GSA Lambros Plaza Geotech Memo.pdf

AECOM

1300 East 9th Street

Suite 500

Cleveland, OH 44114 www.aecom.com

216 622 2300 tel

216 622 2301 fax

January 4, 2018

Ms. Laura Brown

GSA Project Manager

General Services Administration

Public Buildings Service, Great Lakes Region

Dear Ms. Brown, RE: Plaza Repair/Replacement and Security Bollard Design at the Thomas B. Lambros Federal

Building and U.S. Courthouse

This letter presents geotechnical recommendations for the Plaza-Alleyway Repair/Replacement and

Security Bollard Design at the Thomas D. Lambros Federal Building and U.S. Courthouse located at

125 Market Street in Youngstown, Ohio.

Project Understanding

The following section provides a description of our understanding of the existing site conditions and our understanding of the proposed improvements. Description of the proposed improvements is based on the 50% Design Submittal for this project.

The project area is located to the south and west of the existing Federal Building in Downtown

Youngstown, Ohio. The existing conditions consist of paved sidewalks, plazas, and landscape beds with vegetation and trees. The existing sidewalks and plaza are paved with brick pavers and are generally level with very little grade change. Existing surface elevations across the site range from approximately 857 ft (NAVD88) in the northern part of the site to 860 ft (NAVD88) in the southern part of the site.

The project will be constructed in two phases. The first phase will consist of the removal of the outer portion of the existing paved sidewalk, and existing trees along Market Street and East Front Street, to the west and south of the existing federal building. A series of concrete security bollards will be installed along the entire outer perimeter of the exiting sidewalk. The sidewalk along Market Street and the western half of the building along East Front will be repaved with 12-inch by 12-inch brick pavers. The sidewalk along the eastern half of building along East Front Street will be repaved as a concrete sidewalk. The proposed security bollards will consist of 10-inch inner-diameter Schedule 40 pipes filled with concrete, spaced at 48 inches on center. The bollards will be supported by a continuous strip footing foundation, 48 inches in thickness, and 32 inches in width. The foundation is planned to bear at a depth of 55.5 inches below the top of pavement. The existing brick pavers are

2.5 inches in thickness will be replaced in kind after where required. The replacement pavers will be underlain by 5 inches of compacted limestone screenings.

The second phase will consist of the removal and replacement of paved sidewalk areas and landscape areas. New sidewalk and pavement construction will consist of brick pavers, concrete pavement, and asphalt pavement. New pavements will be designed to carry primarily routine pedestrian traffic, but will periodically (twice annually) need to support utility trucks used for window washing operations of the existing Federal Building.

Subsurface Investigation

Drilling and Sampling Procedures

The subsurface investigation for this project consisted of four soil borings numbered B-01 through

B-04. Approximate boring locations are shown in Figure 2 attached to this memorandum.

Borings were drilled on September 14, 2018 by AECOM’s subcontractor Ohio TestBor, Inc. to depths of 10 feet below ground surface (ft bgs). Boring B-02 encountered auger refusal at a depth of 3.6 ft bgs and was offset approximate 18 ft to the north and redrilled as B-02A.

All borings were drilled using a Mobile B-57 truck-mounted drilling rig using 3.25-inch inner-diameter hollow-stem augers. Borings B-01, B-02, B-02A, and B-03 were drilled in the existing paved sidewalk area. Brick pavers were removed as necessary prior to drilling and replaced in kind following drilling completion. Representative soil samples were obtained using split-barrel sampling procedures in general accordance to ASTM D 1586 at depth intervals of 2.5 feet. Representative samples of auger cuttings were collected from layers of very dense, solidified slag was encountered and split-spoon sampling was not possible. Soil samples obtained in the field were logged, labeled, and sealed.

An AECOM geotechnical engineer provided full-time oversight during the field operations to observe subsurface conditions encountered and coordinate soil sampling. Water level observations were made in the boreholes during drilling and sampling operations.

Boring Log Procedures and Qualifications

General soil descriptions are noted on the individual boring logs included in the Attachments. Please note that the strata contact lines represent approximate boundaries between soil types; the actual transition between soil types in the field may be gradual in both the horizontal and vertical directions.

Subsurface conditions and water levels at other locations may differ from the conditions encountered at the boring location. Furthermore, the subsurface conditions may change over time with the construction of additional improvements, excavations, and placement of fill. These variables need proper consideration when utilizing the information presented on the boring logs.

Results

Subsurface Conditions

Subsurface conditions at the site were generally similar among the four soil boring locations and consisted of the following subsurface deposits, described in detail below.

Surficial Materials: Borings B-01, B-02, B-02A, and B-03 were all drilled within the existing paved sidewalk area. Pavement material at the surface consisted of 12-inch by 12-inch square brick pavers,

2.5 inches in thickness. Boring B-04 was drilled in an existing landscaping area where mulch and topsoil were encountered at the surface.

