 Design Considerations
 Initial and long term stability
 Compressibility
 Lateral ground flow
 Slope failure
 Differential settlements
 Reduction of bearing capacity
 Improvement methods
 Solution

Softground is very compressible deposits such as Clay, silty Clay,clayey Silt. Because these kinds of deposit have very low permeability , waterlevel is generally located on the ground surface. And if constructing the embankment over the soft ground or excavating some area, it can result in lots of settlement or failure of the ground.
But, these days, we have to construct embankment over these soft ground due to the lack of suitable land for infrastructures and other developments. So, we have to make a decision for optimized improvement method. GTS NX calculates timedependent consolidation settlement through staged consolidation analysis. Staged fully coupled analysis can be performed in the same sequence as field construction and it is possible to set actual time durations to the modeled stages so can reflects changes in excessive pore water pressure and water level in real time. In addition, the integration capabilities in GTS NX allow for a wide range of stability analyses such as embankment slope, adjacent structures and the interaction of reinforcements and soil materials.

Consolidation analysis is an analytical method that calculates the behavior of pore water pressure when it resists external loading, when excess pore water pressure occurs and as the excess pore water pressure reduces with time for an undrained condition.
Pore water pressure in the ground with a small osmotic coefficient instantaneously displays the same behavior as the undrained condition. Hence, it bears most of the compressive load by the created excess pore water pressure, according to the change in load state. However, as time goes by, excess pore water pressure is redistributed and if there is a drainage boundary, the excess pore water pressure decreases gradually.
Because of this, the load previously resisted by the excess pore water pressure is gradually resisted by the soil frame, causing gradual deformation of the soil frame and increasing effective stress within the frame. The increase in effective stress leads to the deformation of soil structure and this deformation is accumulated in the gravitational direction, eventually displaying settlement behavior in the gravitational direction with time elapse.
This gradual increase in deformation creates settlement at the base of structural foundation and differential settlement at the base foundation greatly affects the stability and safety of the structure.

Slope stability for an embankment or excavation is one of the most frequently dealt problems in geotechnical engineering. The slope always has a selfweight potential energy due to gravity and if external forces such as pore water pressure, applied load, earthquake, wave force etc. act on the slope, its stability is greatly affected.
Here, slope failure can occur if the internal shear stress due to the selfweight and external forces is greater than the shear strength of the slope soil. Calculating the safety for this slope failure due to shear stress and shear force is called Slope stability analysis.
The following slope stability analysis methods can be used on the GTS NX.

Strength Reduction Method (SRM): Nonlinear FEMcoupled strength reduction method

Stress Analysis Method (SAM): Method based on Nonlinear FEM and limit equilibrium theory

Strength Reduction Method (SRM)
Slope stability analysis using the finite element method is a numerical analysis method that analyzes the minimum safety factor and failure behavior using various shapes, loads and boundary conditions. In particular, the strength reduction method can be used to simulate the failure process without any previous assumptions(Griffith et. al. 1999; Matsui, 1990).
It can also be applied to 3D axis symmetric problems.
The strength reduction method gradually decreases the shear strength and friction angle until the calculation does not converge, and that point is considered to be the failure point of the slope. The maximum strength reduction ratio at that point is used to calculate the minimum safety factor of the slope.
Stress Analysis Method based on limit equilibrium theory (SAM)
This method first uses the finite element method to perform stress analysis on the slope and the safety factor for each various virtual slip surface, created from the assumptions of the limit equilibrium theory, is calculated based on the stress analysis results. Here, the calculated minimum safety factor of the various virtual slip surfaces becomes the safety factor, and the critical section is computed. The SAM method can only be used on the 2D environment.

Construction stage analysis can be used to simulate the construction process of the ground using numerical analysis. Construction stage analysis consists of multiple stages and loading/ boundary conditions, as well as elements, can be added or removed at each stage. This loading/ boundary or element change is applied at the start of each stage. GTS NX can use following types of analysis features to conduct Construction stage analysis.
StressSlope Analysis
Analysis of stress and slope stability during the construction process
Seepage Analysis
Stage by stage Steady state seepage analysis, Stage by stage Transient seepage analysis
StressSeepageSlope coupled analysis
Sequential Seepagestress analysis and Slope stability analysis during the construction process
Consolidation analysis
Consolidation analysis for environment change and construction process of embankment
Fullycoupled StressSeepage analysis
Stress analysis fully coupled with Transient seepage phenomenon
When conducting Construction stage analysis, the following should be considered.
 Addition/Removal of element
 Loading/Unloading of weight
 Change in boundary condition
 Change in rock material property
 Definition of load distribution factor
 Step by step underground water level
 DrainedUndrained analysis
 Initialization of displacement
 Stress Analysis for initial construction stage (Consider Ko condition)
 Restart

Analysis that couples the seepage phenomenon and ground stress analysis can be classified in various ways, depending on the coupling.
The simplest way is to obtain the pore water pressure distribution by conducting seepage analysis beforehand, and reflecting it in the total stress/effective stress relationship equation of the stress analysis conducted in the following step. Such analysis is called sequential analysis. This method can be used to understand the static stress state of the given steady groundwater flow. However, since deformation due to stress analysis does not influence the seepage phenomenon inversely, there is no twoway coupling.
Fullycoupled StressSeepage analysis is the twoway coupled analysis between seepage analysis and stress analysis. Both analyses are used to solve the coupled equation. It can display the pore water pressure, stress or deformation changes with time.
The consolidation analysis begins with the assumption that steady state pore water pressure can be maintained, and is used to see the changes in excess pore water pressure. In other words, this analysis is used to simulate the phenomenon of how excess pore water pressure changes with the changes in load/boundary conditions.
Fullycoupled StressSeepage analysis does not follow assumption that steady state pore water pressure is maintained. Hence, it is suitable for simulating the transient seepage phenomenon, stress analysis and stability in abnormal condition in a fully coupled form. Unlike the consolidation analysis, it is possible to define the changes in seepage boundary conditions with time, boundary flow rate etc. In other words, for Fullycoupled StressSeepage analysis, it is possible to use all the transient seepage boundary conditions, structural load and boundary conditions.
This analysis can be applied to the ground stability analysis for rainfall or the of largescale dam stability analysis for water level change. The seepage boundary conditions (Head/Flux) can all be used to analyze not only the changes in excess pore water pressure, but also the consolidation analysis that considers the total change in pore water pressure.