2. Drainage System. To prevent the build-up of hydrostatic water pressure on the retaining wall, a drainage system is often constructed at the heel of the wall. This system will be more effective if highly permeable granular soil is used as backfill. 3. Frost Action. In cold climates, the formation of ice lenses in the backfill soil can cause so much lateral movement that the retaining wall will become unusable. Backfill soil consisting of granular soil and the installation of a drainage system at the heel of the wall will help to protect the wall from frost action. 6.7.1 Retaining Wall Analyses Figure 6.34 shows various types of retaining walls and the soil pressures acting on the walls. Three types of soil pressures act on a retaining wall: (1) active earth pressure, which is exerted on the back side of the wall, (2) passive earth pressure, which acts on the front of the retaining wall footing, and (3) bearing pressure, which acts on the bottom of the retaining wall footing. These three pressures are individually discussed below. Active Earth Pressure. In order to calculate the active earth pressure resultant force (PA), in kN per linear meter of wall or pounds per linear foot of wall, the following equation is used for granular backfill: P  1/ 2 2k  H (6.29) A At where kA  active earth pressure coefficient t  total unit weight of the granular backfill H  height over which the active earth pressure acts as defined in Fig. 6.34a In its simplest form, the active earth pressure coefficient (kA) is equal to: k  tan2(45

1/2) (6.30) A where   friction angle of the granular backfill. Equation (6.30) is known as the active Rankine state, after the British engineer Rankine, who in 1857 obtained this relationship. Equation (6.30) is valid only for the simple case of a retaining wall that has a vertical rear face, no friction between the rear wall face and backfill soil, and the backfill ground surface is horizontal. For retaining walls that do not meet these requirements, the active earth pressure coefficient (kA) for Eq. (6.29) is often determined using the Coulomb equation (see Fig. 6.35). Often the wall friction is neglected (  0
), but if it is included in the analysis, typical values are  3/4 FIGURE 6.34a Gravity and semigravity retaining walls. (From NAVFAC DM-7.2, for the wall friction between granular soil and wood or concrete walls and  20
for the wall friction between granular soil and steel walls such as sheet-pile walls. Note in Fig. 6.35 that when wall friction angle is used in the analysis, the active earth pressure resultant force (PA) is inclined at an angle equal to . Additional important details concerning the active earth pressure are as follows: 1. Sufficient Movement. There must be sufficient movement of the retaining wall in order to develop the active earth pressure of the backfill. For dense granular soil, the amount of wall translation to reach the active earth pressure state is usually very small (i.e., to reach active state, wall translation  0.0005 H, where H  height of wall). 2. Triangular Distribution. As shown in Figs. 6.34 and 6.35, the active earth pressure is a triangular distribution and thus the active earth pressure resultant force (PA) is located at a distance equal to 1/3H above the base of the wall. 3. Surcharge Pressure. If there is a uniform surcharge pressure (Q) acting upon the entire ground surface behind the wall, then there would be an additional horizontal pressure exerted upon the retaining wall equal to the product of kA FIGURE 6.34b Cantilever and counterfort retaining walls. (From NAVFAC DM-7.2, times Q. Thus, the resultant force (P2), in kN per linear m of wall or lb per linear ft of wall, acting on the retaining wall due to the surcharge (Q) is equal to P2  QHkA, where Q  uniform vertical surcharge acting upon the entire ground surface behind the retaining wall, kA  active earth pressure coefficient (Eq. (6.30) or Fig. 6.35), and H  height of the retaining wall. Because this pressure acting upon the retaining wall is uniform, the resultant force (P2) is located at midheight of the retaining wall. 4. Active Wedge: The active wedge is defined as that zone of soil involved in the development of the active earth pressures upon the wall. This active wedge must move laterally in order to develop the active earth pressures. It is important that building footings or other load-carrying members are not supported by the active wedge, or else they will be subjected to lateral movement. The active wedge is inclined at an angle of 45
 /2 from the horizontal. Passive Earth Pressure. As shown in Fig. 6.34, the passive earth pressure is developed along the front side of the footing. Passive pressure is developed when the wall footing moves laterally into the soil and a passive wedge is developed. In FIGURE 6.34c Design analysis for retaining walls shown in Figs. 6.34a and 6.34b. (From NAVFAC DM-7.2, 1982.) order to calculate the passive resultant force (Pp), the following equation is used assuming that there is cohesionless soil in front of the wall footing: P  1/ 2 2k  D (6.31) p pt FIGURE 6.35 Coulombs earth pressure (kA) equation. (From NAVFAC where Pp  passive resultant force in kN per linear m of wall or lb per linear ft of

