Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
Volume 9
Issue 4
Civil Engineering
Available Online: http://www.ejpau.media.pl/volume9/issue4/art-45.html


Mariusz Sobolewski
Department of Civil Engineering and Geodesy, Warsaw Agricultural University, Poland



The standard is that the consistency states of cohesive soils are evaluated on the basis of laboratory tests. This method is accurate, but time-consuming and expensive because of the necessity of sampling the soil specimens. Because of financial considerations, the investors decide to identify the geological conditions of a subsoil mainly on the basis of field research. Only in doubtful situations, when some weak strata or another disadvantageous factors in the zone of the interaction of a building are being occurred, the soil parameters are being verified through laboratory tests. The in situ tests are more popular, because they are fast and relatively cheap way to identify many parameters, including the liqudity index IL. To evaluate the state of a soil, the formulas basing on the cone resistance q c are used more and more frequently in piezocone tests CPTU [8]. In this paper, the flat dilatometer testing (DMT) is proposed to evaluate the consistency state of fine-grained soils. The paper presents the analysis of factors affecting the liquidity index IL. The scaling of the flat dilatometer was carried out on the basis of IL index, obtained from the laboratory tests. The investigation was made on the heavily overconsolidated Pliocene clays from Warsaw region.

Key words: Pliocene clays, liquidity index, consistency state, dilatometer tests.


The development of cities causes the continuous transformations of actual people colonization, site disposal of new areas, construction engineering objects and the realization of investments, whose impact on the environment has various industrial importance in the country. This activity takes place on the subsoil existing at the site of building work, which is carried out. The particular interests of building industry, engineering geology and geotechnics in cohesive soils are the results of the fact that they often exist in small depth under a ground level. In many cases, engineering objects have their foundation on the layers of clays or boulder clays, which are placed directly or indirectly in the interaction zone of a building. In these cases, the engineering activity always demands to definite the consistency state of cohesive soils.

The obligatory classification of cohesive soils introduces the notion of the consistency states of soil. These soils may be characterized by various states: very soft, soft, firm, stiff, very stiff. The whole range of the states is included by three sorts of consistency: solid, plastic and liquid.

The distinction of the state of soil is based on the conventionally accepted limits of the liquidity index IL or consistency index Ic. The values of this parameter and the states of soil corresponding to them are included in the Polish Standard [9], [10] and in the European Standard [3]. The liquidity index is defined as:


wn – the water content, determined by standard oven drying method,
wp – the plastic limit between a semi-solid and plastic consistency states, determined from the rolling-test of a remoulded soil sample,
wL – the liquid limit between a plastic and liquid consistency states, determined according to the percussion method (by using a Casagrande’s liquid limit device or fall cone tests).

The numerical difference between the liquid limit (wL) and the natural water content (wn), expressed as a percentage ratio of the plasticity index (Ip), is termed the consistency index:


The terms for the consistency index Ic of remoulded silts and clays may be found in [3]. The most accurate values of the liquidity index or consistency index are obtained in an experiment – by making the appropriate laboratory tests of the consistency limits. Macroscopic analysis of samples enables merely the preliminary assessment of soil state. It is the field tests of the state of soil which becomes of greater importance in engineering practice. In piezocone tests (CPTU) the formulas depending on the cone resistance qc are being sought [1], [2], [5], [6], and [8]. The geotechnical investigations, carried out in natural conditions, make possible the fast obtaining of strength parameters, determination of deformation, verification of flow and consolidation characteristics and identification of actual and history stress state, including the preliminary recognition of the lithological profile [14]. Another device, which finds an application in field tests aimed on the evaluation of the liquidity index IL or consistency index Ic , is a flat dilatometer.

In the DMT tests, the state of a fine-grained soil can be determined on the basis of dilatometer modulus (ED). Redel e.a. (1997) suggested the linear form of equation for firm-plastic fat clay from Israel, shown in Fig. 1.

