QUESTIONS - 14070

MATERIALS - 14070_80

CHAPTER 4 PROJECT DRAWINGS - 14070_83

Engineering Aid 1 - Advanced Structural engineering guide book
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coral, caliche, tuff, rubble, lime rock, shells, cinders, iron ore, and other select materials. Some of these are primarily soft rock and are crushed or degraded under construction traffic to produce composite base materials. Others develop a cementing action, which results in a satisfactory base. The following text describes the characteristics and usage of some of these materials: 1. CORAL. Uncompacted and poorly drained coral often results in an excessive moisture content and loss of stability. The bonding properties of coral, which are its greatest asset as a construction material, vary with the amount of volcanic impurities, the proportion of fine and coarse material, age, length of exposure to the elements, climate, traffic, sprinkling, and method of compaction. Proper moisture control, drainage, and compaction are essential to obtain satisfactory results. 2 CALICHE. A variable material that consists of sand, silt, or even gravel, that when saturated with water, compacted, and allowed to settle, can be made into high-quality base courses, especially caliches that are cemented with lime, iron oxide, or salt. Caliches vary, however, in content (limestone, silt, and clay) and in degree of cementation; therefore, it is important that caliche of good uniform quality be obtained from deposits and that it be compacted at optimum moisture. 3. TUFF. A porous rock usually stratified, formed by consolidation of volcanic ashes, dust, and so forth, and other cementitious materials of volcanic origin, may be used for base courses. Tuff bases are constructed the same as other base courses except that after the tuff is dumped and spread, the oversize pieces are broken and the base compacted with sheepsfoot rollers. The surface is then graded, compacted, and finished. 4. RUBBLE. It may be advantageous to use the debris or rubble of destroyed buildings in constructing base courses. If so, jagged pieces of metal and similar objects are removed. Bituminous Base Bituminous mixtures are frequently used as base courses beneath high-type bituminous pavements, particularly for rear-area Wields which carry heavy traffic. Such base courses may be used to advantage when locally available aggregates are relatively soft and otherwise of relatively poor quality, when mixing plant and bituminous materials are readily available, and when a relatively thick surface course is required for the traffic. In general, a bituminous base course may be considered equal on an inch-for-inch basis to other types of high-quality base courses. When a bituminous base course is used, it will be placed in lifts not exceeding 3 1/2 inches in thickness. If a bituminous base is used the binder course may be omitted, and the surface course may be laid directly on the base course. QUESTIONS Q1. What is the correct nomenclature for each of the items labeled in figure 3-18? Q2. What feature is normally provided in a horizontal curve to counteract the effect of centrifugal force? Q3. What type of section is used to set slope stakes and to show as-built conditions? Figure 3-18.-Typical section. 3-19

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