The soil-WH fiber composite as randomly distributed fiber reinforced soil (RDFS) and geotextiles was tested for its mechanical strength using a series of Unconfined Compressive Strength (UCS) and California Bearing ratio (CBR) tests, respectively. The compressive strength of soil-WH biochar composite is less than bare soil at all compaction states.
108 4.11 Tensile stress variation with elongation for four types of WH filaments 110 4.12 Tensile load variation with strain for WH geotextiles 111 4.13 Load variation with penetration of CBR stamp for the tested conditions 112 4.14 Increase of WH1 values with addition of CBR1 values. of PLR values with the addition of WH geotextiles 114 4.16 Compaction curve for soil-biochar composites at 5% and UCS of soil-biochar composite (WH, PE) and bare soil together with. 130 5.6 CIF variation for the selected soils for the monitoring period of 105 days 132 5.7 Suction variation for the selected soils in the first 35 days of.
Nomenclature
Introduction
- General
- Motivation of the thesis
- Organization of the thesis
The hydraulic performance was investigated by assessing the soil water retention capacity (SWRC), desiccation potential and infiltration for soil-WH fiber composite along with jute and coir. The vegetation potential along with SWRC and desiccation potential of soil-WH fiber composite was investigated by performing induced drought conditions.
Literature review
- General
- Physio-biochemical properties of natural fibers and their application in soil reinforcement
- Introduction
- Soil-natural fiber composite application
A recent study (Methacanon et al. 2010) advocated the use of Roselle as a soil reinforcement material. Jute fiber has been used in the field as RDFS and woven product used in soil subsoil reinforcement (Hejazi et al. 2012).
CBR 7
Its application is done extensively for soil blocks and increases the compressive strength of the composite. For ML soil, with increase in palm FP there is an increase in CBR value.
CBR 1,2
- Physio-biochemical properties of natural fibers
- Moisture absorption, degradation and treatment of natural fiber
- Gap areas and future scope of natural fiber in geotechnical engineering
- Effect of vegetation on desiccation cracks
- Gap areas and future scope of desiccation cracks in vegetated soil
- Biochar amended soil for geo-environmental application
- Scope and objectives of the thesis
These components serve to form the cellulose superstructure in the form of a matrix (Khalil et al. 2015). The thick middle layer (S2) of the secondary wall determines the mechanical properties of the natural fiber (Azwa et al. 2012). The study by Gassan et al. 2001) correlated the elastic modulus of material with the MFA of the fiber.
Dimensional changes due to fiber swelling lead to a decrease in the friction angle of the composite (Azadegan et al. 2012). The cracking potential in previous studies (Gadi et al. 2017) is quantified using the crack intensity factor (CIF). Cracks formed by desiccation can strongly affect the permeability (Li et al. 2009) and thus the stability of the embankments.
Under the equivalent continuity assumption, Li et al. 2009) derived the permeability function for cracked soil (ks) by superimposing those for crack network (kc) and soil matrix (km). Pore-water pressure is inversely proportional to soil shear strength (Li et al. 2011).
Materials and experimental methodology
- General
- Material properties
- Experimental methodology
- Chloroform/methanol (2:1): Chloroform (666 ml) was added to a 1L volumetric flask
- FDA stock solution (1000 mg): Fluorescein diacetate (0.1 g) (3´6´-diacetyl-fluorescein was dissolved in approximately 80 ml of acetone and the contents of the flask made up to
- Fluorescein stock solution (2000µg): Fluorescein sodium salt (0.2265 g) was dissolved in approximately 80 ml of 60 mM potassium phosphate buffer pH 7.6 and the contents
On the other hand, coconut has the highest percentage of lignin and is the most ductile fiber (i.e. the highest elongation at break). The surface morphology of BC particles is compared with that of the soil and soil WH BC using FE-SEM images as shown in Fig. Minidiskinfiltrometer (MDI) (Fig. 3.7; Decagon devices 2013), is a recent development for determining the infiltration characteristics of the soil.
