Table  15-2  shows  methods  of  underground exploration   and   sampling   in   a   condensed form. TAGGING   SAMPLES Let  us  suppose  that  soil  in  a  given  area is  to  be  tested  (such  as  the  area  on  which a   structure   is   to   be   erected).   The   officer in   charge   of   soil   exploration   decides   how many  points  are  needed  and  where  they  must be  located  to  produce  a  representative  test of  the  soil  in  the  area.  This  information  is recorded  in  a  sketch  like  the  one  shown  in figure  15-3. This   figure   shows   the   locations   of   ex- ploratory  points  along  a  highway,  the  point locations  referenced  by  the  center-line  station and  the  distance  from  the  center  line.  To the  left  of  the  center  line,  between  stations 2   +   80   and   4   +   60,   there   is   a   borrow   pit, from  which  soil  for  fill  is  taken.  The  soil here  is  tested  by  samples  taken  from  a  60-ft trench  (T1),  located  at  station  3  +  20,  300 ft   from   the   highway   center   line;   from   two borings  (B1  and  B2)  at  stations  3  +  60  and 3  +  80,  230  ft  and  420  ft  from  the  center line, respectively; and from a 20-ft- square pit (P2) at  station  4  +  20,  300  ft  from  the  center line. Besides the borrow pit exploration, there is a boring (B3) at station 4 + 80, 125 ft to the right of the center line; another boring (B4) at station 6 + 00, 100 ft to the left of the center line; and a 20-ft-square pit (P3) on the center line at sta- tion  7  +  20. Each  sample  taken  is  tagged  according  to the   location   from   which   it   was   taken.   Loca- tions  are  given  in  consecutive  numbers;  for those  shown  in  figure  15-3,  the  numbers  might run  from  the  bottom  up,  with  T1  being  No.  1; B  1,  No.  2;  and  so  on.  A  sample  is  tagged  with the  project  symbol  (the  symbol  for  the  project shown  in  fig.  15-3  is  BF)  and  the  location  sym- bol (such as T1 or B1). If more than one sample is taken from the same location, you need to use additional  numbers.  For  example,  a  sample  taken from  B2  in  figure  15-3  maybe  tagged  ‘‘BF-B2-4, bag  1  of  6.”  This  means tion  No.  4,  the  first  of  6 location.” “boring  No.  2,  loca- bags  taken  from  that The   sample   identification   is   printed   with a  marking  pencil  or  pen  on  two  tags,  one  of which is placed inside the bag, and the other of which  is  tied  on  the  outside.  Gummed  labels may  be  similarly  used  to  identify  samples  that are  placed  in  moisture  content  boxes,  cylinders, or  jars. DISTURBED SAMPLES Samples  taken  by  hand  scoops,  auger  bor- ings,  shovels,  or  any  other  convenient  hand tool  with  no  attempt  to  obtain  the  material in  its  natural  state  of  structure  or  density  is known as a DISTURBED sample. These samples are  used  for  mechanical  analysis,  plasticity, specific  gravity,  frost  susceptibility,  compaction, and laboratory compacted CBR tests. The size of the  sample  taken  will  depend  upon  the  tests  to  be performed. Individual  Samples When   taking   individual   samples   from   a pit,  trench,  or  exposed  face  (fig.  15-4),  first shave   off   loose   and   dried   soil   to   obtain a  fresh  surface  and  to  expose  any  soil  varia- tions  clearly.  Then  take  a  typical  sample  of each   type   of   soil   or   of   those   requiring   ad- ditional  investigation.  When  sampling  in  auger holes, place typical portions of the soil obtained Figure 15-4.-Obtaining individual bag samples from an exposed face. 15-9