







































 
 

 

9 
© 2022 by the authors; licensee Asian Online Journal Publishing Group 
 

Asian Review of Environmental and Earth Sciences 
Vol. 9, No. 1, 9-17, 2022 

ISSN(E) 2313-8173 / ISSN(P) 2518-0134 
DOI: 10.20448/arees.v9i1.4070 

© 2022 by the authors; licensee Asian Online Journal Publishing Group 

 
 

 
 
 
Prediction of the Strength Behaviour of the Sandy Soil by using Collapse Potential 
in the Kintele Site-Congo 

 
Adolphe Kempena1   
Gampio Urbain Mbilou2 
Dhorjeanny Bissombolo3 
Antonio Olimpio Goncalves4 
Florent Boudzoumou5 

 

 
( Corresponding Author) 

 
1,2,3,5Department of Geology, Faculty of Sciences and Techniques, Marien Ngouabi University, Brazzaville, Congo. 
1Email: akempena@gmail.com Tel: +242069521826 
2Email: gampiombilou@gmail.com Tel: +242069542043 
3Email: bissombolodhorjeanny@gmail.com Tel: +242064393022 
5Email: boudzoumouf@gmail.com Tel: +242066710201 
4Department of Geology, Faculty of Sciences, Agostinho Neto University, Luanda, Angola. 
4Email: Tonygoncalves72@hotmail.com Tel: +244926887944 

 
Abstract 

This work aims to evaluate the water effect on the soils collapse potential. The laboratory tests based on 
the soils samples preparation determined the soils properties. Parameters such as water content, dry 
unit weight, degree of saturation, voids ratio and particles size distribution were determined. The 
collapse potential was analysed indirectly according to various researchers criteria. The results 
confirmed the high vulnerability of the study area to collapse. The oedometer tests determined the 
values of the collapse potential showing the conventional relationship between the collapse potential 
and the water content. It is noted that increasing water content leads to decrease soils strength to 
collapse, and the increasing progress of collapse poses a risk to constructions on silty sand. The collapse 
potential decreases with the increase in the relative density keeping the water content constant. This 
collapse potential caused by soil water content variation can be reduced from compaction.  

 
Keywords: Collapsible soils, Collapse potential, Collapsibility, Saturated soil, Unsaturated soil, Sandy soil, Water content. 

 
Citation | Adolphe Kempena; Gampio Urbain Mbilou; Dhorjeanny 
Bissombolo; Antonio Olimpio Goncalves; Florent Boudzoumou 
(2022). Prediction of the Strength Behaviour of the Sandy Soil by 
using Collapse Potential in the Kintele Site-Congo. Asian Review of 
Environmental and Earth Sciences, 9(1): 9-17. 
History:  
Received: 2 May 2022 
Revised: 5 July 2022 
Accepted: 18 July 2022 
Published: 26 July 2022 
Licensed: This work is licensed under a Creative Commons 

Attribution 4.0 License  
Publisher:  Asian Online Journal Publishing Group 
 

Funding: This study received no specific financial support. 
Authors’ Contributions: All authors contributed equally to the conception 
and design of the study. 
Competing Interests: The authors declare that they have no conflict of 
interest. 
Transparency: The authors confirm that the manuscript is an honest, 
accurate, and transparent account of the study; that no vital features of the 
study have been omitted; and that any discrepancies from the study as planned 
have been explained. 
Ethical: This study followed all ethical practices during writing. 

 

 

Contents 
1. Introduction ...................................................................................................................................................................................... 10 
2. Materials and Methods ................................................................................................................................................................... 11 
3. Results ................................................................................................................................................................................................ 14 
4. Discussion .......................................................................................................................................................................................... 16 
5. Conclusions ....................................................................................................................................................................................... 16 
References .............................................................................................................................................................................................. 16 
 

 
 

 

 

 

mailto:akempena@gmail.com
mailto:gampiombilou@gmail.com
mailto:bissombolodhorjeanny@gmail.com
mailto:boudzoumouf@gmail.com
mailto:Tonygoncalves72@hotmail.com
https://creativecommons.org/licenses/by/4.0/
https://creativecommons.org/licenses/by/4.0/
https://www.doi.org/10.20448/arees.v9i1.4070
https://orcid.org/0000-0002-9938-810X


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Contribution of this paper to the literature 
This work contributes to solve and to make clear problems related to constructions which are 
exposed to the risk of collapse.  

