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