ORIGINAL PAPER

Use of electrical resistivity to identify collapsible soils in Brazil

Jose Augusto de Lollo • Roger Augusto Rodrigues •

Vagner Roberto Elis • Renato Prado

Received: 4 December 2009 / Accepted: 21 December 2010 / Published online: 18 February 2011

� Springer-Verlag 2011

Abstract Three soil profiles in Ilha Solteira, Brazil were

investigated to establish their potential for collapsible

behavior. The soil profiles were identified using terrain

evaluation techniques and simple laboratory tests. Geo-

physical surveys were undertaken as they are quick and

relatively cheap. The results were correlated with trial pit

descriptions and cone and standard penetration tests. The

study has shown that electrical resistivity is a useful tool

for the preliminary identification of horizons of collapsible

soils, before more expensive intrusive and laboratory work

is undertaken.

Keywords Collapsible soils � Geophysics �Environmental geotechnics � Brazil

Resume Trois profils de sols ont ete etudies a Ilha Sol-

teira (Bresil) afin d’evaluer leur aptitude a l’effondrement.

Les profils ont ete identifies a partir de techniques d’eval-

uation de terrain et d’essais de laboratoire simples. Des

reconnaissances geophysiques ont ete mises en œuvre car

elles sont rapides et relativement peu onereuses. Les

resultats ont ete correles avec des descriptions de fosses

d’essai et des essais penetrometriques. L’etude a montre

que la resistivite electrique est un outil utile pour une

identification preliminaire des horizons de sols susceptibles

de s’effondrer, avant d’entreprendre des travaux par forage

et essais de laboratoire plus chers.

Mots cles Sols effondrables � Geophysique �Geotechnique environnementale � Bresil

Introduction

The expression ‘‘soil collapse’’ is used to describe a

wetting-induced deformation in collapsible soils. These

soils have an open structure as the particles are held

together by a temporary bonding such as suction or a

soluble cementing agent. Normally, collapsible soils have

a high porosity and low moisture content. Such soils are

very common in Brazil, mainly in Sao Paulo State where

they are found over some 70% of the area. In Ilha Solteira

city the collapsible soils are responsible for much of the

damage in public and private buildings, which has

resulted in considerable financial loss. In such situations,

the ability to identify the presence of these metastable

soils is very important for urban planning. However,

characterizing collapsible soil properties usually requires

expensive and time-consuming laboratory tests, incom-

patible with the financial conditions of small cities in

Brazil.

The paper reports the use of electrical resistivity studies

in Ilha Solteira, as it was hoped that, in conjunction with

appropriate in situ or laboratory tests, this would prove a

cost-effective way of identifying collapsible soils.

J. A. de Lollo (&)

Univ Estadual Paulista at Ilha Solteira (UNESP),

Alameda Bahia, 550, Ilha Solteira, SP 15385-000, Brazil

e-mail: lolloja@dec.feis.unesp.br

URL: http://www.dec.feis.unesp.br/jose.htm

R. A. Rodrigues � V. R. Elis � R. Prado

University of Sao Paulo (USP), Ilha Solteira, SP, Brazil

e-mail: rogerar@sc.usp.br

V. R. Elis

e-mail: vagnelis@iag.usp.br

R. Prado

e-mail: renato@iag.usp.br

123

Bull Eng Geol Environ (2011) 70:299–307

DOI 10.1007/s10064-011-0357-8

Studied soil profiles

General characteristics

Ilha Solteira (Fig. 1) in Sao Paulo State, Brazil, has 25,000

inhabitants. Lollo (1998) identified three different terrain

elements in its urban area (Table 1, after Rodrigues 2003).

Their spatial distribution is presented in Fig. 2.

In order to characterize the collapsible behavior of these

soils, 11 inspection pits were dug to 10 m depth, from

which non-disturbed soil samples were collected at 1 m

intervals. The locations of the sampling points are shown in

Fig. 3.

Laboratory tests

Preliminary laboratory tests indicate the following soil

profiles described by Rodrigues (2003) for each of the three

landforms:

soil A: upper level 0–8 m depth (A1), lower level

8–20 m depth (A2);

soil B: upper level 0–4 m depth (B1), lower level

4–13 m depth (B2);

soil C: upper level 0–2 m depth (C1), lower level 2–7 m

depth (C2).

