In this study, lime stabilization and geocell reinforcement methods were investigated for a clayey subgrade of unpaved road at different water contents. This study is especially important in terms of determining the soil improvement method for road construction on wet lands. The effects of the geocell height (50, 100, 150, and 200 mm) and lime content (3, 6, and 12%) on the settlement of the subgrade soil at different water contents (25, 28, 30, 32, and 35%) were analyzed. Accordingly, a large scale plate loading test was designed, and it is utilized to achieve loading-settlement curves. The bearing capacity and modulus of subgrade (k) of soil were determined. It was detected that the geocell height and lime content have different effects at different water contents, and the modulus of subgrade reaction became stable beyond a constant height of the geocell. It was understood that none of these two improvements did not meet the Highways Technical Specifications. It is detected that at least these two improvement techniques are needed to be applied together to meet the specifications for the soil examined in this study.
Performance and bearing capacity of the road surfacing significantly depend on the specifications of the ground that it subsides. Therefore, foundation floors must safely withstand the stresses caused by traffic loads. Therefore, base soils need to safely withstand the stresses that traffic loads constitute. Generally, soil type, water content, and degree of compaction affect the bearing capacity of the foundation soil. Swelling or blistering of the base soil depends on its moisture content. No superstructure constructed on this type of base soils can withstand against cracking and settlements. Base soils must be able to withstand high level loads without excessive settlements. Base soils that are not suitable for the road superstructure should be improved and stabilized adequately. With the improvement of the base soil, the bearing capacity and surfacing performance increase, while settlements and, thus, the surfacing thickness decrease [
With the addition of lime to the soil, the strength and modulus of elasticity of the soil increases. Thus, an increase in the strength of the soil occurs [
They concluded that the strength of Terra rossa soil increased rapidly within 7 days with the addition of the cement-bentonite mixture; on the other hand, the increase occurred after 7 days with the addition of the bentonite-lime mixture [
In their study, Keskin and Kavak [
Madhavi Latha and Somwanshi [
Dash et al. [
Zhou and Wen [
Zhang et al. [
In their study, Dash et al. [
It was indicated that the geocell shape of 1 : 1.2 (width : height), which was filled with sand, and the geocell shape of 1 : 0.8, which was filled with sedimentary clay gave the largest ultimate bearing capacity [
Kong et al. [
Yünkül et al. [
Tiwari and Satyam [
In this study, the effect of lime and geocell reinforcement has been studied under varying moisture contents. The overall goal of this study was to analyze the effects of the geocell height (50, 100, 150, and 200 mm) and lime content (3, 6, and 12%) on the settlement of the clayey pavement subgrade at different water contents (25, 28, 30, 32, 35%). This comparison has not been made before in other studies.
In this article, clayey soils with different water contents (25, 28, 30, 32, and 35%) have been subjected to a number of experiments. The soil is classified according to the AASHTO and the unified soil classification system. Accordingly, sieve analysis, consistency limit, and hydrometer analyzes were performed on the soil, respectively. Proctor tests were carried out on the samples in order to determine the optimum water content and dry unit weight of the clay material. In this study, model plate loading experiments were conducted on the mixtures that were prepared from optimum water content (25%) and high water contents (28, 30, 32, and 35%). In these experiments, soil was reinforced at different heights (50, 100, 150, and 200 mm) of the geocell, and lime was mixed to soil at the rates of 3, 6, and 12%. These treatments were made solely and together at different water contents (25, 28, 30, 32, and 35%). The sieve analysis of the soil used as a subgrade is given in Table
Sieve analysis.
Sieve analysis | ||||
---|---|---|---|---|
Sieve no | Sieve diameter (mm) | Residue of sieving (gr) | Sieved (gr) | Sieved percent (%) |
3/8″ | 9, 53 | 0 | 420 | 100 |
4 | 4, 76 | 42, 7 | 377, 3 | 90 |
10 | 2 | 30, 1 | 347, 2 | 83 |
40 | 0, 42 | 18, 73 | 328, 47 | 78 |
100 | 15, 4 | 313, 07 | 75 | |
200 | 0, 074 | 11, 5 | 301, 57 | 72 |
Pan | 301, 57 |
In accordance with ASTM D2487 [
Dry sand was preferred as the infilling material for the geocell (Figure
Filling the geocell with sand.