 
1. Introduction 

In geology and geotechnical engineering, soil collapse phenomena with a significant percentage of fines induce 
differential settlements, leading to damage of infrastructures (building, foundations and retaining structures). 
Sudden collapse potential is occurred many times on unsaturated soils with potential deformations and radical 
rearrangement of grains after wetting. These soils with loose structures are often made of grains ranging from clay 
to fine sand. They are particularly located in areas with a complex relief. These regions have become vital today, in 
view of the demographic and technological evolution of the man who exploits his wealth. The occupation of these 
areas necessarily leads to the modification of their original properties. This favours the ideal environment for soil 
collapse and consequently the ruin of constructions [1]. 

Many existing researches noticed many unsaturated soil problems confronted by engineers, related to 
collapsible and expansive soils under wet conditions. From the volume changes, the soils can remain problematic in 
construction engineering due to their expansion, collapsibility, dispersion, and sometimes excessive settlement 
with a loss of strength. Certain soils behaviours can be referred to their mineralogy, the pore liquids nature, or 
their particles arrangement. Collapsible soils have tendency to collapse as a closely packed, with a significant 
reduction of their volume. The collapsible soils have a non-significant inter-particle link strength which is 
destroyed by either soil filling, saturation of soil or a mixture of both conducting to  soil collapse occurrence [2]. 
Constructions on collapsible soils are often suffered of unexpected settlements, with tendency to produce awful 
failure. In general, an inundation of the soils in metastable state causes collapse in loess soil and engorgement for 
some clayey soils. Then, in geotechnical engineering the collapsible soils instability is associated to the effect of 
water when the soil is under wetting conditions. These types of soils lead to high defies in foundations engineering 
[3].  

Collapsible soils have become a grave engineering problem and a geotechnical challenge all over the world. 
These soils can be formed naturally or by man activity and sometimes represent a natural risk for a man and his 
property [4]. Unexpected collapse happens once wetting or surcharge surpass the yield of the material resistance 
[5]. Collapsible soils are largely formed by silt and fine sandy soils, sometimes with low clay content. The soil can 
be affected by wetting, such as rainfalls and groundwater level growth, or by man activities. Though, collapsible 
soils are conquered for man activities. Many factors can describe the collapse behaviour of soils such as the collapse 
prediction related to any type of unsaturated soils, the compacted soils with perfect water content; the capillary 
action in the soils which yields shear stresses; the increasing compressibility that causes a shear strength reduction 
of soils leading them to failure [6].  

Studies based on soils collapsibility behaviour consider the collapse potential as an essential monitor for 
foundations design [6]. The evaluation of soils collapsibility from many criteria has been well-defined by several 
investigators. Research works related to soils collapsibility could be find in existing literatures [7-14]. 

Collapse potential was firstly revealed by Jennings and Knight [6] and repetitive tests were advanced to 
measure soil collapse. Schwartz [15] systematically revised these works in the art paper state. Foundations for 
collapsible soils have tendency to be predictable when they are built on a collapsible soil layer, excavation and re-
compaction of the material with drainage safety to avoid inundation process.  

The works based on the collapsible soils properties deal with the identification, laboratory tests and 
engineering properties of collapsible soils [16]. Collapsible soils could mostly be recognised by using laboratory 
tests of particles size, Atterberg limits, dry density, saturation degree which are able to predict collapse. 
Oedometric or triaxial laboratory tests could determine the collapse potential with some plain restrictions for 
disturbed soils samples as revealed by Houston, et al. [17]. Fredlund and Gan [18] moved off the collapse 
relationships by using a similar method to consolidation principle and including suction stresses. Lin [19] 
proposed instructive test outcomes for unsaturated soils highlighting the effect of overload stresses, suction 
stresses and saturation degree. Schwartz [15] evoked that the degree of saturation remained important in 
evaluating collapse potential, being a degree of saturation at a critical level during the collapse occurrence. 
Inopportunely this perception can be essentially disregarded in practice, while McKnight [20] replicated the 
Schwartz data and additional information, thus made a convenient illustration of an overall relationship among 
critical saturation degree and percentage of fines. Schwartz [15] also considered the effective pressure in the 
design of any construction structures. 