The physical properties of these six soil layers are pre-

sented in Table 2 which gives the average values from the

metre interval samples for those profiles.

Oliveira (2002) reports tests on samples from wells in

order to define collapsible behavior based on Denisov

(1951), Gibbs and Bara (1967), Priklonskij (in Feda 1966),

URSS Works Code (in Feda 1966), and URSS Construc-

tion Code (in Feda 1966) methods. However, the results

were inconclusive.

Rodrigues and Lollo (2004) undertook double confined

compression tests using two specimens for each test: one at

natural moisture content and the other wetted to a pressure

of 1 kPa. The results are shown in Figs. 4, 5, and 6.

As can be seen from Fig. 6, soil profile C samples

showed little deformation due to wetting, and as they were

N

QUILÔMETROS

0 200 400 800

BRASIL

Ilha Solteira

São Paulo

OCEANO ATLÂNTICO

Fig. 1 Ilha Solteira location in Sao Paulo State and in Brazil

Table 1 Terrain elements in Ilha Solteira urban area (Lollo 1998),

according to Rodrigues (2003)

Profile Landform Soil Occurrence

A Flat top and

convex

slopes

Sand clay, soil

thickness [20 m

Southeast, northeast

and centre areas

(2.5 km2)

B Concave

bottom

slopes

Sand clay, soil

thickness less

than 13 m

South and centre areas

(2.0 km2)

C Straight

slopes

Sand, \7 m

thickness

West area (0.4 km2)

Fig. 2 Soil profile spatial distribution showing terrain elements in

Ilha Solteira urban area (Lollo 1998)

Fig. 3 Inspection well location in Ilha Solteira

300 J. A. Lollo et al.

123

therefore unlikely to be collapsible, these soils were not

considered further in the present study.

In situ tests

Figure 7 shows the SPT results for the descriptive units to

depths of 17 and 13 m for soil profiles A and B (after Lollo

et al. 2003).

For Soil A, the SPT results show values of\5 to a depth

of 8 m depth; in the Ilha Solteira region, such values

usually define a horizon of collapsible soil. With depth, the

SPT values increased and quartz pebbles some 10 mm in

diameter were encountered at 17 m.

In Soil B, SPT values were\5 to 5 m, again indicating a

collapsible soil, while below, in the sandy clay with quartz

pebbles (ca. 6–7 m) the higher N values implied that the

soil was unlikely to be metastable.

a

b

Fig. 5 a Double confined compression test for B1 horizon (Rodri-

gues and Lollo 2004). b Double confined compression test for B2

horizon (Rodrigues and Lollo 2004)

Table 2 Average physical indices obtained for soil profile intervals (Oliveira 2002)

Soil q (g/cm3) qd (g/cm3) qs (g/cm3) w (%) Sr (%) E LL (%) LP (%) IP (%)

A1 1.65 1.52 2.67 10 30 0.8 24 15 9

A2 1.72 1.56 2.71 12 45 0.7 27 19 8

B1 1.62 1.52 2.64 6 26 0.7 25 17 8

B2 1.69 1.55 2.67 9 34 0.7 25 17 8

C1 1.55 1.47 2.69 6 22 0.8 28 16 12

C2 1.68 1.56 2.72 9 33 0.7 28 15 13

q natural density, qd dry density, qs grain density, w wet, Sr degree of saturation, E void ratio, LL liquid limit, LP plastic limit, IP plasticity index

a

b

Fig. 4 a Double confined compression test for A1 horizon (Rodri-

gues and Lollo 2004). b Double confined compression test for A2

horizon (Rodrigues and Lollo 2004)

Resistivity to identify collapsible soils 301

123

Geophysical survey

The geophysical surveys involved both electrical (resis-

tivity and induced polarization, IP) and GPR methods.

However, it was found that the GPR results were affected

by interferences and hence could not be used.

Eight electrical surveys were undertaken in the same

areas as the inspection pits and SPTs. Data from VES 1–8

were collected using a Schlumberger array with a maxi-

mum current electrode spacing AB/2 = 60 m. The data

were interpreted by a 1D forward modeling and inversion

software. The resistivity and chargeability results are

shown in Fig. 8a–h.

