1

Assessment of External Stability of Reinforced Soil Wall using

British Standard BS 8006 and Eurocode 7

Swee-Huat Chan1, Yi-Heng Yoo1, Chee-Siong Lim2, Kim-Chuan Yap2 and Lee-Ching Hiew2

1) University of Nottingham Malaysia Campus, Malaysia 2) Geo-Excel Consultants Sdn. Bhd., Malaysia

ABSTRACT

The design of a reinforced soil wall requires checking of both internal and external stability.

Eurocode 7 (EC 7) does not cover the design of reinforced soil walls, therefore the Malaysia

National Annex requires that the design of reinforced soil walls to be carried out in accordance

with BS 8006. Nevertheless, from the perspective that the reinforced soil block is often

analysed as a gravity retaining structure in the assessment of external stability, the current issue

of EC 7 may be used for assessment of sliding, overturning and bearing capacity. This paper

assesses and compares the external stability of reinforced soil walls using the design

approaches recommended in BS 8006 and EC 7. The parametric study includes height of wall,

width of wall and friction angle of retained soil. The analyses show that BS 8006 gives more

conservative results than EC 7 in the assessment of sliding, overturning and bearing capacity.

In EC 7, EQU limit state is generally more critical than GEO limit state in checking the

overturning. Amongst the different design approaches (DA) recommended in EC 7, DA 1 and

DA 3 give the same but more conservative results than DA 2 in the assessment of sliding, DA

1 and DA 2 give the same but more conservative results than DA 3 in the assessment of

overturning, and DA 2 gives more conservative results than DA 1 and DA 3 in the assessment

of bearing failure.

Keywords: reinforced soil wall, external stability, BS 8006, Eurocode 7

1. INTRODUCTION

Reinforced soil (RS) walls are cost-effective earth retaining structures that have been

commonly used in Malaysia in retaining earth of more than 5 m in height. The applications of

RS wall include bridge abutment, embankment wall, slope retention, river wall, etc. RS wall

consists of two main elements, which are engineering backfill and reinforcements. The

reinforced soil characteristic is contributed by the strength of engineering backfill and the

tensile strength of reinforcements. The main concept of RS wall involves the mobilized

frictional forces between soils and reinforcements.

2

The design analysis requires checking of RS wall for internal and external stability. The

external stability examines the RS wall as a soil block in four different potential failures which

are bearing, sliding, overturning and slip circle failures, whereas the internal stability examines

the tensile strength and frictional resistance of reinforcement against lateral earth pressure. The

limit state design philosophy for RS walls involves increasing soil weight and live loading by

the appropriate partial load factors, and reducing the soil properties and reinforcement strengths

by the appropriate partial material factors. The assessed resistances against potential failures

would also need to achieve the required partial resistance factors.

This paper assesses and compares the external stability of reinforced soil walls using the design

approaches recommended in BS 8006 and EC 7. The parametric study includes height of wall,

width of wall, friction angle of retained soil and friction angle of founding soil.

2. EXTERNAL STABILITY

The external stability analysis for reinforced soil wall is similar to the conventional analysis of

a gravity type retaining wall. The reinforced soil wall is analysed as a gravity soil block, which

follows the standard procedure for checking the external stability. There are four possible

failure mechanisms that may occur externally as shown in Figure 1. The external stability

requires checking of: 1) bearing capacity failure; 2) sliding failure; 3) overturning failure; and

4) slip failure. The proposed length of reinforcements (hence dimension of reinforced soil

block) will have to pass all these external checks. In this paper, the check of slip circle failure

is not included.

Figure 1. Potential external stability failures (source from internet)

3

2.1 Bearing Capacity

In order to avoid bearing capacity failure, the bearing pressure imposed by a reinforced soil

structure must not exceed the allowable bearing capacity of the foundation strata. The subsoil

ultimate bearing capacity is generally determined by using the Terzaghi’s Bearing Capacity

Theory, which is given by:

���� = ��� + ��� + 0.5���

where

���� = ultimate bearing capacity

� = cohesion

= unit weight of soil

D = embedment depth

B = breath of structure

��, �� & �� = bearing capacity factors

2.2 Sliding

Lateral earth pressure and water pressure (if effective drainage is not provided) behind a

reinforced soil structure result in forward sliding. The stability against forward sliding of the

structure at the interface between the reinforced fill and the subsoil should be checked. The

resistance to movement should be based upon the properties of either the subsoil or the

reinforced fill, whichever is the weaker, and consideration should be given to sliding on or

between any reinforcement layers used at the base of the structure (BS 8006).

