GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
INTEGRATED RESISTIVITY, INDEX, AND STRENGTH
CHARACTERISTICS OF SUBGRADE SOILS: IMPLICATION FOR
HIGHWAY PAVEMENT FAILURE STUDIES IN NORTH-CENTRAL
NIGERIA
Daniel Opemipo OBASAJU1 , Mo oo Olasunbo OLORUNTOLA2 , Sunday OLADELE2
1 Kogi S a e Uni e si y, Depa men o Ea h Sciences, Anyigba, Nige ia
2 Uni e si y o Lagos, Depa men o Geosciences, Lagos, Nige ia
E-mail: obasajudan[email p o ec ed]
ABSTRACT
In eg a ed geophysical and geo echnical s udies ha e been ca ied ou o de e mine he geological cause(s) o he
ailu e o sec ions o Ajaoku a – Anyigba Highway, No h-cen al Nige ia. Fo y-eigh (48) Ve ical Elec ical
Soundings (VES) we e conduc ed on ailed and s able sec ions o he highway. Also, wen y-one (21) subg ade
soil samples close o VES s a ions om he uns able and s able sec ions o he highway we e subjec ed o
labo a o y geo echnical analyses which include g ain size dis ibu ion, A e be g limi s, compac ion (Op imum
Mois u e Con en , OMC, and Maximum D y Densi y, MDD) and Cali o nia bea ing a io (CBR) a soaked and
unsoaked s a es ollowing Ame ican Socie y o Tes ing and Ma e ial (ASTM) s anda ds as app op ia e. The
geophysical esul s show ha low esis i i y (10–100 Ohms-m) in e ed as clay/sil o low compe ence
cha ac e izes he subg ade soils o he uns able segmen . While highe esis i i y (148–272 Ohms-m) in e p e ed
as sandy-clay/sil wi h mode a e compe ence was ob ained o he subg ade soils o he s able segmen . Resul s o
Geo echnical es s show ha he subg ade soils o he uns able segmen ha e geo echnical p ope ies ha gene ally
all below equi ed s anda d speci ica ions. S ong co ela ions o R = 0.86, 0.9, and –0.88 we e ob ained be ween
CBR and sand, esis i i y, and he amoun s o ines, while a ai ly s ong co ela ion o R = –0.67 was ob ained
o he plas ici y index. The high le el o co ela ion implies ha CBR can be p edic ed om geophysical da a and
o he geo echnical pa ame e s. The s udy has e ealed ha he ad anced wea he ing o he unde lying Mica-Schis
o clayey/sil y subg ades wi h unsui able geophysical and geo echnical p ope ies is a majo con ibu o o he
ins abili y o he highway.
Keywo ds: A e be g limi ; CBR; G ain size dis ibu ion; Resis i i y; Subg ade soil.
1 INTRODUCTION
The impo ance o oads in d i ing na ional, socie al, and communi y de elopmen canno be o e emphasized [1].
In de eloping coun ies, such as Nige ia whe e means o anspo a ion including unde g ound ubes, ails, and
wa e sys ems a e mos ly unde de eloped, lexible oad pa emen is he mos common means o anspo a ion
[2]. E alua ion o exis ing highways is pa amoun o p oposing be e designs ha can help o cu ail he ala ming
equency o ailed oads all o e he wo ld [3]. In addi ion o he ac ha i is common knowledge in Nige ia ha
highway pa emen ailu e is a no m, mos highways a ely a ain hei design age be o e ailu e [4]. A highway
can be said o ha e ailed when i can no longe pe o m i s p ima y pu pose o when i has s uc u al de ec s.
