> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/truss-bridge-workflow/substructure-tb/soil-structure-interaction-tb/soil-layer-tb.md). # Soil Layer \[TB] 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/Sand (O'Neill)=3/Hybrid Liquefied Sand (Franke and Rollins)=4/c-phi Soil=5/Linear (Subgrade)=6/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/Soft Clay (API)=3/Loess (Johnson)=4/Linear (Subgrade)=5/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/Limestone Uncoupled (McVay)=3/Massive Rock (Liang)=4/Linear (Subgrade)=5/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 (cohesion) of the soil, used for the clay models (Soft Clay (Matlock), Soft Clay (API), Stiff Clay with/without Free Water) and as the cohesion of the c-phi Soil model. **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 the clay models, Soft Clay (API) and Hybrid Liquefied Sand. **Internal Friction Angle:** The internal friction angle of the soil, used for the sand models (Sand (Reese), Sand (API), Sand (O'Neill)) and c-phi Soil. **Subgrade Modulus:** The modulus of subgrade reaction, used for Sand (Reese), Sand (API), Sand (O'Neill), c-phi Soil, Linear (Subgrade) and Stiff Clay with Free Water models. **Residual Shear Strength:** The residual (post-liquefaction) shear strength of the liquefied soil, used for the Hybrid Liquefied Sand model. **Empirical Constant J:** The dimensionless constant of the API soft-clay ultimate resistance, 0.25 to 0.5 (0.5 for Gulf of Mexico clays), used for the Soft Clay (API) model. **CPT Cone Tip Resistance:** The cone penetration test tip resistance, used for the Loess (Johnson) model. **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, Limestone, Limestone Uncoupled and Massive Rock models. **Rock Quality Designation (RQD) %:** The Rock Quality Designation as a percentage, used for Weak Rock (Reese) model. **Poisson's Ratio of Rock Mass, Geological Strength Index (GSI), Hoek-Brown Constant of Intact Rock (m\_i), Intact Rock Modulus:** The rock-mass parameters of the Massive Rock (Liang) model; the pile section stiffness it also needs is taken from the pile. For theoretical details about the models, refer to [Lateral Soil Models](https://github.com/openbrim/platform/blob/master/technical-background/soil-structure-interaction/general.md). ## **Axial:** **Model (Cohesionless) \[Driven Pile (McVay)=0/Drilled Shaft Sand (Reese and O'Neill)=1/Driven Pile Sand (Mosher)=2/Driven Pile Sand (API)=3/Drilled Shaft Gravelly Sand (Rollins)=4/Drilled Shaft Gravel (Rollins)=5/Drilled Shaft IGM Non-Cohesive (Mayne and Harris)=6/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/Driven Pile Clay (Coyle and Reese)=2/Driven Pile Clay (API)=3/Drilled Shaft Clay-Shale (Aurora and Reese)=4/Drilled Shaft IGM Cohesive (O'Neill)=5/Custom T-Z=99]:** Specify the axial soil model for cohesive soils. **Model (Rock) \[Driven Pile (McVay)=0/Drilled Shaft Limestone (McVay)=1/Drilled Shaft IGM Cohesive (O'Neill)=2/Drilled Shaft IGM Non-Cohesive (Mayne and Harris)=3/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 the Driven Pile (McVay), Driven Pile Sand (Mosher), Driven Pile Clay (Coyle and Reese) and Drilled Shaft Limestone (McVay) models. **Undrained Shear Strength:** The undrained shear strength of the clay, used for the Drilled Shaft Clay (Reese and O'Neill), Driven Pile Clay (API) and Drilled Shaft Clay-Shale models. **Initial Modulus of Side Resistance (K\_t):** The initial slope of the Mosher side-resistance curve (6000–18000 lb/ft²/in by relative density). **Internal Friction Angle, Coefficient of Lateral Earth Pressure, Nominal Unit Skin Friction, Displacement at Nominal Unit Skin Friction:** The parameters of the Driven Pile Sand (API) model, the same four as the FB-MultiPier dialog. A nominal unit skin friction above 0 is the ultimate unit skin friction of the curve itself, and the friction angle and K are then not used (this is how FB-MultiPier treats the field; it is neither a cap nor a floor). With 0, where FB-MultiPier returns no side resistance at all, the skin friction is instead computed by API RP 2GEO, f = β p'0 limited to f\_lim, where β = K tan δ with δ = φ − 5° (K = 0.8 for open-ended unplugged piles, 1.0 for full-displacement piles; at K = 0.8 and φ = 25° / 30° / 35° / 40° this gives the tabulated β = 0.29 / 0.37 / 0.46 / 0.56) and f\_lim