Subgrade Sand Fill: In all borings drilled within the paved sidewalk area, a layer of sand fill soils was encountered below the brick pavers that extended to 2.3 to 3.0 ft bgs. Sand fill soils generally consist of silty clayey sand (USCS type SC-SM), silty sand (SM), and clayey sand (SC) with varying amounts of gravel. SPT N-values within the subgrade sand fill unit ranged from 6 to 9 blows per foot with an average around 8 blows per foot, indicating a generally loose compactness.

Slag Fill: Layers of crushed slag fill were encountered in borings B-02 from 2.3 to 3.6 ft bgs and in boring B-03 from 6.5 to 8.0 ft bgs. The slag was visually classified as poorly-graded gravel (GP). No split-spoon samples were able to be collected in the slag fill due to very hard sampling resistance.

The slag was identified through sampling of auger cuttings. Auger drilling within the slag units was very rough and hard, indicating that the slag is very well compacted and/or cemented. Auger refusal was encountered at a depth of 3.6 ft within the slag layer in B-02.

Medium Stiff to Soft Clay: A layer of brown silty clay (CL-ML) was encountered below the subgrade sand fill in B-01 and extended to boring termination at 10.0 ft bgs. Pocket penetrometer reading within the layer ranged from 0.25 to 1.0 tons per square foot (tsf) with an average around 0.6 tsf, indicating a soft to stiff consistency with a medium stiff consistency on average.

Non-Cohesive Fill: Non-cohesive fill soils not including the subgrade sand or slag layers were encountered in borings B-02A from 3.0 ft bgs to boring termination at 10.0 ft bgs; in B-03 from 3.0 ft to

6.5 ft bgs and 8.0 ft bgs to boring termination at 10.0 ft bgs; and in B-04 from 1.4 ft to 5.5 ft bgs, and

8.0 to 9.4 ft bgs. SPT N-values within the subgrade sand fill unit ranged from 5 to 26 blows per foot with an average around 16 blows per foot, indicating a generally medium dense compactness on average.

Cohesive Fill: Cohesive fill soils excluding the medium stiff to soft clay layer encountered in B-01 were encountered in B-04 at depths of 0.5 to 1.4 ft bgs, 5.5 to 8.0 ft bgs, and 9.4 ft bgs to boring termination at 10.0 ft bgs. Pocket penetrometer reading within the layer ranged from 1.5 to 4.5 tons per square foot (tsf) with an average around 2.8 tsf, indicating a stiff to hard consistency with a very stiff consistency on average.

Groundwater:

Groundwater was not encountered in any of the borings during drilling or upon completion of drilling.

It should be noted that the groundwater observations and measurements obtained at the time of drilling may not reflect the long term position of the water table. Additionally, groundwater fluctuations may occur with time and seasonal change due to variations in precipitation, evaporation, and local dewatering. Perched water pockets and a resulting higher water table level may also be encountered during wet weather periods.

Analysis and Recommendations

Bollard Foundation Design and Excavation

The proposed bollard strip foundations is proposed to bear at a depth of 4.5 ft below existing grade.

The soils encountered at that depth in borings B-02A, B-03, and B-04 are suitable for support of the proposed structures. The medium stiff to soft clay encountered in B-01 has a low shear strength and is susceptible to consolidation settlement; therefore it is not suitable for support of the proposed structures and will need to be improved prior to placement of the bollard foundation. The horizontal extent of the unsuitable clay soil shall be determined during construction by a qualified geotechnical inspector. For purposes of cost estimation prior to construction, the unsuitable clay soil may be assumed to extend from the northern end of the bollard footing to approximately 90 ft south of the northern boundary of the project (approximately 110 ft along the length of the foundation).

The bearing surface for the foundation may be improved in the vicinity of B-01 using one of the following methods:

1. Undercut the soft to medium stiff clay to a depth of 5 ft below the proposed bearing elevation

(approximately 9.5 ft below existing grade). Place and compact 36 inches of No. 1 and No. 2 stone or recycled concrete. Place a non-woven filter fabric over the No. 1 and No. 2 stone.

Place and compact 24 inches of crushed stone or recycled concrete matching the gradation requirements of ODOT Item 304.

2. Undercut soft clay until suitable bearing material is encountered. “Suitable bearing material may be determined as cohesive soil with unconfined compressive strength, measured in the field using a pocket penetrometer, of 2.0 tons per square foot or greater. Determination of the suitability of the bearing material shall be made by a qualified geotechnical inspector.

If the proposed bollard footing bearing surface is inspected and prepared as described above, an allowable bearing pressure of 2000 pounds per square foot (psf) may be used for design).

