Software developed to calculate the increase in Shear Resistance and in the Factor of Safety (Sf)
thanks to TVS and PRATI ARMATI®

This software has been developed to calculate the increase in Shear Resistance and in the Factor of Safety (Sf) of soil armed with The Vetiver System (TVS) and PRATI ARMATI® roots. It comes from experiments led at the Agricultural-Hydraulic Institute of Milan University, in cooperation with Prof. Gian Battista Bischetti and Dr. Geol. Fabrizio Bonfanti.

The observation and quantification of TVS and PRATI ARMATI® physical and mechanical parameters, allowed the development of a tool that, considering input parameters such as soil type, slope inclination, soil cohesion and density, roots depth, and so on), determines the value of shear resistance increase of roots-armed soil, providing as output both the additional resistance and the Factor of Safety of an infinite slope.

The integral function reported below derives from Waldron's initial formula (1977) which subsequently has been modified by Bonfanti and Bischetti, 2001:

A large number of Vetiver and PRATI ARMATI® roots have been tested to assess their tensile stress resistance, their diameters have been measured, roots length has been assessed, thus obtaining the functions requested in the formula above.

The tool matches the above mentioned function with the one describing the in-depth behaviour of roots area (safely assumed as a linear function), thus allowing to characterize the roots-armed soil as a whole.

The infinite slope method has been selected since it suits very well the superficial landslides managed with TVS and PRATI ARMATI®.

The tool allows to assess ex-ante and to verify ex-post the results that designers can obtain using TVS and PRATI ARMATI® in terms of additional shear resistance and additional Factor of Safety (Sf) of roots-armed soils. Software output can also be used as input in traditional and more complex geo-technical stability models.

However, it is important to underline that any mathematical model simulates what happens in the real world. In this case, dealing with alive vegetable materials, hard to convert into a sharp model, it is absolutely necessary to consider that root system depth, density and development highly depends on local pedo-climatic conditions (temperatures, rainfalls, type of soil, and so on).

As a consequence, the outputs of this tool need to be used with estreme caution, also taking into account the fact that it does not exist any reference rules for this type of consolidation.

It is though important to highlight that the described model represents a revolotionary standpoint, as an entirely empirical discipline has been modelled and systematized. We also underline that this is the first release of this software, therefore any suggestions and improvements are extremely welcome.

We also wish to remind that the TVS Technology should be applied where stability is verified on its own (Sf > 1,3).

Indeed, TVS and PRATI ARMATI® Technologies can successfully replace traditional consolidation techniques on superficial erosion occurring on intrinsically stable slopes and where there is no immediate risk of landslides, with obvious economic and logistics benefits (saving time and money).

In other cases, where either slope inclination or soil characteristics do not grant slope stability, or there are falling rocks, or in the presence of high risk situations, it is necessary to sinergically combine this new green Technology with traditional civil works or naturalistic engineering. This match will allow to obtain immediate results, solving the urgent problems of slope stability and high risk, at the same time providing long-term results thanks to TVS and PRATI ARMATI® and its self-improving effectiveness over time.