Thus, he ailu e o highways can be s uc u al and/o unc ional. Resea ch in [5] sugges ed ha he pe pe ual
ailu e o some sec ions o oads in sou heas e n Nige ia has no only nega i ely impac ed human and ehicula
mo emen s bu also incu ed huge inancial loss a ising om incessan econs uc ion and ehabili a ion. The
highway is an impo an enginee ing s uc u e ha consis s o subsoil laye s ha include he subg ade, subbase,
and base cou se in lexible pa emen designs. The subg ade soil is he ounda ion soil and a p oduc o he in-si u
wea he ing o he basemen ock (in he Basemen Complex en i onmen ). I is he e o e a p oduc o geology and
47
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
he clima ic ac o o an en i onmen . Un o una ely, geological ac o s a e a ely conside ed in he cons uc ion
and ehabili a ion o se e al highways in Nige ia e en hough he subg ade soil is a p oduc o geology [6]. The
causes o con inuous ailu e o highways in Nige ia a e no adequa ely in es iga ed be o e ehabili a ion [6].
Sou ces o highway ailu e ha e always been a ibu ed o he use o poo cons uc ion ma e ials, a ic loading,
and poo design [7–9]. Simila causes o ailu e a e o en p oposed i espec i e o he geology o he a ea. A ew
s udies ha e, howe e , shown he in luence o geology on he s abili y and o he wise o highways. Resea ch by
[10 and 11] e ealed ha highway ailu e could be p ecipi a ed by geological ea u es which include aul s and
clayey subg ades.
Despi e he widesp ead ailu e o highways na ionwide, mos highway pa emen ailu e s udies in Nige ia
concen a e on he sou hwes e n pa s o he coun y. Many ailed highways (such as Kabba-Isanlu-Egbe, Eki in
– Omuo, and Ajaoku a-Ayingba highways in No h-Cen al, Nige ia) a e common wi h li le o no e o o s udy
he ac o s esponsible o he incessan ailu e o highways in his pa o he coun y. The e o e, he e is a need
o e alua e he causes o highway ailu e in o he pa s o he coun y. This could aid in compa a i e pu pose and
egional managemen s a egies o highways in Nige ia.
An in eg a ed geophysical echnique ( esis i i y su eys) and geo echnical es s in ol ing index (g ain size
dis ibu ion and A e be g limi s) and s eng h (compac ion es and Cali o nia bea ing a io) p ope ies ha e been
employed in his s udy. The combina ion o hese me hods helped o deciphe he na u e o he subg ade soils
unde lying he oad alignmen as well as p o ide a use ul ela ionship be ween hem. Se e al au ho s ha e shown
he success o hese me hods o o he in eg a ed geological me hods in highway subsoil e alua ion. The
geo echnical me hod was adop ed by [12] and [6]; while au ho s [13–15] used he geophysical me hod. A s udy
by [16] employed he geophysical and geo echnical me hods and [17] adop ed he mine alogical, geochemical,
and geo echnical me hods. In addi ion, [18] applied he use o Mul ichannel Analysis o Su ace wa es in highway
subsoil e alua ion. These s udies showed he ele ance o unde s anding he cha ac e is ic na u e o he geology
and subg ade soils be o e highway pa emen cons uc ion.
The highway unde s udy is a dual ca iageway and an impo an oad ha can d i e Nige ia’s economy as i links
se e al s a es in Nige ia. I is si ua ed in Kogi S a e, No h-cen al Nige ia, and is delimi ed wi hin 6°40’30”–
6°48’0” N and 7°22’30”–7°30’0” E (Figu e 1). The highway is unde lain by Mica-Schis and G ani e Gneiss [19]
which a e P ecamb ian in age [20]. While he ailed po ion o he highway is unde lain by subg ade soils ob ained
om Mica-Schis , he s able sec ion es s on he wea he ed p oduc s o G ani e-Gneiss. Bo h dual ca iageways
ha e ailed and a e cha ac e ized by he ex ensi e and comple e ippling o he asphal laye as well as dep essions.
Al hough e y ecen ly, an a m o he ca iageway has been ehabili a ed, some sec ions ha e s a ed ailing again.
