. 5. Information about the soil and test soil nails (Gyeonggi case).

Table 3

Material properties of the weathered soil and soil nail (Gyeonggi case).

Material properties


Weathered soil 34.37 0.30 42 5 6.0 17.67

0 5 10 15 20

Vertical displacement, mm

0

50

100

150

200

250

P u l l o u t l o a

d ,

k N

Nail Length=3mThis study(FEM)

Measured

Nail Length=4mThis study(FEM)

Measured

Pressure-Grouted Soil Nails

Fig. 6. Comparisons of predicted and measured load–displacement relationships

(Gyeonggi case).



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the slope fails, the F start is replaced by the previous F low and F inc is

reduced by 1/5. Then the same procedure is repeated until the F inc is less than user-specified tolerance (e). Fig. 8 shows the flowchartof the procedure to calculate a safety factor [27]. This iterative pro-

Soil Nail

1 5 m

2 5 m

20m

20m

Plate

Unbonded

Length=3m

Bonded

Length=9m

(a) Plan view (X-Z direction)

3m

Soil Nail

(b) 3D view (X-Y-Z direction)

Fig. 7. 3D FE mesh for a slope reinforced with soil nails: (a) plan view ( X – Z direction) and (b) 3D view ( X –Y – Z direction).

Table 4

Material properties for the 3D FE model for slope stability analysis.

Material properties


Weathered soil 100 0.30 25 0 20.0 20.0



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cedure is based on the incremental search method. This final value

of F low, by definition, is identical to the one in limit equilibrium

analysis. The finite element method with shear strength reduction

technique used in slope stability analysis relies strongly on the

determination of global instability of soil slopes, i.e. definition of

a failure [11]. Generally, the failure of slope is defined as: (1) swell-

ing of slope surface [22]; (2) reaching ultimate shear stress of fail-

ure surface [8]; and (3) non-convergence of solutions [33]. In this

study, the slope failure is defined by non-convergence of solution,

and the failure surface of slope is presumed by plotting the ele-

ments where maximum plastic strain occurs. The analysis resultsare represented by relationship between dimensionless displace-

ment (E sdmax/cH 2) and factor of safety, where E s is the Young’s

modulus of soil, dmax is the maximum displacement of the slope,

H is the slope height [33].

3.3. Numerical procedure of the stability analysis

Slope stability analysis including the installation process of

pressure-grouted soil nails are performed based on the 3D FE mod-

el described above to obtain the safety factor for a reinforced slope.

The following seven steps are required for the slope stability anal-

ysis (Fig. 9):

Step 1: The 3D FE mesh including the soil nail and the plate isgenerated (Fig. 9a).

Step 2: The natural slope is modeled by removing the plate ele-

ments and by using soil properties for the soil nail elements. All

boundaries of the model are fixed against displacements. Initial

ground stresses are applied to the 3D FE model ( Fig. 9b).

Step 3: The elements for the soil nails are removed to simulate

the drilling process, then grouting pressures are applied at the

boundaries of the boreholes for the bonded zone while the

boundaries of boreholes for the unbounded zone are fixed

against displacements (Fig. 9c).

Step 4: The boundaries of the borehole for the bonded zone are

fixed against displacements after finishing the pressure grout-

ing process (Fig. 9d).

Step 5: The elements for the plates and the soil nails are added

with their material properties while the displacement bound-

aries for the shafts of the soil nails remain fixed (Fig. 9e).

Step 6 : The displacement boundaries for the shafts of the soil

nails are removed to release and transmit the locked-in stresses

and displacement in the surrounding soil to the soil nail ele-

ments (Fig. 9f).

Step 7 : The slope stability analysis is performed by applying the

gravity forces with unfixed boundaries for the upper sides of

the model (Fig. 9g).

On the other hand, same analysis procedure except the steps for

the pressure grouting is used for the stability analysis of a slope

reinforced with gravity-grouted soil nails.

