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HomeMy WebLinkAboutReport of Excavation Observations RECEIVEL CONSULTANTS AMERICAN •GEOTECHNICAL •MATERIALS A ENGINEERING NOV 1 5 2004 •ENVIRONMENTAL TESTINGS INC, CITY OF ORONO REPORT OF EXCAVATION OBSERVATIONS PROJECT: REPORTED TO: WAYZATA COUNTRY CLUB MCGOUGH CONSTRUCTION ADDITIONS & REMODELING 2737 FAIRVIEW AVENUE NORTH 200 WEST WAYZATA BOULEVARD ROSEVILLE, MN 55113-1372 ORONO, MINNESOTA ATTN: PAUL EGERTSON AET JOB NO.: 20-04684 CC: MEYER BORGMAN & JOHNSON, INC. DATE: NOVEMBER 11, 2004 CITY OF ORONO INTRODUCTION This report presents the results of the soil observations we performed for the referenced project. Our services were conducted on a will-call basis. The scope of our work was limited to the following: • Observing the soils in the bottoms of the footing excavations for the building additions and interior remodeling. • Drilling shallow hand auger borings in the bottoms of the excavations. • Performing hand cone penetrometer probes in the bottoms of the excavations. • Evaluating the suitability of the exposed soils for structural support. • Summarizing the results of our services in a written report. Our work on this project was originally authorized on October 7, 2004, by Tom Nickelsen of McGough Construction. This document shall not be reproduced,except in full,without written approval of American Engineering Testing,Inc. 550 Cleveland Avenue North . St. Paul, MN 55114 • 651-659-9001 • Fax 651-659-1379 Duluth . Mankato. Marshall . Rochester.Wausau . Rapid City. Pierre. Sioux Falls AN AFFIRMATIVE ACTION AND EQUAL OPPORTUNITY EMPLOYER AET Job No. 20-04684 - Page 2 of 4 CONCLUSIONS Based on the results of our observations, hand auger borings, hand cone penetrometer probes and our review of the available information, it is our judgment that the soils exposed at the bottoms of the observed excavations for the footings of the east building addition and interior remodeling were suitable for structural support. These conclusions are intended as a summary. Please read the remainder of the report for specific information. DESIGN INFORMATION We understand or assume that the construction underway will consist of interior remodeling and an addition to the east side of the existing building. We further understand or assume that the construction underway will: • Have two above-grade levels for the east addition. • Have a finished ground floor elevation of 100.0, matching that of the existing building. • Be supported by conventional spread footings designed using an allowable soil bearing pressure no greater than 3,500 pounds per square foot (psf). • Have cast-in-place concrete spread footings, reinforced concrete masonry walls, structural steel framing, a precast concrete panel first-floor ceiling, and wood framing for the second-story. • Have bottom-of-footing elevations at minimum frost protection depths or lower. • Have normal tolerance to settlement. • Be constructed according to applicable building code requirements. AET Job No. 20-04684 - Page 3 of 4 Deviations from the above design information could necessitate altering our conclusions and recommendations. Contact us if the information stated is different from the actual project design. Building location and elevation information obtained at the site, and presented in this report, was referenced to the existing structure and the footing excavations as located by others. BACKGROUND INFORMATION Previously, we performed a subsurface exploration program at the referenced site. The results were presented in our April 12, 2004, Report of Subsurface Exploration and Geotechnical Review (AET Job No. 20-04015). Refer to that report for pertinent background information and for our recommendations to prepare the building area for structural support. EXCAVATION OBSERVATIONS We observed the excavations for the spread footings of the building addition on October 8, 2004, and some of the excavations for the spread footings within the interior for building remodeling on October 28, 2004. We observed the four spread footings along Grid Line 17, from Grid T to about 5' north of Grid M, as well as the spread footings at Grids S-13 and T-14. We were not present at the site on a full-time basis. Our observations were performed during two visits to the site, when requested by McGough Construction. In addition to observing the soils exposed in the excavations, we conducted shallow hand auger borings and hand cone penetrometer probes in the bottoms of the excavations. The soils encountered were classified in general accordance with ASTM:D2488. Estimates were made of their strength properties based on their resistance to advancement of the hand auger and from the hand cone penetrometer readings. The soils exposed in the bottoms of the excavations were classified as naturally deposited alluvial sands and silty sands. Our hand cone penetrometer readings indicated