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File: 218267 November 30, 2018 Actual pier depth, diameter, reinforcement, and spacing should be determined by the structural engineer based upon the following design criteria: A friction value of 500 psf may be assumed to act on that portion of the pier below a depth of 5 feet. Lateral support may be assumed to be developed along the length of the pier below 5 feet, using a passive pressure of 350 pcf Equivalent Fluid Weight(EFW). Passive resistance may be assumed to act over 1.5 projected pier diameters. Above 5 feet,no frictional or lateral support may be assumed. These design values may be increased 1/3 for transient loads (i.e. seismic and wind). Even though piers are designed to derive their vertical resistance through skin friction, the bases of the piers holes should be clean and firm prior to setting steel and pouring concrete. If more than 6 inches of slough exists in the base of the pier holes after drilling,then the slough should be removed. If less than 6 inches of slough exists,the slough may be tamped to a stiff condition. Piers should not remain open for more than a few days prior to casting concrete. In the event of rain, shallow groundwater, or caving conditions it may be necessary to pour piers immediately. All perimeter piers,and piers under load-bearing walls,should be connected by concrete grade beams. Perimeter grade beams should penetrate a minimum of 6 inches below crawlspace grade (unless a perimeter footing drain is installed to intercept water attempting to enter around the perimeter). Interior grade beams do not need to penetrate below grade. All other isolated floor supports must also be pier supported to resist expansive soil uplift, however, they do not need to be connected by grade beams. In order to reduce any expansive soil uplift forces on the base of the grade beams, the beams should have either a uniform 4 inch void between their base and the soil, or should be constructed with a knife edge and triangular shaped void in a rectangular trench. The void can be created by the use of prefabricated cardboard void material (e.g. K-void, SureVoid, Carton-void), half a sonotube faced concave down, or other methods devised by the contractor and approved by our offices. The use of Styrofoam is not acceptable for creating the void. All improvements connected directly to any pier supported structure, also need to be supported by piers. This includes, but is not limited to: porches, decks, entry stoops and columns, etc. If the designer does not wish to pier support these items,then care must be taken to structurally isolate them (with expansion joints, etc.) from the pier supported structure. If the above recommendations are followed, total foundation settlements should be less than 1 inch, while differential settlements should be less than L/2 inches. Basement Foundations,Walls, and Floors Wall Forces -Any basement retaining walls should be designed to resist an active pressure of 45 pcf Equivalent Fluid Weight (EFW), for retained slopes flatter than 4:1 (horizontal:vertical). If it is desired to create steeper retained slopes to reduce the heights of the walls, then the active pressure will need to be increased. An active pressure of 60 pcf EFW should be utilized for retained slopes 8