SOIL STABILIZATION STABILIZATION USING POLYMER INFUSED ROOTS
A SEMINAR REPORT
Submitted by REMYA MOHAN
In partial fulfilment of the requirement for the award of the degree of BACHELOR OF TECHNOLOGY IN CIVIL ENGINEERING
Guided by Asst. Prof. LINU T. KURIAKOSE
DEPARTMENT OF CIVIL ENGINEERING Toc H INSTITUTE OF SCIENCE & TECHNOLOGY ERNAKULAM 682 313 SEPTEMBER 2014
Toc H INSTITUTE OF SCIENCE & TECHNOLOGY ARAKKUNNAM, ERNAKULAM-682 313
DEPARTMENT OF CIVIL ENGINEERING
CERTIFICATE This is to certify that the seminar entitled POLYMER INFUSED ROOTS
”
SOIL STABILIZATION USING
“
is the bonafide work done by REMYA MOHAN
(Reg no: 11123043) under our supervision and guidance. This seminar report is
submitted to Toc H Institute of Science & Technology in partial fulfilment of the requirements for the award of the degree of BACH E LOR OF TE CHNOLOGY in C I V I L E N G I N E E R I N G.
Guided by:
Head of the department:
Asst. Prof. Linu T. Kuriakose
Asso. Prof. Vasudev R
Department of Civil Engineering
Department of Civil Engineering
TIST
TIST
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ACKNOWLEDGEMENT This seminar work is the product of hard work and experience and it goes a long way in shaping a person in his respective profession. If words can be considered as token of acknowledgement and symbols of love, then these words play a vital role in expressing my gratitude. First of all, I’m thankful to God Almighty , for his choicest blessings for the successful completion of my seminar. I would like to express my gratitude to the Management, Toc H Institute of Science and Technology, Arakkunnam for their whole hearted support and for providing with a greater infrastructure necessary for the completion of my seminar. I also like to express my sincere thanks to Dr. D Vincent H Wilson (Principal, TIST) and Dr. P. Rajeev Kumar (Professor in-charge, PG studies, CE) for his kind
support throughout the completion of this venture. With a greater respect, I express my sincere thanks to Asso. Prof. Vasudev R (HOD, Department of Civil Engineering, TIST) for all the proper guidance and
encouragement that helped me to complete this seminar. I express my sincere gratitude to my seminar guide Ms. Linu T. Kuriakose, Asst. Professor, Department of Civil Engineering, TIST, for her valuable
guidance and support. Last but not the least; I’m grateful to all my friends and parents for their valuable motivation and support.
REMYA MOHAN S7, CE
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ABSTRACT
Soil instability is a worldwide problem. As such, there is a need for new technologies for soil stabilization. Among the stabilization methods seen in practice, vegetation and geofibers are two widely used methods to stabilize subsurface soils. This report investigates the use of polymer infused plant roots for soil stability applications. Roots of Ruelliasquarrosa and Artemisia annua plants were infused with a mixture of epoxyresin and polyoxyalkylamine blend hardener. Polymer-infused plant roots can be created without soil excavation by infusing polymer into the roots of plants through the easily accessible above-surface plant stems. Polymer content was determined for infused Artemisia annua plant roots. Soil enhancements are characterized by measuring soil shear strength using a vane shear apparatus and by measuring indirect soil tensile strength using a compression machine. Shear strength enhancements are measured in three different soil settings. Tensile strength enhancements are measured on root laden soil cylinders at two different moisture contents.
KEYWORDS: Polymer-infused root, Durability, Shear strength , Soil stabilization.
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LIST OF FIGURES Figure No.
Description
Page No.
2.1.
Artemisia annua plant.
3
2.2.
Ruellia squarrosa plant.
3
3.1.
Modified proctor test for soil used in laboratory tests.
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3.2.
Insitu shear strength of elastic silt soil reinforced by polymer infused roots and roots of Ruellia squarrosa
3.3.
