Settlement
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Engineering manual No. 11 Updated: 06/2018 Analysis of a consolidation under embankment Program: In this engineering manual, we are going to explain how to analyze a consolidation under a constructed embankment. Introduction Soil consolidation considers the settlement time (calculation of earth deformation) under the effect of external (constant or variable) loads. The surcharge leads to an increase in the earth formation stress and the gradual extrusion of water from pores, i.e. soil consolidation. Primary consolidation corresponds to a situation, in which there is a complete dissipation of pore pressures in soil; secondary consolidation affects the rheological processes in the soil skeleton (the so called "creep effect"). This is a time-dependent process influenced by many factors (e.g. soil permeability and compressibility, length of the drainage paths, etc.). With regards to the degree of the consolidation we distinguish the following cases of ground settlement: − final settlement corresponding to a 100% consolidation from the respective surcharge partial settlement corresponding to a given degree of consolidation from the respective surcharge In order to calculate settlement time, it is necessary to specify the coefficient of permeability " k " or coefficient of consolidation " v ", which determines the speed of consolidation. This parameter can be obtained on the basis of oedometer tests (according to Casagrande or Taylor).

Assignment Determine the settlement value under the center of an embankment constructed on impermeable clay one year and ten years after its construction. Perform the analysis using CSN 73 1001 standards (using oedometric modulus), consider the limit of the influence zone using the coefficient of the structure strength. Scheme of the assignment – consolidation Solution We will use the GEO 5 Settlement program to solve this task. We are going to model this example step by step: − 1st construction stage – interface modeling, calculation of the initial geostatic stress, 2nd construction stage...

Stage 1 First of all, check the "Perform consolidation analysis" checkbox in bottom right corner of the "Settings" frame. Then click on "Select settings" and choose setting No. 8 "Czech republic - old standards CSN". This setting describes the analysis method for calculation of the settlement and the restriction of the influence zone. Analysis settings : Czech republic - old standards CSN (73 1001, 73 1002, 73 0037) Analysis method : Analysis using oedometric modulus Restriction of influence zone : based on structural strength Frame "Settings" Note: This calculation considers the so-called...

Adding interface 2 Note: If there is a homogenous soil, then to calculate the consolidation, it is necessary to enter a fictitious layer (using the same parameters for the two soil layers that are separated by the original interface), preferably at the depth of the deformation zone. Then we’ll move to the frame "Incompressible subsoil", where we’ll input a new incompressible subsoil at a depth of 10 m using the “input incompressible subsoil” button and adding the subsoil points in a similar way that interface points are inputted . No settlement takes place under the incompressible subsoil.

In the next step, open the frame "Soils", where soil parameters are entered. For soils, which are consolidated, it is required to specify either the coefficient of permeability " k" or the coefficient of consolidation " cv ". Approximate values can be found in the program help (F1). Table with the soil parameters Then move to the frame "Assignment", where we assign the soils to the profile as follows: Interface £3 Incompressible subsoil 0 Soils Surcharge =Water Qp) Stage settings Assigned soil Assignment by left-dick Sandy slit |Er| List of pictures Frame "Assignment"

The frame “Surcharge” is not taken into consideration in the 1st construction stage, since in this example it will be represented by the actual embankment body (in stages 2 to 5). In the next step, open the frame “Water”, where we enter the ground water table (hereinafter the "GWT") by adding the interface points textually, in our case at the ground level. GWT input In the frame “Stage settings”, you can only modify the layout and the refinement of the holes. In this case, we will leave the standard settings on.

The first stage represents the geostatic stress at the initial construction time. However, it is necessary to specify the basic boundary conditions for the consolidation calculation in further stages. Input the top and bottom interface of the consolidating soil as well as the direction of the water flow from this layer – i.e. the drainage path. "Analysis" settings – Construction stage 1 Stages 2 to 5 Let's now add the 2nd construction stage using the tool bar at the top of the screen. Toolbar “Construction stage

In the second stage, we will define the embankment by entering the coordinates of its points in the "Embankment" frame: - Point No. 1: x =-10,0 m z = 0,0 m Then move on to the frame "Assign", where the "Embankment" soil type is assigned to the embankment. Embankment £j\ Earth cut 5 Assign iff- Surcharge Assignment by left-dick Clayey soil Soil assignment is the same as in the previous stage. Soils and assi... : 0 Total: 0 [IP1 List of pictures "Stage 2 - Embankment + Assignment” Note: The embankment acts as a surcharge to the original ground surface. It is assumed that a well-executed...

Consolidation I Overall settlement Load action : ^oa^ineaH^nc^asin^unn^h^tog^uration^ Time of stage duration : 30,0 [day] Analysis of consolidation can be done, only if there is 'Overall settlement' selected in any stage of construction. Analysis has not been performed. Analysis Total: Frame "Analysis - Construction Stage 2" Add 3 more stages. In the subsequent stages, enter the duration of each stage: - 3rd stage - 1 year i.e. 365 days - 4th stage - 10 years i.e. 3,650 days - 5th stage - the overall settlement The load action is not important in this case (there is no new surcharge added...