However, the majority of the grain size in the selected soils falls below 2 mm as can be seen in fig. In order to study the effect of the mold dimension, a parameter - mold ratio (MR) is adopted, which is defined by Eq. A higher depth was provided for 4.5 cm mold to ensure that the wetting front does not reach the bottom of the mold for the soils treated in this study.
The area of the disc being previously known, the cumulative depth of water seeping (I) into the soil was obtained and plotted against the square root of time as shown in Fig 3.10. Thus, measurement of enzymatic catalysis characterizes soil fertility and quality, as well as guides soil suitability for microbial growth.
Mechanical characteristics of soil-WH biomaterial composite
- General
- Strength characteristics of soil-WH fiber composite
- Stress-strain response of fiber reinforced sample as compared to bare soil
- Effect of density and moisture content on the UCS of fiber reinforced soil
- Effect of fiber inclusion on the strength and ductility of the soil-fiber composite
- Strength improvement factor (SIF)
- Mobilized peak strain factor (MPSF)
- Normalized ductility index (NDI)
- Strength characteristics of soil-WH geotextile composite
- Water hyacinth filament and geotextile
- Test program and specimen preparation
- Mechanical property of water hyacinth filaments and geotextiles
- Effect of water hyacinth geotextile reinforcement on CBR
- Strength characteristics of soil-WH biochar composite
The difference between peak strength and post-peak strength is quite less for reinforced soil compared to unreinforced soil, indicating that the post-peak ductility of the soil has increased with fiber inclusion. The inclusion of fibers in the soil resulted in an increase in the soil strength and affected the ductility of the soil-fiber composite. The MPSF is defined as the ratio of the peak stress of reinforced soil to the peak stress of bare soil for the same compaction condition.
For the shear stage after reaching the maximum strength, the ductility of the soil is also measured by the brittleness index, Ib (Consoli et al. 1998; The inclusion of fiber with higher moisture content increases the strength of the soil-fiber composite compared to bare soil by increasing the adhesive forces along the soil-fiber interface. Although the stress increase at a higher moisture content is relatively smaller than that of the drier condition (refer to Fig. 4.3), the incorporation of fibers significantly improves the ratio of resisted stress as compared to bare soil.
This is probably due to an increase in the contact area between individual filament units with increasing width. The tensile strength of WH geotextiles is attributed to the presence of a higher percentage of cellulose in the plant stem (Methacanon et al. 2010).
Water content (%) Dry density (kN/m3)
Summary
The summary of this chapter can be discussed as follows for the three soil WH biomaterials that were tested. 1) Ground-WH fiber composite. The post-peak ductility of soil-fibre composite is mainly dependent on the fiber percentage and the compaction condition. The tensile strength properties of both filaments and geotextiles produced from WH demonstrate that it is a potential material for the production of LLGs.
It was found that the weave pattern of WH geotextile affects its tensile strength, as WW-GT geotextile has higher tensile strength compared to C-GT. The observed biochemical characteristics (significant amount of cellulose present in the WH stem) of the WH filament clearly justify its high tensile strength. The compressive strength of the soil-WH biochar composite is lower than that of bare soil at all moisture contents.
Unlike soil PE biochar composite, the UCS for soil WH biochar composite was lower and can be attributed to high intra-pores seen in individual WH biochar particles. In addition, the surface roughness of PE biochar is higher than that of WH biochar given the shape parameters measured by the particle characteristic analyzer.