Passive earth pressure from the embedment soil in front of the reinforced soil structure is often

ignored in evaluating the stability against sliding (as well as overturning and bearing capacity)

due to the potential for the soil to be removed through natural or manmade processes during its

service life (e.g. erosion, utility installation, etc.).

2.3 Overturning

The stability against overturning of a reinforced soil structure is checked by taking moment

about the toe of the reinforced soil structure. The resisting moment is contributed by the weight

4

of reinforced soil block, whereas the overturning moment is caused by the force exerted by the

lateral earth pressure and water pressure (if effective drainage is not provided) behind the

reinforced soil structure.

3. BRITISH STANDARD 8006

BS 8006 contains guidelines and recommendations for the application of reinforcement

techniques to soils. Limit state principles are applied to the design of reinforced soil structures.

The two state limits considered in the analysis are the ultimate limit state and the serviceability

limit state. For checking of external stability, only ultimate limit state is applicable.

The limit state design philosophy for a reinforced soil structure involves increasing soil weight

and live loading by the appropriate partial load factors and reducing the soil properties and

reinforcement base strength by appropriate partial material factors. Limit state design for

reinforced soil employs four principal partial factors all of which assume prescribed numerical

values of unity or greater. Two of these are load factors ff (and ffs) applied to dead loads and fq

applied to live loads. The principal materials factor is fm (and fms). The fourth factor fn is used

to take account of the economic ramifications of failure. This factor is employed, in addition

to the materials factor, to produce a reduced design strength (BS 8006). The summary of partial

factors recommended by BS 8006 is reproduced in Table 1.

Table 1. Summary of partial factors (BS 8006)

Partial factors Ultimate limit state

Load factors Soil unit mass e.g. wall fill ffs Table 2

External live loads e.g. traffic loading fq Table 2

Soil material factors

to be applied to tanφ'p fms 1

to be applied to c' fms 1.6

to be applied to cu fms 1

Partial factors of safety

Foundation bearing capacity: to be

applied to qult fms 1.35

Sliding along base of structure or any

horizontal surface where there is soil-

to-soil contact

fs 1.2

Partial factor for

economic ramifications

of failure

Category of structure = 3

Class of risk = high fn 1.1

5

Table 2. Partial load factors for load combinations associated with walls (BS 8006)

Effects

Combinations

(for ultimate limit state)

Case A Case B

Mass of the reinforced soil body ffs 1.5 1

Mass of the backfill on top of the reinforced soil wall ffs 1.5 1

Earth pressure behind the structure ffs 1.5 1.5

Traffic load: - on reinforced soil block

- behind reinforced soil block

fq 1.5 0

fq 1.5 1.5

According to BS 8006, the design should consider the most adverse load that is likely applied

to the structure. In Table 2, Combination A considers the maximum values of all loads and

therefore normally generates the maximum foundation bearing pressure. On the other hand,

Combination B considers the maximum overturning loads together with minimum self-mass

of structure and superimposed traffic load. This combination is normally the worst case for

sliding along the base.

4. EUROCODE 7

Eurocode 7 is based on the limit state design method set out in EN 1990 - Eurocode: Basis of

Structural Design. For each geotechnical design situation, the possible ultimate limit states

(ULSs) and serviceability limit states (SLSs) shall be identified, and it shall be verified that no

relevant limit state is exceeded. There are a total of five ultimate limit states identified in

Eurocode 7, which are as shown in Table 3:

Table 3. Types of ultimate limit state given in Eurocode 7 (BS EN 1997-1)

Ultimate

limit states Description

EQU

Loss of equilibrium of the structure or the ground, considered as a rigid body, in

which the strengths of structural materials and the ground are insignificant in

providing resistance

STR

internal failure or excessive deformation of the structure or structural elements,

including e.g. footings, piles or basement walls, in which the strength of structural

materials is significant in providing resistance

GEO failure or excessive deformation of the ground, in which the strength of soil or rock

is significant in providing resistance

UPL loss of equilibrium of the structure or the ground due to uplift by water pressure

(buoyancy) or other vertical actions

HYD hydraulic heave, internal erosion and piping in the ground caused by hydraulic

gradients Note: Limit state GEO is often critical to the sizing of structural elements involved in foundations or retaining

structures and sometimes to the strength of structural elements.

