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SUBBASE AND BASE COURSE

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LANDING STRIP. Includes the landing area, end zones,  shoulders,  and  cleared  areas. REVETMENT. A protective pen usually made by excavating into the side of a hill or by constructing earth, timber,  sandbag,  or  masonry  traverse  around  the hardstands.  Such  pens  provide  protection  against  bomb fragments  from  high-altitude  bombing  but  provide  little protection  against  ground  strafing.  They  may  actually draw this type of fire if they are not well concealed. RUNWAY. That portion of the landing strip, usually paved, that is used for the landing and takeoff of aircraft. SHOULDER.   The  graded  and  stabilized  area adjacent to the runway or taxiway. Although it is made capable of supporting aircraft and auxiliary equipment (such  as  crash  trucks)  in  emergencies,  its  principal function  is  to  facilitate  surface  drainage. TAXIWAY. A  specially  prepared  area  over  which aircraft may taxi to and from the landing area. TRANSITION   SURFACE.   A  sloping  plane surface (about 1 foot rise to 7 feet run) at the edge of a landing strip. Its function is to provide lateral safety clearances for planes that accidental] y run off the strip. (See fig. 3-15.) PLANNING AN AIRFIELD Planning  for  aviation  facilities  requires  special consideration   of   the   type   of   aircraft   to   be accommodated;   physical   conditions   of   the   site, including  weather  conditions,  terrain,  soil,  and availability  y  of  construction  materials;  safety  factors, such as approach zone obstructions and traffic control; the  provision  for  expansion;  and  defense.  Under wartime conditions, tactical considerations are also required.  All  of  these  factors  affect  the  number, orientation,  and  dimensions  of  runways,  taxiways, aprons, hardstands, hangars, and other facilities. SUBBASE AND BASE COURSE Pavements  (including  the  surface  and  underlying courses) may be divided into two classes—rigid and flexible. The wearing surface of a rigid pavement is constructed of portland cement concrete. Its flexural strength enables it to act as abeam and allows it to bridge over minor irregularities in the base or subgrade upon which it rests. All other pavements are classified as flexible.  Any  distortion  or  displacement  in  the  subgrade of a flexible pavement is reflected in the base course and upward  into  the  surface  course.  These  courses  tend  to conform  to  the  same  shape  under  traffic.  Flexible pavements  are  used  almost  exclusively  in  the  theater  of Figure 3-17.-Typical pavements using stabilized layers. operations for road and airfield construction since they adapt to nearly all situations and can be built by any construction  battalion  unit  in  the  Naval  Construction Force  (NCF). FLEXIBLE PAVEMENT STRUCTURE A typical flexible pavement is constructed as shown in figure 3-16, which also defines the parts or layers of pavement. All layers shown in the figure are not present in every flexible pavement. For example, a two-layer structure consists of a compacted subgrade and a base course  only.  Figure  3-17  shows  a  typical  flexible pavement using stabilized layers. (The word  pavement, when used by itself, refers only to the leveling, binder, and surface course, whereas flexible pavement refers to the  entire  pavement  structure  from  the  subgrade  up.) The  use  of  flexible  pavements  on  airfields  must  be limited to paved areas not subjected to detrimental effects of jet fuel spillage and jet blast. In fact, their use is prohibited in areas where these effects are severe. 3-17



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