ReSSA+ is an interactive program used to assess the rotational and translational stability of reinforced slopes and walls.
New Features for assessing Internal Stability The Baseline Solution:
- For a given problem (i.e., tiered slope/wall, different soil layers, complex layout of reinforcement, facing units, surcharge loadings, pullout interaction parameters, seismicity, seeping water, and user-specified rear-end reinforcement resistance) and a given target factor of safety, ReSSA+ calculates the maximum tensile resistance in the reinforcement, Tmax, its location, and the connection load, To, for each layer. This baseline solution provides a rational basis for selecting geosynthetic and facing considering long-term strengths values. The baseline solution defines the required reinforcement/connection load at any relevant location so as to produce a user-prescribed limit state. Note that the baseline solution is conducted using Bishops rotational failure considering failures emerging at the face and toe. Since other modes of failure, such as foundation or sliding instability, are possible, it is critically important to also assess global stability available in ReSSA+. However, this should be done after adequately selecting geosynthetic and connectors considering also the baseline solution.
- ReSSA+ enables visualization of the distribution of the required reinforcement resistance along each layer.
- ReSSA+ enables visualization of the location at which each Tmax is acting.
- ReSSA+ displays the Tension Map using a color-coded presentation to assess where reinforcement is hardly stressed or where it is overstressed. This diagnostic tool is critical towards optimizing the layout of the reinforcement system. See FHWA-HIF-17-004 or Leshchinsky et al. (2017).
- ReSSA+ allows for non-uniform reinforcement lengths. Such a feature is important if intermediate reinforcement layers are used. One can then include its impact on design, especially on connection loads.
- ReSSA+ enables visualization of the distribution of pullout resistance as calculated for both the connection and rear of the reinforcement.
- ReSSA+ presents tabulated numerical results for Tmax and To at each layer. The user can export this table to Excel.
- Upon switching to Global Stability mode in ReSSA+, the user can (and should) specify adequate reinforcement and connectors to ensure global stability considering various failure modes.
- Each dialog in ReSSA+ has its own extensive help.
- The user can specify up to 5 different types of interfaces for reinforcement for assessment of pullout resistance.
- In ReSSA+ live and/or dead surcharge loads can be considered. Also, impact of shear strength between stacked facing units can be explored in both Stage I and Stage II analysis.
- In the baseline mode (internal stability), the actual minimum factor of safety of front and rear pullout is calculated and presented graphically and numerically in a tabulated format. Unlike conventional analysis where this factor is a function of Tmax, in ReSSA+ it is a function of the computed distribution of load T(x) in the reinforcement.
- Horizontal displacement at the face of the slope can now be estimated in the baseline solution. This approximate displacement is based on simplified calculations resulting from the elongation (stretching) of each reinforcement layer considering its tensile modulus. This approximation is a consequence of the limit state methodology used to assess the reinforcement tensile load distribution in internal stability.
New Features for assessing Global Stability:
- Rear or back-end pullout can be enhanced by specifying a starting resistance at the end that is greater than zero. Such resistance can be generated by elements such as deadmen or anchors. ReSSA+does not calculate this passive or anchorage resistance but rather enables the user to input these values for each layer. ReSSA+ considers this boundary value in calculating the pullout resistance away from the end. This feature could be useful in shortening upper layers especially considering seepage or seismic loading.
- Facing units, such as small or large blocks or gabions, can be specified for simple or complex slope geometry. The shear between inter-units or unit-foundation is considered in rotational stability (Bishop) as well as in direct sliding (2-part Spencer). Large units may result in shorter and/or weaker reinforcement.
- Some design standards require assessment of bearing capacity. In Direct Sliding run (available only in Global Stability), ReSSA+ also runs 2-part wedge using Spencer along the base of the reinforced soil mass as defined by the length of the bottom layer. Using Spencers results (which includes the normal stress distribution along the base as well as the inclination of the interslice force), the following is calculated: a. Eccentricity of the resultant vertical force acting on the base, b. Magnitude of this resultant, and c. The average bearing load acting over an eccentrically loaded footing (B-2e). This enables one to calculate the implied bearing load corresponding to, for example, Meyerhof approach. Subsequently, the user can assess or rationally estimate the bearing capacity factor of safety as implied through an approximate solution. It is always wise to assess stability considering foundation failure; e.g., use Bishop and Spencer using common slope stability analysis considering foundation failures.
- In seismic Global Stability, 2-part wedge, the user can compute the yield acceleration at the elevation of each reinforcement layer. Using this acceleration, the user can follow given references to calculate the seismic displacement.