7
Compacted soil cylinder setting insitu shear strength of polymer infused roots, roots of Artemisia annua and low plasticity clay soil.
3.4.
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Stress strain diagram of low plasticity clay soil reinforced with polymer infused roots and roots of Artemisia annua.
3.5
10
Tensile strength of non plasticity clay soil reinforced with polymer infused roots and roots.
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CONTENTS
Title
Page No.
CERTIFICATE
i
ACKNOWLEDGEMENT
ii
ABSTRACT
iii
LIST OF FIGURES
iv
1. INTRODUCTION
1
2. POLYMER INFUSED ROOTS FOR SOIL STABILIZATION 3. EXPERIMENTAL INVESTIGATIONS
1 4
3.1. SOIL SETTINGS
4
3.2. STUDY ON REULLIA SQUARROSA
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3.2.1. Infusions
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3.2.2. Vane shear test
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3.3. STUDY ON ARTEMISIA ANNUA PLANT
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3.3.1. Infusions
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3.3.2. Vane shear test
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3.3.3. Split tension test
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4. INFUSED POLYMER VOLUME MEASUREMENTS
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5. CONCLUSION
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REFERENCE
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1.
INTRODUCTION Soil is one of nature’s most abundant construction materials. Almost all
construction is built with or up on soil. When unsuitable construction conditions are encountered, we adopts four options: (1) Find a new construction site (2) Redesign the structure so it can be constructed on the poor soil. (3) Remove the poor soil and replace it with good soil. (4) Improve the engineering properties of the site soils. In general, Options 1 and 2 tend to be impractical today, while in the past, Option 3 has been the most commonly used method. However, due to improvement in technology coupled with increased transportation costs, Option 4 is being used more often today and is expected to dramatically increase in the future. Improving the engineering properties of the soil is referred to as either “soil modification” or “soil stabilization” The term “modification” implies a minor
change in the properties of a soil, while stabilization means that the engineering properties of the soil have been changed enough to allow field construction to take place. Soil stabilization is often necessary to provide a proper foundation , to prevent erosion and slope failure, and even to mitigate natural disasters such as landslides. Soil stabilization methods are mainly divided into mechanical stabilization and chemical stabilization. The most common form of mechanical soil stabilization is the compaction of soil. While addition of cement, lime, bituminous or other agents is referred to as a chemical method of soil stabilization and thereby improving the load bearing capacity of soil. Among the stabilization methods seen in practice, vegetation and geofibers (polypropelene and polysterfibres) are two widely used mechanical methods to stabilize subsurface soils. Stabilization of slopes using plant vegetation is a long-practiced, effective, and environmentally friendly method that results in minimal disturbance to the subsurface soil. By infusing polymer through the easily accessible above surface plant stems, polymer infused roots can be created without subsurface excavation.
2.
POLYMER INFUSED ROOTS FOR SOIL STABILIZATION Soil stabilization can be improved by using polymer infused roots that are
derived from infusing roots with polymers through the above grade stem to form a
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polymer root composite material. This method can be an important alternative for the surficial soil improvement to prevent erosion, to reduce edge cracking of pavements, stabilize subgrades, or even to construct unpaved roadways. Polymer root composite material is created by infusing a two part polymer, bisphenol-A resin and polyoxyalkylamine blend hardener, into the plant roots through the above-grade stems. The plant selected for infusion includes Artemisia annua and Ruellia squarrosa plant. These plants are selected because it has a woody stem and
was easy to attach to the injection tubing. In theory any vascular plant could be used but how much polymer would be infused is unknown for other plants and need further investigations. The resulting polymer volumetric content of the polymer root composites after the infusion process was 54% , and the process provided a 107% increase in tensile strength relative to non-infused roots. This technique for forming polymer infused roots provides a novel alternative method for stabilizing subsurface soil. For soils reinforced with roots, tensile stresses are transferred to the root material during shearing as a result of friction and interlocking between soil particles and roots. Along with the strength enhancement, understanding the durability of polymer infused roots is also important because the stabilized soil needs to survive construction and designed service life. The durability of polymer infused roots is of primary concern because they are formed in part from natural plant material, and those natural plant materials such as cellulose and lignin will decompose biologically over time. Two plant types are tested, namely, Ruellia squarrosa and Artemisia annua. The local names of these plants were Ruellia and Sweet worm wood respectively. The life period of Ruellia squrrosa were about 1-2 years and for Artemisia annua is 7-8 months. These plant types are selected because they have large stem diameters (greater than 3 mm) that are suitable for infusions and they can withstand the mechanical stress without breakage of root during infusion tubing attachment and polymer pressurization. These plants can be cut at the stems to provide a single stem for infusion. Single stem was preferred for infusions because infusion occurring through one stem of multi stem plants tends to pressurize the other stem and cause polymer to leak from other stems in lieu of polymer permeating through the roots as
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desired. Figure 2.1 and figure 2.2 shows the pictures of Artemisia annua plant and Ruellia squarrosa plant.
