2 Design of Cantilever Wall

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Chapter 2. Design of Cantilever wall In this chapter, the design of cantilever wall and its overall analysis is described.

Assignment

Design a cantilever wall with a height of 4,0 m and analyze it by EN 1997-1 (EC 7-1, Design

approach 1). The terrain behind the structure is horizontal. The ground water table is 2,0 meters deep.

Behind the wall acts a strip surcharge with a length of 5,0 meters and with a magnitude of 10 kN/m2.

The foundation soil consists of MS Sandy silt, stiff consistency, 8,0


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Dialog window Settings list

In the frame Geometry choose the wall shape and enter its dimensions.

Frame Geometry


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In the frame Material enter the material of the wall.

Frame Material Input of material characteristics of the structure

Then, define the parameters of soil by clicking Add in the frame Soils. Wall stem

is normally analyzed for pressure at rest. For pressure at rest analysis, select Cohesionless.

Dialog window Add new soils


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Note: The magnitude of active pressure depends also on the friction between the structure and soil.

The friction angle depends on the material of construction and the angle of internal soil friction

normally entered in the interval ( ) ef 3231 Table with the soil parameters

Soil

(Soil classification)

Profile

[ ]m Unit weight

[ ]3mkN Angle of

internal

friction

[ ]ef

Cohesion

of soil

[ ]kPacef

Angle of

friction

structure soil

[ ]= S-F Sand with trace of

fines, medium dense soil 0,0 4,0 17,5 28,0 0,0 18,5

MS Sandy silt, stiff

consistency, 8,0


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Frame Water

In the next frame define Surcharge. Here, select permanent and strip surcharge on the terrain

acting as a dead load.

Dialog window New surcharge

In the frame FF resistance select the terrain shape in front of the wall and then define other

parameters of resistance on the front face.


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Frame FF resistance

Note: In this case, we do not consider the resistance on the front face, so the results will be

conservative. The FF resistance depends on the quality of soil and allowable displacement of the

structure. We can consider pressure at rest for the original soil, or well compacted soil. It is possible to

consider the passive pressure if displacement of structure is allowed. (for more information, see HELP

F1)

Then, in the frame Stage settings choose the type of design situation. In this case,

it will be permanent. Also choose the pressure acting on the wall. In our case, we will choose active

pressure, as the wall can move.

Frame Stage settings

Note: Wall stem is dimensioned always on earth pressure at rest, i.e., the wall cant be moved.

The possibility of evaluating the stem and the wall of the active pressure is considered only in

exceptional cases - such as the effects of the earthquake (seismic design situation with partial coefficient

equals 1.0).


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Now, open up the frame Verification, where you analyze the results of overturning and slip

of the cantilever wall.

Frame Verification

Note: The button In detail in the right section of the screen opens a dialog window with detailed

information about the analysis results.

Analysis results:

The verification of slip is not satisfactory, utilization of structure is

Overturning: 52,8 % 97,10933,208 =>= klvzd MM [kNm/m] SATISFACTORY. Slip: 124,6 % 94,8178,65 =


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Change of the design: change of the geometry of the wall

Return to the frame Geometry and change the shape of the cantilever wall. For increasing

the resistance against slip we introduce a base jump.

Frame Geometry (Changing dimensions of cantilever wall)

Note: A base jump is usually analyzed as an inclined footing bottom. If the influence of the base jump

is considered as front face resistance, then the program analyses it with a straight footing bottom, but

FF resistance of the construction is analyzed to the depth of the down part of the base jump

(More info in HELP F1)

Then analyze the newly designed construction for overturning and slip.


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Frame Verification

Now, the overturning and slip of the wall are both satisfactory.

Then, in the frame Bearing capacity, perform an analysis for design bearing capacity

of the foundation soil 175 kPa.

Frame Bearing capacity

Note: In this case, we analyze the bearing capacity of the foundation soil on an input value, which we

can get from geological survey, resp. from some standards. These values are normally highly

conservative, so it is generally better to analyze the bearing capacity of the foundation soil in the


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program Spread footing that takes into account other influences like inclination of load, depth of

foundation etc.

Next, in the frame Dimensioning chose wall stem check. Design the main reinforcement

into the stem 10 pcs. 12 mm, which satisfies in point of bearing capacity and all design principles.

Frame Dimensioning

Then, open up the frame Stability and analyze the overall stability of the wall. In our case,

we will use the method Bishop, which result in conservative results. Perform the analysis

with optimization of circular slip surface and then leave the program by clicking OK.

Results or pictures will be shown in the report of analysis in the program Cantilever wall.


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Slope stability program

Conclusion/ Result of analysis bearing capacity:

Overturning: 49,5 % 16,10852,218 =>= klvzd MM [kNm/m] SATISFACTORY Slip: 64,9 % 47,6427,99 =>= posvzd HH [kN/m] SATISFACTORY Bearing capacity: 86,3 00,17506,151 =>= dR [kPa] SATISFACTORY Wall stem check: 78,7 % 71,13392,169 =>= EdRd MM [kNm] SATISFACTORY Overall stability: 40,8 % Method Bishop (optimization) SATISFACTORY

This cantilever wall is SATISFACTORY.

2 Design of Cantilever Wall

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