Retaining Wall - Quick Inspection Guide -
by
Urban Development Control Office
City Planning Division
Ministry of Land, Infrastructure and Transport
Translated by
Building Research Institute
International Institute of Seismology and Earthquake Engineering
February 2006
– Retaining wall – Quick inspection guide
1. Introduction
This check sheet is in the draft stage from two standpoints:
1.1. It will be reviewed, if necessary, according to the accumulation of technical
knowledge and
1.2. Local public authorities may include their own data in this sheet to reflect
regionalism prior to the use.
The check sheet has been prepared targeting the residents who desire to get
general information on the degree of risk of retaining wall. Being a structure, the
retailing wall is aged with time, as well as cracked or inclined due to rain falling or
earthquake. The degree of risk is difficult for the residents to know and therefore, this
check sheet is intended to be helpful in heightening their interest in safety of the retailing
wall of their house and getting general information on the degree of risk.
It should be noted that the purpose and accuracy of this check sheet are as
described above, thereby, it is strongly recommended that, even if the retailing wall is
safe, the residents to make regular check and if safety is low, they should make more
detailed check.
2. Type of retaining wall
The retaining walls of house lot are classified into the following types. (Table 1)
□ Radial stone/concrete block retailing wall
□ Gravity concrete retaining wall
□ Reinforced concrete retailing wall
□ Dry masonry retaining wall
□ Stone-added retaining wall
□ Two-level retaining wall
□ Project plate bedding retaining wall
(Select an appropriate type by reference to the examples shown on Table 1)
If the retaining wall is not classified into anyone of the above types, it is not
essentially suitable for the retaining wall of house lot. It is recommended that, even if no
damage is found, to consult a specialist about structural problems, if any.
2
If some damage is found in structure, the retaining wall is under an extremely
hazardous condition; thereby it should be taken a quick action for repairing it.
The house lots with a retailing wall of 1 m or less height are almost safe and
therefore, they are excluded from the targets to be checked. If you have any problem,
consult with a specialist. In this report, disasters caused by flood, high tide, or ground
liquefaction are not described.
Table -1 Types of Retaining Walls
1) Radial stone/concrete
Weep hole
Block retaining wall
Drainage conduit
2) Gravity concrete retaining
Weep hole
wall
Drainage conduit
3) Reinforced concrete retaining
wall Weep hole
Drainage conduit
4) Dry masonry retaining wall
(nozura masonry, cobble
masonry, etc.）
Drainage conduit
5) Stone-added masonry Filling soil
retaining wall
Drainage
conduit
6)
Two-level retaining wall
Drainage
conduit
7) Projected plate bedding
retaining wall
Drainage conduit
4)-7) Excluded from check. It is recommended to consult with a specialist.
3
Concrete retaining walls are largely classified into the gravity type and reinforced
concrete L-shape type.
The gravity concrete retaining wall supports the earth pressure on the back side by
means of its own weight. The L-shape type retaining wall, which is composed of an L-
shaped reinforced concrete wall body and a bottom plate, supports the earth pressure on
the back side including the weight of soil piling on the bottom plate.
The gravity concrete retaining wall has a plain concrete structure, while the L-
shaped retaining wall has a reinforced concrete structure. For the both types, the
backside has been buried in the ground and only the concrete wall on the front side is
visible.
The crown width of the retaining wall is approx. 40 cm for the gravity concrete
type and approx. 20 cm to 30 cm for the reinforced concrete L-shaped type, respectively,
the former being wider than the latter. Digging out the back side of the crown of the
retaining wall, it may be known that the gradient is mild for the gravity concrete type and
vertical to the ground surface and thin in wall thickness for the reinforced concrete L-
shaped type.