Resistivity/IP electrical profiling data were collected

with a dipole–dipole array with electrode spacing

a = 5 m with five investigation levels. The chargeability

NSPT SOIL DESCRIPTION Depth

(m)

Fine Sandy Clay, soft to medium

compact, red-brown.

3 1

2 2

2 3

3 4

3 5

4 6

4 7

5 8

7 9

8 10

9 11

10 12

12 13

15

Fine Sandy Clay, low to medium

compact, yellow-brown.

14

8 15

9 16

51/30 17

NSPT SOIL DESCRIPTION Depth

(m)

Fine Sandy Clay, soft to low

compact, red-brown.

2 1

3 2

4 3

4 4

5 5

* Fine Sandy Clay, soft to low

compact, with quartz pebbles.

6

* 7

18

Fine Sandy Clay, tough to hard

compact, red-brown.

8

16 9

16 10

18 11

25 12

20 13

a

b

Fig. 7 a Typical SPT log for soil A profile (Lollo et al. 2003).

b Typical SPT log for soil B profile (Lollo et al. 2003)

a

b

Fig. 6 a Double confined compression test for C1 horizon (Rodri-

gues and Lollo 2004). b Double confined compression test for C2

horizon (Rodrigues and Lollo 2004)

302 J. A. Lollo et al.

123

data were measured with 2-s integration time and 0.2-s

delay time. The apparent resistivity and chargeability

measurements were interpreted using 2D inversion soft-

ware (Loke 2003). The electrical profiling lines are pre-

sented in Fig. 9a–d.

Vertical electrical sounding

The high resistivity values in all the VES indicate the upper

horizon in both the A and B soil profiles has a sandy

texture. This is particularly important as the most common

type of foundation used in Ilha Solteira is piles, which

rarely exceed 4 m depth (i.e. located in this horizon). The

results are consistent with the laboratory and SPT tests,

which indicated that from 1–2 to 6–8 m depth, the material

would be likely to be collapsible.

The chargeability for these horizons presents small-

to-medium values (2.7–9.97 mV/V). The saturated zone

typically has resistivity values of 13.5–78 Xm and

chargeability values of 11.7–64.1 mV/V.

Fig. 8 a Vertical electrical sounding 1 (Lollo et al. 2003). b Vertical

electrical sounding 2 (Lollo et al. 2003). c Vertical electrical sounding

3 (Lollo et al. 2003). d Vertical electrical sounding 4 (Lollo et al.

2003). e Vertical electrical sounding 5 (Lollo et al. 2003). f Vertical

electrical sounding 6 (Lollo et al. 2003). g. Vertical electrical

sounding 7 (Lollo et al. 2003). h Vertical electrical sounding 8 (Lollo

et al. 2003)

Resistivity to identify collapsible soils 303

123

Electrical profiling

Electrical profiling surveys allowed lateral soil horizon

variations to be established. The results (Fig. 9a–d) indi-

cate high resistivity values near the surface and significant

variations among chargeability values. Although the upper

limit was relatively clear, the lower boundary was defined

only in some sections.

The method of predicting collapsible behavior based on

double consolidation tests proposed by Reginatto and

Ferrero (1973) was used to verify the relationship between

resistivity/chargeability and collapsibility of the studied

soil. Following these authors, truly and conditionally col-

lapsible soils are defined through a coefficient of collaps-

ibility, C, as follows:

C ¼ rfs � ro

rfn � ro

where ro is geostatic stress due to soil self weight; rfs is

pre-consolidation stress for saturated soil; rfn is virtual pre-

consolidation stress for soil at in situ moisture content.

When C \ 0, the soil is truly collapsible (large settle-

ments will take place upon wetting). When 0 \ C \ 1, the

soil is conditionally collapsible (whether collapse occurs

Fig. 8 continued

304 J. A. Lollo et al.

123

will depend on the value of ro in relationship to rfs and

rfn). Finally, when C = 1, rfs and rfn are the same, the soil

is non-collapsible.

Figure 10a and b show the coefficients of collaps-

ibility and resistivity/chargeability values with depth for

soil profiles A and B. In general, the soils are condi-

tionally collapsible according to Reginatto and Ferrero

(1973), supporting a certain level of stress upon wetting.

