ITEM 103 - STRUCTURE EXCAVATION

103.1 Description

This  Item  shall  consist of the  necessary excavation for foundation of bridges,  culverts, underdrains,  and  other  structures  not  otherwise provided for in  the  Specifications. Except as otherwise  provided for pipe  culverts, the  backfilling of completed structures  and the  disposal of all excavated surplus materials, shall be in accordance with these Specifications and  in reasonably close conformity with the   Plans  or as established by the Engineer.

This  Item shall  include necessary diverting of live streams, bailing, pumping, draining, sheeting, bracing, and  the  necessary construction of cribs and cofferdams, and furnishing the materials therefore, and the subsequent  removal  of  cribs  and   cofferdams  and   the   placing  of  all necessary  backfill.

It   shall    also    include   the   furnishing   and    placing   of   approved foundation  fill  material  to replace unsuitable  material  encountered below the foundation  elevation  of structures.

No  allowance  will   be  made   for classification  of  different  types   of material  encountered.

103.2 Construction Requirements

103.2.1    Clearing  and  Grubbing

Prior to  starting  excavation  operations  in  any  area,  all  necessary clearing   and   grubbing   in   that  area  shall    have   been    performed   in accordance with  Item  100,  Clearing  and  Grubbing.

103.2.2 Excavation

1. General,   all   structures.The    Contractor  shall    notify the Engineer  sufficiently   in excavation so that advance   of   the    beginning   of cross-sectional       elevations any and measurements may  be taken on the  undisturbed ground.    The natural ground adjacent to  the structure shall  not be disturbed without permission of the  Engineer.
   
   Trenches or foundation  pits for structures or structure footings shall  be excavated to the  lines and grades  or elevations  shown on  the  Plans  or as  staked by the  Engineer.    They  shall  be of sufficient  size  to  permit the  placing  of structures  or structure footings  of the  full  width and length  shown.    The  elevations  of the   bottoms  of  footings,   as   shown  on   the  Plans, shall  be considered as  approximate  only and  the  Engineer  may  order, in  writing, such changes in dimensions  or elevations  of footings as   may  be   deemed   necessary,   to   secure a satisfactory foundation.
   
   Boulders, logs,  and  other objectionable  materials  encountered in  excavation  shall  be removed.
   
   After each  excavation  is  completed, the  Contractor shall  notify the  Engineer to  that effect and  no footing,  bedding material or pipe  culvert shall   be  placed  until  the  Engineer  has approved the depth  of excavation  and  the  character of the  foundation material.


2. Structures  other than   pipe   culverts.     All   rock   or  other  hard foundation   materials  shall be  cleaned   of  all  loose   materials, and  cut to  a firm surface,  either level,  stepped,  or serrated  as directed  by  the   Engineer.       All   seams  or  crevices  shall   be cleaned  and grouted.     All  loose  and  disintegrated  rocks   and thin  strata shall   be  removed.     When the  footing  is to  rest on material other than  rock,  excavation to final  grade shall  not be made  until just  before the footing  is to be placed.     When  the foundation material is soft  or mucky or otherwise  unsuitable, as determined  by  the   Engineer,  the  Contractor shall remove the unsuitable    material    and     backfill   with    approved   qranular material.    This foundation  fill shall  be placed and  compacted in 150  mm   layers  up to the  foundation elevation.
   
   When  foundation  piles   are  used,   the   excavation  of each pit shall  be completed before the piles  are  driven  and  any placing of foundation fill  shall  be done  after the  piles are driven. After the  driving  is  completed, all loose  and  displaced materials  shall be removed,  leaving a smooth,  solid bed to receive the footing.


3. Pipe  Culverts.    The width  of the  pipe  trench shall  be sufficient to  permit  satisfactory jointing  of the pipe  and  thorough tamping of the  bedding material  under and  around the pipe.
   