6

For checking of the external stability of a reinforced soil structure, Geotechnical (GEO) limit

state is applicable. In addition, static equilibrium (EQU) limit state is also used to check for

overturning failure.

4.1 Partial Factors for EQU Limit State

For the verification of equilibrium limit sate (EQU), the partial factors in Table 4 shall be

applied.

Table 4. Partial factors for verification of equilibrium limit state (EQU)

Parameter Ultimate limit state EQU

Permanent actions (G) Destablizing γG,dst 1.1

Stabilizing γG,stb 0.9

Variable actions (Q) Destablizing γQ,dst 1.5

Stabilizing γQ,stb 0

Angle of shearing resistance (to be applied to tan φ’) γφ’ 1.25

Effective cohesion γc' 1.25

Undrained strength γcu 1.4

Weight density γγ 1

4.2 Partial Factors for GEO Limit State

To accommodate for different local experiences of all CEN members within the framework of

Eurocode 7, three design approaches are made available for verification of GEO limit state.

The design approach for use in a country can be found in its National Annex to Eurocode 7.

For checking of the external stability of a reinforced soil structure, the three design approaches

for verification of GEO limit state are described below. The partial factors applied in each

design approach can be found in Table 5.

(a) Design Approach 1 (DA 1), which has two combinations:

Combination 1: A1 “+” M1 “+” R1

Combination 2: A2 “+” M2 “+” R1

Where A denotes the actions or effects of actions, M the soil parameters, R the

resistances, and “+” implies “to be combined with”.

7

In Combination 1, partial factors are applied to actions while ground strength

parameters and ground resistances are not factored. In Combination 2, partial factors

are applied to ground strength parameters and variable actions while permanent actions

and ground resistances are not factored.

(b) Design Approach 2 (DA 2):

Combination: A1 “+” M1 “+” R2

In this approach, partial factors are applied to actions and ground resistance while

ground strength parameters are not factored.

(c) Design Approach 3 (DA 3):

Combination: A2 “+” M2 “+” R3

In this approach, partial factors are applied to ground strength parameters and variable

actions while permanent actions and ground resistances are not factored, making it the

same as DA 1, Combination 2.

Table 5. Partial factors for GEO limit state (Source: Mike Dobie, 2011)

8

5. FORMULATIONS

The following configuration of a reinforced soil structure is used for study.

5.1 Unfactored Case

In the “Unfactored Case”, no partial factors are applied.

(i) Overturning

Self-weight of RS block � = �

Surcharge pressure on RS block � = ��

Design vertical loads �� = � +� = � + ��

Lever arm of self-weight and surcharge on RS block �� = ��

Characteristic friction angle of soil behind RS block = φ�′ Coefficient of active earth pressure (assume Rankine’s Theory) K = �!"#$ φ%′�&"#$ φ%′ Active earth pressure due to soil behind RS wall '� = 0.5γ��K(

Surcharge pressure behind RS block '� = ��K

Lever arm of active earth pressure �� = )*

Lever arm of surcharge behind RS block �* = )�

Safety factor against overturning = +,-./01,023+45,-./01,023 = 67&89:;

<;:%&<%:== 6>)�&��9?%@.A>)%B.C=&�)B.C%

γγγγ γγγγ,φφφφE ’’’’,c’c’c’c’= 0

γγγγ,,,,φφφφH ’’’’,c’c’c’c’= 0

HHHH

LLLL

qqqq

Dry condition

Figure 2. Configuration of reinforced soil wall

9

(ii) Sliding

Friction angle of soil below RS block = φ*′ Safety factor against sliding = ),-./01,023

)45,-./01,023 = 67&89 L $ φ′<;&<% =6>)�&��9 L $ φ3′@.A>)%B.&�)B.

