The Features

Aspen is a Windows software finalized to the slope stability analysis, according to the classical limit equilibrium methods. It allows to model complex stratigraphic and hydrostatic situation produced by pyezometric surfaces assigned on each soil layer. Excavations, embankments, docks and surface loads, can be enabled or disabled in a simple way. So also, structural reinforcements like retaining walls, sheet-piles, geogrids and anchor rods. In this way, the user can create changed slope configurations to modelling different situations in situ or different chances of reinforcements. The user can define slip surfaces, generic or circular, by single assignments or using centers grids. If the user desires a screening of greater accuracy, he can activate automatic analysis for searching the critical slip surface, departing from a initial assigned surface. The process finds configurations with smaller safety factor, up to the minimum. The user can see the graphical evolution of the search process. The program is endowed with all the necessary functions to execute data insertion, graphic model control, analysis and print reporting. The programs support Dxf and Rtf documents formats. The following figure show a phase of job with the program. You can see the Editing form, the Modeling forms and some inputs grids.

Fields of Use

Aspen is a powerful tools for slope stability analysis. Geologists and engineers can use it to find the critical slip surface of a slope, evaluating the effects of structural and earth reinforcements.

Imput Elements

The programs allows to describe several slope characteristic elements:

• Soil materials,
• Knots (Points)
• Soil layers,
• Pyezometric profiles,
• Excavations profiles,
• Embankments profiles,
• Dock,
• Loads,
• Retaining walls,
• Sheet-piles,
• Anchor rods,
• Geogrids,
• Circular slip surfaces,
• Generic slip surfaces,
• Circular slip surfaces by centers grid.

Essential and optional elements

Essential elements are the first three: Material, Knots and Layers. The simplest slope need them. Optional elements are all the others. These elements are characterized by the fact that their definition doesn't necessarily implicate the application in the model. For instance, you can define a slope without pyezometric surfaces or retaining walls. You can also define several pyezometric surfaces or walls and apply only any of them. This feature is useful to simplify the creation of varied configurations of the slope, that you want to analyze. For instance, you may define several structural reinforcements, but apply only one to find out which of them is the most suitable.

ASPEN foresees four different graphic environments:

• Editing sight,
• Model sight,
• Strips sight,
• Automatic search sight.

You can see then in the following figures, for a simple slope with an applied sheet-piles.

The graphic sights

The program foresees four different graphic environments:

• Editing sight,
• Model sight,
• Strips sight,
• Automatic search sight.

You can see then in the following figures, for a simple slope with an applied sheet-piles.

Editing Sight
In the Editing Sight you can use graphical functions to define input elements. Using mouse, you can insert points, soil layers, excavation and embankments surfaces, walls, etc. The applied elements are visible in the assigned color, the not applied ones is drawn in gray.

Model Sight
The Model Sight brings the sight of the slope after the construction of the model, therefore with the profiles modified from the application of excavations and embankments and with the only interventions indeed applied. If you are defined more slip surfaces, there is a model sight for each slip surface.

The Strips Sight
The Strips Sight brings the subdivision in strips for every slip surface defined. As the preceding one, the sight is available after the construction of the model. Other details are available after the analysis execution, as the diagrams of the tensions mobilized on the slip surface, or the inter-slice forces.

The Automatic Search Sight
The Automatic Search Sight allows to start the automatic searching process and to see its graphical evolution. This is an important feature of the program, that, departing from an assigned initial surface, search for equilibrium configurations with a smaller safety factor, up to reach a point of minimum of the safety coefficient. Each graphic window has its tools bars to implement specific functions, as the graphic input in the Editing Sight. Are also present common functions of management, as zooming, moving, labeling elements, synchronizing elements on data grids, print preview and preferences setup.

Input

The slope model is built in the graphic environment of the Editing Sight, eventually on a Dxf imported background, with the support of the commands of insertion, change, cancellation, available for every element of modeling. In equivalent way, numerical assignment of the data is possible, in data-grids synchronized with the graphic environment. You may want use grid to insert of a new element or to modify an existing one. In the following example we define three circular surfaces and a centers grid using data-grids. Inserting a new element in a data-grid:

• add the line, clicking on the button Insert of the Commands Tools bar,
• assign the data of the element.
  
  

Soil materials definitions requires dry unit weight, wet unit weight, cohesion and friction angle. Besides, you can define the graphical pattern and color you desire.

Soil layers, pyezometric, excavation and embankments surfaces are defined as polyline. In the following figure you can see the definition of two soil layers, using sequences of knots.

The definition of the interventions of consolidation is articulated for typology and, in general line, it foresees the description of detail in geometric terms and mechanics.

Slip Surfaces

The program accepts circular slip surfaces or generic slip surfaces. The generic surfaces are defined through polylines. The circulars ones requires the center point and the radius or other conditions of tie as the passage for assigned points or tangency conditions. For the circulars, besides, the terminal lines can be defined with a straight line of assigned angle. The user can compose a list of surfaces to submit to verification or also define families of circular surfaces using the centers grids.