Compilation delivered by Rogers [2] produced the meanings of collapsible soils from many studies such as a 
soil with a considerable volume variations by wetting, loading, or a mixture of both. Any unsaturated soil with 
particles rearrangement can show significant loss of volume by wetting with or without further loading [14].  
There are additional settlements caused by unsaturated soils, without some increase in practical stresses. Some 
existing works are focused on the wetting state of unsaturated soils under consolidation which is associated to 
apparent cohesion of unsaturated soils. Residual soils sometimes involve minerals decomposition from rocks 
leading the soils willing to collapse. Residual soils have greatest high spatial changes, therefore their potential 
collapse becomes difficult to predict. Aeolian Soils include dunes and loess found as sandy silt covering abundant of 
the earth’s surface where alluvial soils and colluvial soils are moved by water or by gravity and may be extremely 
collapsible [5, 6].  

Sandy soils cover the northern part of Congo Republic including the study area. An amount of problems 
related to these sands were emphasised by existing works [21]. The major geological and geotechnical problem 
was observed to be the great collapse potential of these sands under different conditions.  

In this work is founded on soil sampling with laboratory tests to evaluate the collapse phenomena in the study 
area. Then, the selected site represents the northern area of Ignie department, Congo republic as shown in Figure 
1. 



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2. Materials and Methods 
2.1. Study Area 

Information about the climate, relief and geology of the study area is vital for the soils engineering properties 
and it is a pre-requisite for the design of foundations. The study area is located in the Northern part of Kintele, in 
Southern part of Ignie Department as can be seen in Figure 1. 

Morphologically the study has a flat relief, valleys and hilly areas. The years 80’s were less warm than the 
years 90’s. Two periods plainly characterize the recent evolution of temperatures in Congo before 1970 and after. 
Brazzaville presents a net variation of temperature from 1932 to 2010 showing an increase of +0.5˚C to 1˚C as 
average temperatures in the preceding two decades. But it is noticed the maximum and minimum average 
temperatures in the 1990s with an increase for the two recent decades. The maximum and minimum altitudes are 
1100 m and 360 m respectively. The climate is tropical with a rainy season from October to May, and dry seasons 
between January-February and June-September. The annual rainfall oscillates among 1250 mm and 1350 mm/year 
[22]. The hydrogeological group is part of the Bateke’s water table, with an area of 270 km2. The aquifer 
components are sandstone with a weak contribution to the groundwater mineralogy. But two zones are identified 
using the Ca2+/Mg2+ ratio. The first zone determines the calcium minerals showing weathering process and the 
second one with ratio higher of Ca2+/Mg2+ which shows the dissolution of magnesium [23]. The soils are settled 
on different materials of three sedimentary series from the base to the top, made of the sandstone series of Inkisi, 
the sandstone series of the Stanley Pool and the series of Bateke’s plateau. The soils are ferrallitic and 
hydromorphic. In general, these soils have very low clay content [24]. The Central Basin, involves the 
intracratonic depression of Central Africa with accumulation of sediments, tectonic activity and erosion process 
during a long history. Then the geological background consists of a Precambrian to Paleozoic age formation 
supporting a Mesozoic to Cenozoic sedimentary cover that rests unconformably on a Precambrian basement. Thus, 
the Precambrian to Paleozoic basement which appears downstream from the Stanley Pool and the sedimentary 
cover is formed by essentially sandy materials which outcrop upstream from the Stanley Pool series [25]. 
 

Figure 1. Study area. 

 

2.2. Methodology  
The study used terrain data related to geography, geology, superficial water and ground water to pick out soil 

specimens. The method of pits was selected for this study with four pits excavated followed by soils samples 
collection where, different laboratory tests were performed. The collected information was used to determine the 
collapsible soils localities in the study area. Founding on the field study; there was no important variation in soil 
visual observation, therefore four pits were selected to perform laboratory experiments.  
 