Fig.2.1. Artemisia annua plant
(Source: http://www.google.co.in)
Fig.2.2. Ruellia squarrosa plant
(Source: http://www.google.co.in)
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3.
EXPERIMENTAL INVESTIGATIONS In this chapter the experiments conducted on two plants namely Artemisia
annua and Ruelliasquarrosa are discussed. These two plants are selected for infusing polymer because they have large stem diameter. The soil setting considered for both tests are the same. The polymer is infused into these plants and after an ageing period, Vane shear and Split tensile strength test are conducted with the soil containing this polymer infused plants. 3.1. SOIL SETTINGS Vane shear test was performed in non-compacted soil beds(field test) for Ruellia squarrosa plant. For the testing 16 infused and 16 non infused plants are
selected. According to laboratory tests, the liquid limit and plasticity index of the soil were 66 and 19 respectively. The soil contains 77% fines and is classified as elastic silt in accordance with the unified soil classification system. A hand held vane with cross-blades of dimension 20 × 4mm (diameter times length) was inserted to a depth of 80mm to measure peak in situ shear strength for the field vane test. The vane was capable of a measurement range of 0 – 130 kPa with a manufacturer-reported accuracy of 10%. One vane shear test was performed for each plant, which resulted in 16 tests for infused and 16 tests for noninfused roots. Vane shear testing are also conducted in 14 compacted soil cylinders. Of the
14 cylinders, 8 were planted with Ar temisi a annua and 6 were not planted to serve as soil only control. The soil has a liquid limit and plasticity index of 44 and 24 respectievly, and contains 83% fines which is classified as low-plasticity clay (CL) according to unified soil classification system. Soil samples were compacted in 225 mm long, 100 mm internal diameter cylinders. Samples were compacted to a wet density of 16.7 KN/m 3 at a predetermined moisture content of 33% to a height of 200 mm, leaving 25 mm of freeboard for watering. The achieved compaction was approximately 80% based on the modified proctor test, and graph
is shown in
Figure.3.1. The low compacted density was chosen to provide adequate growth conditions for the plants. After 4 months of growth, all 8 plants were severed at their stem and 4 of the plants were infused to create polymer infused roots. The cylinders were then aged naturally in outdoor condition. After aging, the 4 polymer infused root soil cylinders, 4 root cylinders, and 6 soil cylinders were submerged under tap water
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for 2 days, removed from water, and then subjected to vane shear testing. The vane was inserted 25 mm from the stems. And the testing was conducted.
Fig.3.1.Modified Proctor Test For Soil Used In Laboratory Tests
(Source: Soil-Strength Enhancements from Polymer Infused Roots , American Society of Civil Engineers- 2013) The potential of polymer-infused roots for use in soil stabilization also was assessed through split-tension measurements in Artemisia annua plant . Soil was the same low-plasticity clay as used in the vane shear tests, and conditions were the same.Soil samples were compacted in165 mm long, 75 mm internal diameter molds prepared from Schedule 80 PVC pipe. Seedlings were allowed to grow in the compacted soil for 4 months; thereafter, eight of the planted samples were infused. After infusions, all samples were submerged for 2 days and subsequently allowed to air dry for 8 days to achieve uniform moisture content. During drying, the samples were loosely covered with plastic wrap to minimize crackin g. 3.2.