Fig. 1. Correlation between liquidity index IL and dilatometer modulus ED for fat clay from Poleg site [11]


The laboratory and in situ tests were carried out on Pliocene clays in Warsaw. Almost on the whole area within the administrative boundaries of the city, the clays are covered by the quaternary formations. Clayey deposits often present the subsoil of the foundation of high office buildings as well as the underground. In many places the roof of these soils is glacitectonically dislocated, which is the result of a post-sedimentating process. In some places, however, the deposit is slightly dislocated and the presence of sedimentation cycles in a lithological profile is strongly visible. One of such places, where the roof of the clay deposit occurs near the ground level, is the experimental plot in Stegny near Warneńska St. (Fig. 2).

Fig. 2. Stegny site in Warsaw

The investigations of the physical properties of tested soils carried out in a laboratory allowed to describe the geological structure of the Stegny’s subsoil (Fig. 3). Down to 4.3 m from the surface, there appear dark-yellow homogeneous medium and fine sands that exhibit alternate deposition in the vertical direction. Within these sands, the ground water level is at 3.2 m in depth. Beneath the sands, a complex of Tertiary clays may be found. Pliocene clays consist mostly of clays and silty clays, however there it must be noted that the clays overdominate the silty clays. It is the evidence of a mechanical variability of the clay complex yet on a small section of the profile, which may be seen in Fig. 3 [13].

The bed of clays reveals a clear stratiform structure characterised by different colouring of particular layers at the same time. The horizontal stratification of the clays indicates a natural arrangement of formations and lack of glacitectonical dislocations in the form of xenoliths. The investigated soils, in a firm state, transit into a stiff state along with the thickness. Four different layers of clays may be distinguished there. The shallowest are deposits of the dark-grey clay laid down on the flaming clay of a rusty-red colour. The typical element of the geological structure is an inserted pad of silty motley clay of yellow colour and thickness of 1.2 m. Deeper are motley clays with numerous bright yellowish stains, from which two layers were selected with respect to the differences in geotechnical parameters. The boundary separating these layers runs at the depth of 10.0-10.5 m.

Fig. 3. Type of soils and variations contents of particular fractions in the profile


In most countries, including Poland, the base for a classification of soils are suitably selected and realised identification researches. For this purpose, the mechanical composition of soils is determined by sedimentation methods. The water content, Atterberg’s limits and related dependencies are very useful in the identification and classification of soils. Additionally, as an auxiliary test, the determination of the soil and dry soil density is realised. Such tests were carried out on disturbed and undisturbed samples at the Geoengineering Department of Warsaw Agricultural University (SGGW) in 1999–2000. Soil samples were taken from two boreholes with seven different depths from 5 to 11.5 m, distanced by 1 m. The results of the investigation are shown in Tab. 1.

Table 1. Index properties of clayey deposits at Stegny site [12]



water content wn

liquid limit wL [%]

plastic limit wp [%]

plasticity index

liquidity index

unit density

capacity of fraction

density of soil p[t/m3]

pd [t/m3]




grey clay












red clay












silty clay












motley clay












motley clay












The consistency limits: liquid wL and plastic wp ones were examined simultaneously on the same material taken from 15 depths of the geological profile. The results of the investigations are arithmetic averages of 2 tests for the limit wp, and – in the case of the limit wL, – being determined by Casagrande’s method with 6-9 tests repetitions.

The water content wn in cohesive soils was estimated by use of the classical oven-balance method. The samples have been analysed within a couple of hours since the sampling-moment in field. The fast examination eliminated the possible changes of the water content inside samples, resulted by the process of decompression and the influence of atmospheric factors. Totally, there were 150 measurements that gave 34 results in the form of mean values from 5 tests on the average. Taking into account the water content and Attenberg’s limits, the liquidity index IL and consistency index IC were calculated. The results are shown in Fig. 4.