Crown width
Crown width
400mm
Front side Wall body
Backside
Front
side
Weep hole Backside
Bottom
plate
Concrete retaining wall Reinforced concrete L-shaped
retaining wall
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3. Checking algorithm
1. First, check the surrounding environmental conditions and others
1) Sweep hole
2) Exuded water
3) Drainage facility
A (Reference points of retaining wall)＝(the largest one is used out of scores in 1) to 3) levels)
2. Second, check the retaining wall for any:
1) Crack
2) Horizontal displacement
3) Differential settlement/Clearance between joints
4) Clearance at the external corner
5) Bulge
6) Inclination/Breakage
B （Changed points of retaining wall）＝(the largest one is used out of scores in 1) to 6))
3. Finally, evaluate the retaining wall comprehensively.
According to the obtained total score mentioned above｛(reference points of retaining wall
A＋(changed points of retaining wall B)｝, the safety of the retaining wall is ranked into any of
three levels:
I. Almost safe
II. Relatively unstable
III. High risk
Namely, the retaining wall of house lot with higher total score is at higher risk.
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4. Retaining wall checking
4.1. Surrounding environmental conditions check
1) Weep hole (excluding dry masonry type)
□ Drainage of the retaining wall is good including the ground 0.0
above it.
(Type a) Refer to Table 2
□ There weep holes have been formed but rain water tends to 1.0
permeate into the ground above the retaining wall.
(Type b) Refer to Table 2.
□ There is no weep holes have been formed. (or the retaining 2.0
wall does not satisfy such a condition as one or more weep holes
(75 mm in inner diameter) in each area of 3 m2.)
(Type c) Refer to Table 2.
2) Water exudation
□ The surface of the retaining wall is dry. 0.0
□ The surface of the retaining wall is always wet. 0.5
(Type a) Refer to Table 2.
□ Water always exudes and flows out from the retaining wall. 1.0
(Type b) Refer to Table 2.
3) Drainage facility
□ The drainage facility is good 0.0
□ There is shifted and/or broken point in drainage conduit. Or, a 0.5
crack runs in the ground along the drainage conduit.
(Type a) Refer to Table 2.
□ In addition, water exudes from the crack or joint of the 1.0
retailing wall and a concave has been formed.
(Type b) Refer to Table 2.
□ Moreover, the weep holes are clogged up and damaged, 1.5
deteriorating the drainage function.
(Type c) Refer to Table 2.
Reference points of retaining wall (Fill the largest one out of scores in 1) to 3).)
A=
6
Table 2 Type of surrounding environmental conditions (1)
Item Type Schematic diagrams of types
Drainage
Type a
conduit Crown concrete
Weep hole
1) Weep Drainage of the retailing wall is good including the ground
hole above it.
Permeated
Clogged weep hole rainwater
Type b
There weep holes have been formed but water always exudes
from the surface of the retailing wall
Permeated rainwater
No weep hole
Type c
Raised water level
Weep hole
Type a
2) Exuded The retailing wall is always wet.
water
Weep hole
Type b
Water exuded out from the retailing
wall.
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Table 2 Types of surrounding environmental conditions (2)
Item Type Schematic diagrams of types
Displacement Weed
Clearance
Type a between joints
Cracked ground
Deposited sediment
3)
Drainage
facility Displaced and broken drainage conduit
Weed growing at
Displacement joints
Clearance Concave
between joints
Type b
Deposited sediment
Water exuded from joints.
Displacement due
to settlement
Type c
Destroyed side ditch
8
4.2. Type of damages corresponding to each type of retaining walls
Referencing to Table 1, select an applicable type of retaining wall and based on
Table 3, check the retaining wall according to the items to be check for the radial stone
masonry/concrete block type, to the items to be check for the gravity type, and to the
items to be check for the reinforced concrete type.
Type (1) Radial stone (2) Gravity concrete type (3) Reinforced concrete
Damage masonry/ type
concrete block type
Horizontal
crack
1) Crack Vertical/
oblique A
crack
Crack at
external
corner
crack
2) Horizontal B C
displacement
D
3) Differential
settlement
(Clearance between
joints)
C
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4) Clearance at external E F
corner －
5) Bulge
―
－
6) Inclination/breakage
A – Clearance formed, or forth-and-back/up-and-down displacement
B – Enlarged displacement
C – Back-and-forth displacement
D – Up-an-down displacement
E – Displacement
F – Displacement due to extrusion
4.3. Radial stone/concrete block retaining wall
1) Crack
Horizontal crack
□ No horizontal crack 0.0
□ Horizontal crack along the joint of masonry in the vicinity of 3.5
the center of the retaining wall.
