# Soil Layer \[STG]

The Soil Layer definition is used to specify the characteristics of the soil. Various models are available in OpenBrIM.

Regarding soil models, note that when a soil model is selected, only the necessary parameters for that model are displayed to the engineer.

## **General:**

**Soil Type \[Cohesionless=0/Cohesive=1/Rock=2]:** Specify the soil type. Avaliable Soil Models are filtered according to the Soil Type.

**Unit Weight:** Specify the unit weight of the soil.

**Top of Layer Elevation:** This parameter specifies the global elevation of top layer of the soil.

**Bottom of Layer Elevation:** This parameter specifies the global elevation of bottom layer of the soil.

## **Lateral:**

**Model (Cohesionless) \[Sand (Reese)=0/Sand (API)=1/Liquefied Sand (Rollins)=2/Custom P-Y=99]:** Specify the lateral soil model for cohesionless soils.

**Model (Cohesive) \[Soft Clay (Matlock)=0/Stiff Clay without Free Water (Welch and Reese)=1/Stiff Clay with Free Water (Reese)=2/Custom P-Y=99]:** Specify the lateral soil model for cohesive soils.

**Model (Rock) \[Weak Rock (Reese)=0/Strong Rock (Turner)=1/Limestone (McVay)=2/Custom P-Y=99]:** Specify the lateral soil model for rock.

**Custom P-Y:** When Custom P-Y model is selected, define the custom P-Y curve data points. The first point must be \[0,0], all values must be positive, and at least three points are required.

**Undrained Shear Strength:** The undrained shear strength of the soil, used for clay models (Matlock Soft Clay, Stiff Clay with/without Free Water).

**Average Undrained Shear Strength:** The average undrained shear strength over the depth, used for Stiff Clay models.

**Major Principal Strain at 50%:** The strain at 50% of the maximum principal stress difference, used for clay models.

**Internal Friction Angle:** The internal friction angle of the soil, used for sand models (Reese Sand, API Sand).

**Subgrade Modulus:** The modulus of subgrade reaction, used for Sand (Reese), Sand (API), and Stiff Clay with Free Water models.

**Mass Modulus:** The initial mass modulus of the rock, used for Weak Rock (Reese) model.

**Stiffness Constant (k\_rm):** A dimensionless constant relating rock mass modulus to intact rock modulus, used for Weak Rock (Reese) model.

**Unconfined Compressive Strength:** The unconfined compressive strength of the rock, used for Weak Rock, Strong Rock, and Limestone models.

**Rock Quality Designation (RQD) %:** The Rock Quality Designation as a percentage, used for Weak Rock (Reese) model.

For theoretical details about the models, refer to [Lateral Soil Models](https://docs.openbrim.org/technical-background/soil-structure-interaction/general).

## **Axial:**

**Model (Cohesionless) \[Driven Pile (McVay)=0/Drilled Shaft Sand (Reese and O'Neill)=1/Custom T-Z=99]:** Specify the axial soil model for cohesionless soils.

**Model (Cohesive) \[Driven Pile (McVay)=0/Drilled Shaft Clay (Reese and O'Neill)=1/Custom T-Z=99]:** Specify the axial soil model for cohesive soils.

**Model (Rock) \[Driven Pile (McVay)=0/Custom T-Z=99]:** Specify the axial soil model for rock.

**Custom T-Z:** When Custom T-Z model is selected, define the custom T-Z curve data points. The first point must be \[0,0], all values must be positive, and at least three points are required.

**Poisson's Ratio of Soil:** The Poisson's ratio of the soil, used for Driven Pile (McVay) model.

**Shear Modulus:** The shear modulus of the soil, used for Driven Pile (McVay) model.

**The ultimate shear stress (Skin friction):** The ultimate unit skin friction resistance along the pile shaft, used for Driven Pile (McVay) model.

**Undrained Shear Strength:** The undrained shear strength of the clay, used for Drilled Shaft Clay (Reese and O'Neill) model.

For theoretical details about the models, refer to [Axial TZ Soil Models](https://openbrim.atlassian.net/wiki/spaces/OBrIM/pages/3049685025/Axial+TZ+Curves).

## **Tip:**

**Model \[Driven Pile (McVay)=0/Drilled Shaft Sand (Reese and O'Neill)=1/Drilled Shaft Clay (Reese and O'Neill)=2/Custom Q-Z=99]:** Specify the appropriate model according to the definition of the soil material.

**Custom Q-Z:** When Custom Q-Z model is selected, define the custom Q-Z curve data points. The first point must be \[0,0], all values must be positive, and at least three points are required.

**Poisson's Ratio of Soil:** The Poisson's ratio of the soil, used for Driven Pile (McVay) tip model.

**Shear Modulus:** The shear modulus of the soil, used for Driven Pile (McVay) tip model.

**Ultimate Tip Resistance:** The ultimate unit tip resistance at the pile base, used for Driven Pile (McVay) model.

**Uncorrected SPT N:** The uncorrected Standard Penetration Test (SPT) blow count, used for Drilled Shaft Sand (Reese and O'Neill) tip model.

**Undrained Shear Strength:** The undrained shear strength of the clay at the pile tip, used for Drilled Shaft Clay (Reese and O'Neill) tip model.

For theoretical details about the models, [Axial QZ Soil Models](https://docs.openbrim.org/technical-background/soil-structure-interaction/general).

## **Torsional:**

**Model \[Hyperbolic Curve=0/Custom T-θ=99]:** Specify the appropriate model according to the definition of the soil material.

**Custom T-θ:** When Custom T-θ model is selected, define the custom torque-rotation curve data points. The first point must be \[0,0], all values must be positive, and at least three points are required.

**Shear Modulus:** The shear modulus of the soil, used for Hyperbolic Curve torsional model.

**Torsional Shear Stress:** The ultimate torsional shear stress at the soil-pile interface, used for Hyperbolic Curve torsional model.

{% hint style="info" %}
About **Custom Models**:

* The first point must be **\[0,0]**.
* All other points must have only positive values.
* At least three points must be entered.
  {% endhint %}

For theoretical details about the models, [Torsional Soil Models](https://docs.openbrim.org/technical-background/soil-structure-interaction/general).