Introduction

Swelling soils are the generic description of all soils containing montmorillonite mineral, as it is all over the world especially in arid and semiarid areas. Cyclic volumetric changes in expansive soils with seasonal moisture fluctuation cause loss of shear strength while increasing moisture content and is a severe problem to civil engineers (Sefene 2021). The planning, design, and construction are seriously affected by the existence of swelling soils (SS) especially in infrastructure work (Blayi et al. 2020). Construction processes, environmental changes, and surcharge loading, which are field conditions, promote shrinkage-induced crack formation or shrinkage in the soil. Many factors influence soil expansion behavior, including the type of soil, whether fill or natural; the amount of water in the soil and its dry density; the amount of non-expansive materials in the soil, such as cobble-size particles or gravel; the magnitude of the surcharge pressure; and the age of the soil. Moreover, the type and amount of particle size of clay in the soil affect the soil expansion. Generally, as moisture content increases and dry density increases, expansion potential increases in the soil (Al-Omari et al. 2019). Specific minerals as montmorillonite which are present in clays absorb water and let the soil increase in size. A force that occurs due to the increase in volume of soil causes damage to buildings, pipelines, driveways, sidewalks, basement floors, and foundations (Li et al. 2020). The work of Sideek (2019) has indicated that the treatment by seawater only is unpractical technique since it has to be applied throughout the lifespan of the structure which is very expensive to apply. This leads to dryness of the soil if seawater did not reach the soil as seepage of fresh water may lead to higher swelling potential. Billions of dollars are being lost in repairing and rehabilitating these damaged structures due to expansive soils (Onyelowe et al. 2021). The work of Radwan and Bahloul (2019) concluded that there is direct proportion relation between plasticity index, swelling pressure, and free swell as by decreasing the PI, a reduction occurs to the swelling properties of the SS.

The work of Elmashad presents a solution for the swelling characteristics of bentonite by measuring the effects of adding chemicals to the soil as sodium chloride, ammonium chloride, lime, and sodium carbonate on the swelling characteristics of bentonite (Elmashad 2017). It was observed that by increasing the chemical additives concentration to 20% of the weight of the sample when mixed with water, a major decrease in swelling characteristics, liquid limit, plastic limit, and plasticity index is caused. Furthermore, there is a direct proportional ratio between the reduction in the swelling of bentonite and the water infiltration inside the bentonite. There is a significant increase of water infiltration due to increasing the percentage of lime and ammonium chloride. Adding chemicals are considered a way to solve the problem of SS. Sefene (2021) evaluated the effectiveness of adding wood ash on the swelling soil. According to the experimental analysis, liquid limit, plastic limit, and swelling ratio have been reduced due to the addition of the wood ash. Another field and an experimental study on engineering properties and swelling behavior of soil treated by lime mixed with sea water as a substitute of potable water are presented in the work of Emarah and Seleem (2018). Mixing with sea water shows significant swelling potential reduction and forms a new fabric structure having high shear strength together with high rigidity which makes it more capable in resisting the compression process. Sakr et al. (2020) studied the effect of adding micro silica fumes on properties of expansive soil which was studied through laboratory tests. The tests performed include free swell index, compaction, XRD analysis, and swelling pressure on the swelling soil with various percentages of micro silica fume. The observed results showed that swelling ratio and swelling pressure of soils significantly decreased. The aim of this work is to evaluate the changes to the swelling characteristics of SS and how it is affected by adding different percentages of LS and NaCl to the swelling soil.

Methodology and materials

Scheme of study

Free swell, liquid limit, plastic limit, plasticity index, standard oedometer swelling test, combined 1-D infiltration, and swelling and physical swelling model were performed on expansive soils with different LS and NaCl percentages. Additionally, the chemical analyses of all mixtures were analyzed with the contribution of a researcher in the chemical laboratory. Chemical analysis is included in the tests to determine predominant chemical characteristics such as chloride, sulfate, pH, and total dissolving solids (T.D.S) which is the term used to describe the small amounts of organic matter and the inorganic salts present in solution in water. The tests were held in the National Water Research Center in Cairo.

Materials used

Swelling soil (SS)

In this study, the expansive soil was obtained from the city of 6 October near Cairo, Egypt. As shown in Fig. 1, the hydrometer test was performed to determine the particle size distribution of fine-grained soil (smaller than 0.075 mm diameter grains) according to the ASTM D7928-17 standards. Table 1 shows the main physical properties of expansive soil. The soil has high swell potential with dark gray color.

