Loadcap > About general data

The project data must be changed from the "General data" menu:

Soil type

Chose between loose soil and rock, according to the type of soil the foundations rests upon. For foundations upon rock, the program automatically adjusts the data in the "Soil stratigraphy" window (ex. RQD).

Correction of parameters

For mainly sandy soils, Terzaghi suggested applying a correction to the geotechnical parameters, namely reducing the cohesion to 2/3 and the tangent of the shearing resistance angle to 0,67·tan(φ).

Foundation system data

Enter the geometrical data relevant to the foundations according to the instructions provided in the window for geometrical data input.

Amongst other geometrical dimensions, the depth of bearing surface D compared to the natural surface level as well as the foundation soil embedment are required: if you type in both and check the “Embedded height = Bearing surface depth” option, the program will consider the D depth in the calculation of the first term of the bearing capacity (γ·D·Nq). Otherwise, the program will assign to the D variable the Embedded height value. In the presence of plans of foundations fully or partially embeded, the excessive depth of the bearing surface can lead to high values of the bearing capacity due to the high value of the term (γ·D·Nq), therefore it can be useful to perform the computation with the embedded height, by clearing the option above, and enter the actual embedded part of the foundation in the ground.

Soil stratigraphy

The geotechnical data used by the program for the calculation of the bearing capacity and settlement must be entered in the window displayed when pressing the command "Soil stratigraphy".

Notes on geotechnical parameters

Loads

The input of the loads is only necessary in order to allow the calculation of the settlements. The input of a load for the evaluation of the bearing capacity of the soil is only used to determine the safety level as a Qlim/Qd bearing capacity – design load ratio. The program calculates different load conditions, both for the bearing capacity and for settlements, to be defined in the "Loads" window.

For each condition defined, the Type must be chosen: it will be meant as a Design type for the purposes of the assessment of the safety level on the soil bearing capacity; it will be meant as a Serviceability type for the purposes of the assessment of the settlements.Each load condition must be entered under the form of "Design normal pressures" or N normal stress, moments Mx and My and shears Hx and Hy. For instance, in the case of spread footings, the availability of such stresses is more immediate than the normal design pressure. In any case, the load entered refers to the foundation bearing surface and must therefore include the weight of the foundation as well. Besides, each load condition must be assigned already amplified of possible factors on the loads.

In order to define the safety levels acceptable by the user or imposed by applied regulations, it is necessary to insert in the Vertical and Horizontal Reduction Coefficients of the Bearing Capacity. In the same box (Earthquake + Partial coeff. soil geotechnical parameters + Resistances) are also defined the partial coefficients on the geotechnical properties of the soils (c’, cu, tanj, g): these coefficients represent the Mi partial coefficients introduced by Eurocodes, which reduce the geotechnical parameters defined in "Soil stratigraphy". This type of coefficients is only considered for the load conditions belonging to Design type and not for those belonging to Serviceability type.

The seismic correction on the bearing capacity too is only referred to the load conditions concerning the bearing capacity and consequently belonging to the Design type. The values of the seismic reduction coefficients are described in the report produced in the text format ("Output" Menu > "Create report" command).

The "Generate combination" and "Assign loads" buttons shown in the window activate the number and type of combination to be adopted according to the choice of the regulations to be implemented, respectively, and assign the normal design pressure an indicative value in case this datum is not available.

Distributed Loads

These are additional loads which can be assigned to the right or left sides of the foundations in order to take into account the presence of overloads adjoining the foundations (ex. bordering buildings). Their effect is only considered as an increase in the subsurface strain for the assessment of the settlements and in the interference of the bulbs.

Calculation methods

The analytic methods for the assessment of the soil bearing capacity are the classical ones present in the geotechnical literature: Terzaghi, Vesic, Meyerhof, Hansen and Brinch-Hansen, for soils; Terzaghi and Zienkiewicz, for rocks.

Calculation

The program includes calculation controls for the bearing capacity and the settlements.

Bearing capacity: The calculation of the bearing capacity gives the results of each Design load condition entered in the "Loads" window. The control proposes once more the same window as for loads with the addition of a results chart. The user can therefore make the necessary changes both in the loads and in the coefficients without exiting the control and entering again the "Loads" window from the "General data" menu.

For each load, the safety factor is returned as a Qlim/Qass ultimate bearing capacity – assigned load ratio (design strain or pressure) and the Checked/Unchecked condition, according to whether the safety factor found is higher or not than the safety level imposed by the user in the "Loads" window.

Finally, for each author, the Winkler coefficient of subgrade reaction (ks) is calculated by means of the method proposed by Bowles:

ks = qlim/ΔH

with ΔH = 2,5 cm displacement considered as admissible.