This is because he possible cause(s) o his ailu e is (a e) ye o be s udied and ehabili a ion exe cise wi hou an
unde s anding o he na u e o geology would con inue o lead o huge inancial loss and was age o esou ces
h ough epea ed ailu es. The p esen s udy combines geophysical and geo echnical in es iga ion o cha ac e ize
he subg ade soils o he highway and es ablishes ela ionships be ween geophysical and geo echnical pa ame e s.
Figu e 1. Geologic map o he s udy a ea showing geophysical su ey and soil sampling poin s [mod. om 19]
48
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
2 METHODOLOGY
Bo h geophysical and geo echnical echniques we e deployed in his s udy. The loca ions o he geophysical su ey
poin s and he es pi s om which he samples we e ob ained we e dic a ed by he geology o he a ea and he
s abili y o o he wise o he sec ions. The elec ical esis i i y echnique using he Schlumbe ge a ay was adop ed
o he geophysical s udy. Fo y-eigh Ve ical Elec ical Soundings (VES) we e conduc ed wi h o al cu en
sepa a ion (AB/2) be ween 65–100 m). Fo y- wo VES we e on he uns able sec ion and six on he s able sec ion
o se e as he con ol. The p ocedu es o he acquisi ion, p ocessing, and in e p e a ion o he VES ha e been
well documen ed by [21 and 22].
Twen y-one (21) soil samples o med om he in-si u wea he ing o he pa en ocks we e ob ained; eigh een om
he ailed sec ion and h ee om he s able sec ion o con ol. The samples we e ob ained om ele en es pi s
dug (0.1–1 m dep h) close o VES s a ions. This was o enable he in eg a ion o geo echnical and geophysical da a
as well as o es ablish ela ionships be ween he wo me hods h ough eg ession analysis. The subg ade soil
samples we e subjec ed o geo echnical index o classi ica ion es s which include, g ain size dis ibu ion and
A e be g limi (Plas ic and Liquid limi ); s eng h es which in ol es compac ion (s anda d p oc o ) and
Cali o nia bea ing a io (CBR) in unsoaked and soaked condi ions. All he es s we e pe o med acco ding o he
app op ia e codes o he Ame ican Socie y o Tes ing and Ma e ials (ASTM). A sligh modi ica ion was howe e
made in he de e mina ion o he g ain size dis ibu ion which in ol ed adding abou 2% Calgon (Sodium
hexame aphospha e) o soil solu ion o abou 24 hou s o e ec i ely sepa a e he clayey agmen s om he sands.
This is documen ed in [23 and 24].
3 RESULTS AND DISCUSSION
3.1 Resis i i y esul s
The esul s o he esis i i y alues o he subg ades soils a e summa ized by he Box and Whiske plo (Figu e 2).
The esis i i y o subg ade soils can be used o p edic hei compe ence. This is because he esis i i y o a ma e ial
is la gely dependen on he luid con en and ma ix o mechanical p ope ies. A s udy by [26] p oposed soils’
compe ency a ing based on esis i i y ange (Table 1). This was used o classi y he soils. The esis i i y o he
subg ade soils o he uns able and he s able sec ions anged om 10–100 Ohms-m and 148–272 Ohms-m. The
subg ade soils o he uns able sec ion, he e o e, classi y as soils wi h incompe en a ings while hose o he s able
sec ion a e mode a ely compe en . The e y low esis i i y alues o he subg ade soils o he uns able sec ion
indica ed ha he pa en ock (Mica-Schis ) has unde gone in ensi e and ex ensi e wea he ing o o m wea he ed
p oduc s domina ed by e y ine g ain soils which a e sil y and clayey. These clayey/sil y soils a e inimical o he
s abili y o he highway due o hei low bea ing capaci y when subjec ed o he axle loads o ehicles and ucks
ha ply he highway egula ly. By con as , he ela i ely highe esis i i y o he subg ade soils o he s able
sec ion e lec s he p eponde ance o coa se-g ained soils (sand/g a el) o e he ine-g ained soils (clay/sil s)
