ReSSA

ReSSA+ is an outgrowth of ReSSA(3.0).  It includes most of the features of ReSSA(3.0) — see the ReSSA(3.0) description on this website for details. However, ReSSA+ does NOT include an explicit use of inextensible reinforcement.  ReSSA+ can received exported data files generated in by program MSEW(3.0), excluding metallic reinforcement, for further in-depth global stability analysis.  Note that ReSSA+, like most limit equilibrium analysis, is in the realm of ASD.  It means that designs generated using MSEW(3.0) in LRFD mode will be analyzed in ASD.

Added features in 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 deadman or anchors. ReSSA+ does not calculate this passive or anchorage resistance but rather enable the user to input these values for each layer.  ReSSA+ considers this boundary value in calculating the pullout resistance away from the end.  Such feature could be useful in shortening upper layers especially under water 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 Spencer’s 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 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 deep seated failures.   

Features in Baseline Solution (aka Internal Stability):

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 Bishop’s 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 based on the baseline solution.

ReSSA+ shows graphically the distribution of the required reinforcement resistance along each layer.  

ReSSA+ shows graphically the location at which each Tmax is acting.

ReSSA+ displays the Tension Map using a color-code presentation to assess where reinforcement is hardly stressed or where it is overstressed. This diagnostic tool could be helpful in optimizing the layout of reinforcement. See FHWA-HIF-17-004 or Leshchinsky et al. (2017).

ReSSA+ allows for non-uniform length of reinforcement. Such feature is important if intermediate reinforcement layers are used. One can then include its impact on design, especially on connection loads.

ReSSA+ shows graphically the distribution of pullout resistance as calculated (integrated) from the rear and front end.  Displaying the front end pullout enables one to realize as the minimal connection load is rationally determined by shifting the front-end pullout upwards until sufficient resistance is rendered enabling the reinforcement to mobilize the resistance needed for limit state condition.

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 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 Baseline Solution mode is available only in General geometry in ReSSA+.  This is done for logistical reasons and should not considered as a drawback.

The user can specify up to 5 different types of interfaces of reinforcement interfaces for assessment of pullout resistance. 

 

 

 

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