Fibrous Peat Research Articles

Effect of Cement-Sodium Silicate Grout on the Compressibility Parameters of Fibrous Peat

The distribution of peat deposits can be found in many countries and peat-land constituents from 5 to 8% of earth land surface, where approximately 60% of the wetlands are peat. An increasing growth of the population leads to the necessity of peat-land utilization for development purposes. This article describes a laboratory study on the effect of sodium silicate on the compressibility parameters of peat, which are settlement, void ratio, compression index and coefficient of secondary compression. The effect of the sodium silicate and ordinary Portland cement on the compressibility parameter of peat is investigated through Rowe Cell consolidation test. At the end of this study, it is shown by increasing sodium silicate (within 2.5%), cement on treated peat, they are able to improve compressibility parameters of fibrous peat much more than conventional binders like pure cement.

Effect of fibre content and structure on anisotropic elastic stiffness and shear strength of peat

This paper presents the results of a laboratory testing program involving consolidated undrained triaxial tests and direct shear tests on remoulded peat, remoulded peat fibre, and Shelby specimens of peat obtained from a field site located in the Edson subdivision of the Canadian National railway in Alberta, Canada. These results were analyzed within the frameworks of elastic behaviour of cross-anisotropic materials and shear strength of fibre-reinforced soil. Shelby specimens were found to be inherently cross-anisotropic, whereas the remoulded peat and peat fibre specimens showed a transition from isotropic to cross-anisotropic with increasing vertical strain and effective confining pressure. The horizontal stiffness of Shelby specimens was found to be 2.6 to 2.9 times their vertical stiffness. The shear strength of intact peat is made up of interparticle friction as well as tension in the peat fibres. A novel procedure for estimating the interparticle frictional strength of fibrous peat from CU triaxial test results is proposed. It involves extrapolating the linear strain-hardening portion of the stress–strain curve to obtain the deviatoric stress at zero axial strain and plotting the deviatoric stress values thus obtained against initial mean effective confining pressure to obtain the frictional strength. Using this procedure, a value of 31° was obtained for the interparticle friction, which compares favourably with a value of 31° obtained from direct shear tests. It is recommended that further studies be undertaken to assess if interparticle frictional strength is an appropriate strength parameter for evaluation of the stability of structures founded on fibrous peat.

A Study on Factors Influencing the Determination of Moisture Content of Fibrous Peat

Fibrous peat is an undrained peat that usually possesses very high moisture content. However, not all experimental procedures are applicable for determination of moisture content of fibrous peat. This research is aimed at examining the determination of insitu moisture content of fibrous peat using field measurements. The peat soil samples were collected at shallow depths from Asajaya at Kota Samarahan and Taman Kopodims at Matang , Kuching Sarawak by using peat auger. The laboratory tests such as determination of moisture content, fiber content, particle density and ash content were conducted on the collected samples in order to establish relationships between the parameters. Undisturbed peat samples from Matang were subjected to falling head permeability test to determine the saturated permeability. The saturated sample were then allowed to drain freely to simulate the moisture loss possible during sampling when samples were brought out of boreholes. The test results showed that moisture content varies according to the drying temperature and position of the soil sample (top, middle and bottom) during sampling. Comparing samples from both locations, peat soil from Kota Samarahan possessed higher moisture content. The saturated permeability of peat sample was in the range of 2.62 – 3.05 cm/s. The free draining trial showed that moisture loss during sampling significantly influence the moisture content measurement. The variation in value of moisture content for fibrous peat may occurs due to several factors such as existing ground water table, sampling method by boring, existing standard test procedure which is not suitable for peat soils requirement and also because of the physical properties which varied according to depth of soil.

First insights into mid-Holocene environmental change in central Vanuatu inferred from a terrestrial record from Emaotfer Swamp, Efaté Island

Here we present the first terrestrial record of mid-Holocene environmental changes in Vanuatu. This preliminary multi-proxy analysis of core Tfer 06 from Emaotfer Swamp (Efaté Island) indicates changes in environmental conditions are mainly related to variations in climate over the last 6500 cal yr BP. Drier periods are broadly correlated with an increase in sustained El Niño events recorded in the Pacific on a decadal timescale. The earliest change is the disappearance of mangroves adjacent to the site around 3200 cal yr BP, this could well be due to both local tectonic uplift with subsequent hydrostatic adjustment and the onset of a drier period. From c. 3250–2500 cal yr BP the prevailing drier conditions can be linked to more persistent El Niño conditions. Local volcanic events had limited ecological impact on the area. Freshwater diatoms indicate a hydroseral succession, species living on submerged plants being common in muds from c. 3250–1500 cal yr BP, but rare in fibrous peat deposited later. Palaeoecological indicators of human impact have not been identified throughout this work.