STUDY ON RUELLIA SQUARROSA PLANT
For an uncontrolled field study, the vane shear test is performed in a previously established landscaping bed of Ruellia squarrosa. This plant is drought tolerant perennial that provides ground cover and grows to a height of approximately 0.3m. Growth conditions, such as temperature, humidity, sunshine, and nutrition were not known or controlled. Testing of the plants occurred when the diameters of plant 5
stem were approximately 6mm, which could ensure proper connection to the infusion apparatus. The soil infusions, and the result of vane shear test are given below. 3.2.1 Infusions
The polymer used for infusions was a mixture of epoxy resin with a number averaged gram molecular weight less than 700g/mol and polyoxyalkylamine blend hardener. This polymer was selected based on its long cure times(up to 2 hr) and has a low viscosity. This polymer may be viable option for such applications as this resin and similar hardener undergo minimal biodegradation, characterized as 1% mass loss after buried in soil for one year. Polymer was mixed in accordance with manufacturer recommendations with 5 part resin to two part hardener by volume with a mixed viscosity of 0.25 Ns/m 2 at 24oc and a density of 1.1 g/cm 3. Infusions were conducted with a high pressure syringe pump loaded with 10-60 mL of polymer within a 60 mL volume polypropylene syringe. A luer fitting attached to the syringe to the polypropylene tubing. In this procedure, polymer administered at the plant root stem above ground, travels approximately longitudinally through the roots within the plant xylem and phloem, and radial outward from the xylem and phloem through the root tissue. For vane shear testing of the previously established beds of Ruellia squarrosa, infusions were conducted using a manifold system constructed of tees and tubing sections to connect stem stumps in series and up to 6 root samples were infused simultaneously. If leakage at tubing connections was observed, infusions were repeated for samples that appeared not to have been infused sufficiently. Depending on the number of plants connected to the tubing manifold, infusion rates varied between 2.5 and 60 mL/h per plant for durations of 6 – 30 min. Infusions were initially conducted at 2.5 mL/h and were increased to 60mL/h to accommodate faster curing rates of the polymer because of higher temperatures (32ºC) at the site. Laboratory pot life of the polymer was approximately 2 hr, whereas field pot life was limited to approximately 30 min. Infusions were conducted until the infusion pump stalled at the stall pressure of 1,100 kPa. Soil tests were conducted 1 day after infusions to ensure that the polymer had cured fully.
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3.2.2
Vane shear test
An uncontrolled field test was performed to examine the effectiveness of the infused roots by comparing with roots only. Because the in situ tests were performed over a relative small area and no significant soil inhomogeneity was observed, the influence of soil variation was considered limited. The measured peak shear strength in the soil beds for Ruellia squarrosa roots and polymer-infused roots as shown in Figure.3.2. For the roots, a shear strength of 80 ± 8 kPa was measured, whereas the polymer infused roots had a shear strength of 102 ± 9 kPa. Measured values are significantly different at a 95% confidence level, and polymer infusions of the roots provided a 28% increase in soil shear strength. It was diffic ult to locate regions within the test bed that were totally void of root materials; hence no shear-strength results for nonplanted soil (i.e., soil only) are presented in Figure.3.2.
120
100
80 Shear strength
Volume
60
High
(KPa)
Low
40
20
0 Polymer Roots Infused Roots
Fig.3.2.In Situ Shear Strength Of Elastic Silt Soil Reinforced By Polymer Infused Roots And Roots Of RuelliaSquarrosa.
