Report of Excavation Observations

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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.