# General

### Group Interaction

When a pile group is exposed to lateral forces, its overall lateral resistance is typically not simply the sum of the resistances of the individual piles. In most cases, the group’s resistance is lower than that of the individual piles and depends on factors like the piles’ arrangement within the group and their spacing. These factors, P-Multipliers, can be assigned using Pile Layout library component in OpenBrIM. For more details, refer to [Pile Layout](/templates/steel-i-girder-bridge-workflow/substructure-sig/pile-sig/pile-layout-sig.md).

### Layered Soil Profile: Method of Georgiadis

In some cases, the soil profile near the ground surface consists of multiple different soil types. Under such conditions, when calculating p-y curves for different soil layers, certain modifications are required.\
The method proposed by Georgiadis \[Georgiadis, 1983] is based on determining the equivalent depths of all layers below the top layer. The p-y curves are developed based on the depth into soil, this is a critical part when generating p-y curves. To represent the depths of all layers below the top layer, the integrals of the ultimate soil resistance over depth are equated for the two layers. For example,

$$
F = \int\_{0}^{z\_1} p\_{ult1} , dz
$$

$$
F = \int\_{0}^{z\_2} p\_{ult2} , dz
$$

where **z₁** is the depth of the top layer and **z₂** is the depth of the layer below. **z₂** is found for the second layer and the same concept is applied for the layers below.

### Effect of Pile Section on Material Curves

For non-circular pile cross sections, an equivalent diameter is used by equating the cross sectional area with the area of a circle and solving for the diameter.

### Effect of Batter Angle on P-Y Curves

The batter angle factors specified in \[Kubo, 1965] is used when a batter angle is entered for a pile. Ultimate soil resistance is modified by multiplying by a factor with respect to the movement of pile head.\
The batter angle can be assigned using [Single Pile](/templates/steel-i-girder-bridge-workflow/substructure-sig/pile-sig/single-pile-sig.md) in OpenBrIM.

![Factors of Soil Resistance for Battered Piles \[Reese and Van Impe, 2011\]](https://openbrim.atlassian.net/wiki/download/attachments/3050340356/BatteredPile_Kubo1964.jpg?api=v2)

### Buoyancy

Buoyancy load must be considered for structures located below the water table elevation.

In OpenBrIM, the buoyancy load needs to be defined separately. OpenBrIM has the capability to automatically calculate the uplift force based on the submerged volume of piles, footings, and pier columns. For more details, refer to [Buoyancy](/templates/steel-i-girder-bridge-workflow/loading-sig/loads-sig/water-load-sig/buoyancy-sig.md).

### Buried Footing

Loading due to soil on the footing must be defined separately in OpenBrIM. The engineer is responsible for calculating the load applied to the footing. The [Footing Surface Load](/templates/steel-i-girder-bridge-workflow/loading-sig/loads-sig/element-loads-sig/footing-surface-load-sig.md) library component can be used to assign this loading.

***

\[Georgiadis, 1983] Georgiadis, M. (1983). Development of py curves for layered soils. In *Geotechnical practice in offshore engineering*, pages 536–545. ASCE.

\[Kubo, 1965] Kubo, K. (1965). Experimental study of the behavior of laterally loaded piles. In *Soil Mech & Fdn Eng Conf Proc/Canada/*.

\[Reese and Van Impe, 2011] Reese, L. C. and Van Impe, W. F. (2011). *Single piles and pile groups under lateral loading*. CRC Press/Balkema.


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