(iii) Bearing Capacity

Resultant moment at wall toe NOPQ = N"L R#S"#$T −NVW"L R#S#"#$T Eccentricity of resultant force X = �

�− +YZ[\4

Effective breadth � = � − 2X = � − 2 ^��− +YZ[\4 _ = 2+YZ[

\4

Bearing pressure �` = \4a

Terzaghi’s ultimate bearing capacity equation �bSL = Nd�e + Nf� + 0.5N>�γ

where Nd =(Nf − 19 cotφ3′ Nf = ekL $ φltan� o45°+ φ3′2 q

N> = 26Nf − 19 tanφ3′ For cohesion less soil at the base and by ignoring the embedment depth, the above ultimate bearing

capacity equation can be simplified to: �bSL = 0.5N>�γ

Safety factor against bearing capacity =�r1-�s

5.2 British Standard 8006

The partial factors applied are given in Tables 1 and 2.

(i) Overturning

Self-weight of RS block � = �

Surcharge pressure on RS block � = ��

Design vertical loads �V = tu"�+ tf� =tu"� + tf��

Lever arm of self-weight and surcharge on RS block �� = ��

Characteristic friction angle of soil behind RS block = φ�′ Design friction angle of soil behind RS block φV = tan!�6L $ φ%′vw, 9 Coefficient of active earth pressure (assume Rankine’s Theory) K = �!"#$ φd�&"#$ φd Active earth pressure due to soil behind RS wall '� = 0.56tu"γ9��K

10

Surcharge pressure behind RS block '� = 6tf�9�K

Lever arm of active earth pressure �� = )*

Lever arm of surcharge behind RS block �* = )�

Safety factor against overturning = +,-./01,023+45,-./01,023 = 67&89:;

<;:%&<%:==6vy,>)�&vz��9?%

@.A>vy,)%B.C=&vz�)B.C%

(ii) Sliding

Characteristic friction angle of soil below RS block = φ*′

Safety factor against overturning = ),-./01,023)45,-./01,023 = 67&89-.2φl{w,

v,6<;&<%9 = 6vy,>)�&vz��9-.2φ3′{w,v,6@.A>vy,)%B.&vz�)B.9

(iii) Bearing Capacity

Resultant moment at wall toe NOPQ = N"L R#S"#$T −NVW"L R#S#"#$T Eccentricity of resultant force X = �

�− +YZ[\4

Effective breadth � = � − 2X = � − 2 ^��− +YZ[\4 _ = 2+YZ[

\4

Bearing pressure �` = \4a

Terzaghi’s ultimate bearing capacity equation �bSL = Nd�e + Nf� + 0.5N>�γ

For cohesion less soil at the base and by ignoring the embedment depth, the ultimate bearing

capacity equation can be simplified to: �bSL = 0.5N>�γ

Safety factor against bearing capacity = �r1-vw,�s

5.3 Eurocode 7

The partial factors applied for EQU and GEO limit states are given in Tables 4 and 5,

respectively.

(i) Overturning

Characteristic self-weight of RS block �| = �

Characteristic surcharge pressure on RS block �} = ��

Lever arm of self-weight and surcharge of RS block �� = ��

Design vertical actions:

EQU limit state: Unfavourable �V = |,V"L�| + },V"L�}

11

Favourable �V,u ~ = |,"LR�| + },"LR�}

GEO limit state: Unfavourable �V = |�| + }�}

Favourable �V,u ~ = |,u ~�| + },u ~�}

Characteristic friction angle of soil behind RS block = φ�′ Design friction angle of soil behind RS block φV = tan!�6L $φ2e>φe 9 Coefficient of active earth pressure (assume Rankine’s Theory) K = �!"#$φ4�&"#$φ4

Active earth pressure due to soil behind RS wall:

EQU limit state 'V� = 0.5K 6|,V"Lγ9��

GEO limit state 'V� = 0.5K 6|γ9��

Surcharge pressure on RS block:

