171419A Geotechnical Report Addendum USDA Ames Building 21 Addition.pdf

ALLENDER BUTZKE ENGINEERS INC.

GEOTECHNICAL • ENVIRONMENTAL • CONSTRUCTION Q. C.

3660 109TH STREET • URBANDALE, IOWA 50322 • PHONE 515-252-1885 • FAX 515-252-1888

May 30, 2018

Stanley Consultants, Inc.

100 Court Ave, Ste 300

Des Moines, IA 50309

Attn: Raymond Lukkarinen, P.E.

RE:

Geotechnical Exploration

USDA Building 21 Addition

USDA Ames Lab, 1920 Dayton Ave

Ames, Iowa

PN 171419A

Dear Mr. Lukkarinen:

A partial basement, with plan dimensions of approximately 110 by 55 feet, will be added below the proposed USDA Building 21 Addition at the USDA Ames Lab in Ames, Iowa. The approximate location of the partial basement level below the addition is shown in the following

Figure No. 1. As requested, Allender Butzke Engineers Inc. (ABE) has reviewed the updated project information for the proposed basement level provided by Stanley Consultants and prepared the following letter providing additional recommendations for the proposed basement level. This letter is an addendum to the original geotechnical report (PN 171419) issued

November 30, 2017. Other geotechnical recommendations discussed in the original report remain valid.

Figure No. 1 - Basement Level Plan (Stanley Consultants)

Andrea Bickford, P.E. with Stanley consultants indicated that the basement slab will be a poured mat foundation which will support building columns with maximum vertical loads of

242 kips. The depth of the basement level slab will be approximately 9 feet 5 inches from the top of ground floor slab. Based on a main level finish floor elevation of 995.25 feet, we estimate the top of the basement slab will be near elevation 985.8 feet.

Stanley Consultants further indicated that the limits of the basement walls will be a minimum of 18 feet horizontally from the existing building shallow foundations. As shown in the following Figure No. 2, there will be a row of new shallow foundations between the existing shallow foundations and the new basement walls. Ms. Bickford, P.E. indicated that shallow spread footings on grids 11.5 and A.5 (north and west exterior walls) will have max vertical column loads of 25 kips. The shallow spread footings on grids 18.5 and A.1 (east and south walls of the addition) will have max vertical column loads of 90 kips, except for the footings at 18.5-

A.3 and 18.5-A.2, which will have a max vertical column load of 136 kips.

Figure No. 2 - Approximate Basement Location and Proposed Spread Foundations (Stanley Consultants)

ANALYSES AND RECOMMENDATIONS

Based on boring data, the basement level mat foundation will bear in stiff natural sandy lean clay (CL) Wisconsinan glacial till. Moisture seepage was encountered in the borings above the proposed basement floor elevation of 985.8 feet and the basement level is expected to extend below the seasonal high groundwater level. In our opinion, a subsurface drainage system should be installed to protect the lower level from excess subsurface moisture seepage and reduce hydrostatic uplift. The underfloor drainage system could consist of perforated or slotted rigid

PVC pipes having a minimum diameter of 4 inches spaced approximately 30 feet or less, center to center, and be surrounded by free draining granular material. Drainlines should be spaced to avoid being located below column locations.

Granular material below the mat foundation should be a minimum of 12 inches thick, extend 9 inches or more beyond the outside edges of the mat foundation, and be compacted to a minimum 98 percent of the material’s Standard Proctor (ASTM D698) maximum dry density.

The lower 8 inches or more of granular material surrounding the drainlines should be free draining material with less than 3 percent passing the No. 200 sieve. The upper few inches of the granular material below the proposed mat slab could contain fines which would provide a more stable, workable surface for construction of the mat slab/foundation. The free draining granular material surrounding the drain lines should be hydraulically connected to the free draining granular material directly beneath the mat slab. The pipes should be sloped to drain to a sump pit and outlet to a storm sewer.

The recommended 12 inches of compacted granular material and the stiff natural sandy lean clay Wisconsinan glacial till encountered below the assumed mat foundation level of 10.5 to

11.5 feet below the main level slab would provide a design support capability equivalent to a modulus of subgrade reaction value of 175 pounds per cubic inch. Assuming the mat foundation will generate pressures on the order of 2,000 pounds per square foot or less, we estimate long-term total settlement of the mat foundation will be less than 1 inch and differential settlement would be less than ½ of total settlement. Foundations should be adequately reinforced to limit deflections caused by non-uniform soil support characteristics.

New shallow spread foundations will be located between the shallow foundations of the existing building and the new basement walls of the addition. To avoid increased lateral stresses behind the basement level walls, we recommend that new shallow spread foundations be deepened to bear below a 1:1 line extending up from the bottom of the mat foundation. Based on provided maximum loads for the shallow spread foundations and assumed footing sizes based on a net allowable soil bearing pressure of 2,000 pounds per square foot provided in the