(Source: Soil-Strength Enhancements from Polymer Infused Roots , American Society of Civil Engineers- 2013)
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The error bar in the graph indicates how much precise the value is. However, based on three measurements where minimal root material was observed, the average soil shear strength was approximately 50 kPa. It is reasonable to believe that the shear strength of the soil (i.e., without any roots) should be no greater than 50 kPa. Thus the presence of root material appears to enhance the shear strength of the soil by approximately 30 kPa or 60%. This amount of reinforcement provided by the roots is in the range observed by others for soil shear-strength enhancements (4 – 40 kPa) by grasses with low root density and low moisture content (<10%) for a sandy-clay-loam soil . Polymer-infused roots contributed an additional 22 kPa of soil shear strength, which confirms that infusing polymers into the roots does improve shear strength. 3.3.
STUDY ON ARTEMISIA ANNUA PLANT
For controlled laboratory studies, Artemisia annua was chosen because of successful prior experience of infusing polymer into the roots. This plant grows to a height of approximately 2m and as shown in suitability for infusions because it has high survival rate after transplanting. Seeds were germinated in 825 cm3 ceramic pots filled with potting soil placed inside a growth room with regulated temperature, humidity and day light time and watered daily. Temperature was 24±1 oc, relative humidity was 50 ± 5%, and 18 h of daylight was supplied to the plants. Daylight was simulated using fluorescent light bulbs and 60 Watt incandescent light bulb. The seedlings were allowed to grow for 2 weeks in one pot. This growth condition in the laboratory was considered ideal for plant growth and was used to shorten the time needed for growth. Individual seedlings were then transplanted into compacted soil cylinders to prepare samples for split tension testing and vane shear testing. The transplanted seedlings were allowed to grow for an additional 4 months in the growth room to reach sizes suitable for testing with roots fully penetrating soil depths. Infusions and results of vane shear and split tensile strength are given here. 3.3.1 Infusion
The infusion procedure is same as that done in Ruellia squarrosa plant. Artemisia annua used in split-tension tests and vane shear tests were individually infused at a rate of 60mL/h. This infusion rate produced Artemisia annua plant roots with 26% volumetric polymer content. Infusions were conducted until 16 mL of polymer was exhausted or until the infusion pump stalled. In some infusions, leaks
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occurred at the glue connection of the tubing to the plant stem. Leaking polymer was collected using a paper towel or nytrile glove tied around the stem of the plant, and tests were conducted 1 day after infusions . 3.3.2 Vane shear test
Results from soil shear-strength measurements in the compacted soil-cylinder setting
of
polymer-infused roots, roots, and soil are shown in Figure.3.3. The
moisture content of the samples was 32.5 ± 3.1%, and the polymer-infused roots had average an shear strength of 65.6 ± 14.6 kPa; roots had an average shear strength of 52.5 ± 7.4 kPa; and the soil had an average shear strength of 41.7 ± 8.6 kPa. The error bar in the bar graph indicates how much precise the value is.
90 80 70 60 Volume
Shear strength (kPa)
50
High
40
Low
30
Close
20 10 0 Polymer Infused Roots
Roots
Soil
Fig.3.3.Compacted Soil Cylinder Setting In Situ Shear Strength Of Polymer Infused Roots, Roots Of Artemisia Annua, And Low Plasticity Clay Soil.
(Source: Soil-Strength Enhancements from Polymer Infused Roots , American Society of Civil Engineers- 2013) In terms of the trend observed, the roots improved the shear strength of soil by 25%, and the polymer infused roots improved the shear strength of soil by 57%. The tensile strength of the roots was doubled by polymer infusions. The results shown that, enhancement of soil shear strength was also nearly double, and this observation
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may support the conclusion that soil shear strength enhancement can be attributed to the tensile strength enhancements of the roots. 3.3.3 Split Tension Test
Stress-strain diagrams of the split-tension test on soil with Artemisia annua roots and polymer-infused roots are shown in Figure.3.4. Non-planted samples were prepared for this test, but the samples experienced severe cracking and breakage during the drying period, making them unusable for testing after removal from the PVC molds. As such, no results for non-planted soil are provided. However, the observed ability of roots to prevent breakage of the planted soil during drying is an indicator of the reinforcement benefit provided by the roots. Clear differences in the stress-strain diagrams between polymer-infused roots and roots can be seen in Figure.3.4.Tensile strength and fail ure strain were determined from recorded values at the time that the sample developed a visual vertical crack. Figure.3.5, shows the tensile strengths of polymer-infused roots and roots. Polymer infused roots had tensile strength and failure strain of 38.2 ± 4.9 kPa and 2.9 ± 0.5%, respectively, whereas for roots these values were 24.6 ± 4.0 kPa and 2.9 ± 0.4%. The polymer infusion increased the tensile strength by 13.6 kPa (55%). These results confirm that the polymer provides additional enhancement. The polymer infusions did not affect the failure strain of the soil. This may be an indication that the polymerinfused roots fail by the same mechanism as roots.