The technical properties of the geocell specified by the manufacturer are given in Table
Technical properties of the geocell.
Properties | Values |
---|---|
Density (gr/cm³) | 0.94 |
Welding size (cm) | 40 |
Cell length (mm) | 300 |
Cell width (mm) | 250 |
Thickness (mm) | 2 |
Cell height (cm) | 5-10-15-20 |
Laboratory scale loading tests were used to investigate the influence of lime stabilization (3 different lime contents were used) and geocell (4 different geocell heights were used) reinforcement on increasing the bearing capacity of clayey soil with 3 different water contents in a steel box.
The inner dimensions of the box are given in Figure
Schematic diagram for the set-up of the plate loading test.
Dash et al. [
The acceptable range of settlements was not considered in some studies [
In this study, the peak load was selected to simulate a single wheel load of 40 kN (equivalent to an axle load of 80 kN and a tire contact pressure of 550 kPa).
The test box was filled with clayey soil with optimum water content (25%) and high water contents (28, 30, 32, and 35%). The soil was used as a subgrade and placed in 3 layers with 25 cm thickness for each layer. The placed layers were compacted in lifts inside a box using a vibratory plate compactor. After preparing the subgrade, three strain gages were installed on the top of the subgrade. 5 pressure cells were installed on the surface of the subgrade at the center, 15 cm, and 30 cm away from the center of the loading plate, respectively. A linear variable differential transducer (LVDT) was also placed on the footing model to provide the value of footing settlement during the loading (Figure
After the installation of pressure cells and strain gages, a geocell was placed on top of the subgrade. The top of the geocell mattress was at a depth of 3 cm from the bottom of the footing to get optimum test results as Tafreshi and Dawson [
32 unpaved road test sections were prepared in the test box. Settlements of lime stabilized and geocell (with different heights) reinforced soils with different water contents were examined.
Comparison between the improvement of the clayey unpaved road subgrade with geocell and lime stabilizations at different water contents was made in the laboratory. The height of the geocell used in this study was 50, 100, 150, and 250 mm. The lime content was 3, 6, and 12%. The water content was 25 (optimum), 28, 30, 32, and 35%.
Effects of lime stabilization at a rate of 3, 6, and 12% at 25, 28, 30, 32, and 35% water contents are shown in Figure
Loading-settlement curve for lime stabilizations at different water contents.
The settlement in soil with 25, 28, 30, and 32% water contents was 0.80, 0.85, 0.87, and 0.96 times the settlement in soil with 35% water content under 550 kPa, respectively.
Lime stabilization at a rate of 12, 12, 12, 6, and 6% was most effective at 35, 32, 30, 28, and 25% water contents, respectively. The settlement in soil with 35% water content was 1.8, 1.6, and 1.3 times the settlement of 12, 6, and 3% lime-stabilized soil at the same water content under 550 kPa, respectively. The settlement in soil with 32% water content was 1.8, 1.6, and 1.3 times the settlement of 12, 6, and 3% lime-stabilized soil at the same water content under 550 kPa, respectively. The settlement in soil with 30% water content was 2, 1.8, and 1.4 times the settlement of 12, 6, and 3% lime-stabilized soil at the same water content under 550 kPa, respectively. The settlement in soil with 28% water content was 1.8, 2, and 1.6 times the settlement of 12, 6, and 3% lime-stabilized soil at the same water content under 550 kPa, respectively. The settlement in soil with 25% water content was 1.6, 2.2, and 2 times the settlement of 12, 6, and 3% lime-stabilized soil at the same water content under 550 kPa, respectively. Adequate quantities of lime must be added into the soil to get minimum settlements under loading. Although better results were obtained by using 12% lime content for soils at 30, 32, and 35% water contents, it was seen that the lime content must be decreased to 6% for soils with 28 and 25 (optimum)% water contents. Dash and Hussain [
Soil settlements under pressure when the soil is reinforced by geocell with 4 different geocell heights at 3 different water contents are shown in Figure
Loading-settlement curve for geocell reinforced soil at different water contents.