Walls and Roofs. Heat loss through the walls and roofs of a building constitutes most of the total heat loss in cold weather. These losses are calculated with Eq. (13.19), Q  UA (t2
t1), with the appropriate temperature differential between inside and outside design temperatures. Architectural drawings should be carefully examined to establish the materials of construction that will be used in the walls and roofs. With this information, the overall coefficient of heat transmittance, or U factor, can be determined as described in Art. 13.3. Also, from the drawings, the height and width of each wall section should be determined to establish the total area for each wall or roof section for use in Eq. (13.19). TABLE 13.8 Below-Grade Heat Losses Ground water temp, Basement floor loss,* Btu per hr per sq ft Below-grade wall loss, Btu per hr per sq ft * Based on basement temperature of 70
F. Heat Loss through Basement Floors and Walls. Although heat-transmission coefficients through basement floors and walls are available, it is generally not practicable to use them because ground temperatures are difficult to determine because of the many variables involved. Instead, the rate of heat flow can be estimated, for all practical purposes, from Table 13.8. This table is based on groundwater temperatures, which range from about 40 to 60
F in the northern sections of the United States and 60 to 75
F in the southern sections. (For specific areas, see the ASHRAE HandbookFundamentals.) Heat Loss from Floors on Grade. Attempts have been made to simplify the variables that enter into determination of heat loss through floors set directly on the ground. The most practical method breaks it down to a heat flow in Btu per hour per linear foot of edge exposed to the outside. With 2 in of edge insulation, the rate of heat loss is about 50 in the cold northern sections of the United States, 45 in the temperate zones, 40 in the warm south. Corresponding rates for 1-in insulation are 60, 55, and 50. With no edge insulation the rates are 75, 65, and 60

If concreting must be suspended between planned horizontal construction joints, level off the layer cast, remove any laitance and excess water, and make a straight, level construction joint, if possible, with a small cleat attached to the form on the exposed face (see also Art. 9.39). Concrete placement in horizontal elements follows the same general principles outlined in Art. 9.32. Where the surface will be covered and protected against abrasion and weather, few special precautions are needed. For concrete slabs, careless placing methods result in horizontal segregation, with desired properties in the wrong location, the top consisting of excess water and fines with low abrasion and weather resistance, and high shrinkage. For a good surface in a one-course slab, low-slump concrete and a minimum of vibration and finishing are desirable. Immediate screeding with a power-vibrated screed is helpful in distributing low-slump, high-quality concrete. No further finishing should be undertaken until free water, if any, disappears. A powered, rotary tamping float can smooth very-low-slump concrete at this stage. Final troweling should be delayed, if necessary, until the surface can support the weight of the finisher. When concrete is placed for deep beams that are monolithic with a slab, the beam should be filled first. Then, a short delay for settlement should ensue before slab concrete is cast. Vibration through the top slab should penetrate the beam concrete sufficiently to ensure thorough consolidation. When a slab is cast, successive batches of concrete should be placed on the edge of previous batches, to maintain progressive filling without segregation. For slabs with sloping surfaces, concrete placing should usually begin at the lower edge. For thin shells in steeply sloping areas, placing should proceed downslope. Slump should be adjusted and finishing coordinated to prevent restraint by horizontal reinforcing bars from causing plastic cracking in the fresh concrete. The surface of hardened concrete should be rough and clean where it is to be bonded with fresh concrete. Vertical surfaces of planned joints may be prepared easily by wire brushing them, before complete curing, to expose the coarse aggregate. (The timing can be extended, if desired, by using a surface retarder on the bulkhead form.) For surfaces fully cured without earlier preparation, sandblasting, bush hammering, or acid washes (thoroughly rinsed off) are effective means of preparation for bonding new concrete. (See also Art. 9.33.) Horizontal surfaces of previously cast concrete, for example, of walls, are similarly prepared. Care should be taken to remove all laitance and to expose sound concrete and coarse aggregate. (See also Art. 9.32. For two-course floors, see Art. Floor surfaces highly resistant to abrasion and impact are required for many industrial and commercial uses. Such surfaces are usually built as two-course construction, with a base or structural slab topped by a wearing surface. The two courses may be cast integrally or with the heavy-duty surface applied as a separate