Fig. 1
figure 1

Hydrometer test

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Table 1 The physical properties of expansive soil
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Sodium chloride salt (NaCl)

NaCl is considered a cheap additive which is an ionic compound consisting of sodium and chloride ions with ratio 1:1. It is considered as the extracellular fluid for a lot of multicellular organisms in addition to the responsibility for the salinity of sea water (Dilauro et al. 2019). NaCl is used in de-icing the roads in freezing weather due to its high melting efficiency (Łuczak, et al. 2020).

Lime sludge (LS)

The material was obtained from a company in El Minya called “abo karkash.” The material consists of wastes of sugar cane. The massive industrial wastes can be two-fold benefit to soil stabilization and cleaned environment. Firstly, LS is crushed to be in a powder form and then mixed with NaCl. Secondly, distilled water is added to the mixture to be finally added to the swelling soil.

Experimental testing program

Thirty-eight experimental tests were performed to investigate the behavior of swelling soil (SS) when mixing with various percentages of sodium chloride (NaCl) and lime sludge (LS). The SS was mixed with NaCl and LS either individual or in combination with different weight percentages for each additive. NaCl was added in percentages (1%, 2%, 3%) by weight, while LS was added in percentages (3%, 5%, 6%, 9%, 10%, 12%, 15%, 20%). The geotechnical properties were determined by adding distilled water to all the mixtures. To evaluate the effect of the different additives on the behavior of swelling soil, consistency limits, swelling properties, chemical analysis, and mineralogical change applying X-ray diffraction (XRD) technique were determined for all tested samples.

LL, PL, PI, and FS experiments were performed on all of the samples while swelling pressure was held only on the best results samples of consistency limits and FS experiments. After performing swelling pressure test on the samples, the results were filtered to undergo “combined 1-D infiltration and swelling” to take the best results to construct a physical model. Mineralogical tests were performed to ensure that the geo-technical properties of the soil are in accord with the mineralogical changes. Figure 2 shows a flow chart of the tests used and the sequence of performing each test. Table 2 shows the description of the samples used with the percentages of NaCl and LS.

Fig. 2
figure 2

Sequence of the performed experiments

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Table 2 The description of the samples used with different NaCl % and LS%
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Experimental results and discussion

The laboratory tests have included geotechnical engineering tests and chemical and analytical techniques as X-ray diffraction (XRD). Mixture samples of SS, LS, and NaCl previously described were carried out in the laboratory.

Geotechnical engineering tests

A group of tests including FS, PL, LL, PI, and oedometer were performed in the laboratory on SS mixtures in addition to the swelling infiltrometer which measures the infiltration and swelling of the soil simultaneously (Elmashad and Ata 2016). In addition, physical models were performed to ensure the results on a larger scale.

Consistency limits

The tests of the standard consistency limits were performed on the SS only as a control and mixed with NaCl and LS using distilled water with different percentages. Additionally, the tests were performed on different percentages of NaCl only. Figures 3a, b and 4 present the results of LL and PL where the effect of increasing the ratio of LS and NaCl was noticed on the consistency limits. As shown in Figs. 3a, b and 4, sample 32 gives a result of 80.2% and 21.5% for LL and PL, respectively, as a consequence of using the highest ratios which were 3% of NaCl and 20% of LS added to SS mixed with distilled water. It should be noticed that there is a significant reduction in LL and PL with 16.8% and 36.5%. In addition to the observed results shown in Fig. 5, a reduction occurs by 27.5% in PI. It is highlighted from the results that increasing the ratio of LS% and NaCl% changes the properties of the mixture from very highly plastic to relatively low plastic soil which decreases the LL and PL. Furthermore, the LL, PL, and PI results of adding different percentages of NaCl without adding LS are shown in Figs. 6, 7, and 8. It was observed that when increasing NaCl percentage, the LL, PL, and PI were decreased.

Fig. 3
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a LL of SS with different percentages of LS and NaCl. b LL of SS with different percentages of LS and NaCl

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Fig. 4
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PL of SS with different percentages of LS and NaCl

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Fig. 5
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PI of SS with different percentages of LS and NaCl

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Fig. 6
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LL of SS when added to different percentages of NaCl without LS

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Fig. 7
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PL of SS when added to different percentages of NaCl without LS

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Fig. 8
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PI of SS when added to different percentages of NaCl without LS

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The equation used to determine the reduction of LL:

$$\mathrm{\alpha }=\frac{LLf-LLi}{LLi}*100 (\mathrm{\%})$$
(1)
α:

liquid limit reduction.

LLi:

liquid limit of the swelling soil.

LLf:

liquid limit after adding the additives.

