(d) Extrusion Welding. Suitable for all polyethylenes. A ribbon of molten polymer is extruded over the edge (fillet weld) or between the geomembrane sheets (flat weld). This melts the adjacent surfaces, which are then fused together upon cooling. 6.11.4 Geonets and Geocomposites Geonets are three-dimensional netlike polymeric materials used for drainage (flow of water within the geosynthetic). Figure 6.52 shows a photograph of a geonet. Geonets are usually used in conjunction with a geotextile and/or geomembrane and hence are technically a geocomposite. Depending on the particular project requirements, different types of geosynthetics can be combined together to form a geocomposite. For example, a geocomposite consisting of a geotextile and a geomembrane provides for a barrier that has increased tensile strength and resistance to punching and tearing. Figure 6.53 shows a photograph of a geocomposite consisting of a textured geomembrane, geonet, and geotextile (filter fabric). 6.11.5 Geosynthetic Clay Liners Geosynthetic clay liners are frequently used as liners for muncipal landfills. The geosynthetic clay liner typically consists of dry bentonite sandwiched between two geosynthetics. When moisture infiltrates the geosynthetic clay liner, the bentonite swells and creates a soil layer having a very low hydraulic conductivity, transforming it into an effective barrier to moisture migration.

17.14.1 Methods of Payment for Change Orders Either an owner or a contractor may request a change order. Changes or extras may be priced in any of the following ways: Unit Prices. At the time of either the bid or the signing of the contract, unit prices are listed by the contractor for various classes of work that may be subject to change. Usually, unit prices are easily administered for such trades as excavation, concrete, masonry, and plastering. The task of the purchaser is to obtain unit prices from subcontractors for various classes of work for the same trades that are in the contract. Although usually the same unit price is agreed for both added and deducted work, occasionally the unit prices for deducted work will be agreed to be 10% less than those for added work. Cost of Labor and Materials, plus Markup. Another method of computing the value of changes or extra work is by use of actual certified costs, as derived from record keeping as the project proceeds. Rates for wages and fringe benefits must be verified, and the amount of percentage markup must be agreed to either in the contract or before the work is started. Usually, the general contractor is allowed a markup over and above subcontractors costs and markup, but the general contractors markup is less than the subcontractors allowance in such cases. FIGURE 17.18 Order issued by a general contractor to a subcontractor to proceed with a change in work not covered by the contract documents. When work is done on a cost-plus-markup basis, the contractor must maintain an accurate daily tabulation of all field costs. This document should be agreed to and signed by all parties responsible for the record keeping for the change. It will form an agreed-on certification that the work has been performed and of the quantities of labor and material used. A daily work-report certification is shown in Fig. Negotiation by Lump Sum. If the owner desires to have changes or extra work performed and does not want it done on a cost-plus or unit-price basis, owner and contractor may negotiate a lump-sum payment. In this situation, a cost estimate is prepared by the contractor or subcontractor involved, and a breakdown of costs is submitted, together with the estimate total. If the owner accepts the lump sum, the owner or the architect writes a change order, and the work is performed. Such a change order is shown in Fig. 17.18 as issued to a subcontractor.

Miscellaneous Sources of Heat Gain. In an air-conditioning unit, the fan used to circulate the air requires a certain amount of brake horsepower depending on the air quantity and the total resistance in the ductwork, coils, filters, etc. This horse- TABLE 13.9 Rates of Heat Gain from Occupants of Conditioned Spaces* Degree of activity Typical application Total heat adults, male, Btu/hr Total heat adjusted, Btu/ hr Sensible heat, Btu/hr Latent heat, Btu/hr Seated at theater Theatermatinee 390 330 225 105 Seated at theater Theaterevening 390 350 245 105 Seated, very light work Offices, hotels, apartments 450 400 245 155 Moderately active office work Offices, hotels, apartments 475 450 250 200 Standing, light work; walking Department store, retail store 550 450 250 200 Walking; standing Drugstore, bank 550 500 250 250 Sedentary work Restaurant 490 550 275 275 Light bench work Factory 800 750 275 475 Moderate dancing Dance hall 900 850 305 545 Walking 3 mph; light machine work Factory 1000 1000 375 625 Bowling Bowling alley 1500 1450 580 870 Heavy work Factory 1500 1450 580 870 Heavy machine work; lifting Factory 1600 1600 635 965 Athletics Gymnasium 2000 1800 710 1090 *Tabulated values are based on 78
F room dry-bulb temperature. For 80
F room dry bulb, the total heat remains the same, but the sensible-heat value should be decreased by approximately 20% and the latent heat values increased accordingly. All values are rounded to the nearest 5 Btu / hr. Adjusted total heat gain is based on normal percentage of men, women, and children for the application listed, with the postulate that the gain from an adult female is 85% of that for an adult male, and that the gain from a child is 75% of that for an adult male. Adjusted total heat value for eating in a restaurant includes 60 Btu / hr for food per individual (30 Btu sensible and 30 Btu latent). For bowling, figure one person per alley actually bowling, and all others as sitting (400 Btu / hr) or standing and walking slowly (550 Btu / hr). Reprinted by permission of ASHRAE from ASHRAE HandbookFundamentals, 1989, American Society of Heating, Refrigerating and Air-Conditioning Engineers. power will dissipate itself in the conditioned air and will show up as a temperature rise. Therefore, we must include the fan brake horsepower in the air-conditioning load. For most low-pressure air-distribution duct systems, the heat from this source varies from 5% of the sensible load for smaller systems to 31/2% of the sensible load in the larger systems. Where the air-conditioning ducts pass through nonconditioned spaces, the ducts must be insulated. The amount of the heat transmitted to the conditioned air through the insulation may be calculated from the duct area and the insulation heat-transfer