Fig. 4. Variations of water content, liquidity and consistency index in the profile [13]

The in situ tests concern to relatively the same depths, where the sampling for the laboratory tests had been carried out. To recognize a subsoil structure, standard Marchetti’s dilatometer tests (DMT) were carried out in 7 profiles. The results of the laboratory measurement of the liquidity index had been accepted as a model, referring to the in situ tests.


The flat dilatometer test (DMT) was developed by Prof. Silvano Marchetti in the middle of 1970’s [7]. The construction of the dilatometer, which is shown in Fig. 5, was applied in field testing. The crucial part of the Marchetti’s dilatometer is a steel blade, where an elastic membrane is mounted. This membrane is deformed by the pressure of the gas supplied there. The device is also equipped with a measuring-control unit, which enables to read the pressure-values.

Fig. 5. The crucial parts of the flat dilatometer DMT: 1 – dilatometer blade, 2 – electric-pneumatic cable, 3 – control unit
(photo: M. Sobolewski)

A standard testing with the DMT consists of two phases, i.e. pushing the flat blade into a subsoil and carrying out a measurement. The dilatometer test are usually carried out every 0.2 m and the circular steel membrane is expanded horizontally while the pressure required for specific horizontal movement is recorded. After a measuring tip had been inserted into the subsoil, the values of a gas pressure by the three positions of a membrane may be measured. These values present a readout A, B and C.

The results of test are presented against depth and generally include three parameters: the material index (ID), horizontal stress index (KD) and dilatometer modulus (ED). These parameters are being used by the description of the sort of a soil and its geotechnical parameters [15].

The basis of this interpretation is an empirical correlation between the dilatometer indices and the soil parameters being sought. The empirical correlations have been established to obtain proper estimation of the soil type basing on the material index (ID). The similar correlations have also been worked out to describe relatively simple relationships between the horizontal stress index (KD) and the coefficient of lateral earth pressure (K0) as well as between the dilatometer modulus (ED) and the compressibility modulus (M).

Since the obtained correlations are influenced by many factors, the derived relations should be verified and adopted to local conditions. To determine the model values of a given soil parameters, which serve to scale the dilatometer, another methods of research are necessary – both laboratory and field tests. The scaling may be carried out also in the calibration chambers. In the research of the liquidity index IL of clayey deposits, the laboratory investigations of the water content wn and consistency limits (wp and wL) turned out to be helpful [12].

The research of the state of Pliocene clays in Stegny allowed for the determination of empirical relationships, which describe the liquidity index. To find the form of the proposed relationships, the method of multiple step regression as well as the mean values of the dilatometer modulus ED from 7 profiles of DMT have been used [15].

The results indicate the increasing trend of the dilatometric module ED along with the thickness. As well, the scattered values of ED increase. It disables the description of the state of soils solely by using the ED modulus (Fig. 6). The horizontal stress index (KD) is the other analysed parameter. It assumes the constant value KD = 5.6 in the whole profile. Because of the lack of relationship between (IL) and (KD), the horizontal stress index has been omitted in the analysis of results. However, the material index (ID) turned out to be an appropriate parameter. It shows a decreasing trend in the upper and lower zone of subsoil. Both parameters, ED and ID, are inversely to the thickness and the IL index. This observation is confirmed by a one-factor regression. In the upper zone the modulus (ED) dominates (R2 = 0.77), while in the lower one – the ID index (R2 = 0.81).

Fig. 6. Variations of dilatometer modulus (ED), material index (ID), and their ratio (ED/ID) in the profile


From the analysis of mechanical composition of Pliocene clays, one concludes that a considerable decrease in the clay fraction is marked in the deposits while observing along the thickness. The silt fraction, however, increases what shows that two sedimentation cycles have taken place (Fig. 3). The first one is located at 4.3–10.0 m, the second – between 10.0 and 12.5 m. The character of the observed cycles indicates that the sedimentation took place in a water environment (bigger particles deposit first, then the finer ones). The exception is silty interbedding with 30-34% content of the clay fraction [12], [13].