the naturally deposited soils AET Job No. 20-04684 - Page 4 of 4 should be capable of supporting unit stresses of at least 3,500 psf. The naturally deposited soils were judged suitable for support of the footing loads. The observed footing excavations terminated at approximately planned bottom-of-footing elevations. CLOSURE To protect the client, the public and American Engineering Testing, Inc., this report (and all supporting information) is provided for the addressee's own use. No representations are made to parties other than the addressee. Our services for this project have been conducted to those standards considered normal for services of this type at this time and location. Other than this, no warranty, either express or implied, is intended. SIGNATURES Report Prepared By: Report Reviewed By: American Engineering Testing, Inc. American Engineering Testing, Inc. &/s/71 ,/ i(didpi4/ J septi G. Bentler, EIT Michael P. McCarthy, PE Staff Engineer I Principal Engineer MN License No. 16688 Attachments: Earthwork Quality Control Information Freezing Weather Effects on Building Construction EARTHWORK QUALITY CONTROL INFORMATION EXCAVATION BASE EVALUATION Judgments of supporting soils are based on soils exposed, and on local samples of soils retrieved by hand augering and probing. Because conditions in the subsurface are hidden, it is not possible to fully characterize the subsurface conditions. Therefore,the client must accept that our judgments are limited to those soils which are directly observable to us. As soil conditions may be variable at depth,it is best that excavation base observation be aided by deeper exploratory test borings(usually done prior to construction).Although these deeper borings may not totally reveal what is in the subsurface, they greatly reduce the risk of deeper poor soils going undetected. The presence of ground water within the excavation can also limit the supporting soil evaluation process. Also, if standing ground water is present, there is a risk to the client that compressible soils may not be observed and remain beneath the water during excavation.The compressible materials can become trapped beneath or within the subsequently placed fill. FILLING Structural fill placement is commonly monitored by performing local compaction tests, which entails comparing a field density test to a laboratory Proctor test to arrive at a percent compaction. Density tests of fill only provide the compaction level of the fill at the location and elevation of the test. As many factors control compaction, such as fill lift thickness, moisture content, material type and compactive effort, compaction variation within fill can exist which may not be represented by the tests. Density(compaction)tests are considered representative when used in a conscientious program of controlled fill placement,where the factors influencing compaction are closely monitored. Conclusions about fill suitability to support structural loadings from the results of a limited number of compaction tests includes increased risk,unless the individual drawing the conclusions has complete knowledge of the aforementioned variables during placement. For this reason,part-time testing on a"will-call or trip"basis includes more risk to the client than"full-time"monitoring/testing. OVERSIZING Structural elements also exert loadings laterally; and because of this,the excavation and subsequent fill system needs to be oversized to accommodate these loadings. The extent of lateral oversizing is normally associated with the movement sensitivity of the structure and the strength/compressibility properties of the soils remaining along the excavation sidewalls. Oversizing on the order of 1 (horizontal):1 (vertical) is typically provided for foundations in "normal" conditions. However, oversizing on the order of 11/2:1 or more is usually needed in highly compressible situations such as swamp deposits. AET does not practice in the field of surveying and must rely on location and elevation staking of proposed construction by the client or their representative. Our measurements in the field are made in relation to those stakes or other location and elevation information provided to us. The reliability of AET's opinions, conclusions and recommendations based on those measurements is dependent on the accuracy of the staking or information provided by the client or their representative. FREEZING WEATHER Soils which are allowed to freeze will heave and lose density. Upon thawing,these soils will not regain their full original strength and density. The extent of heave and density/strength loss depends on the soil type and moisture condition;and is usually more pronounced in finer grained soils, and particularly silty soils. Foundations, slabs, and other improvements affected by such frost movements should be protected from frost intrusion during freezing weather. If filling takes place