18111DVAMCPETCTGeotechAddendumNo1.pdf

S&ME, Inc. | 862 East Crescentville Road | Cincinnati, OH 45246 | p 513.771.8471 | www.smeinc.com

March 16, 2020

CBLH Design, Inc.

7850 Freeway Circle

Cleveland, Ohio 44130

Attention: Mr. Jae Duk Cho, AIA NCARB jcho@cblhdesign.com

Reference: Geotechnical Addendum No. 1

Dayton VAMC PET/CT Addition

Dayton, Ohio

S&ME Project No. 1178-20-007

Dear Mr. Cho:

In accordance with your request S&ME is submitting an addendum to our report for the above referenced site.

S&ME previously completed a Geotechnical Exploration and submitted our recommendations in a report dated

February 28, 2020. This Geotechnical Addendum supersedes our Geotechnical Exploration for this building addition.

S&ME provided two alternatives for foundation and floor slab support in regards to the existing fill material encountered in each of the boring (except B-201) in our Geotechnical Exploration report: 1) Remove any existing fill and buried topsoil to expose the natural soils and backfill up to the proposed building pad subgrade exploration in a controlled manner, or 2) Leave the existing fil in place for support of the foundations and floor slab if the subgrade is deemed suitable via a favorable proofroll. This option has the potential risk of differential settlement of foundations and a floor slab supported on fill that may not have been controlled.

After receiving and reviewing our geotechnical explorations report, we were informed the Dayton VA does not have a record of the existing fill. CBLH did not want to overexcavate the existing fill material due to the proximity to the existing MRI Building (Alternative #1) and the Dayton VA was not willing to accept the risk associated with the potential differential settlement of Alternative #2.

Based on the response from the Dayton VA and the request of CBLH for a deep foundation alternative, S&ME is providing the following foundation support alternative.

Drilled Shaft Foundations

As an alternative to complete removal and replacement of the existing fill material or accepting the potential risk for differential settlement, CBLH can support the proposed building addition on drilled shafts bearing on bedrock.

S&ME recommends that the drilled shafts penetrate the existing fill and extend to bear on bedrock. However, the minimum shaft depth should extend at least 10 feet below the finished floor elevation. We anticipate that the drilled shafts will bear at approximate elevation 950 based on the depth to rock encountered in our borings.

Geotechnical Addendum No. 1

Dayton VAMC PET/CT Addition

Dayton, Ohio

S&ME Project No. 1178-20-007

March 16, 2020 2

However, the actual shaft length must be determined in the field based on the encountered conditions. We did not encounter bedrock in boring B-204 but anticipate the elevation of the top of bedrock is similar across the project site. We recommend that loose soil and groundwater be removed from the shaft excavation prior to placement of structural concrete. The structural concrete should be placed the same day as the excavation. Drilled shafts having a minimum diameter of 2.0 feet and constructed in accordance with the recommendations contained herein, may be proportioned based on an allowable end bearing pressure of up to 8,000 psf. Drilled shafts should have a minimum length of 3 times the diameter (3D) and have a minimum spacing of 3D with respect to new and existing drilled shafts. Drilled shafts designed in accordance with these recommendations should have a factor of safety of at least 3 with respect to shearing strength.

Because of the presence of the variable existing fill soil at this site, it is recommended that the contractor be prepared to case the drilled shafts if caving conditions are encountered. If it is intended to fully reinforce the shafts, provisions will need to be made to enable, either, lengthening or shortening of the reinforcing cages to be performed as required on site so that the cages are capable of reaching the shaft bottom. A S&ME representative should be retained to observe the shaft installation to document that proper installation procedures are being followed and to observe that the required bearing conditions are present at the bottom of each drilled shaft.

S&ME recommends that the structural engineer design the drilled shafts in accordance with these recommendations.

Drilled Shaft Construction Considerations

The following construction considerations are recommended for drilled shaft construction:

Clean the foundation bearing area so it is nearly level or suitably benched and is free of ponded water or loose material.

Provide a minimum drilled shaft diameter of 24 inches.

Make provisions for groundwater removal from the drilled shaft excavation. It is common to encounter perched (trapped) water in excavations that penetrate previously placed fill material. If water is flowing into the drilled shaft at less than 20 gallons per minute, pumps may be used to maintain less than 2 inches of water in the drilled shaft during cleaning and inspection. After approval of the bearing surface, the pumps should be pulled and concreting commenced immediately. If more than 20 gallons per minute are flowing into the drilled shaft, the water level should be allowed to stabilize before attempting to place the concrete. For this condition, concrete placement should be accomplished using a tremie pipe or concrete pumping equipment.

Specify a designed concrete slump of 7 to 9 inches for the drilled shaft construction. This slump is recommended to fill irregularities along the sides and bottom of the drilled shaft, displace water as it is placed, and permit placement of reinforcing cages into the fluid concrete.

Retain S&ME personnel to observe foundation excavations after the bottom of the hole is leveled, cleaned of any mud or extraneous material, and de-watered.

Install a temporary protective steel casing to prevent side wall collapse in shafts adjacent to existing structures, and to prevent excessive mud and water intrusion.

Observe the drilled shaft excavation after the bottom of the hole is leveled, cleaned of any mud or extraneous material, and de-watered.

Geotechnical Addendum No. 1

Dayton VAMC PET/CT Addition

Dayton, Ohio

S&ME Project No. 1178-20-007

March 16, 2020 3

The protective steel casing may be extracted as the concrete is placed provided a sufficient head of concrete is maintained inside the steel casing to prevent soil or water intrusion into the newly placed concrete.

Direct the concrete placement into the drilled shaft through a centering chute or tremie to reduce side flow or segregation.

Drilled Shaft Quality Control Requirements

We recommend that the drilled shaft construction be observed by a S&ME geotechnical engineer or a S&ME special inspector experienced in drilled shaft construction. The observation should address the following items:

Top location within tolerances

Correct plan dimensions

Plumbness within tolerances

Materials excavated agree with borings

Statement of bottom cleanliness

Construction procedure

Based on the structural loads provided and on our experience with similar structures and the site geology, total settlements of the foundations are anticipated to be less than 1 inch, provided the foundations are constructed in accordance with the recommendations provided in this report.

We appreciate remaining involved in this project. Please don’t hesitate to reach out to us with questions.

Sincerely, S&ME, Inc.

Rebecca E. Scherzinger, EI Benjamin C. Dusina, PE

Staff Professional II Senior Engineer