The changes of mechanical composition in these two cycles correspond to variations of the water content wn. The large similarity of changes characterizes also the liquidity index of clays. The changes of the state of these soils mainly result from the character of the water content.

There are two visible diminishing trends of the liquidity index. Stegny clays, being in a firm state, transit into a stiff from along with the thickness (Fig. 4). Consistency limits and the plasticity index Ip do not reflect the character of the variations of IL index, because they do not describe the soil structure. They are determined on remoulded soil samples.

The comparison of the in situ tests and laboratory method gives the possibility of verifying the existing empirical formulas connecting the liquidity index IL and the dilatometer modulus ED. The performed analysis has shown very significant differences. Thus, it is necessary to adapt the relationship described above to the local conditions of Stegny site. The effect of this analysis is the elaboration of the new methodology of measurement of the liquidity index from DMT test.

The associate influence of the (ED) modulus and (ID) index on the liquidity index (IL) is finally pronounced on the basis of the multiple linear regression. Both parameters (ED and ID), assume the normal distribution. The multiple linear correlation coefficients calculated for the both cases (in the upper and lower zone) are similar: r > 0.93. Both the first and the second parameter show the dispersion of the values. To describe a soil medium a ratio ED/ID has been introduced, which has a high coefficient of determination R2 = 0.9 (Fig. 6). The proposed empirical formulas are completed in Tab. 2.

Table 2. Proposed equations of liquidity index in DMT tests

For elaborated formulas the high agreement of the results from the field and laboratory tests was observed. The coefficient of determination in every case is higher than R2 = 0.8. The comparison of the results obtained in the dilatometer and laboratory tests is shown in Fig. 7.

Fig. 7. The comparison of dilatometer’s value of liquidity index ILDMT and laboratory value tests IL


For geotechnical engineers, who apply the theoretical rules in practice, the liquidity index is probably the most important parameter which rules the behaviour of clayey deposits. The consistency state of cohesive soils may be determined on the basis of the interpretation of dilatometer tests’ results supplied by the laboratory analysis of the liquidity index.

The results of site and laboratory investigations show that the proposed formulas describing the IL index with the use of dilatometer tests readings give a high coincidence between these results and the empirical values in heavily overconsolidated Pliocene clays. The comparison of calculated and measured values confirms the credibility of the applied methodology of the evaluation of the state of clayey soils. The flat dilatometer tests (DMT) are the easy way to evaluate sought soil parameters in the place of its natural occurrence. Taking into consideration the results of laboratory and in situ tests, it may be concluded that the existing formulae should be adapted to the local conditions and the history of soil deposits.

The Pliocene clays exist at the significant area in Poland, taking up ca. ¾ of the state area. Those soils are lying at various depths under the blanket of quaternary deposits and appear over the surface in places. The Pliocene clays are non-homogenous and show anisotropy of stress, structure and the geotechnical parameters [4]. Taking all that into consideration, the proposed formulas may be valid only in the research of clays in the firm state with the clay fraction content fi = 30 ÷ 80%. As the next stage, the methodology should be broadened by the new elaborated examples of Pliocene clays in stiff and very stiff state for ED/ID > 30 as well as soft and very soft state for ED/ID < 10. A verification and eventual re-scaling of the Marchetti’s dilatometer is necessary in order to adopt it to the local conditions of subsoil (for different Polish regions and other kind of fine-grained soils).


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  15. Szymański A., Sobolewski M., 2003. The use of dilatometer test for determination of permeability coefficient in cohesive soils. VI Conf. Aktual problems science-research archtecture. Olsztyn-Kortowo, 381-387.


Accepted for print: 7.12.2006

Mariusz Sobolewski
Department of Civil Engineering and Geodesy,
Warsaw Agricultural University, Poland
Nowoursynowska St. 159
02-776 Warsaw, Poland
email: mariusz_sobolewski@sggw.pl

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