o med om he wea he ing o he unde lying g ani e-gneiss. Field mac oscopic s udies o he Mica-schis and
G ani e-Gneiss showed ha he mine alogy o he o me is essen ially made up o micas (bio i e and musco i e),
eldspa and qua z and possess schis osi y. The schis osi y desc ibes he ease wi h which his ock can be spli
along a plane. The da k mica (bio i e) howe e appea s o domina e, making he ock en i ely da k in colou . A
li le amoun o qua z is isible in he pa en ock. Bio i e and Feldspa disin eg a e ela i ely easily o o m clay
while he musco i e o ms mo e sil upon wea he ing as e idenced by he shining lus e o he sampled wea he ed
p oduc s. Qua z in he pa en ock is he mos esis an o wea he ing and emains i ually unchanged bu o ms
a mino amoun o sand and hus o e s a minimal con ibu ion o he s abili y o he highway. On he o he hand,
he g ani e gneiss is domina ed by qua z and eldspa wi h mino amoun s o micas. Al hough eldspa and micas
wea he o clay and sil , he high esis ance o qua z o wea he ing makes he disin eg a ion p oduc o he pa en
ock o be domina ed by sand, which o e s a signi ican con ibu ion o he s abili y o he highway due o highe
bea ing capaci y.
49
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
Figu e 2. Box and Whiske Plo s o esis i i y o he clayey (wea he ed) subg ade soils
o uns able and s able sec ions
Table 1. Classi ica ion o esis i i y alues based on compe ence a ing [25]
Appa en esis i i y ange (Ohm-m)
Li hology
Compe ence a ing
< 100
Clay
Incompe en
100 – 350
Sandy clay
Mode a ely Compe en
350 – 750
Clayey sand
Compe en
>750
Sand/la e i e/bed ock
Highly Compe en
3.2 Geo echnical esul s
3.2.1 G ain size dis ibu ion
Figu e 3 shows he g ain size dis ibu ion o he subg ade soil samples. Samples “S1–S9” a e om he uns able
sec ion while “S10–S11” a e om he s able sec ion. Figu e 4 shows he AASHTO classi ica ion plo o he ine-
g ained ac ions subjec ed o he A e be g limi es .
50
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
Figu e 3. G ain size dis ibu ion o subg ade soils
Figu e 4. AASHTO Soil Classi ica ion o subg ade soils

51
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
Table 2 summa izes he esul s o he g ain size dis ibu ion and he A e be g limi es . The pe cen age o sand
in he subg ade soils o he uns able and s able sec ions anged om 36–48% and 71–80%, espec i ely. While he
amoun s o ines (sil +clay) in he subg ades o he uns able and s able sec ions anged om 52–64% and 20–29%,
espec i ely. Acco ding o he Uni ied Soil Classi ica ion Scheme (USCS), soils wi h >50% sand a e essen ially
coa se-g ained while hose below 50% a e ine-g ained. This implies ha he subg ade soils o he uns able sec ion
a e p ima ily ine-g ained. This ag ees wi h he esul o he geophysical s udy as well as he geology. On he o he
hand, subg ade soils o he s able sec ion a e p incipally coa se-g ained, and his con i ms he indings o he
geophysical s udy. In he same ein, he subg ade soils o he uns able sec ion ha e poo o ai subg ade a ing
acco ding o The Ame ican Associa ion o S a e Highway and T anspo a ion O icials (AASHTO) classi ica ion
o subg ade soils wi h ines >35%. The subg ade soils o he s able sec ion classi y as good o excellen subg ade
soils consequen ly.
The A e be g limi es esul s (Table 2) and Figu e 4 e ealed ha he subg ades o he uns able segmen ha e
Liquid limi and Plas ici y index anging om 21.3–46.0% and 12.7–38.8% While subg ades o he s able sec ion
espec i ely ha e 23.2–25.5% and 0.4–8.1%. The subg ades o he uns able sec ion classi y as A-7-6 and A-6
clayey soils wi h low o high plas ici y while hose o he s able sec ion a e A-2-4 sil y soils wi h low plas ici y.
