Chapter 12. Analysis of consolidation under embankment In this chapter, we are going to explain how to analyze consolidation under a constructed embankment. Introduction: Soil consolidation takes into account the settlement time (calculation of earth deformation) under the effect of external (constant or variable) loads. The surcharge leads to an increase in earth formation stress and the gradual extrusion of water from pores, i.e. soil consolidation. Primary consolidation corresponds to the situation in which there is a complete dissipation of pore pressures in soil, secondary consolidation affects rheological processes in the soil skeleton (the so called "creep effect"). This is a time-dependent process influenced by a number of factors (e.g. soil permeability and compressibility, length of drainage paths, etc.). With regards to the degree of consolidation we distinguish the following cases of ground settlement: − final settlement corresponding to 100% consolidation from the respective surcharge − partial settlement corresponding to a particular degree of consolidation from the respective surcharge Assignment: Determine the settlement value under the centre of an embankment constructed on impermeable clay one year and ten years after its construction. Make the analysis using CSN 73 1001 standards (using oedometric modulus), limit of influence zone consider using coefficient of structure strength. Scheme of the assignment - consolidation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Chapter 12. Analysis of consolidation under embankment In this chapter, we are going to explain how to analyze consolidation under a
constructed embankment.
Introduction:
Soil consolidation takes into account the settlement time (calculation of earth
deformation) under the effect of external (constant or variable) loads. The surcharge leads to
an increase in earth formation stress and the gradual extrusion of water from pores, i.e. soil
consolidation. Primary consolidation corresponds to the situation in which there is a complete
dissipation of pore pressures in soil, secondary consolidation affects rheological processes
in the soil skeleton (the so called "creep effect"). This is a time-dependent process influenced
by a number of factors (e.g. soil permeability and compressibility, length of drainage paths,
etc.). With regards to the degree of consolidation we distinguish the following cases of ground
settlement:
− final settlement corresponding to 100% consolidation from the respective
surcharge
− partial settlement corresponding to a particular degree of consolidation from
the respective surcharge
Assignment:
Determine the settlement value under the centre of an embankment constructed
on impermeable clay one year and ten years after its construction. Make the analysis using
CSN 73 1001 standards (using oedometric modulus), limit of influence zone consider using
coefficient of structure strength.
Scheme of the assignment - consolidation
Solution:
The GEO 5 – Settlement program will be used to solve this task. We are going to
model this example step by step:
− 1st construction stage – interface modelling, calculation of the initial geostatic
stress.
− 2nd construction stage – adding a surcharge by means of an embankment.
− 3rd up to 5th construction stages – calculation of embankment consolidation
at various time intervals (according to the assignment).
− Evaluation of results (conclusion).
− Basic assignment (procedure): Stage 1
Check the "Perform consolidation analysis" field in the "Settings" frame. Then select
specific settings for calculation of the settlement from "Settings list". This setting describes
the analysis method for calculation of the settlement and restriction of influence zone.
Frame "Settings"
Note: This calculation considers the so called primary consolidation (dissipation of pore
pressure). Secondary settlement (creep), which may occur mainly with non-consolidated and
organic soils, is not solved within this example.
Then we enter the layer interface. The objective is to select two layers between which
the consolidation takes place.
Frame "Interface"
Note: If there is a homogeneous soil, then in order to calculate the consolidation,
it is necessary to enter a fictitious layer (use 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 define the "Incompressible subsoil" (IS) (at a depth of 10 m) by means of
entering coordinates similarly to interface modelling. No settlement takes place under the IS.
The soil parameters are entered in the next step. For soils being consolidated, it is
required to specify either the coefficient of permeability " k " or the coefficient of
consolidation " vc ". Approximate values can be found in HELP (F1).