EQU limit state 'V� = 6},V"L�9K �

GEO limit state 'V� = 6}�9K �

Lever arm of active earth pressure �� = )*

Lever arm of surcharge behind RS block �* = )�

Safety factor against overturning = +,-./01,023+45,-./01,023 = 6\4,y.�9?%

<4;:%&<4%:=

(ii) Sliding

Friction angle of soil below RS block = φ*′

Safety factor against overturning = ),-./01,023)45,-./01,023 = \4,y.�6

-.2φ3′�φl 9���6<4;&<4%9

(iii) Bearing Capacity

Resultant moment at wall toe NOPQ = N"L R#S"#$T −NVW"L R#S#"#$T Eccentricity of resultant force X = �

�− +YZ[\4

Effective breadth � = � − 2X = � − 2 ^��− +YZ[\4 _ = 2+YZ[

\4

Bearing pressure �O = \4�

Terzaghi’s ultimate bearing capacity equation �bSL = Nd�e + Nf� + 0.5N>�γ

For cohesion less soil at the base and by ignoring the embedment depth, the ultimate bearing

capacity equation can be simplified to: �bSL = 0.5N>�γ

Safety factor against bearing capacity = �r1-Rv�s

12

6. RESULTS AND DISCUSSIONS

This sections presents the results of a parametric study on the RS wall configuration shown in

Figure 2. Different L/H ratios and friction angles of retained soil are used for study of the

external stability of the RS wall, inclusive of overturning, sliding and bearing capacity. In

order to pass a stability check, the computed factor of safety must be equal to or larger than

one.

The range of friction angle of retained soil (φ�e ) under study is from 20° to 35°. The unit weights

of the reinforced soil block, retained soil and foundation soil adopted are all 20 kN/m3. The

friction angle of foundation soil (φ*e ) adopted is 28°. The computed factors of safety against

overturning, sliding and bearing failures are presented in the following sections.

6.1 Overturning

Figures 3(a) and 3(b) show the computed factors of safety against overturning for all the design

approaches studied. In general, a minimum L/H ratio of 0.5 is required in order to pass the

overturning check in accordance with BS 8006 and Eurocode 7. On the other hand, BS 8006

also states the requirement of L ≥ 0.7H (3m minimum), thus the design approach in BS 8006

is more conservative.

Comparing the various design approaches in Eurocode 7, EQU limit state is generally more

critical than GEO limit state in checking the overturning. Thus, EQU limit state should be used

for checking of overturning.

The analysis results also show that amongst the three design approaches in GEO limit state,

DA 1 Combination 1 and DA 2 give the same but more conservative results than DA 3 in the

assessment of overturning.

13

Figure 3(a). Computed factor of safety against overturning for φφφφEe = 20°°°° (L=0.5H)

Figure 3(b). Computed factor of safety against overturning for φφφφEe = 35°°°° (L=0.5H)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 10 20 30 40

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Overturning (φ2'=20˚ L=0.5H)

BS-A

BS-B

EC7-DA1C1

EC7-DA1C2

EC7-DA2

EC-DA3

EC7-EQU

FoS=1.0

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 5 10 15 20 25 30 35 40

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Overturning (φ2'=35˚ L=0.5H)

BS-A

BS-B

EC-DA1C1

EC-DA1C2

EC-DA2

EC-DA3

EC-EQU

FoS=1.0

14

6.2 Sliding

Figures 4(a) to 4(c) show the computed factors of safety against sliding for all the design

approaches studied. In general, a minimum L/H ratio of 0.5 is required in order to pass the

sliding check in accordance with Eurocode 7. Amongst the three design approaches in

Eurocode 7, DA 1 Combination 2 and DA 3 give the same but more conservative results than

DA 2 in the assessment of sliding.

For low friction angles, a minimum L/H ratio of 0.8 is required in order to pass the sliding

check in accordance with BS 8006, see Figure 4(b). This probably explains why BS 8006

requires L ≥ 0.7H (3m minimum) in the design. In general, the design approach in BS 8006

gives more conservative results than those in Eurocode 7.