The plas ici y index o subg ade soil p o ides clues on po en ial olume ic changes, pe meabili y, and dis ess
condi ion unde uns able g oundwa e si ua ions a e cons uc ion [26]. Soils wi h low plas ici y and liquid limi
a e o en desi ed as subg ades soils o highway cons uc ion o p e en la gely olume changes in soils ha could
igge he ailu e o he highway du ing al e na e we ing and d ying o he soils in we and d y seasons. The
speci ica ions in [27] s ipula e ha subg ade soils’ Liquid limi and Plas ici y Index should be less han 50% and
30%, espec i ely. The majo i y o subg ade soils o he uns able sec ion howe e sa is y hese c i e ia. This is
a ibu ed o he sil y na u e o he musco i e mica in he subg ade soils which educes he plas ici y e ec . All he
subg ade soils o he s able loca ion mee hese equi emen s.
Table 2. G ain size dis ibu ion and A e be g esul s o subg ade soils
S/N
Pa en
ock
Pi
no.
Sampling
dep h (m)
Sand
(%)
Amoun s o
Fines (%)
AASHTO
S anda d
(F≤35%)
Liquid
Limi
(LL)
Plas ici y
Index (PI)
= (LL-PL)
AASHTO
Classi ica i
on
Geologic
ma e ial
Gene al
Ra ing as
Subg ade
1
Mica-
Schis
1
0.50
36
62
33.8
12.7
A-6
Clay/Sil
Fai o Poo
2
Mica-
Schis
1
1.00
38
61
28.2
15.1
A-6
Clay/Sil
Fai o Poo
3
Mica-
Schis
2
0.30
39
61
24.0
24.0
A-6
Clay/Sil
Fai o Poo
4
Mica-
Schis
2
0.40
43
57
38.8
38.8
A-6
Clay/Sil
Fai o Poo
5
Mica-
Schis
3
0.60
45
55
32.9
19.5
A-6
Clay/Sil
Fai o Poo
6
Mica-
Schis
3
0.80
38
62
34.3
25.2
A-6
Clay/Sil
Fai o Poo
7
Mica-
Schis
4
0.30
45
55
29.4
23.5
A-6
Clay/Sil
Fai o Poo
8
Mica-
Schis
4
0.60
45
55
31.2
22.4
A-6
Clay/Sil
Fai o Poo
9
Mica-
Schis
5
0.20
48
52
21.3
14.3
A-6
Clay/Sil
Fai o Poo
10
Mica-
Schis
5
0.60
47
53
27.5
18.2
A-6
Clay/Sil
Fai o Poo
11
Mica-
Schis
6
0.40
45
55
31.0
20.5
A-6
Clay/Sil
Fai o Poo
12
Mica-
Schis
6
0.80
44
56
24.0
16.0
A-6
Clay/Sil
Fai o Poo
13
Mica-
Schis
7
0.50
36
64
26.3
21.2
A-6
Clay/Sil
Fai o Poo
14
Mica-
Schis
7
0.60
40
60
23.8
23.8
A-6
Clay/Sil
Fai o Poo
15
Mica-
Schis
8
0.30
36
64
38.5
18.6
A-6
Clay/Sil
Fai o Poo
52
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
16
Mica-
Schis
8
0.40
36
64
46.0
17.4
A-7-6
Clay/Sil
Fai o Poo
17
Mica-
Schis
9
0.60
45
55
40.0
17.5
A-6
Clay/Sil
Fai o Poo
18
Mica-
Schis
9
0.80
42
58
30.0
18.4
A-6
Clay/Sil
Fai o Poo
19
G ani e
-Gneiss
10
0.10
71
29
23.2
8.1
A-2-4
Sil y Sand
Excellen o
Good
20
G ani e
-Gneiss
10
0.50
80
20
25.5
7.3
A-2-4
Sil y Sand
Excellen o
Good
21
G ani e
-Gneiss
11
0.50
77
21
25.0
0.4
A-2-4
Sil y Sand
Excellen o
Good
3.2.2 S eng h cha ac e is ics
The compac ion and Cali o nia Bea ing Ra io (CBR) esul s a e p esen ed in Table 3. The compac ion cu es a e
p esen ed in Figu e 5. Compac ion o soil is a mechanical me hod u ilized in imp o ing soil geo echnical
p ope ies. The pu pose o compac ion is o enhance he densi y o he soil and educe he po e space illed by ai
o inc ease he bea ing o load-ca ying capaci y o he soil. Two key compac ion pa ame e s a e e alua ed which
include he Op imum Mois u e Con en (OMC) and he Maximum D y Densi y (MDD). Gene ally, he highe he