3.4. Reinforcing effects of pressure-grouted soils on slope stability

In order to investigate the reinforcing effects of the pressure-

grouted soil nails, numerical slope stability analyses for a slope

are performed under three different conditions: (1) natural slope

without any reinforcement; (2) reinforced slope with gravity-gro-

uted soil nails; and (3) reinforced slope with pressure-grouted soil

nails. Fig. 10 shows results of stability analyses for a slope under

these three different reinforcement conditions. Safety factors for

the natural slope, the gravity-grouted soil nail reinforced slopeand the pressure-grouted soil nail reinforced slope are 1.15, 1.55

and 1.72 respectively. Based on the analysis results, using pres-

sure-grouted soil nails exhibits obvious reinforcing effect for the

slope stability with increasing the safety factor by around fifty

and eleven percent compared with safety factors for natural slope

and gravity-grouted reinforced slope, respectively.

Fig. 11 shows developed slope failure surfaces for the gravity-

grouted and pressure-grouted soil nails from the maximum plastic

strain distribution plots. The slope reinforced with pressure-grout-

ed soil nails exhibits expanded failure surface from the slope sur-

face compared with that for the gravity-grouted reinforced slope.

This expanded failure surface was also observed in the laboratory

load tests on the model soil nail reinforced retaining wall per-

formed by Kim et al. [13]. It was found fromtheir tests that the fail-ure surface expanded toward the backfill as the stiffness of the wall

increased. Therefore, it is presumed that the grouting pressure may

increase the stiffness of the reinforced slope system.

3.5. Behavior of a pressure-grouted soil nail installed in the reinforced

slope

The axial and shear loads developed along the soil nails are ob-

tained from the previous analysis results to investigate the rein-

forcing effects of soil nails for slope stability. Fig. 12 illustrates

the distributions of axial loads and shear loads developed along

the lower soil nails for both gravity-grouted and pressure-grouted

soil nail reinforced slopes at the limit state. It is noted that higher

axial loads distribution is observed for the pressure-grouted soilnail than the gravity-grouted soil nail, whereas the shear loads

Fig. 8. Flowchart for calculation of a safety factor.



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(a) Step 1

modeled with soil properties

remove plate elements

Initial ground stress

(b) Step 2

grouting pressure

remove soil nail elements

fixed boundaies

(c) Step 3

fixed boundaries

(d) Step 4

add plate elements

add soil nail elements

fixed boundaries

(e) Step 5

remove fixed boundaries

(f) Step 6

gravity

(g) Step 7

Fig. 9. Numerical procedureof slope stabilityanalysis for a slope reinforcedwith pressuregroutedsoil nails: (a) step 1, (b)step 2, (c)step 3, (d)step 4, (e)step 5, (f) step 6, and

(g) step 7.



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developed along both types of soil nails are very low and can be

ignored.

Basically, the axial loads may develop at the soil–grout interface

in the form of shear stresses around the soil nail perimeter. These

shear stresses are represented by the axial loads within the soil

nail. Since the shear stresses act along the circumferential area of

the soil nail, the axial loads at the ends of the soil nails must be

zero. And the maximum axial loads were developed at the upper

part of soil nail (2–4 m from the soil nail head) where shear stres-

ses at the soil–grout interface reverse directions. The location of

maximum axial loads may coincide with the divide between the

active soil wedge and the stationary soil mass. However, the actual

magnitude and location of maximum axial loads varies with the

soil deformation pattern, construction sequence, and requiredreinforcement [2].

Additional slope stability analyses are performed for three dif-

ferent slope angles of 45, 60 and 80 to investigate the effects

of slope angle on the behavior of soil nails. Fig. 13 shows the distri-

butions of axial and shear loads developed along the soil nails with

different slope angles. The distribution of axial resistance increases

with increase in the slope angle. Changes in the distributions of

shear loads with different slope angles are negligible and the over-

all values of shear loads are very lowand can be ignored. Therefore,

as shown in Figs. 12 and 13, it is shown that the pullout resistance

of a soil nails is the main factor for reinforcing the slope stability

rather than shear resistance along the failure surface, regardless

of the nail location and angle of soil nail.

0 0.4 0.8 1.2 1.6 2

Safety factor

0

0.5

1

1.5

2

2.5

3

Type of ReinforcementNatural Slope

Gravity-Grouted Soil Nails

Pressure-Grouted Soil Nails

FS=1.15

FS=1.55

FS=1.72

Fig. 10. Safety factors for a slope under three different reinforcement conditions.