Influence of Peat Characteristics on Cementation and Pozzolanic Reactions in the Dry Mixing Method

Peat is a naturally occurring material that is high in organic matter, extremely soft, has a high moisture content, and exists in an unconsolidated state. Due to its high compressibility and low shear strength, peaty soils are geotechnically problematic. One of the most common methods for improving these soils is the dry mixing method. Important characteristics of peat are the presence of carbon dioxide (CO2), nitrogen (N), and acidic or alkaline media, with a high ground water level. This paper presents the results of a study of the effects of peat characteristics on cementation and pozzolanic reactions over time when treating peats with cement and slag. The mechanical properties of the samples, cured for up to 180 days, were determined by performing an unconfined compressive strength test. Scanning electron microscopy was also carried out for selected samples to study the micro-structural changes taking place. It was observed that CO2 dissolved in peat water caused an increase in the depth of carbonation by decomposition of calcium-silicate-hydrate (C–S–H) gel to form calcite (CaCO3). The presence of increasing amounts of N had no tangible effect on cementation or pozzolanic reactions in the treated peats. Acidic media had a negative effect on cementation and pozzolanic reactions, whereas alkaline media improved the strength of the treated peats due to higher production of C–S–H gel. The strength of treated fibrous peat in water containing dissolved CO2, and also in acidic media, was lower than that of the other peats due to its physico-chemical characteristics.

Strength evaluation of air cured, cement treated peat with blast furnace slag

This article describes laboratory research done on strength evaluations for stabilized samples made of tropical fibrous peat. The stabilizing agents used were ordinary Portland cement (OPC) as binding agent and blast furnace slag (BFS) as additive. Stabilized samples were tested for their strength through unconfined compressive strength (UCS) and California bearing ratio (CBR). Different dosage rates of OPC and BFS were used in trial and error experiments for the most effective combination for stabilized peat samples that were at their natural moisture content. Stabilized trial samples were air cured for 90 days. After detecting the most effective dosage rate in the trial samples, their values were used to prepare CBR samples at their optimum moisture content (OMC). CBR samples were then air cured from 1 to 90 days and tested under un-soaked and soaked conditions. The most effective dosage rate for the stabilized peat samples was found to be close to when 75% for OPC and 25% of BFS per total weight of OPC, and BFS. As an example, if 11.25% OPC, and 3.75% BFS are mixed with peat and compacted at their OMC and air cured for 90 days, stabilized peat will have an increase in CBR of 0.8% to 45 % for un-soaked and 20% for soaked conditions.

In situ strength characterisation of peat and organic soil using full-flow penetrometers

Full-flow penetrometers have been shown to overcome problems experienced with the cone penetrometer when measuring resistance in very soft peat and organic soil, and give a much more uniform measure of resistance than the cone in fibrous peat. However, at present there is no guidance on the interpretation of strength parameters in these soils using the T-bar and ball. This paper examines the results of tests using these devices at two research sites in the Netherlands in conjunction with high-quality Sherbrooke sampling for laboratory testing. In fibrous peat, the T-bar and ball provided a more uniform measure of resistance with a lower degree of scatter than the cone. The in situ testing results have been compared with the laboratory tests to assess the range of resistance factors relating penetration resistance to the undrained shear strength (su) and have been shown to occupy a lower range of values than the cone penetrometer. However, penetration tests in these soils are likely to be influenced by partial drainage effects and this should be considered during testing and the subsequent interpretation of results. Recommendations are made for the use of full-flow penetrometers to obtain strength parameters in these soils.