The Construction of the Model

Departing from the native configuration and applying all the selected optional elements, the program builds the model of the slope and performs the strips decomposition, for every slip surfaces defined and applied. The operation is performed by clicking on the button Build Model , you can find in the Frequent Commands Tool Bar. The button also has the function to reset the model, if this has already been built. The performed modeling is visible in the Model Sight and in the Strips Sight, both characterized by an elevated level of detail. During the construction of the model, the program performs a deepened control of the data and in the case it find some incongruities, it releases warning messages. The messages preceded by exclamation point signals serious incongruities that don't allow the generation of the model. In these cases it is necessary to modify or integrate the definition, to resolve the incongruity. The other messages signal situations of incongruity that the program can temporarily resolve disabling of authority a particular element and continuing with the construction of the model. The user will pay attention to the signaled situations and will intervene for correcting them.

We see in the following figure the Editing Sight for a simple slope.

Analysis features
Analysis is performed with the limit equilibrium method. Available formulations are

• Morgerstern-Price.
• Bell.
• Janbu.
• Bishop.
• Fellenius

implemented in ASPEN in a optimized form, to improve convergence and to widen the field of applicability. The slope is analyzed under the action of the proper weights, of the assigned loads, of the lateral hydrostatics force acting on the top and the horizontal and vertical seismic acceleration, that you can define in autonomous way. The horizontal seismic action is applied in direction of the Strip, while the vertical one is applied in both the verses, correspondents to the increase and the decrement of the weights, and appraising the safety factor for both the cases.

Effects of stabilizing structures

The effect of stabilizing structures is dependent from the mechanic characteristics of the intervention and from the geotechnical local situation. For the anchor rods and the geogrids the program calculates the effects due to incomplete development of the anchorage. For walls and sheet-piles, the maximum available stabilizing force is appraised, compatible with different possible mechanisms of crisis: horizontal sliding of the structure, overturning of the structure, earth rupture on the front of structure or in the interval between piles, structural crisis. Once performed analysis it is possible to know the contribution offered by the intervention with an immediate interrogation from mouse. Also, these information are available in the reports.

In Editing, Model and Strip Sight, you can get information on the stabilizing effect offered by the reinforcement, using the tool Find of the tools bar. The procedure in detail is the following:

• select the tool Find from the tools bar,
• click on the wall, sheet-piles, anchor rod or geogrid to get the information,
• the information appears to the top-left corner of the form and disappears when you release the mouse button.

In the following figure you can see the contributions of a continuous and discontinuous sheet-pile.

Analysis of assigned surfaces

The program foresees the simultaneous analysis of all the surfaces assigned by the user, as single surfaces or centers grid. You can see the safety factors in a results grids. In the Strip Sight it is available instead the diagram of the mobilized tensions on the slip surface. In the case of the of centers grid definitions, you can see the contour lines of the safety factors.

Automatic search analysis

One of the characteristics of excellence of the program is automatic analysis, based on a numerical strategy that, beginning from an initial trial surface, search configurations with lower safety factor, up to reach to a solution of minimum. The trial is effected seeking the point of minimum of the function safety coefficient, in terms of opportune descriptive parameters of the slip surface. The graphic evolution of the surface and the decreasing course of the safety coefficient can be seen on video in graphic animation, up to the attainment of the critical configuration. In the trial, all the effects due to geotechnical, hydrostatics, loads and reinforcements condition are considered.

In the preceding figures you see the result of the automatic analysis search on generic surface. The first figure show the initial state of the trial, with initial surface from which the process of search departs. The second show the final state of the analysis, with the surface gotten by the minimizing process. The initial and final safety coefficients are brought in the title and you can estimate the safety difference among the two configurations.

PRINTOUTS

Numerical Data Report
The user can select the table to print out and see the print preview. The default composition includes the introductory relationship with the legislative references and the theoretical criterions of analysis, the explanatory notes and the sheet containing data definition and numerical results. Print preview allows video reading, paper printing, report exporting as Rtf document.

Drawings Report
The drawings produced by the program can be selected and paginated, as for numerical report. The drawings are organized in paper sheets, according to the format currently selected in the active printer and in the respect of the preferences of pagination planned. The drawing sheets are visible in preview and you can print them or export in Dxf format.

Fasi Operative

Analizzando la tipica sessione di lavoro, si individuano alcune fasi operative caratteristiche.

• Definizione del pendio con l'assegnazione dei dati riguardanti i materiali, i profili stratigrafici, il profilo della falda, i carichi e gli interventi strutturali disposti su di esso.
• Definizione delle superfici di scorrimento da analizzare, assegnate singolarmente o per maglia di centri, ottimizzabili con l'analisi automatica.
• Scelta del metodo di analisi ed esecuzione della verifica di stabilità per superficie assegnata, per famiglie di superfici o con ricerca automatica.
• Valutazione dei risultati ottenuti ed eventuali riesecuzioni dell'analisi, con altro metodo o con variazione dell'assetto dei carichi, degli interventi di consolidamento, della superficie di falda, ecc.
• Stampa del tabulato di calcolo, comprensivo della relazione, dei dati di definizione e dei risultati dell'analisi. Stampa o esportazione in CAD dei disegni prodotti dal programma.