Pile Spring Supports

 

 

Assign the springs for the soils adjacent to piles. Lateral springs for the soils adjacent to piles are modeled as symmetric nonlinear elastic springs () and vertical springs for the soils adjacent to piles are modeled as linear elastic springs ().

The stiffness of soil springs is automatically calculated and entered into Point Spring Supports. The entered data can be checked from Point Spring Supports Table.

 

 

 

From the Main Menu select Model > Boundaries > Pile Spring Supports.

 

Select Geometry > Boundaries > Pile Spring Supports in the Menu tab of the Tree Menu.

 

 

New for V.7.6.1

 

 Pile Spring Data

Soil Type: Soil Types are classified into Sand / Soft Cray / Stiff Cray. Depending upon the selected Soil Type, stiffness calculation method will be different. Methods of calculating spring stiffness are explained at the bottom.

Ground Level: Z coordinate of ground

Pile Diameter(D)

Unit Weight of Soil(γ)

Earth Pressure Coeff. at rest(K0): Coefficient of earth pressure at reat

Coeff. of Subgrade Reaction(Kh): Modulus of subgrade reaction

Internal Friction Angle (Φ): Angle of internal friction of soil

Initial Soil Modulus(k1): Constant determined according to the relative density. Determines the stiffness of nonlinear elastic lateral springs for the soils adjacent to piles. Refer to Computation of Points k and m shown below.

The Stiffness of Nonlinear Elastic (Lateral) Springs for the Soils adjacent to Piles

 

The relationship between the lateral soil resistance and the lateral displacement Y at a specific depth X is represented as shown in the left figure.

The values of Pk, Pm, Pu, Yk, Ym and Yu are defined at a specific depth (i.e., where pile springs are).

The method of calculating Pu varies with Soil Types. The values of Pk, Pm, Yk, Ym and Yu are calculated using Pu as explained below.

The calculation method is divided into two major cases - Sand and Clay. Different J values are used for Soft Clay and Stiff Clay, respectively.

Calculation of Pu in case of Sand Soil

The value of Xt denotes the depth when the following two Pu values are equal. Make the right terms of two equations equal, rearrange the equation in terms of X and solve the quadratic equation.

 

Calculation of Pu  in case of Clay Soil

 

Computation of Points k and m

 

Spring Stiffness
 

The final spring stiffness is determined by multiplying the stiffness per unit area calculated above by the area. 

 

The Stiffness of Linear Elastic (Vertical) Springs for the Soils adjacent to Piles

The direction of the linear elastic vertical springs for the soils adjacent to piles should be perpendicular to the ground (GCS '-'Z direction). Even though the piles are not perpendicular to the ground, the z-direction (Node Local Axis) of the nodes for Piles should coincide with the GCS Z-direction.