Hydraulic characteristics of soil-WH composite
- General
- Soil-water retention and desiccation characteristics of soil-WH fiber composite
- Test Setup and Procedures
- Measurement of crack intensity factor (CIF)
- Soil water retention of soil-WH Fiber composite
- CIF variation with time and drying cycles
- Effect of fiber inclusion on resisting cracks at varying suction
- Infiltration characteristics of soil-WH fiber composite
- Measurement of infiltration rate
- Test setup and procedure
- Effect of fiber reinforcement on the infiltration rate of the soil-fiber composite
- Dye tracer experiment to investigate preferential flow path in soil-fiber composite
- Effect of fiber type on infiltration rate
- Soil water retention and desiccation characteristics of soil-WH biochar composite
- Test plan and preparation of soil column tests
- Effect of WH biochar on soil water retention curve
- Effect of WH biochar on crack intensity factor
- Summary
A digital camera (model: Canon EOS 700d) with an adjustable frame was also mounted on top of the soil column to obtain periodic time-lapse images (method described in next section) of the soil surface for studying the crack development patterns during drying cycles. This is because the presence of hemicellulose biopolymer in the natural fibers improves the water holding capacity of the soil. The aim of the experiment was to delineate the distribution of water in the soil-fiber composite during infiltration of MDI.
However, the soil water retention (SWR) and cracking potential of soil-WH biochar composite were not investigated. The tension in the air-water menisci induces tensile stresses on the soil particles, which are represented by the suction forces (Li et al. 2011). This increase in crack opening is accompanied by soil contraction, which is intrinsic to the cohesive nature of soil (Cordero et al. 2017).
This is the maximum soil cracking potential and indicated by the peak CIF in the present study (Fig. 5.15). This is due to water flowing along the soil-fiber interface along with flow through the soil pores.
Hydraulic characteristics of Vegetated soil-WH composite
- General
- Hydraulic characteristics of Vegetated soil-WH composite
- Test plan, setup and instrumentation
- Test procedure
- Interpretation of monitoring results
- Summary
A monitoring period of 73 days starting from rhizome transplantation was carried out to mimic early plant establishment (critical period in soil biotechnological applications towards erosion resistance; Schmidt et al. 2001). Two grass species (Axonopus Compressus and Cynaodon Dactylon) were selected based on their easy availability, drought tolerance and use in green infrastructure (Ng et al. The irrigation period was kept at 7-day intervals based on the observed suction near the wilting point (around 1500 kPa; Feddes et al. al. 1982) generated in the root zone.
The rate of evapotranspiration (Etr) and evaporation (Er) was measured by the weight change of the plant and bare column in the drying cycle (Leung et al. 2015). The highest CIF for the same soil compacted at 0.8 MDD and similar irrigation patterns was previously reported as CIF 3.15 (Gadi et al. 2017). It is clearly seen that SG shows higher water retention for most of the suction range (25-1000 kPa) compared to BS.
FE-SEM images show the surface morphology of the fiber and it is stacked with fine pores that are conducive to absorbing moisture (Methacanon et al., 2010). SG shows higher water retention for most of the suction range (25-1000 kPa) compared to BS.
Bio-degradation and treatment of WH fiber
- General
- Bio-degradation assessment of natural fibers in compacted soil
- Test plan and setup
- Bio-chemical composition change with bio-degradation
- Effect of bio-degradation on UCS of soil-fiber composite
- Nano-coating of water hyacinth fiber
- Treatment process of WH fibers
- Morphology and physical properties of untreated and treated fiber
- Unconfined compressive strength, direct shear and CBR test of soil-treated fiber composite
- Effect of nano-coating fiber inclusions in strength characteristics of soil
The experiment was conducted in the field where compacted soil-fiber composite was buried in the soil and exposed to natural environmental conditions. After the samples were buried and at different time intervals (as shown in Fig. 7.1), the biochemical properties of the fibers were measured by taking 3 fibers from the top, bottom, and center of each soil-fiber composite (coconut, jute, and WH). Of all soil-fiber composites, jute-reinforced soil showed the highest decline from its original state (22.72%).
This is because the fibers form an additional food source for various microorganisms in the soil. Efforts have been made in this research to improve the life of the fiber and improve the mechanical performance of the soil-fiber composite. In addition, the moisture content in the soil-fiber composites was cross-checked by oven drying after completion of the UCS test.
This phenomenon is due to the fact that the fiber tensile strength is mobilized under load and the subsequent increase in the strength of the bottom-fiber composite (Tang et al. 2007, Tang et al. 2010). Among the bottom-fiber composites, (TF + S) showed higher UCS values for all compaction states.
