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How to Read a Soil Report

written by: Jayant R Row • edited by: Lamar Stonecypher • updated: 9/26/2014

Geotechnica !oi! report! indicate whether a particuar !ite i! !uitabe "or the con!truction o" a permanent or

temporary !tructure#

$o!t pannin% and de!i%n department! o" companie! into any "orm o" con!truction wi u!e !oi report! to aow

them to a!!e!! the !a"ety o" the !tructure that i! bein% panned# &hi! can reate to amo!t any "orm o"

con!truction and can in'o'e buidin%!( road!( municipa pro)ect!( tunne!( dam!( and many other !tructure!# &he

report! wi indicate whether the !oi and %eoo%ica condition! wi %i'e the nece!!ary !upport "or the panned

!tructure#

Need for Soil Reports

Loca authoritie! in mo!t town! and citie! wi in!i!t on !uch %eotechnica !oi report! "rom accredited a%encie!

be"ore they wi %i'e any con!ent to a buidin%# &he idea o" !uch report! i! to en!ure that !tabiity and "oundation

probem! that can occur are *nown to the !tructura en%ineer! who are de!i%nin% the !tructure#

Such report! +uite o"ten in'o'e driin% a re+uired number o" borehoe! dependin% on the area in'o'ed# ,

machine driin% ri% i! u!ed to e-tract !ampe! o" the !oi( and the!e !ampe! are then !ent to %eotechnica

!er'ice te!tin% aboratorie! "or "urther anay!i!# .and operated au%er! are a!o u!ed to e-tract !ampe! i" they

are re+uired at e!!er depth! and the !ite i! imited in area# uite o"ten !tren%th te!t! are a!o made durin% the

!ampin% proce!!# Some !tructura con!utant! a!o in!i!t on carryin% out actua oad te!t! on the "oundation

!trata to obtain readin%! that are con!idered more reiabe#

ma%e !ource: i*imedia

Items Included in Geotechnical Soil Reports

Geotechnica !oi! report! wi brie"y re'iew the %eoo%ica hi!tory o" the area couped with a reconnai!!ance

report o" the particuar !ite and it! !urroundin%!# &he detai! o" !ampin% wi indicate the ocation o" each

borehoe( it! ee'ation and depth and a rou%h indication o" the !oi! encountered at each e'e o" the borehoe#

Groundwater condition! are a!o noted which aow "or e!timatin% "uture !eepa%e into "oundation!( upi"t

pre!!ure! on "oundation! and the need "or ade+uate draina%e# &he report wi %i'e a ca!!i"ication o" a the

'ariou! type! o" !oi! encountered aon% with their !tren%th! a! determined in the aboratory or on !ite# inay themo!t important in"ormation in the!e report! wi be the bearin% capacity o" the !oi( it! !hear !tren%th( and the

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po!!ibiitie! o" !ettement or con!oidation# 3ertain !oi! may ha'e a potentia "or e-pan!ion( which can cau!e

uphea'a and other probem!#

Understanding the Soil Report

 , de!i%n en%ineer need! to *now the condition o" the !oi beneath the !tructure

propo!ed to be buit and it! capacity to !upport the !tructure !a"ey# " main importance to the en%ineer wi be

the aowabe !oi bearin% pre!!ure on the !oi and the po!!ibiitie! o" !ettement in the "oundation a"ter oad!

ha'e been appied on it "or a period o" time# &he e-i!tin% %roundwater tabe( the po!!ibiity o" upi"t pre!!ure! on

the "oundation! becau!e o" thi!( and whether !uch %roundwater need! to be drained away or the !tructure

propery treated to counter any e""ect! o" dampne!! are a!o point! that need con!ideration#

ma%e !ource: i*imedia

&here are time! when the %enera !ope o" the and can tri%%er the po!!ibiity o" a !tructure !idin% once oad! are

impo!ed# &he!e are countered by the !idin% "riction "actor inherent in !oi! and which need to be part o" the

report# &he chemica compo!ition o" the !oi can +uite o"ten ha'e deeteriou! e""ect! on concrete and !tee( and

en%ineer! need to be "orewarned o" the!e "actor! be"orehand !o that they can ta*e action by !u%%e!tin% di""erent

"orm! o" cement or other method! to counter the!e corro!i'e e""ect!#

 , %eotechnica report ha! to be "irm in it! recommendation "or "oundation! and the depth! at which !a"e !oi

bearin% capacitie! wi be a'aiabe# &hey may a!o ma*e recommendation! "or deeper "oundation! or piin%#

Geotechnica report! a!o need to indicate the !ei!mic condition! pre'aent in that area and the need "or the

de!i%ner to incude the!e in !tructura de!i%n!#

.ow to read a !oi report i" you are a contractor: a contractor may oo* at %eotechnica !oi! report! with a

di""erent per!pecti'e# &he contractor wi be concerned with the %round water tabe and probem! that can be

encountered in the dewaterin% o" "oundation!# " roc* i! pre!ent either in !heet "orm or bouder "orm( it can

hamper the pro%re!! o" the "oundation e!peciay i" time con!umin% driin%( brea*in%( and ba!tin% i! re+uired#

&he report woud a!o indicate to the contractor whether it wi be po!!ibe to u!e ripper! and e-ca'ator! toremo'e the !oi to reach the de!ired "oundation e'e# Some de!i%ner! do not permit thi! beyond a certain depth

to pre'ent di!turbance o" the !oi#

 , !oi te!t report wi a!o indicate !a"e !ide !ope! "or temporary e-ca'ation# " the!e !ope! are not !teep( it

%reaty increa!e! the amount o" materia that re+uire! remo'a# t may a!o re+uire !ide! to be !hored up in

e-treme condition!( and thi! %reaty increa!e! con!truction co!t!# , contractor woud a!o need to *now "rom the

report whether !oi remo'ed "rom the e-ca'ation can be reu!ed "or bac*"i# Soi! with poor chemica propertie! or 

which are corro!i'e in nature may re+uire compete remo'a "rom the !ite( thu! increa!in% the co!t o" tran!portin%

thi! !oi out and repacin% it with an accepted "i materia#

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$unicipa and ci'ic authoritie! wi need !uch report! to 'eri"y the de!i%n! !ubmitted by en%ineer! a!*in% "or

buidin% con!ent# t can a!o hep them to prepare an o'era %eoo%ica and !oi report "or the entire town which

can away! be u!e"u to !et parameter! "or "uture con!truction#

References