5. Soil Deformation

Chapter 1) What Is soil Deformation? 

• Introduction to soil deformation.  
• Detailed discussion on Immediate settlement.  
• method of numerical solution for the soil deformation  

Chapter 2) Example 

• Modelling, boundary condition setting, applying load using Midas GTS NX software to simulate the settlement of the continuous foundation installed on the elastic ground. 
• analysis and see the results for the same. 

Chapter 3) Comparison of results.  

• Compare the results with those obtained manually and using the program.

Summary

When a load is applied to the ground, deformation occurs. One of the typical ground deformation problems related to the ground is settlement of structures.
The magnitude and shape of ground deformation are generally controlled by the relative stiffness of the ground and the structure, as shown in Figure 5.1(a).

Generally, ground deformation (settlement) is divided into immediate settlement and long-term settlement.

Immediate settlement refers to elastic settlement caused by the induced load, while long-term settlement is the result of time-dependent behavior such as compression and creep.

Total settlement (𝑆t) of soil = Immediate settlement (𝑆𝑖) + Consolidation settlement (𝑆𝑐)

1. Immediate settlement (elastic settlement)

(1) Immediate Settlement Theory

When the induced stresses are ∆𝜎𝑥, ∆𝜎𝑦, and ∆𝜎𝑧 respectively, the normal strain is:

Since the settlement is the integration of the vertical strain with respect to depth, it can be expressed as follows.

In the case of multi-layer ground, the sum of settlements for each layer can be expressed as follows.

2. Immediate Settlement in Numerical Analysis

The immediate settlement proceeds with numerical analysis based on the theory of elasticity.

Therefore, it corresponds to the linear numerical analysis discussed in Chapter 2.

The vector relationship between displacement and load can be expressed as a system equation as follows. ([𝐾𝐺]: ground behavior properties, [𝑅𝐺]: load, [𝑢𝐺]: displacement)

The numerical analysis process is as follows.

(1)Modeling

In order to model theoretical analysis conditions with numerical analysis, the same analysis conditions must be assumed.
However, since the theoretical analysis assumes a semi-infinite elastic body, in order to model the semi-infinite body as a finite region, the model boundary must be sufficiently separated from the load so that the boundary condition does not affect the result.

If it can be considered that there is sufficient length for a single section to be continuous, it is possible to model 2D plane deformation.
In the case of axisymmetric structures such as circular foundations, it is possible to model 2D axisymmetric deformation.

(2) Ground modeling

Since the elasticity theory can be applied to obtain the immediate settlement, a linear isotropic elastic model is used, and the necessary properties for this are the elastic modulus and Poisson's ratio.

(3) Initial conditions and boundary conditions

The initial stress state is implemented using unit weight and horizontal stress coefficients (assuming horizontal ground).
The boundary of the model is selected far enough from the load application point so that the boundary conditions do not affect the analysis results.

(4) Load modeling

The elastic analysis is performed by applying a load at once.