Swelling properties

The swelling properties of the soil were determined by the free swell test, standard swelling test (oedometer), combined swelling and infiltration test, and physical models (Elmashad 2017). The swelling soils contain clay minerals which absorb and attract water, as when the water is introduced to the SS, the molecules of water are pulled into the gaps between soil particles (Kumar et al. 2021).

Free swell

The tests of free swell index were held according to the Egyptian Code 202–2001. At temperature 105 °C, the soil was oven dried, then grounded by using mortar and pestle passing the 0.02-mm standard sieve (Elmashad 2017). The volume of water poured in 100-ml graduated cylinder is 30 ml. Moreover, 10 g of dry soil which is sieved is placed to the water under free fall in 1-g increments. After 24 h of hydration, the final volume of the soil which is swollen is measured.

The method of free swell index is calculated using the following equation:

$$FSI=\frac{Vf-Vi}{Vi}*100 (\mathrm{\%})$$
(2)
FSI:

free swell index (%).

Vi:

initial volume (mm3).

Vf:

final volume (mm3).

The results of free swell index (FSI) of SS mixtures of NaCl and LS mixed with distilled water are presented in Figs. 9 and 10. The highest reduction that occurred in FSI was 42.8% when reduced from 210 to 120% on mixing SS with a percentage of 20% of LS without adding NaCl. Additionally, the highest reduction that occurred in FSI was 54.7% when reduced from 210 to 95% when mixing 1% NaCl and 20% LS to the SS. The highest reduction that occurred when mixing 2% NaCl and 20% LS with SS was 57.1% reduced from 210 to 90%. The optimum reduction occurs in sample 32 which was 3%NaCl and 20% LS which reduced from 210 to 70% improving the swelling properties by 66.67%. The results indicate that as the percentage of NaCl and LS increases, the FSI decreases.

Fig. 9
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FSI of the samples with different LS % and NaCl%

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Fig. 10
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Influence of LS% and NaCl % on FSI

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Standard 1-D swelling test (oedometer)

Swelling tests of oedometer were carried out in a standard one-dimensional apparatus according to ASTM D 2435. A fixed stainless-steel ring is used to compact the soil samples which has a diameter of 75 mm. For each case, three samples are tested under stress increments of 98 kPa, 196 kPa, and 392 kPa. The increment of stress is applied to the sample in a dry form and sustained until the vertical movement stops. After that, water is added to the cell while recording the swelling with time. The swelling ratio is given by the percentage of total swell divided by the initial height of the sample.

$$SR=\frac{Hf-Hi}{Hi}*100 (\mathrm{\%})$$
(3)
SR:

swell ratio (%).

Hi:

initial height (mm).

Hf:

final height (mm).

The swelling ratio results are introduced in Fig. 11 of samples 12, 14, 16, 22, 24, 30, 31, and 32 which are 12%, 27%, 11%, 11%, 45%, 10%, 7%, and 11%, respectively, at stress of 392 kPa which presents the least swelling.

Fig. 11
figure 11

SR of samples no. 12, 14, 16, 22, 24, 30, 31, and 32

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Furthermore, Fig. 12 presents the results of samples 6, 7, and 9 which are SS mixed with LS only without adding NaCl whereas samples 36 and 37 shown in Fig. 13 are SS mixed with NaCl only. The results emphasize that the stress of 392 kPa also has the least SR. The samples 6, 7, and 9 resulted in 6% SR whereas the SR of samples 36 and 37 were 5% and 20%, respectively. It can be concluded from the results that sample 31 has the lowest SR which indicates that when increasing LS% and NaCl%, the SR decreases.

Fig. 12
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SR of samples no. 6, 7, and 9

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Fig. 13
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SR of samples no. 36 and 37

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Combined 1-D swelling and infiltration

During the study of the swelling behavior of clay, there is a significant characteristic that should be taken into consideration which is the speed of penetration of water in the soil, named infiltration. The depth of water which penetrates the soil measured in millimeter (mm) in 1 h is called the infiltration rate. For example, if the infiltration rate is 15 mm/h, this is an indication that 1 h is required for a 15-mm water layer to infiltrate through the soil surface. In dry soil, the water rapidly infiltrates through the soil initially; this mechanism is called initial infiltration rate. Another mechanism called basic infiltration rate takes place when the pores are replaced by more water instead of air. Saturation and moisture content responsible for swelling of the clay soil are directly proportional to the infiltration rate. A ring infiltrometer is the most common method used for measuring the infiltration rate in the field to correlate between the infiltration rate and the swelling of the soil. It consists of a plexiglass tube which is transparent with a total height of 300 mm and diameter of 150 mm. Firstly, 50 mm of clean sand is compacted at the tube’s bottom. Secondly, a 200-mm thick dry swelling soil sample is added after it has been compacted into 5 equal layers. Moreover, the samples of the soil are inundated with water maintaining its level above the soil surface samples. An analog dial gauge is used to measure the soil swelling with elapsed time which is attached at the top end of the apparatus as shown in Fig. 14. Furthermore, the infiltration of water that occurs in the soil sample is visually measured and monitored throughout the transparent plexiglass tube (Łuczak et al. 2020).