Backfill on either side of bollard footings should consist of No. 57 limestone with horizontal extents to be defined by the bollard manufacturer. The No. 57 limestone backfill should be placed and compacted with tamper plate excavator attachments or other means of vibratory compaction.

Subgrade Preparation

Any subgrades of proposed new or replacement brick pavers, concrete, or asphalt pavement shall be properly inspected and prepared as follows: Prior to placement or replacement of pavement, the entire subgrade should be proof rolled to identify any areas of instability. Proof-rolling should proceed using heavy pneumatic-tired equipment, such as a fully-loaded, tandem-axle dump truck or other equivalent equipment, with a minimum of three overlapping passes. The equipment used for proof-rolling should weigh a minimum of 35 tons. Proof rolls should be observed and interpreted by qualified geotechnical personnel. Areas that yield, i.e. rut or permanently deform under the weight of the proof-roll, should be mitigated. Mitigation can include removal and subsequent drying/compaction of the in-place soils, or excavation and complete replacement with crushed aggregate or engineered fill. Where this undercut and replace method is utilized in the field, the undercut depth should be 12 inches, unless otherwise determined by the Engineer.

Engineered Fill

All engineered fill materials (structural or general) should be essentially free of organic matter (the organic content of a material to be used as engineered fill should not exceed 3%), frozen materials, cobbles, boulders, and other rubble greater than 6 inches in largest dimension. Upon preparation of an adequate subgrade, all engineered fill should be placed horizontally in loose lifts not exceeding 8 inches in thickness when using full size compaction equipment and not greater than 4-inches in thickness when using manual or other small compaction equipment. Fills located under structures, slabs, or roads and fills forming sloping ground (structural engineered fills) should be compacted to at least 98% of the maximum dry density and within 2% of the optimum moisture content, as established by the Standard Proctor Tests (ASTM D698) performed during prequalification.

Pavement/Slab Design

If the proposed subgrade preparation and engineered fill placement is performed as described above, the proposed concrete pavement may be designed using a modulus of subgrade reaction of 100 pounds per cubic inch (pci) and an allowable bearing pressure of 2000 pounds per square foot (psf).

Utility Trench Backfill

Utility trenches should be excavated a minimum of four inches below the bottom of pipes or conduits and have clearances of at least four inches on both sides of the pipe springline. Where necessary, trench excavations should be shored and braced to prevent cave-ins and in accordance with current safety regulations. Backfill for utility trenches should be performed according to Section 611.06 of the

2016 ODOT Construction and Material Specifications (CMS). Utility trench backfills should be compacted in maximum 6-inch loose lifts and to at least 95% of the Standard Proctor maximum dry density. Jetting of trench backfill should not be permitted. Special care should be taken in controlling utility backfilling in structure or road areas. Poor compaction may result in excessive settlements and damage to exterior improvements.

Water Management

Surface drainage of the site should be properly maintained during construction such that subgrades are kept free of standing water. Up to the time of subgrade preparation, elevations of areas to be excavated should remain several inches above the final bearing elevation to minimize potential exposure to wet weather and softening of the subgrade soils.

While groundwater was not encountered during the geotechnical exploration, some water infiltration into excavations should be anticipated during construction, particularly after heavy rainfall or snowmelt. Water incursion into excavations from surface runoff, perched water within minor granular soil layers in the excavation walls, and elevated groundwater table. Such groundwater incursion is expected to be manageable using conventional dewatering techniques such as sumps and pumping.

General Qualifications

General Qualifications applicable to subsurface exploration are attached and are an integral part of this letter report. This letter report has been prepared in accordance with generally accepted soil and foundation engineering practices to aid in the evaluation of this property and to assist the owner and the architect and/or engineer in the design of this project. No other warranty, expressed or implied is made. The scope of this report is limited to the specific project and location described herein, and our description of the project represents our understanding of the significant aspects relevant to soil and foundation characteristics.

We recommend that AECOM be provided the opportunity to review the final project plans and specifications to confirm that the recommendations contained in this report have been interpreted in accordance with our intent. AECOM should be retained to observe and verify that the foundation bearing strata are consistent with the findings of this report. Without this oversight and special testing, we cannot be responsible for misinterpretations of our data, our analyses, and/or our recommendations, or how these items are incorporated in the final design.

We appreciate this opportunity to be of service to you. If there are any questions with regard to the information contained in this report, or if we may be of further assistance, please contact us.

Respectfully, Erik J. Bogen, P.E. Makarand Jakate, P.E.

Geotechnical Engineer Senior Geotechnical Engineer

AECOM AECOM

Attachments

Figure 1 – General Location Map

Figure 2 – Soil Boring Location Plan

Attachment A – Soil Boring Logs