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Speeding up slip circle analysis

Meeting users' needs is the key to the successful development of proven design packages, says software developer CADS

Software developer Computer and Design Services (CADS) has just added a fourth module to its Piled Wall Suite (PWS) software package. Version 3.0 now includes a module enabling engineers to use slip circle analysis to check overall stability of embedded retaining walls.

Incorporating feedback from software users is the key to the continuing development of proven design packages, says CADS technical director Bob Hairsine. He singles out user group events and exhibitions as a source of useful feedback, because users and developers can get together to discuss the product. He adds that extensive telephone and e-mail support provided to customers also proves worthwhile.

'By liaising closely with customers we have been able to identify how the application can be enhanced. Too often, programs seem to have been designed in a vacuum without regard to the needs of users. Making all our programs user-friendly has always been a priority. Issues raised by users frequently suggest how products can be improved.'

He adds that feedback from the first release of PWS revealed that a method of calculating sheet piled wall deflections was required by some users.

'Engineers working on very large cofferdams in the Far East, and those involving multi level piled walls asked for a deflection function to be incorporated in Version 2. We provided this, based on an empirical interpretation of deflection calculations. This feature has been enhanced again for Version 3 after further feedback from users.'

Version 3 also includes the option of factoring passive pressures, to reduce the passive resistance used in calculating wall force effects such as moments, shears and prop loads, in situations where the available factor of safety on passive soil failure is less than that required for the design standard being used. Traditional methods of embedded wall analysis use a factor of safety of 1.0, but for a bottom or toe cantilever condition the factor of safety against rotation depends on the sum of the wall bending strength and the soil passive resistance, so it is particularly important not to overestimate the latter.

While BS8002 factored soil strength method of analysis (included to allow analysis in line with draft Eurocode EC7) does not suffer from this problem, because calculations are done at the ultimate limit state. CADS says that 'passive factoring' was introduced in an effort to achieve a similarly rational analysis for force effects while using the traditional moment equilibrium method.

The new release also features enhanced results pages. A detailed results table shows all pressures acting on the wall during all stages of installation and whether they arise from active earth pressure, groundwater, surface flood water or from the minimum design pressure.

PWS has already become well established with more than 100 users. Hairsine says that part of this success is down to the modular approach, which 'provides customers with the option to purchase a version appropriate to their needs'.

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