2.2.1. Sampling Techniques 
Founded on the pits locations, disturbed soil samples from four sites were taken at 1.4 m depth. The soil is 

considered non-cohesive and difficult to obtain undisturbed soils samples. And also, the undisturbed samples have 
tendency to be affected through transportation due to the large distance from the study area to the Laboratory site. 
Therefore disturbed samples were taken for laboratory tests and soil samples preparation, considering the scarce 
investigation in the study area, and the analogous and continuous soil layers observed using visual description of 
the soil from the pits.  
 



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2.2.2. Experimental Study 
The tests performed are: Determination of water content in natural state, particles size determination, 

Atterberg Limit, density, Proctor test, Specific gravity, consolidation tests. After different tests performed, the soils 
classification was carried out according to AASHTO and USCS systems.  
 

2.2.2.1. Preparation of soils specimens  
Using a 1.4 m depth for each soil sample, the soil samples were kept in plastic bags and brought to the 

laboratory. The preparation of samples followed the AASHTO T87-86 standard.   

 
2.3. Laboratory tests  

The laboratory tests considered at first the preparation of the soils specimens submitted to experiments to 
determine the soils properties. The tests included the distribution of grains size, proctor test for the maximum dry 
density and the optimum water content, Atterberg limits, specific gravity, and to end the oedometer test to 
determine the collapse potential of the soil. Soil samples collected for various laboratory tests are important to 
determine the sectors where collapsible soils are met in the study area. The majority of the laboratory tests were 
performed founded on the AASHTO manual in the case of soil testing, and the use of ASTM manual for certain 
laboratory tests.  

 

2.3.1. Oedometer Tests 
The tests were performed with a standard front loaded odometer, carefully following standard trials [6]. For 

the double odometer tests, dry soil samples were loaded in phases to σv = 200 kPa for the residual water content 

and inundated soil samples. For the single odometer tests, dry samples received a load in phases to σv = 100 kPa 

before being inundated just after loading to σv = 200 kPa. The swamping of samples just once loading in the 12 
and 200 kPa is a deviation after usual practice [6], in which swamping is made next a full unsaturated soil samples 
by loading phase. Though, the the results of the oedometer tests including the data repeatability recommend that 
values of collapse potential are comparable to those found by using normal practice. All soil samples were 

discharged in phases to σv = 12 kPa. For the stages with pressures of 12 and 200 kPa, there were successions of 
tests at wn = 6%, during the unloading phase.  

 
2.4. Collapse Potential Assessment 

The collapse potential recognition by international criteria is used from data provided by the Genesis and 
collapsible soils properties being a large variety of dry densities for collapsible soils [16]. Soil properties 
identification involves diverse mechanisms as a vital procedure. Collapsible soils can be studied by using indirect 
and direct approaches.  
 

2.4.1. Direct Methods 
These methods are based on values measurement by using single and doble oedometer tests in the laboratory 

considering the resultant stresses. Then the results can predict the settlement potential including the evaluation of 
the collapse potential by using the ASTM D 5333 method in the laboratory. This method is based on the 
determination of the collapse potential ratio that will occur for a certain vertical pressure and an index for 
assessing the collapse potential. This method can be used for soil samples in different consevation states.   
 

2.4.2. Indirect Methods  
In general, there are diverse approaches to study the susceptibility of soil to collapse, founded on the 

Coefficient of subsidence (K) and KD values as shown in Table 1 [26, 27].  
 

Table 1. Criteria reported for the identification of soils susceptibility to collapse. 

Authors Year Criterion 

 
Denisov 

 
1951 

Coefficient of saturation 
k = (Saturated void index)/(Natural void index) 
k = 0.5-0.75: highly collapsible soils 
k = 1.0: loamy clay soils not collapsible 
k = 1.5-2.00: non-collapsible soils 

 
Priklonski 

 
1952 

K= (Natural Water Ccontent - Liquid Limit)/(Plasticity Index) 

KD ˂ 0: soils with high collapsibility 
KD ˃ 0: non-collapsible soils 

KD ˃ 0: swelling soils 

 
Soviet Bulding Code 

 
1962 

L =(e0-el)/(1 + e) e0 
e0: natural voids index  
L: saturated voids index 
When a saturation degree is 60%, if L> -0.1: collapsible soils 

 
Feda 

 
1964 

kL= wo/sr-Ip/LL 
wo: natural water content 
sr: natural degree of sturation 
Ip: Plasticity index 
LL: Liquiquity limit 

When sr ˂100%, kL ˃ 0.85: collapsible soil  

 
Table 2 shows a summary of several authors’ proposals to determine the potential collapse.  

