Observations/Finding

At the request of the client’s representative, our AS ENGINEERING AND CONSULTING, LLC (ASEC) representative visited the job site to observe the contractor’s work activities from a quality standpoint to verify compliance with project drawings/specifications, applicable codes, and materials submittals and conducted QC testing per the project drawings and specifications.  The following observations were made during our evaluation:

Project: Hawthorne Reserve (185 Old Griffin Road, Dallas, GA)
Objective: Perform Dynamic Cone Penetrometer (DCP) testing to evaluate soil bearing pressures and assess rock depths for four (4) proposed above ground sewer line pier locations.

Testing Procedure:

• Hand auguring followed by Dynamic Cone Penetrometer (DCP) was used to measure soil bearing pressures.
• Auguring was conducted for 4 independent test holes, three of which were marked with stakes and green ribbon by the contractor.  The fourth location would have been in the adjacent creek and was moved to several feet from the creek’s edge.

Test Results:

Test Hole #1 (Most West Pier):

• Depth: 1 ft – Light brown silty sand.  DCP = 20 blows (most likely elevated due to the presence of underlying gravel in the soil matrix).
• 2nd Foot: Auger refusal (suspected due to encountering small rocks).
• Auger Refusal @ 2′

Test Hole #2 (Next Pier Inline):

• Initial and Offset Attempts: Auger refusal less than 1 foot in both cases (suspected due to encountering small rocks).
• Auger Refusal @ less than 1′

Test Hole #3:

• 1st Foot: Light brown silty sand. Light brown silty sand.  DCP = 14 blows.
• 2nd Foot: Light brown silty sand.  DCP = 8 blows.
• 3rd Foot: Moist Grey silty clay.  DCP = 20 blows (most likely elevated blow counts due to underlying gravel in the soil matrix).
• 4th Foot: Moist Grey silty clay, auger refusal due to rock material.
• Auger Refusal @ 4′
• No water intrusion observed after 30 minutes.

Test Hole #4 (Most east, adjacent to the creek):

• Note: Test location augured 5 feet west from the intended location (which would have been in the creek).
• 1st Foot: Light brown silty sand.  DCP = 10 blows.
• 2nd Foot: Wet dark brown sandy clay. DCP = 3 blows.
• 3rd and 4th Feet: Wet dark brown sandy clay.  DCP = 10 blows.  Note that water seeping into the test location occurred almost immediately.
• 5th Foot: Immediate auger refusal (small rocks suspected).
• Auger Refusal @ 5′

Observations and Concerns:

• It is our understanding that based on county specifications, the footings (piers) for this utility line must be embedded at least 5 feet below grade.  Based on the results of hand auger/dynamic cone penetrometer readings, at least two of the piers will not be able to be placed at the specified depth (but see below).

Recommendations:

• Hand auguring within rocky soils (soils with small rock/gravel embedded within the soil matrix) will often hit refusal on these materials.  We recommend that test pit excavations be performed to verify the required footing minimum depth of 5 feet without rock refusal.

Location of Hole #4 is shown by auger inside silt fence, 5 feet from center of creek (and Pier location).

Rock mixed in soil

Rock mixed in soil causing Auger refusal.

Photo of creek and auger locations, facing west.

Section cleared containing 3 of the 4 future pier locations.