Fig.3.4. Stress Strain Diagram Of Low Plasticity Clay Soil Reinforced With Polymer Infused Roots And Roots Of Artemisia Annua.
(Source: Soil-Strength Enhancements from Polymer Infused Roots , American Society of Civil Engineers- 2013) 10
45 40 35
Split tensile strength in
30
KPa
Volume
25
High 20
Low
15 10 5 0 Polymer Infused RootsRoots
Fig.3.5. Tensile Strength Of Non Plasticity Clay Soil Reinforced With Polymer Infused Roots And Roots.
(Source: Soil-Strength Enhancements from Polymer Infused Roots , American Society of Civil Engineers- 2013)
4.
INFUSED POLYMER VOLUME MEASUREMENTS Infused polymer volume was measured on washed Artemisi a annua roots.
Plants were severed at their stems, washed of potting soil, and infused at two different rates (2.5 and 60 mL/h) to assess which rate yielded higher polymer content in the plant. Prior to infusion, plants were either air dried or submerged in water for 24hr to assess if the plant moisture content affects the infused polymer content. Volumetric polymer content, expressed as a percentage, was estimated from the ratio of infused polymer volume to plant volume, which was measured using volumetric water displacement. The volume of polymer infused into roots was determined as the difference between infused volume and leaked volume. The infused volume was obtained directly from syringe readings, where as the leaked volume was calculated from the mass of the collected leakage as the density of the polymer is a constant. Polymer leaking through the roots at other locations besides the tubing connection 11
was not observed in these test. All syringe readings were made without the syringe pressurized as the syringes were observed to deform under pressure, leading to error in infused volume estimates. The polypropylene tubing that connected the plant to the syringe was filled with polymer before infusions to exclude the volume of the tubing from calculations.
5. CONCLUSIONS This study shows that polymer infused roots increase the soil strength compared with non- infused roots. Polymer infusions of Ruellia squarrosa roots provided a 22 kPa (28%) increase in soil shear strength. A limitation of this study is that the Ruellia squarrosa results are based on uncontrolled field measurements, and further investigations are necessary. Polymer infusions of Artemisia annua roots provided a 13.6 kPa (55%) increase in soil tensile strength and 13.1 kPa (25%) increase in shear strength for low plasticity clay. This process allows for in situ formation of polymer-infused roots for soil stabilization applications with minimum soil disturbance. This process can be potentially used for many applications such as surficial stabilization, erosion prevention, mitigation of surface cracking of clayey soil, and even unpaved roadways. Compared with other stabilization methods, such as cement or lime based stabilization or soil stabilization using geosynthetics, this process requires minimal disturbance on soil especially for existing structures and is a more environmentally friendly alternative.
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REFERENCES 1. Eisenacher, K .W., et al, (2013). “Strength enhancement of plant roots through polymer infusions.” Journal of Composite Material, 47(11).
2. Sauceda, M., et al. (2014). “Durability of Polymer Infused Roots for Soil Stabilization.” ASCE Journal of Materials in Civil Engineering, vol. 1561.
3. Sauceda, M., et al. (2013). “Soil strength enhancements from polymer infused roots.” Journal of Geotechnical and Geoenvironmental Engineering, vol. 241.
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