Fig. 14
figure 14

Infiltrometer apparatus

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The measured depth of infiltration is presented versus the elapsed time in Fig. 15 where the test is held on sample 1, 22, and 24. The readings of infiltration were measured over 5 days where each reading was taken every 24 h. It was concluded from Fig. 15 that the effect of the additives increases the infiltration depth. In case of sample 1, 40-mm infiltration was achieved in about 5805 min, while for samples 22 and 24, the infiltration in 5805 min was 80 mm which is almost double the infiltration depth in the same elapsed time. Figure 16 shows the swelling behavior of the 3 samples in the same test of combined swelling and infiltration. It was noticed from the results that the swelling decreases in samples 22 and 24. After 5805 min, SR was 30.1%, 16.2%, and 15.8% for samples 1, 22, and 24, respectively. The results show that increasing the percentage of LS decreases the SR.

Fig. 15
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Infiltration depth for samples 1, 22, and 24

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Fig. 16
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SR of samples 1, 22, and 24

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Physical swelling models

In order to be realistic in presenting the swelling properties of soil, the smaller models have to be scaled. Therefore, 2 physical models were performed on SS to simulate the swelling of soil in the field. The first model is SS only with distilled water while the second model is SS mixed with distilled water, 2% NaCl, and 12% LS. The model’s setup is similar to the swelling and infiltration test. The soil samples are compacted in 3 equal layers in a fixed cylindrical stainless steel with an external diameter of 360 mm, internal diameter of 67 mm, and the total height 450 mm as shown in Fig. 17. After adding the soil, the used additives are mixed with water then placed in the cylinder. The objective of the first model is to observe the swelling properties of SS only whereas the second model to observe the swelling properties when adding percentage of NaCl and LS on a larger scale model. The SR has been monitored with elapsed time for 15 days using an analog dial gauge attached to the top end. The SR is expressed by subtracting the reading of the dial gauge at specific time from the initial dial gauge reading divided by the total wetted height.

Fig. 17
figure 17

Experimental setup of the physical model

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The SR is expressed by:

SR:

\(\frac{\mathrm{Hf}-\mathrm{Hi}}{L}\)* 100.

SR:

swell ratio (%).

Hi:

initial height (mm).

Hf:

final height (mm).

L:

total wetted length (mm).

Figure 18 shows the SR of sample 1 with elapsed time to have a 38% SR at the end of the examined time and depth of water penetration of 90 mm. Moreover, Fig. 18 presents the SR of SS of sample 22 which is reduced to 33.4% and water is penetrated to a depth of 190 mm. This concludes that the additives added cause decrease in SR and increases the penetration of water through the soil.

Fig. 18
figure 18

SR of sample 1 and the SR of sample 22

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Chemical analysis

The chemical analyses of all mixtures were analyzed with the contribution of a chemist researcher in the chemical laboratory. Chemical analysis is included in the tests to determine predominant chemical characteristics such as total dissolving solids (T.D.S), chloride, sulfate, and pH. The TDS increases by increasing the percentage of NaCl and the percentage of LS throughout the study. The previous studies have reported that the wastes of chemicals have a strong effect on the swelling behavior of soil, especially on the swelling mineral called montmorillonite which is considered as mineral in the clay having highly swelling structure (Pan et al. 2021).

The physical properties of soil can be affected by the salinity causing the fine particles to bind together into aggregates which gives a positive effect on soil stabilization and aggregation (Xiao et al. 2022). Table 3 shows the chemical analysis of the SS used.

Table 3 Chemical analysis of natural expansive soil
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Mineralogical change

The change in the soil volume is caused due to its mineralogical composition. The most important minerals are montmorillonite, illite, and kaolinite but with different compositions. Montmorillonite expanding lattice has higher effect than illite on the swelling of the soil. It consists of an alumina sheet held between two silica sheets bonding together forming three weak sheet layers. The interchange of the elements between the sheets occurs causing large variations in its characteristics. For instance, the aluminum may replace the silicon in the silica sheets and the silicon may replace the aluminum in the alumina sheet causing large volume changes when water is added. Furthermore, by decreasing the percentages of montmorillonite, the swelling of the soil will decrease. On the contrary, the mechanism of kaolinites minerals is non-swelling which does not affect the swelling of the soil. The mineralogical composition is determined by X-ray diffraction (XRD) technique (Man et al. 2019).