is read from the same table through the friction angle (1.4 / 1.7 / 2.0 / 2.4 kips/ft², interpolated linearly). The displacement at nominal unit skin friction is the z\_peak of the RP 2GEO t-z table, 0.25 % to 2 % of the pile diameter; 0 = 1 % of the pile diameter. **Shaft Friction Factor beta, Load Transfer Trend Line \[Lower=0/Average=1/Upper=2]:** The β factor of the Rollins gravelly sand and gravel models (0 computes it from depth) and the fitted trend line to use. **Residual to Peak Adhesion Ratio:** The residual skin friction of the Driven Pile Clay (API) curve as a fraction of the peak, 0.70 to 0.90 (0.90 by default; 0 is read as 0.90). It is reached at twice the displacement of the peak and held beyond. The Driven Pile Clay (API) model also reads the Displacement at Nominal Unit Skin Friction above as the displacement of its peak; 0 = 1 % of the pile diameter, which is the value FB-MultiPier fixes for this model. **Shear Strength Reduction Factor alpha:** The α of the Drilled Shaft Clay-Shale model, 0.5 for the slurry or casing method and 0.75 for the dry method. **Unconfined Compressive Strength of IGM, Mass Modulus of IGM (Socket), Mass to Intact Modulus Ratio, Borehole Wall \[Smooth=0/Rough=1], Split Tensile Strength of IGM, Unit Weight of Shaft Concrete, Concrete Slump, Characteristic Parameter n (Smooth Socket), Side Resistance Factor alpha (Smooth Socket):** The parameters of the Drilled Shaft IGM Cohesive model (O'Neill et al., 1996, Model 1); the socket length and the concrete modulus are taken from the pile. **SPT Blow Count N60, Poisson's Ratio of IGM, Drilled Under Slurry \[No=0/Yes=1], Side to Base Modulus Ratio (E\_sL/E\_b):** The parameters of the Drilled Shaft IGM Non-Cohesive model (Mayne and Harris, 1993); the socket length and the shaft modulus are taken from the pile. 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/Driven Pile Sand (Mosher)=3/Driven Pile Sand (API)=4/Drilled Shaft Gravelly Sand and Gravel=5/Driven Pile Clay (Skempton)=6/Driven Pile Clay (API)=7/Drilled Shaft Clay-Shale (Aurora and Reese)=8/Drilled Shaft IGM Cohesive (O'Neill)=9/Drilled Shaft IGM Non-Cohesive (Mayne and Harris)=10/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. **The 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 the Drilled Shaft Sand (Reese and O'Neill) and Drilled Shaft Gravelly Sand and Gravel tip models. **Undrained Shear Strength:** The undrained shear strength of the clay at the pile tip, used for the Drilled Shaft Clay (Reese and O'Neill), Driven Pile Clay (Skempton), Driven Pile Clay (API) and Drilled Shaft Clay-Shale tip models. **Ultimate Unit End Bearing, Critical Tip Displacement, Tip Curve Exponent n:** The parameters of the Driven Pile Sand (Mosher) tip curve (Vijayvergiya, 1977): 0.25 in and 1/3 by default. **Internal Friction Angle, Nominal Unit End Bearing, Bearing Capacity Factor N\_q:** The parameters of the Driven Pile Sand (API) tip model, the same three as the FB-MultiPier dialog. The unit end bearing is q = N\_q p'0 limited to the nominal unit end bearing (0 = no limit). A bearing capacity factor above 0 is used as entered (12 to 50 in the API RP 2GEO design parameter table); with 0 it is read from that table through the friction angle (8 / 12 / 20 / 40 / 50 at φ = 20° / 25° / 30° / 35° / 40°, interpolated linearly), and the friction angle is used only in that case. **Major Principal Strain at 50% (Tip), Displacement Exponent n:** The parameters of the Driven Pile Clay (Skempton) tip curve (n = 0.5 for clays). **Bearing Capacity Factor N\_c:** The N\_c of the Drilled Shaft Clay-Shale tip model, 7 for the slurry displacement method and 8 for the casing or dry method. **Mass Modulus of IGM below the Tip:** The mass modulus of the bearing IGM for the Drilled Shaft IGM Cohesive tip model; the socket modulus, socket length and concrete modulus are shared with the side-resistance model. For theoretical details about the models, [Axial QZ Soil Models](https://github.com/openbrim/platform/blob/master/technical-background/soil-structure-interaction/general.md). ## **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://github.com/openbrim/platform/blob/master/technical-background/soil-structure-interaction/general.md). --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. 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