□ Horizontal crack at the joint of masonry in the vicinity of the 5.0
center of the retaining wall, as well as in the masonry itself.
□ Horizontal open crack at the joint of masonry in the vicinity of 6.5
the center of the retaining wall, as well as in the masonry
itself.
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Vertical/oblique crack
□ No vertical/oblique crack 0.0
□ Vertical/oblique crack found along masonry on the front side 2.0
of the retaining wall
□ Vertical/oblique crack found along masonry, forming a 3.5
clearance
□ Back-and-forth or up-and-down displacement at the 5.0
vertical/oblique crack
Crack at external corner
□ No crack at external corner 0.0
□ An oblique crack found at external corner 2.5
□ An oblique crack found at external corner, from which water 4.0
has exuded.
□ An oblique and displacement found at external corner. 5.5
Note that cracks are defined to be 1 mm or larger in width.
2) Horizontal displacement
□ No horizontal displacement 0.0
□ 5 mm or smaller of displacement in the joint of the retaining 3.0
wall.
□ 5 mm to 2 cm of displacement in the joint of the retaining wall 4.5
□ 2 cm of back-end-forth displacement in the joint of the 6.0
retaining wall
3) Differential settlement (clearance between joints)
□ No differential settlement (clearance between joints) 0.0
□ 5 mm or smaller back-and-forth or right-and left clearance 4.0
between joints of the retaining wall
□ 5 mm to 2 cm or smaller back-and-forth or right-and left 5.5
clearance between joints of the retaining wall
□ 2 cm or larger back-and-forth or right-and left clearance 7.0
between joints of the retaining wall
4) Clearance at external corner
□ No external corner 0.0
□ A small clearance at external corner 4.0
□ Enlarged clearance at external corner 5.5
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□ Further enlarged external corner and back-and-forth 7.0
displacement in the retaining wall
5) Bulge
□ No bulge 0.0
□ 5 mm or smaller of displacement in the joint of the retaining 4.5
wall.
□ The entire retaining wall has further bulged with a clearance 6.0
between stones in the middle of it
□ The entire retaining wall severely bulged with some stones 8.0
falling down in the middle of it.
6) Inclination/breakage
□ No inclination/breakage 0.0
□ The surface of retaining wall has slightly inclined forward 5.0
(backward)
□ The entire surface of retaining wall has apparently inclined 6.5
forward (backward)
□ The entire surface of retaining wall has apparently inclined 9.0
forward (backward)/ retaining wall with a breakage in the
middle of it.
Damage points in retaining wall (Fill in the largest one out of those in 1) to 6).)
B=
4.4. Gravity concrete retaining wall
1) Crack
Horizontal crack
□ No horizontal crack 0.0
□ 5 mm or smaller of displacement in the joint of the retaining 3.0
wall.
□ A horizontal crack found along the joint in the vicinity of the 4.5
center of the retaining wall, as well as in section of the
retaining wall itself
□ A horizontal open crack found along the joint in the vicinity of 6.0
the center of the retaining wall, as well as in section of the
retaining wall itself
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Vertical/oblique crack
□ No oblique crack 0.0
□ A vertical/oblique crack along section on the front side of 1.5
retaining wall.
□ A wide and open vertical/oblique crack along section of 3.0
retaining wall
□ A back-and-forth or right-and-left displacement found at a 4.5
vertical/oblique crack in retaining wall
Crack at external corner
□ No crack at external corner 0.0
□ An oblique crack at external corner 2.0
□ An oblique crack at external corner, from which water has 3.5
exuded
□ An oblique crack at external corner with a displacement 5.0
Note that cracks are defined to be 1 mm or larger in width
2) Horizontal movement
□ No movement 0.0
□ Smaller than 5 mm of back-and-forth displacement between 2.5
joints retaining wall
□ 5 mm to 2 cm or smaller of back-and-forth displacement 4.0
between joints of retailing wall
□ 2 cm or larger of back-and-forth displacement between joints 5.5
of retaining wall
3) Differential settlement (clearance between joints)
□ Differential settlement (no clearance between joints) 0.0
□ 5 mm of up-and-down or right-and-left displacement or 3.5
clearance between joints of retaining wall
□ 5 mm to 2 cm or smaller of up-and-down or right-and-left 5.0
displacement or clearance between joints of retaining wall
□ 2 cm or larger of up-and-down or right-and-left displacement 6.5
or clearance between joints of retaining wall
6) Inclination/breakage
□ No inclination/breakage 0.0
□ The retaining wall has slightly inclined forward (backward) 4.5
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□ The entire retaining wall has apparently inclined forward 6.0
(backward)
□ The entire retaining wall has apparently inclined forward 8.5
(backward) with a breakage in the middle of it
Damage points in retaining wall (fill in the largest one out of those in 1) to 3) and 6).)
