Impact of biochar and dairy manure on the hydraulic properties and their measurements in boreal agricultural podzols

Soil hydraulic properties such as hydraulic conductivity and volumetric soil moisture content are the basis for understanding flow and transport processes in the vadose zone. In addition, hydraulic properties of surface soils influence the partition of input water (by precipitation / irrigation) into runoff and soil water storage and are altered with the use of soil amendments in agricultural soils. Therefore, the present study has two different parts i.e. first section looking into hydraulic conductivity and second section into volumetric moisture content measurements. The first study was focused on field unsaturated (Kunsat) and near saturated (near Ksat) hydraulic conductivity of agricultural soil with an emphasis on amending the soil with dairy manure (DM) and biochar (BC). The study was conducted at both field and the laboratory scales using mini disk infiltrometer (a tension infiltrometer). The second study evaluated the effect of BC incorporation on TDR (Time Domain Reflectrometry) based soil moisture measurements. TDR is a well-established method for measuring volumetric soil moisture content (VSMC) at point scales using soil’s dielectric properties. To calculate VSMC from dielectric constant obtained from a TDR cable tester (MOHR CT 100), Topp’s equation–M1, mixing model–M2 and the forest soil model–M3 were used. The three models were compared with a standard (M0) VSMC calculated using gravimetric moisture and soil bulk density. According to the results, there was no significant effect of DM and BC on near Ksat. BC was observed to have no considerable influence, while IN+DM 1, IN+DM 2 and IN+DM 1+BC had significantly lower Kunsat under 2 cm suction (p=0.009, 0.002 and 0.031, respectively) compared to the control. The results from regression analysis showed the M1 and M2 reported significantly lower VSMC values, while M3 reported higher values than M0 for both powdered and granular BC treatments (p<0.001). However, for powdered BC treatment, the relationships between M1, M3 with M0 were not significant (p=0.228, 0.052), while it was significant for M2 with M0 (p=0.028). For granular BC treatments, the M2, M3 with M0 regressions have shown significant similarity (p=0.009 & 0.032); this was not true for the M1 to M0 comparison (p=0.571). These results show that the effects of types and rates of BC on VSMC prediction models based on soil dielectric constant need to be further studied under both laboratory and field conditions. Since these soil amendments can influence soil hydrology such as reduced infiltration and increased surface runoff, carefully monitored agronomic practices are recommended

An Influence of Thermally-Induced Micro-Cracking under Cooling Treatments: Mechanical Characteristics of Australian Granite

The aim of this study is to characterise the changes in mechanical properties and to provide a comprehensive micro-structural analysis of Harcourt granite over different pre-heating temperatures under two cooling treatments (1) rapid and (2) slow cooling. A series of uniaxial compression tests was conducted to evaluate the mechanical properties of granite specimens subjected to pre-heating to temperatures ranging from 25–1000◦C under both cooling conditions. An acoustic emission (AE) system was incorporated to identify the fracture propagation stress thresholds. Furthermore, the effect of loading and unloading behaviour on the elastic properties of Harcourt granite was evaluated at two locations prior to failure: (1) crack initiation and (2) crack damage. Scanning electron microscopy (SEM) analyses were conducted on heat-treated thin rock slices to observe the crack/fracture patterns and to quantify the extent of micro-cracking during intense heating followed by cooling. The results revealed that the thermal field induced in the Harcourt granite pore structure during heating up to 100◦C followed by cooling causes cracks to close, resulting in increased mechanical characteristics, in particular, material stiffness and strength. Thereafter, a decline in mechanical properties occurs with the increase of pre-heating temperatures from 100◦C to 800◦C. However, the thermal deterioration under rapid cooling is much higher than that under slow cooling, because rapid cooling appears to produce a significant amount of micro-cracking due to the irreversible thermal shock induced. Multiple stages of loading and unloading prior to failure degrade the elastic properties of Harcourt granite due to the damage accumulated through the coalescence of micro-cracks induced during compression loading. However, this degradation is insignificant for pre-heating temperatures over 400◦C, since the specimens are already damaged due to excessive thermal deterioration. Moreover, unloading after crack initiation tends to cause insignificant irreversible strains, whereas significant permanent strains occur during unloading after crack damage, and this appears to increase with the increase of pre-heating temperature over 400

Guest editorial for the topical collection: sustainable development and utilization of geothermal systems

--Abstract Not Available-

An influence of thermally-induced micro-cracking under cooling treatments: mechanical characteristics of Australian granite