Figure 4(a). Computed factor of safety against sliding for φφφφEe = 20°°°° (L=0.5H)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

0 5 10 15 20 25 30 35 40

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Sliding (φ2'=20˚ L=0.5H)

BS-A

BS-B

EC7-DA1C1

EC7-DA1C2

ED7-DA2

EC7-DA3

FoS=1.0

15

Figure 4(b). Computed factor of safety against sliding for φφφφEe = 20°°°° (L=0.8H)

Figure 4(c). Computed factor of safety against sliding for φφφφEe = 35°°°° (L=0.5H)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

0 5 10 15 20 25 30 35 40

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Sliding (φ2'=20˚ L=0.8H)

BS-A

BS-B

EC7-DA1C1

EC7-DA1C2

EC7-DA2

EC7-DA3

FoS=1.0

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

0 5 10 15 20 25 30 35 40

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Sliding (φ2'=35˚ L=0.5H)

BS-A

BS-B

EC7-DA1C1

EC7-DA1C2

EC7-DA2

EC7-DA3

FoS=1.0

16

6.3 Bearing Failure

Figures 5(a) to 5(c) show the computed factors of safety against bearing failure for all the

design approaches studied. In general, a minimum L/H ratio of 0.6 is required in order to pass

the bearing stability check in accordance with Eurocode 7. Amongst the three design

approaches in Eurocode 7, DA 2 gives more conservative results than DA 1 and DA 3 in the

assessment of bearing failure.

For low friction angles, a minimum L/H ratio of 0.7 is required in order to pass the bearing

stability check in accordance with BS 8006, see Figure 4(b). This probably explains why BS

8006 requires L ≥ 0.7H (3m minimum) in the design. In general, the design approach in BS

8006 gives more conservative results than those in Eurocode 7.

Figure 5(a). Computed factor of safety against bearing failure for φφφφEe = 20°°°° (L=0.6H)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 5 10 15 20 25 30 35

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Bearing Failure (φ2'=20˚ L=0.6H)

BS-A

BS-B

EC7-DA1C1

EC7-DA1C2

EC7-DA2

EC7-DA3

FoS=1.0

17

Figure 5(b). Computed factor of safety against bearing failure for φφφφEe = 20°°°° (L=0.7H)

Figure 5(c). Computed factor of safety against bearing failure for φφφφEe = 20°°°° (L=0.6H)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0 5 10 15 20 25 30 35

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Bearing Failure (φ2'=20˚ L=0.7H)

BS-A

BS-B

EC7-DA1C1

EC7-DA1C2

EC7-DA2

EC7-DA3

FoS=1.0

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

5.50

0 5 10 15 20 25 30 35 40

Fa

cto

r o

f S

afe

ty

Height of Reinforced Soil wall (m)

Bearing Failure (φ2'=35˚ L=0.6H)

BS-A

BS-B

EC-DA1C1

EC-DA1C2

EC-DA2

EC-DA3

FoS=1.0

18

7. CONCLUSIONS

(a) The analyses showed that BS 8006 gives more conservative results than EC 7 in the

assessment of sliding, overturning and bearing capacity.

(b) Comparing the various design approaches in Eurocode 7, EQU limit state is

generally more critical than GEO limit state in checking the overturning. Thus,

EQU limit state should be used for checking of overturning.

(c) Amongst the different design approaches (DA) recommended in EC 7, DA 1 and

DA 2 give the same but more conservative results than DA 3 in the assessment of

overturning.

(d) DA 1 and DA 3 give the same but more conservative results than DA 2 in the

assessment of sliding.

(e) DA 2 gives more conservative results than DA 1 and DA 3 in the assessment of

bearing failure.

(f) The analysis results also showed that in general the sliding is often critical compared

to overturning and bearing stability.

REFERENCES

• BS 8006:1995. Code of practice for strengthened/reinforced soils and other fills. British

Standard Institution, London.

• BS EN 1990:2002+A1:2005. Eurocode – Basis of structure design. British Standard

Institution, London.

• BS EN 1997-1:2004. Geotechnical design - Part 1: General rules. British Standard

Institution, London.

• Mike Dobie. Technical talk to the Annual General Meeting IEM GETD on 11th June 2011.