The ratio between the settlement of the soil at 35% water content under 550 kPa and geocell reinforced soil with 200 mm height at the same water content was 2.6. The ratio between the settlement of the soil at 30% water content under 550 kPa and geocell reinforced soil with 200 mm height at the same water content was 2.5. The ratio between the settlement of the soil at 25% water content under 550 kPa and geocell reinforced soil with 200 mm height at the same water content was 2.5.
When the height of the geocell was 50 mm at geocell-reinforced soil at 35% water content, the settlement was 1.1, 1.3, and 1.4 times the settlement when the height of the geocell was 100, 150, and 200 mm under 550 kPa, respectively. When the height of the geocell was 50 mm at geocell-reinforced soil at 30% water content, the settlement was 1.1, 1.2, and 1.3 times the settlement when the height of the geocell was 100, 150, and 200 mm under 550 kPa, respectively. When the height of the geocell was 50 mm at geocell-reinforced soil at 25% water content, the settlement was 1.1, 1.2, and 1.3 times the settlement when the height of the geocell was 100, 150, and 200 mm under 550 kPa, respectively.
The effect of the height of the geocell on settlement of soil was different for soils at different water contents. Soil settlement differences between different heights of geocell at 25, 30, and 35% water contents are shown in Figure
Settlement differences between different heights of the geocell at different water contents.
The modulus of subgrade reaction values (k) for lime-stabilized soil at different water contents was calculated with the help of Figure
Modulus of subgrade reactions (k) for lime-stabilized soils and geocell reinforcements.
States | Modulus of subgrade reaction (k) (kN/m³) |
---|---|
35% water content | 6.550 |
32% water content | 6.880 |
30% water content | 8.100 |
28% water content | 9.050 |
25% water content | 11.460 |
3% lime at 35% water | 8.490 |
12% lime at 35% water | 15.100 |
3% lime at 32% water | 9.170 |
6% lime at 32% water | 14.470 |
12% lime at 32% water | 14.600 |
3% lime at 30% water | 14.030 |
6% lime at 30% water | 15.800 |
12% lime at 30% water | 24.700 |
3% lime at 28% water | 14.750 |
6% lime at 28% water | 24.750 |
12% lime at 28% water | 15.350 |
3% lime at 25% water | 25.000 |
6% lime at 25% water | 27.500 |
12% lime at 25% water | 15.280 |
Geocell height 200 mm at 35% water content | 27.500 |
Geocell height 150 mm at 35% water content | 26.190 |
Geocell height 100 mm at 35% water content | 22.900 |
Geocell height 50 mm at 35% water content | 18.300 |
Geocell height 200 mm at 30% water content | 28.950 |
Geocell height 150 mm at 30% water content | 27.230 |
Geocell height 100 mm at 30% water content | 25.000 |
Geocell height 50 mm at 30% water content | 18.350 |
Geocell height 200 mm at 25% water content | 29.570 |
Geocell height 150 mm at 25% water content | 28.650 |
Geocell height 100 mm at 25% water content | 26.250 |
Geocell height 50 mm at 25% water content | 18.950 |
Lime stabilization increased the “k” value 2.1, 1.9, 2, 1.8, and 1.4 times the value in soil at 35, 32, 30, 28, and 25% water contents, respectively. As it is seen, these increments decrease while water content decrease. The best lime content to get the highest “k” value was 6% for soils at 25 and 28% water contents. 12% lime content was the best alternative to get the highest “k” value for soil at 30, 32, and 35% contents.
It was determined that the modulus of the subgrade reaction increases when the height of the geocell increased. It was also observed that the modulus of the subgrade reaction increase stopped at 200 mm geocell height at 25, 30, and 35% water contents.
