Problem Statement

You are a civil engineer tasked with designing the foundation for a bridge pier. The site investigation includes a detailed boring log$,$ providing essential information about the soil profile at the location of the said bridge pier. The objective of the foundation system design is to ensure a safe transfer of vertical loads from the bridge pier to the underlying soil for a given load case considering both strength and service limit states.

Notes

This problem intends to assess your ability to think through a design problem for a foundation based on typically available information. Accordingly, your answers should be structured to clearly convey your thought process and your ability to apply your knowledge to the problem at hand. Attempt all questions.

Clearly state every assumption made in your analysis and design. Justify your decisions with sound engineering principles and calculations.

Data Provided

Boring Log:

Depth and description of soil layers, and depth of groundwater table.

Results for SPTs$,$ Atterberg limits$,$ and moisture content tests.

Lab reports for two single$-$point unconsolidated undrained $($UU$)$ shear strength tests for undisturbed samples collected from the clay layers.

Pier vertical load $($compression$)$: Nominal load $=380$ kips; Ultimate load $=532$ kips $.$

Requirements

Based on the location of the project $($approximately$,15$ miles north of Richmond, VA; see coordinates on the boring log$),$ discuss if the following aspects need to be considered in the foundation design.

a$.$ Potential earthquake hazard. Provide an estimate for the peak ground acceleration $($PGA$)$ at top of bedrock at the site location for $1000-$year return period.

b$.$ Potential landslide hazard.

c$.$ Potential frost depth. Provide an estimate for the frost depth at the site location.

d$.$ Potential presence of problematic geologic units $($e$.$g$.,$ expansive soils, collapsible soils, karst$).$

Propose a suitable foundation type$($s$)$ based on the site conditions, structure type, and superstructure loads. Justify your choice.

If you opt to use drilled shafts, select appropriate depths for the shaft head and tip. Justify your selections.

Provide a sketch of a simplified soil profile to use in the design of the drilled shafts.

Estimate the soil parameters that you will use for every layer to design the drilled shafts. Show steps, discuss the data, methods, and references you used to develop these estimates.

Choose an appropriate shaft cross$-$section size and estimate the required number of shafts to support the vertical pier load.

Choose an arrangement for the shafts and specify appropriate spacings between the shafts and appropriate dimensions for the pile cap.

Estimate the settlement of the individual shaft and shaft group after load application.