Water Removal. Table 6.21 lists several different types of water removal site improvement techniques. If the site contains an underlying compressible cohesive soil layer, the site can be surcharged with a fill layer placed at ground surface. Vertical drains (such as wick drains or sand drains) can be installed in the compressible soil layer to reduce the drainage path and speed up the consolidation process. Once the compressible cohesive soil layer has had sufficient consolidation, the fill surcharge layer is removed and the building is constructed. Site Strengthening. Many different methods can be used to strengthen the onsite soil (see Table 6.21). For example, deep vibratory techniques are often used to increase the density of loose sand deposits. Grouting. In order to stabilize the ground, fluid grout can be injected into the ground to fill in joints, fractures, or underground voids. For the releveling of existing structures, one option is mudjacking, which has been defined as a process whereby a water and soil-cement or soil-lime cement grout is pumped beneath the slab, under pressure, to produce a lifting force that literally floats the slab to the desired position. Another commonly used site improvement technique is compaction grouting, which consists of intruding a mass of very thickconsistency grout into the soil, which both displaces and compacts the loose soil. Compaction grouting has proved successful in increasing the density of poorly compacted fill, alluvium, and compressible or collapsible soil. The advantages of compaction grouting are less expense and disturbance to the structure TABLE 6.21 Site Improvement Methods Method Technique Principles Suitable soils Remarks

Electrical plans should be drawn to scale, traced or reproduced from the architectural plans. Architectural dimensions may be omitted except for such rooms as meter closets or service space, where the contractor may have to detail his equipment to close dimensions. Floor heights should be indicated if full elevations are not given. Locations of windows and doors should be reproduced accurately, and door swings shown, to facilitate location of wall switches. For estimating purposes, feeder or branch runs may be scaled from the plans with sufficient accuracy. Electrical plans may be drawn manually or by using a computer-aided drafting and design (CADD) system. Although a significant initial investment is required, CADD can make the preparation of drawings fast and efficient and can make the interchange of information between electrical and the other engineering disciplines much easier. Indicate on the plans by symbol the location of all electrical equipment (Table 15.1). Show all ceiling outlets, wall receptacles, switches, junction boxes, panelboards, telephone and interior communication equipment, fire alarms, television master-antenna connections, etc. A complete set of electrical plans should include a diagram of feeders, panel lists, service entrance location, and equipment. Before these can be shown on the plans, however, wire sizes should be computed in accordance with procedures outlined in the following paragraphs. Where there is only one panelboard in an area, and it is clear that all circuits in that area connect to that box, it is not necessary to number the panel other than to designate it as, for example, apartment panel. In larger areas, where two or more panelboards may be needed, each should be labeled for identification and location; for example, L.P. 1-1, L.P. 1-2 . . . for all panelboards on the first floor; L.P. 2-1, L.P. 2-2 . . . for panels on the second floor. 15.8.4 Branch Circuits It is good practice to limit branch runs to a maximum of 50 ft for 120-V circuits and 100 ft for 277-V circuits by installing sufficient panelboards in efficient locations. Connect each outlet with a branch circuit and show the home runs to the panelboard, as indicated in Table 15.1. General lighting branch circuits with a 15-A fuse or circuit breaker in the panelboard usually are limited to 6 to 8 outlets, although most codes permit 12. No more than two outlets should be connected in a 20-A appliance circuit. It is good practice to use wire no smaller than No. 12 in branch circuits, though some codes permit No. 14. Special-purpose individual branch circuits for motors or appliances should be sized to suit the connected load. 15.8.5 Electric Services For economy, alternating current is transmitted long distances at high voltages and then changed to low voltages by step-down transformers at the point of service. Small installations, such as one-family houses, usually are supplied with threewire service. This consists of a neutral (transformer midpoint) and two power wires with voltage differing 180 in phase. From this service, the following types of interior branch circuits are available: Single-phase two-wire 230-Vby tapping across the phase wires Single-phase two-wire 115-Vby tapping across one phase wire and the neutral Single-phase three-wire 115/230-Vby using both phase wires and the neutral For larger installations, the service may be 480/277-V or 208/120-V, threephase four-wire system. This has a neutral and three power wires carrying voltage differing 120 in phase. From this service, the following types of interior branch circuits are available: Single-phase two-wire 480-V or 208-Vby tapping across two phase wires Single-phase two-wire 277-V or 120-Vby tapping across one phase wire and

vm). Using the calculated values of Cr and Cc , the primary consolidation settlement (sc) due to an increase in load ( v) can be determined from the following equations: 1. For underconsolidated soil (OCR  1): Ho vo   v   v s  C log (6.19) c c 1  e  o vo 2. For normally consolidated soil (OCR  1): Ho vo   v s  C log (6.20) c c 1  e  o vo 3. For overconsolidated soil (OCR  1): Case I: vo   v  vm Ho vo   v s  C log (6.21) c r 1  e  o vo Case II: vo   v  vm Ho vm Ho vo   v s  C log  C log (6.22) c r 1  e  c 1  e  o vo o vm where sc  settlement due to primary consolidation caused by an increase in load Cc  compression index, obtained from the virgin consolidation curve (Fig. 6.22) Cr  recompression index, obtained from the recompression portion of the consolidation curve (Fig. 6.22) Ho  initial thickness of the in-situ saturated cohesive soil layer eo  initial void ratio of the in-situ saturated cohesive soil layer