MDD and he lowe he OMC, he be e he soil as highway ounda ion ma e ial. [27] p oposed MDD alues
abo e 1.7 g/cm3 while OMC should be less han 18% o soil o be sui able o subg ade. MDD and OMC alues
o subg ade soils o he uns able sec ion anged om 1.68–2.03 g/cm3 (a e age o 1.77g/cm3) and 9.62–18.7%
(mean o 13.2%). The subg ade soils he e o e gene ally mee he equi emen excep o one sample. This esul
sugges s ha i he subg ade soils a e well compac ed on he ield wi h highe ene gy, he ca ying capaci y o he
soil will be enhanced. The MDD and OMC alues o he subg ade soils om he s able sec ion howe e show
be e compac ion cha ac e is ics han he o me . MDD and OMC anged om 1.89–2.69 g/cm3 (mean o 2.2
g/cm3) and 10.4–13.2% (a e age o 11.6%). The compac ion cu es show ha u he addi ion o wa e o he soils
beyond he maximum d y densi y leads o a con inuous dec ease in he d y densi y. Thus, ca e should be aken
du ing ield compac ion o a oid he addi ion o wa e beyond he OMC. This is because he in illing o wa e in
he po e spaces will educe soil g ain o g ain con ac he eby lowe ing he ic ional o ce be ween g ains. This
would a he cause he loosening and weakening o he soils and consequen ly, educe he bea ing capaci y o he
soils.
Figu e 5. Compac ion cu es o he subg ade samples
53
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
The CBR o soil is di e en om he compac ion es . The CBR is speci ically a es designed o e alua e subg ade
soils’ esis ance o pene a ion. The CBR is ca ied ou bo h in unsoaked and soaked condi ions o simula e he
esis ance o load pene a ion du ing d y and ainy seasons espec i ely. The soaked CBR gi es an idea o he
s eng h ha would be los du ing ing ess o wa e in he subg ade soils which is he wo s scena io. I is hus be e
o oad pa emen o be designed wi h he soaked esul s. Gene ally, he highe he CBR he be e he soil is as
subg ade ma e ial. [27] ecommends a CBR alue o no less han 10% o subg ade soils. The subg ade soils o
he ailed sec ion ha e unsoaked and soaked CBR anging om 4–9% and 2–4%, espec i ely. The pe cen age
loss in s eng h as a esul o soaking anged om 20–78%. This implies ha he e will be an app eciable loss in
he subg ade s eng h du ing ain all o ing ess o wa e . A d ainage sys em is he e o e equi ed as he ob ious
absence o his could ha e con ibu ed o he ailu e o he highway. The CBR in unsoaked and soaked condi ions
alls below he equi ed speci ica ion. This sugges s ha he subg ade canno wi hs and he pene a ion caused by
axle loads o ehicles and ucks ha egula ly ply he highway. The subg ade soils would he e o e equi e
s abiliza ion. The subg ade soils o he s able sec ion ha e CBR unsoaked and soaked anging om 15–17% and
7–10%. While he unsoaked CBR sa is ies he c i e ia, he soaked alls jus below he ecommenda ion. The
con ac o s howe e had aken ca e o his by p o iding d ainages a he lanks o he s able sec ion which help o
keep he subg ade soils well-d ained and una ec ed by he ing ess o wa e . I is hus ecommended ha he
uns able sec ion should no only be s abilized bu also be p o ided wi h d ainages a i s lank as hese a e absen .