XRD

The reaction products or the raw materials minerals can be identified from the lines of diffraction. The understanding and interpretation of the patterns of diffraction are based on a fact stating that each crystalline mineral has its characteristic atomic structure that diffracts X-ray in a pattern which is characteristic (Sakr et al. 2021).

Figure 19 illustrates the appearance of SS mixed with distilled water (sample 1). The XRD pattern of the SS indicates the presence of quartz, montmorillonite, and kaolinite with ratios 93.75%, 50%, and 37.51%, respectively. The XRD shows that montmorillonite has nine main broad peaks. The results show that the montmorillonite peaks are sharper than the other components due to its complex crystalline structure. There are also other peaks less than that from quartz and kaolinite.

Fig. 19
figure 19

Spectrum X-ray diffraction of SS only

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Figure 20 shows the general appearance of SS when 2% of NaCl and 12% of LS are added and mixed in distilled water (sample 22). The pattern of XRD of this mixture shows that the percentage of montmorillonite, quartz, and kaolinite decreased to 35.42%, 85.42%, and 31.26%, respectively. Moreover, albite and calcite appeared with percentages equal to 29.17% and 70.84%, respectively. These results indicate that the swelling of the soil has decreased due to the additives used. The percentage of montmorillonite decreases when the LS and NaCl are added which shows improvement of the swelling characteristics of the soil.

Fig. 20
figure 20

Spectrum X-ray diffraction of SS + 2% NaCl + 12%LS

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Results analysis and discussion

In this study, results show that the reduction that occurs in FSI is 66.7% which is more than the reduction obtained in Elmashad and Ata (2016) by 41.7% and more than Sakr et al. (2020) by 21.7% of the original value of FSI which indicates an improvement in the swelling properties of the soil. The work of Sideek (2019) shows that seawater only is very expensive technique as it requires to be added throughout the lifespan of the structure while in this study the LS is very cheap material which is obtained from waste of sugar cane. The proposed work shows that the FSI is more than the work of Al-Omari et al. (2019), as the FSI of the previous paper was reduced by 19% and 42% as using geogrid while reduction by 34% and 64% by mixing the original soil with sand which is still less than the reduction of the present work. In the present study, the results show that in the XRD test, the montmorillonite, which is a characteristic component of swelling soil, has changed to kaolinite, which is a non-swelling mineral, while the work of Sakr et al. (2020) and Sakr et al. (2021) show no change in the XRD test.

Conclusion

Experimental laboratory tests were performed to analyze the effect of mixing SS with different percentages of NaCl and LS on consistency and swelling properties of SS. According to the results of the tests, the outcomes are summarized as follows:

  1. 1-

    Based on the above results, it can be concluded from the study that by increasing the percentage of LS and NaCl, the swelling properties and consistency limits show significant improvement. The best result was obtained when 3% NaCl and 20% LS were used, which is considered as an efficient method to overcome the problems of expansive soils.

  2. 2-

    The LL shows significant reduction by increasing the % of LS and the % of NaCl. On mixing SS with 20% LS and 3% NaCl, the reduction of LL was 16.8% which is the least reduction of all samples.

  3. 3-

    The reduction occurred in PI was 27.5% and this refers to reduction in free swell and swelling pressure.

  4. 4-

    The swelling ratio decreased as the percentage of LS increased and was further decreased by increasing the percentage of NaCl to the SS for the same percentage of LS. The maximum reduction ratio in the FSI was 42.8% when using LS only and 66.7% when using LS and 3% NaCl.

  5. 5-

    Analytical technique which is X-ray diffraction was used to detect the reaction of chemical additives added to the expansive soil on clay minerals (montmorillonite). The results show that montmorillonite was transformed to kaolinite which is a non-swelling clay mineral.

  6. 6-

    The results shown from the swelling oedometer test at stress 392 kPa give the least swelling ratio.

  7. 7-

    The results concluded from the laboratory test which measure the swelling and infiltration in one simple test (the swelling infiltrometer) emphasize that when the percentages of NaCl and LS increase, the swelling of SS decreases and infiltration increases.

  8. 8-

    By performing the physical model, the swelling ratio was significantly decreased in sample 22 as the additives were added to the SS by 13% less than sample 1.