Half of the stress corresponding to 10 mm settlement at the load-deformation curve obtained from the plate loading experiment gives the bearing capacity of the base soil. By starting from this information, half of the stresses corresponding to 10 mm at load-deformation curves were calculated, and bearing capacity values were determined. The bearing capacity values for lime-stabilized soils are given in Table
Bearing capacities of lime-stabilized soils and geocell reinforcements.
States | Bearing capacity (kN/m2) |
---|---|
35% water content | 28 |
32% water content | 31 |
30% water content | 38 |
28% water content | 43 |
25% water content | 60 |
3% lime at 35% water | 38 |
12% lime at 35% water | 86 |
3% lime at 32% water | 44 |
6% lime at 32% water | 74 |
12% lime at 32% water | 75 |
3% lime at 30% water | 74 |
6% lime at 30% water | 95 |
12% lime at 30% water | 110 |
3% lime at 28% water | 86 |
6% lime at 28% water | 115 |
12% lime at 28% water | 95 |
3% lime at 25% water | 127 |
6% lime at 25% water | 142 |
12% lime at 25% water | 86 |
Geocell height 200 mm at 35% water content | 138 |
Geocell height 150 mm at 35% water content | 121 |
Geocell height 100 mm at 35% water content | 93 |
Geocell height 50 mm at 35% water content | 86 |
Geocell height 200 mm at 30% water content | 140 |
Geocell height 150 mm at 30% water content | 135 |
Geocell height 100 mm at 30% water content | 120 |
Geocell height 50 mm at 30% water content | 103 |
Geocell height 200 mm at 25% water content | 148 |
Geocell height 150 mm at 25% water content | 138 |
Geocell height 100 mm at 25% water content | 120 |
Geocell height 50 mm at 25% water content | 112 |
As it is seen from Table
When the height of the geocell was 200 mm, the highest bearing capacities were obtained as it was expected. The effect of height of the geocell on the bearing capacity of soil decreases at all water contents in this study.
The bearing capacity was increased 5, 3.7, and 2.5 times by geocell reinforcement of soil at 35, 30, and 25% water contents, respectively. The bearing capacity ratio between the geocell reinforcement and lime stabilization (maximum bearing capacity by using geocell/maximum bearing capacity by lime stabilization) was 1.60, 1.27, and 1.04 at 35, 30, and 25% water contents, respectively. It was determined that, when the water content decreases, lime stabilization can be used instead of geocell reinforcement.
Lime stabilization and geocell reinforcement can be used to improve soil. In this study, lime stabilization and geocell reinforcements were made at different water contents for clayey subgrade of the unpaved road. Different lime contents and geocell heights were investigated for this purpose. Model plate loading experiments were done in the laboratory. Thirty-two different unpaved road test sections were examined. The peak load was selected to simulate a single wheel load of 40 kN (equivalent to an axle load of 80 kN and a tire contact pressure of 550 kPa). The effects of lime content and geocell height were investigated on the bearing capacity and the modulus of subgrade reaction of soil at different water contents. It was examined whether those improvements met the requirement of Highways Technical Specifications or not. These comparisons have not been made before in the literature for thirty-one different states examined in this study.
From the data presented in this study, the following conclusions can be drawn: The settlement in lime-stabilized soil was at most between 1.8 and 2.2 times the settlement in unstabilized soil. The settlement in geocell reinforced soil was at most between 2.5 and 2.6 times the settlement in unreinforced soil. The effect of the height of the geocell on the settlement of soil under pressure decreases when the water content of the soil decreases. It was observed that, when the height of the geocell increased, the modulus of the subgrade reaction also increased and became stable beyond 200 mm geocell height at 25, 30, and 35% water contents. The bearing capacity was increased maximum 5 times by geocell reinforcement.
It is recommended that at least lime stabilization and geocell reinforcement need to be applied together to meet the Highways Technical Specifications for wetlands.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no competing interests.