The aim of this study is to characterise the changes in mechanical properties and to provide a comprehensive micro-structural analysis of Harcourt granite over different pre-heating temperatures under two cooling treatments (1) rapid and (2) slow cooling. A series of uniaxial compression tests was conducted to evaluate the mechanical properties of granite specimens subjected to pre-heating to temperatures ranging from 25–1000◦C under both cooling conditions. An acoustic emission (AE) system was incorporated to identify the fracture propagation stress thresholds. Furthermore, the effect of loading and unloading behaviour on the elastic properties of Harcourt granite was evaluated at two locations prior to failure: (1) crack initiation and (2) crack damage. Scanning electron microscopy (SEM) analyses were conducted on heat-treated thin rock slices to observe the crack/fracture patterns and to quantify the extent of micro-cracking during intense heating followed by cooling. The results revealed that the thermal field induced in the Harcourt granite pore structure during heating up to 100◦C followed by cooling causes cracks to close, resulting in increased mechanical characteristics, in particular, material stiffness and strength. Thereafter, a decline in mechanical properties occurs with the increase of pre-heating temperatures from 100◦C to 800◦C. However, the thermal deterioration under rapid cooling is much higher than that under slow cooling, because rapid cooling appears to produce a significant amount of micro-cracking due to the irreversible thermal shock induced. Multiple stages of loading and unloading prior to failure degrade the elastic properties of Harcourt granite due to the damage accumulated through the coalescence of micro-cracks induced during compression loading. However, this degradation is insignificant for pre-heating temperatures over 400◦C, since the specimens are already damaged due to excessive thermal deterioration. Moreover, unloading after crack initiation tends to cause insignificant irreversible strains, whereas significant permanent strains occur during unloading after crack damage, and this appears to increase with the increase of pre-heating temperature over 400◦C. © 2018 by the authors

Experimental and Numerical Investigation of the Flow Behaviour of Fractured Granite under Extreme Temperature and Pressure Conditions

As a result of negligible connected porosity—and thus, minimal matrix permeability—the fluid-transport characteristics of crystalline rocks are strongly influenced by the fractures at all scales. Understanding the flow behaviour of fractured rock under extreme stress and temperature conditions is essential for safe and effective deep geo-engineering applications, such as deep geothermal recovery, geological nuclear waste disposal, oil and gas extraction, geological storage and deep mining operations. Therefore, this study aims to investigate the flow characteristics of mechanically fractured Australian Strathbogie granite under a wide range of stress (confining pressures 1–80 MPa) and temperature conditions (20 °C to 350 °C). The study utilised a sophisticated high-temperature, high-pressure tri-axial setup capable of simulating extreme geological conditions, followed by a numerical simulation. According to the experimental results, a linear increment in the steady-state flow rate was observed, with increased injection pressure for the experimental conditions considered. Therefore, linear laminar Darcy flow was considered, and the fracture permeability was calculated using the cubic law. It was found that stress and temperature strongly depend on the flow of fluid through fractures. The steady-state flow rate decreased exponentially with the increase in normal stress, showcasing fracture shrinkage with an increment in effective stress. With regard to permeability through the fractures, increasing temperature was found to cause an initial reduction in fracture permeability due to an increased interlock effect (induced by thermal overclosure), followed by increments because of the thermally induced damage. Furthermore, the increasing temperature caused significant non-linear increments in the fluid flow rates due to the associated viscosity and density reduction in water. Considering the laboratory-scale flow-through exercises, a fully coupled numerical model that can predict hydro–thermo–mechanical variations in the reservoir rocks was developed using the COMSOL Multiphysics simulator. The developed model was calibrated, utilising the temperature- and pressure-dependent properties of granite rocks and fluid (water); was validated against the experimental results; and was used to predict the permeability, pressure development and strain of rock samples under extreme conditions, which were difficult to achieve in the laboratory

A Hybrid Approach to Rock Pre-conditioning Using Non-explosive Demolition Agents and Hydraulic Stimulation

This study presents a novel approach to rock pre-conditioning to promote the sustainability of low-grade ore mining applications such as in-situ recovery and cave mining. The proposed method involves a two-stage hybrid approach, utilizing soundless cracking demolition agents (SCDAs) to initiate radial fractures in a predrilled host rock, followed by hydraulic stimulation to extend the fractures. SCDA injection in the first stage creates multiple radial fractures around the injection well. However, the extent of fractures is limited to the near vicinity of the injection well. To overcome this limitation, the second stage involves the application of hydraulic stimulation to extend the initiated fractures, which produces a greater fracture density compared to pure hydraulic stimulation. The concept was assessed using a fully coupled hydro-mechanical discrete element model that simulated the hybrid fracturing method on crystalline rock at the grain scale. The results indicate that the proposed method can create a high density of fractures around the injection well. Additionally, we identify and evaluate the key factors affecting the performance of the proposed method, including rock mass heterogeneity, stress anisotropy, and pre-existing defects, providing valuable insights for further experimental design and execution. Overall, the study offers promising results for a potential solution to enhance the efficiency of low-grade ore mining through the hybrid rock pre-conditioning method.ISSN:1434-453XISSN:0723-263

Synergistic Hybrid Marine Renewable Energy Harvest System

This paper proposes a novel hybrid marine renewable energy-harvesting system to increase energy production, reduce levelized costs of energy and promote renewable marine energy. Firstly, various marine renewable energy resources and state-of-art technologies for energy exploitation and storage were reviewed. The site selection criteria for each energy-harvesting approach were identified, and a scoring matrix for site selection was proposed to screen suitable locations for the hybrid system. The Triton Knoll wind farm was used to demonstrate the effectiveness of the scoring matrix. An integrated energy system was designed, and FE modeling was performed to assess the effects of additional energy devices on the structural stability of the main wind turbine structure. It has been proven that the additional energy structures have a negligible influence on foundation/structure deflection (<1%) and increased system natural frequency by 6%; thus, they have a minimum influence on the original wind system but increased energy yield