 

 



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Table 2. Potential collapse classification for constructions [6]. 

Cp (%)  Severity of the problem 

From 0 to 1 None 
From 1 to 5 Moderate 
From 5 to 10 Problematic soils 
From 10 to 20 Serious 
> 20 Very serious 

 
While the oedometric tests are the most widely used in the laboratory to assess the possibility of collapse 

occurrence. Although there are embodiments of oedometric tests, then for the present work the double odometric 
test was used under the conditions of natural water content and under saturated condition for the same sample. 
The methods for evaluating collapse potential in this research are summarized in the Table 2. The validation of 
these methods presented in Table 2 was carried out by comparison with the collapse potential, considering the 
following equations [6]: 

I=(∆ec)/[1+(enat/eonat)eomean]                                                                              (1) 
∆ec =[(enat/eonat) - (esat/eosat)eomean]                                                                     (2) 
eomean =[(eonat+ eosat)/2]                                                                                        (3) 

Where; eonat and eosat are initial void ratios in the natural and saturated conditions, respectively. These 
parameters are obtained following the completion of the oedometric tests. The criteria for categorizing the collapse 
potential can be found in Table 2.  

 
Table 3. Particles size. 

Particles size (µm) Type of soil Percentage 

< 2 Clay 6% 
2 - 63 Silt 18% 

˃ 63 Sand 77.9% 

 
Table 4. Soil density. 

Specimens M0 MS M1 M2 γs (g/cm3) Average 

1 69 100 195 176 3  
2 68 106 199 175 3 3 
3 68 102 197 175 3  
4 69 102 195 177 3  

 
Table 5. Results of Atterberg limits. 

Parameters Specimen 1 Specimen 2 Specimen 3 Specimen 4 

Coefficient of uniformity (Cu) 3.1 4.2 2.6 3.2 
Coefficient of Curvature (Cc) 1.5 1.7 1.6 1.8 
Liquidity limit, WL 17 16 19 18 
Plastic limit, Wp 14 12 13 12 
Plasticity Index, (P) 5.0 5.0 5.0 5.0 

 
Table 6. Classification of settling soils according to collapse potential values [6]. 

Collapse Potential (Cp), % Problem gravity  

0 - 1 Non-collapsible soil 
1 - 5 Moderately collapsible soil 
5 - 10 Problematic soil 

10 - 20 Very collapsible soil 
> 20 Very severe collapsible soil 

 
Table 7. Soil properties. 

Ec 20 40 60 20 40 60 20 40 60 

Wo (%) 2 2 2 4 4 4 6 6 6 
eo 0.881 0.853 0.822 0.756 0.715 0.675 0.681 0.641 0.611 

𝛾d 14.18 14.46 14.59 15.18 15.90 16.10 15.86 16.24 1.655 

Cp (%) 14.88 12.30 12.40 15.56 13.72 12.79 16.88 14.07 13.98 

 

 
Figure 2. Water content vs Void ratio. 

 



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Table 8. Values of collapse potential in the study area. 

 
Sample 

 
Locality 

Authors 
Denisov Priklonski Soviet Building Code Feda 

Parameter (K) Parameter (kD) Parameter (L) Parameter (kL) 

1 Kintélé 0.65 -0.87 -0.08 0.98 
2 Lifoula 0.58 -0.67 -0.06 0.88 
3 Mandiélé 0.61 -0.31 -0.02 0.91 
4 Ignie  0.55 -0.29 -0.05 0.89 

 

 
3. Results  

Cu = 3.3 and Cc = 1.8 and the soil is well graduated. Based on the methylene blue test, the soil is classified as a 
silty sand (0.2 - 1.5). Particles densities are shown in Table 4. Then the soil is collapsible [6]. Indeed, for the 

different pressures (σ) as well as the different energies of compaction (Ec), the collapse potential (Cp) differs from 
12.40% to 14.88% (for an initial water content; w = 2%), from 12.79% to 15.56% for an initial water content w = 
4%, and from 13.98 to 16.88% for an initial water content w = 6%). The void ratio reduction considered as one of 
the collapse index can be observed in Figure 2. 