   Where    rock,     hardpan,    or   other   unyielding    material    is encountered,  it  shall   be removed  below   the foundation  grade for a depth of at least  300  mm  or 4 mm  for each  100 mm  of fill over the top  of  pipe,  whichever is  greater,  but  not  to  exceed three-quarters of the  vertical inside diameter of the  pipe.     The width  of  the  excavation  shall   be  at least 300  mm  greater  than the  horizontal  outside  diameter of the  pipe.      The  excavation below grade shall  be  backfilled with selected fine  compressible rnaterial,  such  as  silty  clay  or loam,  and  lightly  compacted  in layers  hot  over  150  mm   in   uncompacted   depth  to form a uniform but yielding foundation.
   
   Where  a  firm  foundation   is   not  encountered   at  the   grade established,  due to  soft, spongy,  or other unstable  soil,  such unstable  'soil  under  the   pipe   and  for a  width  of  at least  one diameter  on  each  side   of  the   pipe   shall   be  removed  to  the depth  directed  by the  Engineer and   replaced  with  approved granula•r foundation fill  material  properly compacted to  provide adequate    support    for    the    pipe,     unless    other    special construction  methods are  called for on the  Plans.
   
   The   foundation   surface  shall    provide  a   firm  foundation   of uniform  density  throughout the   length  of  the   culvert  and,   if directed  by  the  Engineer,  shall   be  cambered  in  the direction parallel to the  pipe  centerline.
   
   Where pipe  culverts are to  be  placed   in trenches excavated in embankments,    the   excavation    of   each   trench   shall     be performed  after the  embankment  has   been   constructed  to  a plane  parallel to the  proposed profile grade  and  to such height above  the   bottom  of  the   pipe   as   shown  on   the   Plans   or directed  by the  Engineer.

103.2.3   Utilization  of Excavated Materials

All   excavated  materials,  so  far  as   suitable,  shall   be   utilized  as backfill  or embankment. The surplus  materials  shall  be disposed  off in such  manner  as  not  to  obstruct  the   stream  or otherwise  impair  the efficiency or appearance of the  structure.    No .excavated  materials  shall be deposited  at any  time  so as to endanger the  partly finished structure.

103.2.4   Cofferdams

Suitable   and    practically   watertight   cofferdams   shall    be    used wherever water-bearing  strata are  encountered  above   the  elevation  of the  bottom of the  excavation.    If requested, the Contractor shall  submit drawings  showing  his  proposed  method  of cofferdam  construction,  as directed by the  Engineer.

Cofferdams or cribs for foundation construction shall  in general,  be carried  well  below  the bottoms  of the  footings and  shall  be well  braced and   as   nearly  watertight  as   practicable. In general,  the   interior dimensions  of  cofferdams shall  be  such as  to  give. sufficient  clearance for the  construction of forms and  the  inspection of their exteriors, and  to permit  pumping  outside of the  forms.  Cofferdams or cribs which  are tilted or moved   laterally during the  process of sinking shall  be righted or enlarged  so as to provide the  necessary clearance.

When    conditions  are  encountered  which,  as  determined  by  the Engineer,   render  it impracticable  to   dewater  the   foundation   before placing  the   footing,  the   Engineer  may require  the   construction  of  a concrete  foundation   seal   of  such  dimensions   as  he   may consider necessary,  and  of such thickness as  to  resist any possible uplift.    The concrete  for  such seal   shall   be   placed  as   shown on the  Plans or directed  by the  Engineer. The  foundation shall then  be dewatered  and the  footing  placed.When weighted  cribs  are  employed and  the mass is utilized  to  overcome partially  the  hydrostatic  pressure  acting   against the  bottom  of the foundation  seal,  special  anchorage such as dowels or keys   shall   be  provided  to  transfer the entire  mass   of the  crib  to  the foundation  seal. When a foundation seal is placed under water,  the cofferdams shall  be vented  or ported  at low water level  as directed.

Cofferdams  shall   be  constructed  so  as  to  protect  green  concrete against  damage  from    sudden rising    of  the   stream  and   to   prevent damage to the foundation  by erosion.   No timber or bracing  shall  be left  in  cofferdams  or cribs  in  such  a  way  as to  extend  into  substructure masonry,  without written  permission  from the  Engineer.