B=
4.5. Reinforce concrete retaining wall
1) Crack
Horizontal crack
□ No horizontal crack 0.0
□ A horizontal crack along the joint of sections in the vicinity of the 2.5
center of retaining wall
□ A horizontal crack along the joint of sections in the vicinity of the 4.0
center of retaining wall, as well as in section of the retaining wall
itself
□ A horizontal open crack along the joint of sections in the vicinity of 5.0
the center of retaining wall, as well as in section of the retaining wall
itself
Vertical/oblique crack
□ No vertical/oblique crack 0.0
□ A oblique crack along section on the front side of retailing wall 1.0
□ A wide vertical/oblique crack along section with a clearance 2.5
□ A back-and-forth or up-and-down displacement in the retailing wall 4.0
at a vertical/oblique crack.
External corner crack
□ No external corner crack 0.0
□ A oblique crack at external corner 1.5
□ A oblique crack at external corner, from which water has exuded 3.0
□ A oblique crack at external corner with a displacement 4.5
Note that cracks are defined to be 1 mm or larger in width.
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2) Horizontal movement
□ No horizontal movement 0.0
□ Smaller than 5 mm of displacement at the joint of retailing wall 2.0
□ 5 mm to 2 cm of back-and-forth displacement at the joint of retailing 3.5
wall
□ 2 cm or larger back-and-forth displacement at the joint of retailing 5.0
wall
3) Differential settlement (Clearance between joints)
□ Differential settlement (No clearance between joints) 0.0
□ 5 mm or smaller of up-and-down displacement or right-and-left 3.0
clearance at the joint of retailing wall
□ 5 mm to 2 cm or smaller of up-and-down displacement or right-and 4.5
left clearance in the joint of retailing wall
□ 2 cm or larger of up-and-down displacement or right-and-left 6.0
clearance at the joint of retailing wall
4) External corner (at external corner) clearance
□ No external corner clearance 0.0
□ A small clearance at the external corner of retailing wall 3.0
□ Enlarged clearance between joints of retailing wall 4.5
□ Further enlarged clearance between joints retailing wall with a back- 6.0
and-forth or up-and-down displacement in retailing wall itself
6) Inclination/breakage
□ No inclination/breakage 0.0
□ The entire retailing wall has apparently inclined forward (backward) 4.0
□ The entire retailing wall has apparently inclined forward (backward), 5.5
which is visible
□ The entire retailing wall has apparently inclined forward (backward) 8.0
with a breakage in the middle of it
7) Corroded reinforcing steel
□ No corroded reinforcing steel 0.0
□ A short vertical or horizontal crack on the front side of retailing wall 4.5
□ A relatively extensive vertical or horizontal crack on the side of 6.0
retailing wall with a trace of liquid rust flow
□ An extensive vertical or horizontal crack on the side of retailing wall 8.0
with cover concrete pealed off and reinforcing steel corroded
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Damage points in retailing wall (Fill in the largest one out of those 1) to 4) described
above)
B=
5. Retaining wall evaluation
The safety of the retaining wall is evaluated based on the score obtained in
surrounding environmental check (reference points A of retaining wall) and the score in
damage points of retaining wall check (damage points in retaining wall B).
Total score = A points + B points
The safety class of a retaining is shown in Table 4. based on the number of total
points obtained in the evaluation shown above.
Table 4. Retaining walls safety class
Total Score Safety Class Total Evaluation
5.0 points or less III. Almost stable retailing wall of
house lot
5.0 points or more/ II. Relatively unstable retailing
9.0 points or less wall of house lot ∆
more than 9.0 points I. High risk retailing wall of house
lot X
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