Chemico-geomechanical sensitivities of tropical peat to pore fluid pH related to controlling electrokinetic environment

Peat is an accumulation of partially decayed vegetation with high noncrystalline content (humus), which is formed in wetland systems. Chemico-geomechanical sensitivities of a fibrous (very slightly decomposed) and a sapric (highly decomposed) peat to peat-water pH gradients in terms of resulting effects on cation exchange capacity (CEC), zeta potential (ζ), particle density, liquid limit (LL), particle size distribution, dry density–moisture content relationship, permeability, and undrained shear strength (Su) have been investigated. The specimens were treated for a 20-day period under acidic and basic conditions. It was found that in both fibrous and sapric peat, the CEC and ζ decreased; the LL, permeability, Su, and the optimum moisture content (OMC) increased, and the grain size distribution became skewed toward larger particles because of acidic conditions, while basic conditions had a contrary effect. The sensitivities of the fibrous peat to peat-water pH gradients were not of such intensity as were observed in the sapric peat because of the naturally inherited peat structure, degree of decomposition, ion change capacity, particle size, surface charges, and specific surface area. Our results are important, in that they confirm the link between the degree of peat humification and the chemico-geomechanical sensitivities of the peat to peat-water pH gradients.

Effect of Cement on Compressibility and Microstructure of Tropical Peat

Peats are geotechnically problematic soil due to their high compressibility and low shear strength. Cement is widely used for the stabilization of peat by deep mixing method (DMM). This paper presents the results of the model study of compressibility property of peats stabilized with cement columns formed by DMM. The results of consolidation test, scanning electron micrographs (SEM) and energy dispersive x-ray spectrometer (EDX) showed that the compressibility of peats can be improved significantly by the installation of cement stabilized columns. The amount of cement used to form the column was observed to influence the engineering behaviour of treated tropical peats and it had more influence on sapric peat than on hemic and fibrous peats.

Influence of ground tire rubber on the transient loading response of a peat biofilter

The effect of using ground tire rubber (GTR) as an adsorptive material in the removal of a 2:1:1 weight mixture of n-butyl acetate, toluene and m-xylene by using a peat biofilter under different intermittent conditions was investigated. The performance of two identical size biofilters, one packed with fibrous peat alone and the other with a 3:1 (vol) fibrous peat and GTR mixture, was examined for a period of four months. Partition coefficients of both materials were measured. Values of 53, 118 and 402 L kg −1 were determined for n-butyl acetate, toluene and m-xylene in peat, respectively; and values of 40, 609 and 3035 L kg −1 were measured for the same compounds in GTR. Intermittent load feeding of 16 h per day, 5 days per week working at an EBRT of 60 s and an inlet VOC concentration of 0.3 g C m −1, resulted in removal efficiencies higher than 90% for both biofilters, indicating that the addition of GTR did not adversely affect the behavior of the bioreactor. Full removal of n-butyl acetate was obtained for both biofilters. GTR improved the removal of the aromatics in the first part of the biofilter, facilitating lower penetration of the toluene and m-xylene into the bed. A 31-day starvation period was applied and intermittent operation subsequently restarted. In both biofilters, high removal efficiencies after a re-acclimation period of two days were achieved. A shock loading test related to 1-h peaks of three- and four-fold increases in its baseline concentration (0.30 g C m −3) was applied in both biofilters. For the biofilter packed with the peat and GTR mixture, attenuation greater than 60% was observed in the maximum outlet concentration when compared to the biofilter packed with peat alone.

A study of the compressibility behavior of peat stabilized by DMM: Lab model and FE analysis

Peats are considered as extremely soft, unconsolidated deposits. These soils are geotechnically problematic, due to their high compressibility and low shear strength. Cement is widely used for the stabilization of peat by deep mixing method (DMM). This paper presents the results of the model study of compressibility properties of fibrous, hemic and sapric peats, stabilized with columns formed by DMM. The columns were formed of peat, treated with cement in different proportions. Rowe cell tests were performed after curing the samples for 28 days, to evaluate the compressibility characteristics. The results showed that the compressibility properties of peat can be improved significantly by the installation of cement stabilized columns. The amount of cement used to form the column and its diameter were observed to influence the engineering behavior of peats. The effect of cement was the highest on sapric peat among all, due to its physico-chemical properties. The results of Rowe cell were used to simulate the consolidation behavior using finite element software, PLAXIS and the results agree well. The parameters from the simulated model behavior were used to predict the ultimate bearing capacity of peat with full size cement stabilized columns. Key words: Peat, cement column, compressibility, finite element analysis, bearing capacity.