Any  pumping   that  may  be   permitted   from    the  interior  of  any foundation enclosure shall  be done in such a manner as  to  preclude the possibility  of any portion  of the   concrete  material  being carried  away. Any pumping required  during  the placing  of concrete, or for a  period  of at least 24 hours thereafter, shall be  done from a suitable sump located outside  the  concrete forms.     Pumping to  dewater a  sealed cofferdam shall   not  commence  until  the seal   has  set sufficiently  to withstand the hydrostatic  pressure.

Unless  otherwise  provided,   cofferdams  or cribs,  with  all  sheeting and  bracing  involved therewith,  shall be  removed by the Contractor after the completion  of the substructure.     Removal shall be  effected in  such manner as  not to disturb  or mar finished masonry.

103.2.5   Preservation of Channel

Unless otherwise permitted, no excavation shall be  made outside of caissons, cribs,  cofferdams, or sheet piling, and  the natural stream bed adjacent to  structure shall not be  disturbed without permission from the Engineer. If  any excavation  or dredging   is   made  at  the  side of  the structure before. caissons,  cribs,  or cofferdams  are  sunk  in   place,  the Contractor shall after the foundation base is  in  place, backfill  all  such excavations to  the original  ground  surface  or stream  bed  with material satisfactory to the Engineer.

103.2.6    Backfill and  Embankment for Structures Other Than   Pipe Culverts

Excavated  areas  around  structures  shall  be  backfilled  with  free draining  granular  material approved   by  the   Engineer  and    placed  in horizontal   layers not  over  150   mm     in   thickness, to  the  level   of  the original  ground  surface.      Each layer  shall   be  moistened  or dried  as required  and  thoroughly compacted with mechanical tampers.

In   placing backfills   or  embankment,   the  material   shall  be placed simultaneously   in so   far  as possible   to approximately  the same elevation  on   both sides  of  an  abutment,  pier,  or wall. If conditions require  placing  backfill or embankment  appreciably  higher  on  one side than   on  the opposite  side,  the  additional  material  on  the  higher  side shall not  be  placed until  the masonry has  been in  place for 14  days, or until tests made by the laboratory under the supervision of the Engineer establishes   that  the   masonry   has   attained   sufficient   strength   to withstand  any pressure  created  by  the   methods  used  and   materials placed without damage  or strain beyond a safe factor.

Backfill  or  embankment  shall  not  be   placed  behind  the  walls  of concrete  culverts  or abutments  or  rigid   frame  structures   until  the  top slab  is  placed and  cured. Backfill  and embankment  behind abutments held   at  the top by  the  superstructure, and behind the  sidewalls  of culverts, shall be  carried  up simultaneously  behind opposite abutments or sidewalls.

All   embankments  adjacent  to  structures  shalt   be   constructed  in horizontal  layers  and compacted  as  prescribed   in Subsection   104.3.3 except   that   mechanical   tampers   may   be used.  for  the   required compaction.  Special care shall be taken to  prevent any wedging action against  the  structure,  and   slopes  bounding  or within  the   areas  to  be filled   shall    be   benched or  serrated  to   prevent  wedge  action.  The placing  of  embankment  and   the  benching  of slopes shall   continue  in such  a   manner  that  at  all   times   there  will    be   horizontal   berm  of thoroughly compacted material  for a distance  at  least equal to the  height of  the  . abutment  or wall to   be  backfilled  against  except  insofar  as undisturbed  material  obtrudes upon  the area.

Broken   rock  or  coarse  sand   and   gravel J  shall, be   provided   for  a drainage filter at weep holes as shown on the  Plans.

103.2.7   Bedding, Backfill, and  Embankment for Pipe  Culverts

Bedding,  Backfill and   Embankment  for pipe culverts  shall   be  done in  accordance with Item 500,  Pipe Culverts and  Storm  Drains.

103.3       Method of Measurements

103.3.1   Structure Excavation

The  volume of excavation to  be  paid  for will  be the  number of cubic meters measured in original position of material acceptably excavated in conformity with the Plans or as  directed by the Engineer, but in no case, except as  noted,  will   any of the following  volumes  be  included  in  the measurement for payment:

1. The volume outside of vertical planes 450  mm  outside of and parallel to  the   neat  lines  of footings  and  the   inside  walls of pipe     and     pipe-arch    culverts   at   their   widest   horizontal dimensions.