Failure Surface

(Gravity-Grouted

Soil Nail)

Soil Nail

(a) Gravity-grouted soil nails

Failure Surface

(Pressure-Grouted

Soil Nail)

Effect of grouting preesure

Failure Surface

(Gravity-Grouted

Soil Nail)

(b) Pressure-grouted soil nails

Fig. 11. Failure surfaces for a reinforced slope with (a) gravity-grouted soil nails and (b) pressure-grouted soil nails from the maximum plastic strain distribution plots.

0 2 4 6 8 10 12 14

Distance from the head of soil nail, m

0

20

40

60

80

100

120

140

A x i a l l o a d

, k N

Type of Soil NailsPressure-Grouted

Gravity-Grouted

Maximum axial load=113kN

Maximum axial load=85kN

(a) Axial loads

0 2 4 6 8 10 12 14


0

0.02

0.04

0.06

0.08

0.1

0.12

S h e a r l o a d ,

k N

Type of Soil NailsPressure-Grouted

Gravity-Grouted

(b) Shear loads

Fig. 12. Distribution of loads developedalong thesoil nail for twodifferenttypes of

soil nails: (a) axial loads and (b) shear loads.



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4. Conclusions

In this study, a 2D axisymmetric FE model is developed to sim-

ulate the pullout behavior of a pressure-grouted soil nails. The sim-

ulation of the pressure grouting process is included in the FEmodel. This numerical model and analysis result is favorably veri-

fied by field pullout test results. Based on the analysis, a 3D FE

model for stability analysis of a slope reinforced with pressure-gro-

uted soil nails is proposed implementing the numerical analysis

technique used in the 2D FE model using the shear strength reduc-

tion method. A series of numerical slope stability analyses are per-

formed for three different types of slopes to investigate the effects

of grouting pressure on the slope stability and the behavior of the

soil nails at the limit state. Based on the findings of this study, the

following conclusions can be drawn:

1. Based on the analysis results from the soil nail pullout simula-

tions, a reasonably good agreement of load–displacement rela-

tionships is obtained between the numerical analysis resultsand field pullout test results for both gravity-grouted and pres-

sure-grouted soil nails. Moreover, the load–displacement

behavior with different length of pressure-grouted soil nail is

well predicted by the proposed 2D FE model.

2. The pressure-grouted soil nails exhibits obvious reinforcing

effects for the slope stability with increasing the safety factor

by around fifty and eleven percent compared with safety factors

for natural slope and gravity-grouted reinforced slope, respec-

tively. The slope reinforced with pressure-grouted soil nails

exhibits expanded failure surface from the slope surface com-

pared with that for the gravity-grouted reinforced slope. The

expanded failure surface can be explained by the increased

stiffness of the reinforced slope system due to grouting

pressure.

3. Higher pullout resistance distribution is observed for the pres-

sure-grouted soil nail than the gravity-grouted soil nail. The

shear resistance developed along both types of soil nails are

very low and can be ignored. The distribution of pullout resis-

tance increases with increase in the slope angle while the neg-

ligibly low shear resistance is developed along the soil nail

without reference to the slope angle. These analysis results con-

firm the fact that the pullout resistance of a soil nail is the main

factor for stabilizing slopes.

Acknowledgments

This work was supported by the National Research Foundation

of Korea (NRF) grant funded by the Korea government (MEST) (No.

2011-0030842).

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0 2 4 6 8 10 12 14


0

20

40

60

80

100

120

140

A x i a l l o a d

, k N

Slope=80o

Slope=60o

Slope=45o

(a) Axial loads

0 2 4 6 8 10 12 14


-0.8

-0.6

-0.4

-0.2

0

0.2

S h e a r l o a d ,

k N

Slope=80o

Slope=60

o

Slope=45o

(b) Shear loads

Fig. 13. Distribution of loads developed along the soil nail for three different angles

of slope: (a) axial loads and (b) shear loads.



11/11

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the effect of pressure-grouted soil nail

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