during freezing weather, all frozen soils, snow and ice should be stripped from all areas to be filled prior to new fill placement; and the new fill should not be allowed to freeze during or after placement. For this reason, it is usually more beneficial to perform excavate/refill operations during freezing weather in smaller plan areas where grade can be attained quickly rather than working larger areas where a large amount of frost stripping may be needed. STRUCTURAL SUPPORT ON UNCONTROLLED FILL Risks are associated with supporting structures on fill which has not been placed in a controlled and well documented manner. Even where existing fill appears to be well compacted(including when soil borings have been performed),hidden poorer or looser soils can potentially exist below or within the fill; or previous excavation and extension of the compacted fill may not have been provided with sufficient oversize in all directions to accommodate the new lateral loadings. Risks can be reduced by means of increasing the amount of testing and observations. 20-E.FLD013(2/01) AMERICAN ENGINEERING TESTING,INC. FREEZING WEATHER EFFECTS ON BUILDING CONSTRUCTION GENERAL Because water expands upon freezing and soils contain water, soils which are allowed to freeze will heave and lose density. Upon thawing, these soils will not regain their original strength and density. The extent of heave and density/ strength loss depends on the soil type and moisture condition. Heave is greater in soils with higher percentages of fines (silts/clays). High silt content soils are most susceptible, due to their high capillary rise potential which can create ice lenses. Fine grained soils generally heave about 1/4" to 3/8" for each foot of frost penetration. This can translate to 1" to 2" of total frost heave. This total amount can be significantly greater if ice lensing occurs. DESIGN CONSIDERATIONS Clayey and silty soils can be used as perimeter backfill, although the effect of their poor drainage and frost properties should be considered. Basement areas will have special drainage and lateral load requirements which are not discussed here. Frost heave may be critical in doorway areas. Stoops or sidewalks adjacent to doorways could be designed as structural slabs supported on frost footings with void spaces below. With this design, movements may then occur between the structural slab and the adjacent on-grade slabs. Non-frost susceptible sands (with less than 12% passing a #200 sieve) can be used below such areas. Depending on the function of surrounding areas, the sand layer may need a thickness transition away from the area where movement is critical. With sand placement over slower draining soils, subsurface drainage would be needed for the sand layer. High density extruded insulation could be used within the sand to reduce frost penetration, thereby reducing the sand thickness needed. We caution that insulation placed near the surface can increase the potential for ice glazing of the surface. The possible effects of adfreezing should be considered if clayey or silty soils are used as backfill. Adfreezing occurs when backfill adheres to rough surfaced foundation walls and lifts the wall as it freezes and heaves. This occurrence is most common with masonry block walls, unheated or poorly heated building situations and clay backfill. The potential is also increased where backfill soils are poorly compacted and become saturated. The risk of adfreezing can be decreased by placing a low friction separating layer between the wall and backfill. Adfreezing can occur on exterior piers (such as deck, fence or other similar pier footings), even if a smooth surface is provided. This is more likely in poor drainage situations where soils become saturated. Additional footing embedment and/or widened footings below the frost zones (which includes tensile reinforcement) can be used to resist uplift forces. Specific designs would require individual analysis. CONSTRUCTION CONSIDERATIONS Foundations, slabs and other improvements which may be affected by frost movements should be insulated from frost penetration during freezing weather. If filling takes place during freezing weather, all frozen soils, snow and ice should be stripped from areas to be filled prior to new fill placement. The new fill should not be allowed to freeze during transit,placement or compaction.This should be considered in the project scheduling,budgeting and quantity estimating. It is usually beneficial to perform cold weather earthwork operations in small areas where grade can be attained quickly rather than working larger areas where a greater amount of frost stripping may be needed. If slab subgrade areas freeze, we recommend the subgrade be thawed prior to floor slab placement. The frost action may also require reworking and recompaction of the thawed subgrade. 01REP015(2/01) AMERICAN ENGINEERING TESTING, INC.