2. The volume  of  excavation  for culvert and   sections  outside the vertical  plane for culverts stipulated  in  (1)  above.


3. The volume outside  of neat  lines  of underdrains  as  shown on the Plans, and  outside  the limits  of foundation  fill  as  ordered by the  Engineer.


4. The  volume included within the staked limits of the roadway excavation,  contiguous  channel  changes,  ditches,  etc.,  for which payment  is  otherwise  provided  in  the Specification.


5. Volume  of  water   or  other   liquid   resulting  from   construction operations  and  which  can  be pumped or drained away.


6. The  volume   of  any  excavation  performed  prior  to  the  taking of elevations  and  measurements  of the  undisturbed  ground.


7. The  volume   of any  material  rehandled,  except   that  where   the Plans indicate or the Engineer directs  the excavation after embankment    has    been    placed     and    except     that when installation  of  pipe  culverts  by  the  imperfect  trench   method material  re-excavated as directed will  be included.


8. The   volume    of  excavation  for  footings  ordered  at  a  depth more  than  1.5  m below  the lowest elevation for  such  footings shown on   the   original    Contract  Plans,     unless    the Bill   of Quantities  contains  a pay  item  for  excavation  ordered  below the  elevations shown on the  Plans   for  individual footings.

103.3.3     Foundation  Fill

The  volume   of  foundation  fill  to  be  paid  for  will  be  the  number  of cubic   meters   measured in final  position  of the  special   granular  material actually     provided    and    placed     below    the foundation    elevation    of structures  as specified,  completed  in place  and  accepted.          

103.3.4    Shoring, Cribbing,  and  Related Work

Shoring,    cribbing  and   related   work   whenever    included  as  a  pay item  in Bill  of Quantities will  be paid  for  at the  lump  sum  bid  price.     This work   shall   include   furnishing, constructing, maintaining,   and   removing any  and  all  shoring, cribbing,  cofferdams,   caissons,   bracing, sheeting, water    control,    and    other    operations   necessary   for   the    acceptable completion  of excavation  included  in the  work  of this  Section,  to a depth of     1  .5   m  below the  lowest elevation   shown   on  the   Plans   for   each separable  foundation structure.

103.3.5  Basis   of Payment

The  accepted  quantities,   measured  as  prescribed  in Section  103.3, shall  be  paid  for  at the contract   unit  price  for  each  of  the  particular pay items   listed   below   that   is   included   in  the Bill   of  Quantities.  The payment shall  constitute full compensation  for  the  removal and  disposal of   excavated  materials    including     all    labor,    equipment,     tools    and incidentals   necessary to  complete   the   work   prescribed   in  this   Item, except  as follows:

1. Any  excavation  for  footings  ordered  at a depth   more  than  1.5 m  below  the  lowest elevation  shown   on  the  original   Contract Plans  will  be paid  for  as provided in Part  K, Measurement and Payment,   unless  a  pay   item   for   excavation   ordered  below Plan elevation appears   in the  Bill of Quantities.


2. Concrete  will   be  measured  and   paid   for  as  provided  under Item  405,  Structural Concrete.


3. Any  roadway  or  borrow   excavation   required  in  excess   of  the quantity  excavated  for structures  will  be  measured  and  paid for as provided under  Item  102.


4. Shoring,  cribbing,  and   related   work   required  for  excavation ordered  more  than  1  .5 m below  Plan  elevation will  be paid  for in accordance  with  Part  K.

Payment will   be made  under:

Pay  Item Number	Description	Unit of Measurement
103 (1)	Structure Excavation	Cubic Meter
103 (2)	Bridge Excavation	Cubic Meter
103 (3)	Foundation Fill	Cubic Meter
103 (4)	Excavation ordered below Plan elevation	Cubic Meter
103 (5)	Shoring, cribbing, and related work	Lump sum
103 (6)	Pipe culverts and drain excavation	Cubic Meter