EVALUATION OF GROWING MEDIA COMPONENTS FOR PHALAENOPSIS

Several growing media containing pine bark, coarse slightly decomposed peat, peat fibres, coarse wood fibres, sphagnum moss or coconut husk chips were compared as potting mixes for Phalaenopsis 'Pauline'. The eight different growing media were amended with 0.5 g/L of a water soluble complete fertilizer (N+P 2 O 5 +K 2 O+MgO = 15+10+15+2 plus micronutrients) and adjusted to a pH (CaCl 2 ) of about 5.5. During the cultivation period, all plants were fertilized weekly with 50 ml of a standard nutrient solution containing (mg/L): 105 N, 15 P, 88 K, 9 Mg plus micronutrients. Additional nitrogen was added in all treatments except for 100% sphagnum moss, at a total rate of 120 mg N per plant, given in seven parts from week 9 to 15 after potting. Good or adequate quality plants could be produced in all tested growing media. There was no effect of the growing medium on plant size except for mixtures with coco chips, in which the plants remained smaller. The growing medium had a clear effect on flowering traits. Plants cultivated in mixes containing coarse wood fibres developed an equally high number of flower spikes and flowers as plants cultivated in the standard mixture of 70% pine bark and 30% coarse peat. Plants in mixes with coco chips had significantly less spikes and flowers whereas media containing sphagnum moss showed equally high numbers of flowers, but fewer spikes than plants in the standard mixture. Plants grown in mixes containing wood fibres or sphagnum moss had a well developed, superior root system.

Evaluating the effect of using artificial pore water on the quality of laboratory hydraulic conductivity measurements of peat

AbstractPore dilation, the compaction of humic acids on peat fibres due to the process of flocculation, causes the hydraulic conductivity of peat to increase with increasing pore water electrical conductivity. This is a reversible process and a reduction in the pore water conductivity produces a decrease in the hydraulic conductivity due to the constriction of pores. We verify how this dilation and constriction of pores, resulting from the application of artificial pore water (primarily deionized water), affects laboratory measurements of the hydraulic conductivity of peat. Repeat measurements of the hydraulic conductivity were performed on samples of Sphagnum peat. It is shown that the application of deionized water during constant head permeameter tests causes a significant decrease in the hydraulic conductivity. Between tests, the hydraulic conductivity of the peat continues to decline without an associate decrease in the pore water electrical conductivity because of a lagged pore constriction effect. We suggest that the use of artificially high or low pore water electrical conductivities, during laboratory hydraulic conductivity measurements, is likely to lead to significant errors. Experimental protocols must, therefore, be revised to take better account of the pore water chemistry. The ionic concentrations of the natural pore fluid should be replicated during hydraulic conductivity tests, either by using pore fluid extracted from the study site or by artificially replicating the major ionic composition of the natural pore fluid. In addition, prior to the hydraulic conductivity measurements, peat samples should be flushed with this solution until the hydraulic conductivity stabilizes and the samples subsequently allowed to equilibrate. Copyright © 2010 John Wiley & Sons, Ltd.

Subsidence and degradation of agricultural peatlands in the Fenlands of Norfolk, UK

Historical drainage of peatlands across the East Anglian Fenlands has led to subsidence and degradation of the vast majority of the regional peat resource, to the extent that many areas can no longer be classified as peatland. Water-table management strategies have been introduced to reduce the rate at which these peatlands subside and physically and biochemically degrade. We assessed the rate of subsidence and extent of peat soil degradation across an intensively farmed peatland where such water management measures have been introduced. When compared against historical reports of subsidence across the East Anglian Fenlands, the rate of subsidence does appear to have reduced over the last two decades. The rate of subsidence does, however, vary spatially and is dependent on the geographical distribution of peat types and underlying mineral deposits. The rate of subsidence and peat degradation has been greater in soil profiles which had a higher proportion of semi-fibrous and fibrous peats in 1982/3, compared against those with a higher proportion of humified peat in 1982/3. Over the last 22 years the proportion of more fibrous peat in all peat deposits has decreased to the extent that areas once classified as fibrous peat are now dominated by humified peat. This suggests that future subsidence will be less influenced by shrinkage and controlled by biochemical processes. Where Fen Clay underlies a peat deposit it acts as an impermeable boundary, thus keeping the overlying peat more saturated and reducing the degree of peat consolidation. However, the presence of Fen Clay also increases the degree of biochemical degradation of overlying fibrous peat horizons. Indeed, where drains have been laid within such mineral strata there is an increase in soil acidity. During autumnal drainage operations the environment is therefore optimised for sulfate reducing bacteria, resulting in acid sulfate soils with increased rates of degradation.

