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— RECOMAfENDATIONS <br /> We recommend that columns of the proposed extension be supported on caissons (drilled <br /> — piers) bearing on the very dense naturet giecial till. Floor slabs may be constructed on grede in <br /> eaisting fill soil �hat hes been properly prepared. We further rocommend that the pedestrian <br /> � tunnel be designed as e long rigid mat and constructed on grede in the existing fill soil after <br /> — proper subgrede preparation. Detaits concerning these recommendations are presented below. <br /> During the course of the project, we examined other support methods for the building and <br /> — tunnels, including the use of auger-cast piles end a reinforced concrete diaghram wall. <br /> — BUILDING SUPPORT <br /> Ceisson Ceoacities <br /> __ We recommend that columns for the proposed extension be supported on caissons drilled et <br /> least 4 feet into the glecial till. Streight sheft ceissons will derive downward capecity from of <br /> - end bearing and from akin friction for that portion of the sheft embedded in the till. The <br /> _ caisson�may elso be constructed with bells formed entirely in the tiil, end will derive downwerd <br /> capecity from end bearing only. The ceissons may be designed using an alloweble henring <br /> � ^ cepacity of 20 kips per square foot (KSF) and an allowable skin frictiuu (edhesion) velue of 2 <br /> _ KSF. The ailowable end beering capacity mey be increased by one third for transient loeds from <br /> wind or earthquakes. A design diegram presenting the alioweble capacity of both straight sheft <br /> " end belled caissons as e function of the sheft diameter is prosented in Piate 4. This chert assumes <br /> that the diameter of the bell is twice the diemeter of the sheft. <br /> � Uplift capacities mey be calculeted using an allowable skin friction(adhesion)velue of 2 KSF <br /> applied only to por�ions of straight shaft caissons embedded within the glacial till. <br /> I ^ The existing fill soii is eesumed to have e negligible contribution to the downwerd or uplift <br /> i . capacities of the caissons. <br /> '- Lateral load capacitiee of the ceissons will be directly proportional to their diameter. <br /> Recommended allowable laterel toad capacities for selected caisson diameters ere prosented in <br /> Teble 1 below: <br /> 4 <br /> � � Dames R Moore <br />