In some cases, the resistivity and chargeability values

indicate non-collapsible soils near the ground surface

(\2 m depth) and calculated values suggest a lower

susceptibility to collapse in this horizon. This can be

explained in several ways. For example, seasonal varia-

tion with drying and wetting cycles induces changes in

Fig. 9 a C1 electrical profiling line (Lollo et al. 2003). b C2 electrical profiling line (Lollo et al. 2003). c C3 electrical profiling line (Lollo et al.

2003). d C4 electrical profiling line (Lollo et al. 2003)

Resistivity to identify collapsible soils 305

123

the stress state of soils (stiffness) and the activity of

fauna and flora are more influential in the near-surface

layers.

Conclusions

1. The study used geophysical survey to show the lateral

extent and consistency with depth of various soil

profiles, some of which had physical properties indi-

cating their propensity to collapse.

2. Although vertical electrical sounding was efficient in

determining the top of the collapsible soil horizon, the

bottom of the layer was less clearly defined.

3. The study indicated that although the combination of

laboratory and in situ tests as well as geophysical

surveys gave the best results in terms of characterizing

collapsible soil behavior, geoelectrical surveys can be

Fig. 9 continued

306 J. A. Lollo et al.

123

very useful for a preliminary identification of collaps-

ible soil horizons, supplying important basic informa-

tion for urban planning.

Acknowledgments The authors would like to express their grati-

tude to Fapesp (Fundacao de Amparo a Pesquisa do Estado de Sao

Paulo) who supported the project with financial resources.

References

Denisov NY (1951) Mechanical properties of loess and loams.

Gosstroiizdat, Moscow (in Russian)

Feda J (1966) Structural stability of subsident loess soil from Praha-

Dejvice. Eng Geol 1(3):201–219

Gibbs HJ, Bara JP (1967) Stability problems of collapsing soil. J Soil

Mech Found Div ASCE 93(4):577–594

Loke MH (2003) RES2Dinv ver. 3.52. for Windows 98/Me/2000/NT/

XP—rapid 2D resistivity and IP inversion using the least-squares

method. Geotomo Software User0s Manual, Penang, Malaysia

Lollo JA (1998) Caracterizacao geotecnica da area de expansao

urbana de Ilha Solteira (SP). In: Simposio Brasileiro de

Cartografia Geotecnica, vol 3, CD-ROM (in Portuguese)

Lollo JA, Elis VR, Prado R (2003) Carta de solos colapsıveis para a

area urbana de Ilha Solteira (SP). FAPESP, Ilha Solteira (in

Portuguese)

Oliveira CMG (2002) Carta de risco de colapso de solos para a area

urbana do municıpio de Ilha Solteira (SP). FEIS/UNESP, Ilha

Solteira (in Portuguese)

Reginatto AR, Ferrero JC (1973) Collapse potential of soils and soil-

water chemistry. In: Proceedings of international conference on

soil mechanics and foundation engineering, vol 2. pp 177–183

Rodrigues RA (2003) A influencia do esgoto domestico como fluido

de saturacao no colapso de um solo arenoso. FEIS/UNESP, Ilha

Solteira (in Portuguese)

Rodrigues RA, Lollo JA (2004) Caracterısticas estruturais, fisiograf-

icas e mecanicas de perfis de solos colapsıveis de Ilha Solteira—

SP. Solos e Rochas 27(2):131–146 (in Portuguese)

0

1

2

3

4

5

6

7

8

9

10-1 0 1 2

Coeficient of Collapsibility

Dep

ht

(m)

Soil Profile A

Non-collapsibleTruly collapsible Conditionallycollapsible

(m)

( .m) /

417 / 4.0

M (mV/V)

2016 / 5.0

789 / 25

0

1

2

3

4

5

6

7

8

9

10-1 0 1 2

Coeficient of Collapsibility

Dep

ht

(m)

Soil Profile B

ConditionallycollapsibleTruly collapsible Non-collapsible

( .m) /

114 / 16

319 / 2.4

M (mV/V)

1759 / 1.6

5242 / 5.1

a

b

Fig. 10 a Coefficient of collapsibility 9 resistivity/chargeability for

soil profile A. b Coefficient of collapsibility 9 resistivity/chargeabil-

ity for soil profile B

Resistivity to identify collapsible soils 307

123