Discontinuous late Pleistocene‐Holocene pollen records from Auckland Domain, northern New Zealand

Two sediment sequences from Pukekawa crater, Auckland Domain, contain silty clay underlain by fibrous peat. The peat contains a pollen flora and wood indicating the presence of a warm‐temperate, conifer‐hardwood forest with Metrosideros, Agathis, Prumnopitys taxifolia, P. ferruginea, and especially Dacrydium. Radiocarbon dates indicate that the peat was deposited before the Last Glacial Maximum (LGM). Absence of tephras and small amounts of Fuscospora pollen indicate probable non‐preservation of the LGM. The pollen flora of most of the clay contains Metrosideros, Ascarina, and ferns, indicating post‐LGM warmer, wetter conditions. The two uppermost samples contain exotic pollen, indicating that they are post‐European in origin. Excavation and levelling to form sports fields and parkland appears to have curtailed and mixed the Holocene record.

A Review on Hydraulic Conductivity and Compressibility of Peat

This study reviews the results of several experimental and field investigations on the behavior of peat in hydraulic conductivity and compressibility. A study on the mechanical properties of peat is important in order to gather sufficient information on the response of the soil to preloading in terms of the soil permeability and deformation. Preloading technique is normally employed as a method to improve peat ground so that the improved ground can be used as a soil foundation to support road embankment. Findings on the initial hydraulic conductivity of peat revealed that the initial coefficient of vertical permeability (kv0) of the soil ranged from 10-5 to 10-8 m sec-1 with the value was found to be lower in amorphous peat as compared to that of fibrous peat. Such findings indicated that the initial hydraulic conductivity of peat is influenced by the soil degree of decomposition. The higher is the soil degree of decomposition, the lower is its initial rate of hydraulic conductivity. Results from oedometer tests on Portage peat showed that while the soil coefficient of secondary compression (cI±1) ranged from 0.17 to 0.18, its coefficient of tertiary compression (cI±2) varied from 0.6 to 0.18. At high consolidation pressure, the soil cI±1 approached its cI±2 indicating the merging of secondary and tertiary compression components. It can be concluded that the behavior of peat is different from that of inorganic soil in that it exhibited high to moderate initial hydraulic conductivity, rapid primary consolidation and large secondary compression.

Compressibility Behavior of Fibrous Peat Reinforced with Cement Columns

This paper presents the compressibility of fibrous peat reinforced with cylindrical cement columns. The effects of the cement column diameter on the compressibility have been investigated in this study. The results indicated that compressibility index C c and C α decreased with increasing diameter of the cement column. Specimens with 45 mm (area ratio = 0.09) diameter and 60 mm (area ratio = 0.16) diameter of cement columns were cured for 7, 14 and 28 days, after which they were subjected to Rowe Cell consolidation test. Results are also presented from tests conducted on groups of cement columns using four (area ratio = 0.04) and nine (area ratio = 0.09) columns of 15 mm diameter each to investigate the influence of the number of cement columns on compressibility of peat. Apart from that various proportions of cement were used to form cement columns in order to study the influence. Based on the results obtained, it shows that cement columns can successfully reduce the compressibility of fibrous peat.

Regression Models for Dynamic Properties of Highly Organic Soils

Regression models are presented for the dynamic properties of highly organic soils. The models are based on a database of triaxial and resonant-column/torsional-shear cyclic loading tests on thin walled tube samples mainly retrieved from the Sacramento-San Joaquin Delta. The soils in this database range from highly fibrous peat to amorphous organic clays with organic contents OC ranging from 14-81%, water contents ranging from 88-495%, total densities ranging from 1.056-1.450 Mg/m 3 , and effective consolidation stresses vc ranging from 11-135 kPa. The secant shear modulus G and equivalent damping ratio were modeled as variables dependent on the shear strain amplitude c, consolidation stress vc , and OC. The residuals of the regression models were analyzed against other predictor variables including undisturbed density , loading frequency f, and number of loading cycles N. A regression model for was developed, and conditional probabilities were used to improve the estimation of G and when measurements were available. The database of in situ measurements of shear wave velocity Vs was used to adjust the regression model for in situ conditions. Variances and correlations in the regression models are presented.