Values obtained correspond to the category of very collapsible soil as shown in Table 6. The collapse potential 
(Cp) decreases when the energy of compaction (Ec) increases. This can be noticed that the collapse is exalted by the 
action of water which easily eliminates the inter-granular bonds produced by capillary action and links formed by 
low clay content [28, 29]. These soils remained stable in wet conditions and become vulnerable to collapse after 
water infiltration. These types of soils have particular features with contribution to collapse such as metastable 
structure which results in great void ratio, young deposit, significant sensitivity, and weak inter-particles 
attachment.   

Some compacted soil at optimum and small dry density can experience a metastable structure which is 
governed by shear strength, being bonds with a high dependence on capillary action. Then the bonds can lose 
strength when an increase in water content can cause the collapse of soil structure at critical saturation degree. The 
collapse occurrence is often due to an increase in surcharge or water content and sometimes a combined action of 
these two parameters. In addition, the capillary effects between aggregates and granular particles decrease. This 
makes it easier to break the bonds among the particles and therefore collapse occurs. Collapse behaviours are often 
seen in fine soils in which the fine particles are shown as connectors or sometimes as the blanket of granular 
particles [14]. It is noted the increase in the subsidence potential for an energy of compaction corresponding to 20 
strokes for soils with a loose structure and many voids, causing the displacement of fine particles in different 
directions. Conversely, in the case of compaction with 60 strokes once the soil becomes relatively dense the 
destruction of inter-granular bonds and the movement of fine particles are reduced, yet the subsidence potential 
still remains high. Jennings and Knight [6] gave a classification of soils according to the severity of the problem 
and the values of the subsidence potential from following equations:  

Initial void index (e0) = (γs/γd) – 1 (4) 

CP (Subsidence coefficient or Collapse potential) = ∆h/h0 = ∆e/(1 + e0)   (5) 

This classification is shown in the Table 6. Considering as an indication, we can consider that a soil is not very 
compressible when Cc < 0.2, compressible when 0.2 < Cc <0.7, very compressible when 0.7 < Cc. Others results 
related to soil mechanical properties can be seen in Table 7.   

The susceptibility of soils to collapse is founded on the geotechnical properties of soils and the collapse 
potential obtained from laboratory tests, considering the soils under dry condition. The LL and PI played also a 
vital role for collapsible soils classification. From Table 6, the results of collapse potential notice that all soil 
samples used showed high sensitivity to collapse. Commonly the soils under study showed a certain similarities 
about collapsibility analysis.  
 

 
Figure 3. Soil curve before compaction. 



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The Figures 3, 4 and 5 show the soil conditions under oedometric tests. In Figure 5, it is shown the curves for 
the dry and saturated conditions, respectively. These curves show that the collapse occurrence depends on the 
water content. Then, it is noticed that once the water content increases in the soil, it becomes unstable causing a 
sudden collapse with the decrease in the shear strength [1].  

Due to the non-cohesive nature of the soil samples, the difficulty of collecting undisturbed samples was 
pronounced. Therefore, the tests of single oedometer considered soil samples prepared according to ASTM D 5333 
procedures. Also, the loading conditions indicated in ASTM D 5333, supplementary oedometer tests were 
performed on remoulded samples swamped at the real loading conditions after final samples preparation. Then the 
collapse potential for remoulded samples and considering the natural densities based on the severity of collapse is 
minor to reasonable as shown in Figure 3. 

In addition, the collapse potential for soil samples with maximum dry densities is met within the very slight 
severity of collapse (Figure 4 and Table 6).  

 

 
Figure 4. Soil curve after compaction. 

 

 
Figure 5. Double oedometer test curve. 