Table 3. Compac ion and CBR esul s o subg ade soils
Sample
no.
Pi
no.
Pa en ock
Op imum Mois u e
Con en (OMC) %
Maximum D y
Densi y (MDD)
g/cm3
*CBRu
*CBRs
S eng h Loss
(%)
1
1
Mica-Schis
9.62
1.68
5
3
40
2
1
Mica-Schis
14.7
1.81
6
2
67
3
2
Mica-Schis
9.95
2.01
9
3
67
4
2
Mica-Schis
18.7
1.9
4
3
25
5
3
Mica-Schis
13.2
1.9
6
2
67
6
3
Mica-Schis
14.9
1.95
6
2
67
7
4
Mica-Schis
12.1
1.96
8
3
63
8
4
Mica-Schis
11.4
1.76
8
4
50
9
5
Mica-Schis
12.9
2.0
4
3
25
10
5
Mica-Schis
11.9
1.8
5
3
40
11
6
Mica-Schis
10.2
2.01
9
2
78
12
6
Mica-Schis
11.2
2.03
8
3
63
13
7
Mica-Schis
9.72
2.01
6
4
33
14
7
Mica-Schis
11.07
1.82
5
4
20
15
8
Mica-Schis
18.1
1.81
6
4
33
16
8
Mica-Schis
18.3
1.7
8
4
50
17
9
Mica-Schis
14.5
1.86
6
3
50
18
9
Mica-Schis
14.5 (*A 13.2)
1.82 (A . 1.77)
7
4
43
19
10
G ani e-Gneiss
10.4
1.89
15
7
53
20
10
G ani e-Gneiss
11.1
2.04
17
8
53
21
11
G ani e-Gneiss
13.2 (*A . 11.6)
2.69 (A . 2.2)
16
10
38
*CBRu and CBRs a e unsoaked and soaked Cali o nia Bea ing Ra io; A : A e age
3.2.3 Rela ionship be ween esis i i y, index p ope ies, and Cali o nia bea ing a io
The ela ionship be ween esis i i y o he subg ade soils and he amoun s o sand, ines, plas ici y index, and
Cali o nia Bea ing Ra ion was in es iga ed (Figu es 6–9). The CBR is he di ec measu emen o s eng h. I is
howe e cos ly and ime-consuming o de e mine CBR bo h in he unsoaked and soaked condi ion, especially
when se e al samples a e in ol ed. The empi ical ela ionship be ween CBR and hese p ope ies can be a eliable,
less cos ly, and ime-e ec i e al e na i e o he de e mina ion o CBR. In his s udy, he unsoaked CBR was used
o he co ela ion.
54
GeoScience Enginee ing Vol. 68 (2022), No. 1
geoscience.cz pp. 46–57, ISSN 1802-5420
DOI 10.35180/gse-2022-0068
30 40 50 60 70 80
2
4
6
8
10
12
14
16
18
CBRu (%)
Sand (%)
Figu e 6. Reg ession plo o CBR and pe cen age sand
20 30 40 50 60 70
2
4
6
8
10
12
14
16
18
CBRu
Fines
Figu e 7. Reg ession plo o CBR and pe cen age ines
050 100 150 200 250
2
4
6
8
10
12
14
16
18
CBRu (%)
Resis i i y (Ohm-m)
Figu e 8. Reg ession plo o CBR and esis i i y
CBR = 20 – 0.23686 X % Fines
R = –0.88; R2 = 0.76
CBR = 0.05682 X Res. + 3.24808
R = 0.9; R2 = 0.82
CBR = 0.2686 X % Sand – 4.562
R = 0.86; R2 = 0.73