The role of soil moisture, temperature and nutrient amendment on CO 2 efflux from agricultural peat soil microcosms

Extensive drainage of UK lowland peat soils for agricultural production is considered a major contribution to the rate of degradation and the loss of peat resources. Microbial oxidation resulting from drainage accelerates decay rates of organic matter and the release of CO 2 to the atmosphere and contributes to severe subsidence. We examined the effect of soil moisture, temperature and nutrient amendment on soil CO 2 respiration rates from a low-lying peat grassland and a low-lying peatland under intensive arable farming in the UK. Soil samples were obtained from three different depths and equilibrated at a range of moisture contents under four prescribed soil water potentials (− 0.1 to − 10 m). The samples were incubated in the laboratory and the influence of temperature (10, 22 and 30 °C) and N addition (C/N ratio of 10:1, 5:1 and 2.5:1) on peat respiration was measured. In addition, field soil samples were analysed to determine the microbial community structure using the phospholipid fatty acid (PLFA) analysis technique. Respiration ranged from 0.8 to 15.0 µg CO 2–C g − 1 h − 1 at 10 °C and from 4.0 to 9.9 µg CO 2–C g − 1 h − 1 at 30 °C for different peats. Q 10 value between 22 and 30 °C ranged from 0.9 to 8.2. In contrast, Q 10 value between 10 and 22 °C varied from 0.2 to 2.2 suggesting, in some cases, an increase in respiration rate with decreasing temperature. Generally, temperature had a greater effect on the soils respiratory activity than the moisture content in drier peats, however soil moisture was determined to be the dominant parameter at higher moisture content. At high moisture content, the respiration rates at 10 °C exceeded those at 22 and 30 °C in four of the soils. Respiration varied with the degree of peat degradation and soil moisture content. Variations in soil moisture content did not always have a significant effect on CO 2 emission in the humified surface peats but at higher soil moisture the CO 2–C mineralisation rate of deeper, more fibrous peat horizons was higher at 10 °C than at 30 °C. Metabolic quotient ( qCO 2) ranged from 3.6 to 10.2 mg CO 2–C h − 1 g biomass-C − 1 in surface horizons and from 5.6 to 12.3 mg CO 2–C h − 1 g biomass-C − 1 in more fibrous peats, suggesting less available organic carbon at depth. N additions increased CO 2–C mineralisation, with the maximum rate of respiration occurring at pressure potentials between − 0.5 and − 1 m. Peat samples at field moisture content were also analysed to determine phenotypic microbial community structure using PLFA analysis. This indicated that, microbial community structure varied between drained surface and saturated subsurface horizons. However, there was no difference in the microbial community structure between horizons when subjected to greater drainage. The effects of temperature and moisture on respiration found in deeper horizons and the phenotypic microbial community structure suggest that psychrophilic microbes predominate and that minimal drainage optimises their oxidation of peat.

Impact of the process of isolating humic acids from peat on their propertiesA paper submitted to the Journal of Environmental Engineering and Science.

Humic substances (HS) can be isolated in preparative quantities from low rank coal, peat, and soil. Traditionally, treatment with solutions of NaOH, KOH, or metal salts (K4P2O7) has been used for their isolation. The aim of this article is to study the effectiveness of different technologies in extracting HS from peat as well as the impact of the different extractive technologies on the properties of the isolated HS. Yields of HS depend very much on the extraction process (extractant, temperature, pretreatment procedures, solvent, mixing intensity); however, the properties of the substances obtained (molecular mass, number of functional groups, spectral characteristics) differ significantly. Yields of HS can be associated with the degree of destruction of the peat fibres and intensive destruction technologies provide opportunities to obtain HS from peat in higher yields than traditional extraction methods. However, during the extraction process, significant degradation of the humic molecules takes place.