 



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Figure 6. Soils behaviour using the double oedometer test. 

 
From the Figure 6 it is observed that the soil remains collapsible and its collapse potential can be considerably 

reduced by compaction. This compaction has tendency to reduce the soil void index and makes it denser to resist 
against collapse phenomena.  

In general, founded on the results obtained from the field and laboratory tests; one may assess the collapse 
potential in accordance with different criteria. The collapse potential evaluation by using the soils physical 
properties as an indirect method is based on the values of the collapse potential. 
 

4. Discussion  
Different collapse criteria were suggested to determine the soil responsibility face to collapse. Priklonski’s 

criterion, is based on the liquidity index for soil collapse expectations, where the soil is collapsible when the 
liquidity index is lesser than zero [26]. Therefore, using the Priklonski’s criterion the soil in the study area is 
collapsible by compaction. The results showed that all soil samples showed moderate to high collapse. Generally 
some similarities found on the collapsible soils met in the study area refer to geological and environmental 
conditions. From Tables 5, 6, 7 and 8, comparison can be made among the properties of collapsible soils for a good 
acknowledge about the collapse phenomenon in the study area. 

Even though Clevenger [30] criterion was not used in the current study, but comparing results obtained from 
this criterion with those obtained in this study, this method stated by using the natural dry density. Then it is 
noticed that, when the natural density is inferior to 12.6 kN/m3, an important settlement can be produced whereas 
once it is larger than 14.1 kN/m3, slight settlement can be produced [31]. This criterion using clay percentage 
indicates that once the clay content is among 16.0 % and 24.0 % the soil is collapsible and it becomes highly 
collapsible when the clay percentage is inferior to 16.0 %. Then, the soil met in the study area is highly collapsible 
with a clay content lesser than 16% Table 3.  

The soils parameters provide the soils susceptibility to collapse potential. It is noted that keeping the water 
content constant, it is observed a decrease in the collapse intensity with the increase of relative density [32]. It is 
also defined  the maximum value of the collapse potential (Cp) at 200 Kpa pressure. This result can be explained by 
the intensity of the collapse which increases up to a certain level of stresses after which the collapse decreases [33]. 
Table 7 also shows that the collapse potential (Cp) decreases almost linearly, when the water content or the energy 
of compaction increases for a 200 kPa pressure and this type of soil behavior is the same regardless of the applied 
pressure. Results observed in Tables 7 and 8 agree with those obtained by some researchers [34]. 

 

5. Conclusions 
In general, founded on the results obtained from the field and laboratory tests; one may assess the collapse 

potential in accordance with different criteria. The collapse potential can be evaluated by using the soils physical 
properties as an indirect method and using values of the collapse potential as a direct method.  

Soil collapse is a very complex phenomenon that involves a large number of intrinsic and adjacent parameters. 
Results obtained defined the soil behaviour in the face of collapse potential. The results of identification tests, 
consistency and compressibility confirmed the collapsible behaviour of the soils found in the study area.  

The collapse potential may be reduced by using compaction. The compaction and the consolidation tests 
contribute to a suitable description of the collapsible soil. 

This work determined the cause of collapse experienced by different types of constructions built in the study 
area and can be used as a policy statement for similar areas to reduce the collapse incidence on constructions.  
 

References 
[1] D. G. Fredlund and H. Rahardjo, Soil mechanics for unsaturated soils, 1st ed. Canada: John Wiley&Sons, 1993. 
[2] C. D. F. Rogers, "Hydroconcolidation and subsidence of loess: Studies from China, Russia, North America and Europe: in memory 

of Jan Sajgalik," Engineering Geology, vol. 37, pp. 83-113, 1994. 
[3] S. L. Houston, W. N. Houston, and D. J. Spadola, "Prediction of field collapse of soils due to wetting," Journal of Geotechnical 

Engineering, vol. 114, pp. 40-58, 1988.Available at: https://doi.org/10.1061/(asce)0733-9410(1988)114:1(40). 
[4] J. Ian and D. F. Chris, Chapter 32 Collapsible soils. In ICE manual of geotechnical engineering vol. 39: Thomas Telford Ltd, 2012. 



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