## Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

## Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

(OP)

Hi all,

I am using Wallap to design a 3.5m high basement wall. The soil is made ground sand/silt layer to 1.5m over clay to 20m plus (shear strength of 50-125kPa). There was some discussion on what type of retaining wall to use but we have arrived at a secant piled wall. For a worst case ULS event (i.e. factored soil parameters, groundwater at 1m below surface and 10kPa surcharge), to achieve a FoS of 1.2 i need roughly 12m of embedment. (Seems excessive to me,but thats what WALLAP is telling me, i suppose there is a lot of load with reduced soil parameters. I am newish to Wallap so my design will be check by another engineer and also by my line manager.

The top of the wall will eventually be restrained with a concrete slab so i would like to consider that as a prop/strut force.

When modelling props/struts in WALLAP gives the options of youngs modulus or Pre stress or both. What would be the most appropriate way to model this as to simulate the restraint provided by the slab. Not specifically i WALLAP but i general good practice.

I am using Wallap to design a 3.5m high basement wall. The soil is made ground sand/silt layer to 1.5m over clay to 20m plus (shear strength of 50-125kPa). There was some discussion on what type of retaining wall to use but we have arrived at a secant piled wall. For a worst case ULS event (i.e. factored soil parameters, groundwater at 1m below surface and 10kPa surcharge), to achieve a FoS of 1.2 i need roughly 12m of embedment. (Seems excessive to me,but thats what WALLAP is telling me, i suppose there is a lot of load with reduced soil parameters. I am newish to Wallap so my design will be check by another engineer and also by my line manager.

The top of the wall will eventually be restrained with a concrete slab so i would like to consider that as a prop/strut force.

When modelling props/struts in WALLAP gives the options of youngs modulus or Pre stress or both. What would be the most appropriate way to model this as to simulate the restraint provided by the slab. Not specifically i WALLAP but i general good practice.

## RE: Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

## RE: Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

And yes there may be some clients money wasted but isnt that what happens! Some times you have to learn on the job. Plus i am only charging for half of my time.

## RE: Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

It's inappropriate to use factored soil properties in Wallap.

## RE: Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

Why would it be inappropriate, can you expand on that?

WALLAP has a function that allows factored soil properties, these have to be used in accordance with Eurocodes.

Deflection is generally limited to 30mm for the SLS case and we generally state that WALLAP over estimates deflection by 50-60% adn therefore we would expect 10-15mm actual. I understand this 'rule of thumb' is based on case histories of embedded walls in London Clay.

## RE: Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

## RE: Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

Factored soil parameters have no physical meaning and could give you wrong depth of max bending/shear in finite element/difference analyses. Using factored parameters in hand calculations is alright.

My experience on Wallap is its prediction is reasonable (use pseudo 2-D option) if it's a symmetrical problem. Only when the excavation is too narrow you need a full 2-D numerical program like Plaxis/Flac.

Good luck

## RE: Retaining Wall Strut - Youngs Modulus or Pre stress (kN) per load

HZ - Secant piled walls are more common for permanent works than Sheet piles. Sheet piles are definitely quicker to install but the additional RC wall inside would slow it down. I would think a secant wall with a shotcrete finish would be more practical. I suppose there are a lot of factors to consider.

Re Wallap and Factored parameters - would it matter where the max bending and shear is located as long as the values were correct and that the wall/reinforcement had sufficient structural capacity to resist them.