Slurry Pressure Research Articles

Prediction of geology condition for slurry pressure balanced shield tunnel with super-large diameter by machine learning algorithms

Real-time and precise prediction of geological conditions is extremely beneficial to the safe and efficient construction of slurry pressure balanced shield machines (SPBMs), especially for super-large diameter tunnels. Machine learning algorithms provide an effective way to predict geological conditions and have been successful in hard-rock tunnel boring machine (hard-rock TBM) tunnels or earth pressure balance shield machine (EPBM) tunnels. However, the effectiveness of machine learning in predicting geological conditions for super-large diameter SPBM tunnels is still unknown. This study systematically demonstrated the application of machine learning algorithms to the prediction of geological conditions in super-large diameter SPBM tunnels based on field data from the Heyan Road crossing river tunnel. The relationship between SPBM parameters and geological conditions was first evaluated, and subsequently, an adaptive model was proposed to determine the number of input variables. The performance of three algorithms, random forest (RF), AdaBoost, and support vector machine (SVM), in rock mass classification, and seven algorithms, multi-objective random forest (MORF), single-target-RF, regressor chain-RF, single-target-AdaBoost, regressor chain-AdaBoost, single-target-SVM, and regressor chain-SVM, in formation percentage prediction, were compared. The results showed that machine learning algorithms can effectively predict the geological conditions in super-large diameter SPBM tunnels. Specifically, RF had the best performance in rock classification compared with AdaBoost and SVM. MORF outperforms the other six algorithms in terms of formation percentage prediction. Additionally, sensitivity analysis indicates that the newly proposed parameters, including slurry system parameters and cutter type, have a clear positive effect on the performance of geological condition prediction.

Theoretical Research on Diffusion Radius of Cement-Based Materials Considering the Pore Characteristics of Porous Media.

In engineering, loose sandy (gravelly) strata are often filled with cement-based grout to form a mixed material with a certain strength and impermeability, so as to improve the mechanical properties of sandy (gravelly) strata. The tortuosity effect of sandy (gravelly) strata and the time-varying viscosity of slurry play a key role in penetration grouting projects. In order to better understand the influence of the above factors on the penetration and diffusion mechanism of power-law slurry, based on the capillary laminar flow model, this research obtained the seepage motion equation of power-law slurry, the time-varying constitutive equations of tortuosity and power-law fluid viscosity were introduced, and the spherical diffusion equation of penetration grouting considering both the tortuosity of porous media and time-varying slurry viscosity was established, which had already been verified by existing experiments. In addition, the time-varying factors of grouting pressure, the physical parameters of the injected soil layer, and slurry viscosity on penetration grouting diffusion law and the influencing factors were analyzed. The results show that considering the tortuosity of sandy (gravelly) strata and the time-varying of slurry viscosity at the same time, the error is smaller than the existing theoretical error, only 13~19%. The diffusion range of penetration grouting in the sandy (gravelly) strata is controlled by the tortuosity of sandy (gravelly) strata, the water-cement ratio of slurry, and grouting pressure. The tortuosity of sandy (gravelly) strata is inversely proportional to the diffusion radius of the slurry, and the water-cement ratio of slurry and grouting pressure are positively correlated with the diffusion radius. In sandy (gravelly) strata with a smaller particle size, the tortuosity effect of porous media dominates the slurry pressure attenuation. When the particle size is larger, the primary controlling factor of slurry pressure attenuation is the tortuosity effect of porous media in the initial stage and the time-varying viscosity of slurry in the later stage. The research results are of great significance to guide the penetration grouting of sandy (gravelly) strata.

Field mechanical properties of large section concrete pipes during jacking in fractured moderately weathered siltstone

In the construction of pipe jacking, due to the effect of jacking force, slurry pressure, axis deviation, stoppage and geological conditions, the mechanical behaviors of pipe are very complex. Additionally, most of the calculation models of pressure around the pipes in the existing standards only consider water and earth pressure, which is different from the actual situation. Therefore, this work aims to reveal the mechanical properties of concrete pipe during jacking and explore the calculation method of jacking force and frictional resistance. Based on the field monitoring of the pipe jacking project for utility tunnel in Hubei, China, the variation law of the contact pressure, slurry pressure and pipe strain were analyzed, and the jacking force and frictional resistance were calculated through the above parameters. The results show that it is more appropriate to use the rock collapse height instead of Terzaghi theory to calculate the earth pressure at the pipe crown in fractured rock mass. There is a significant negative correlation between the slurry pressure around the pipe and the jacking force. In the stratum with high permeability, choosing an appropriate lubricant injection interval can effectively improve the lubrication efficiency and reduce construction cost. In addition, the axial strain of pipe can reflect the variation of the jacking force, and the frictional resistance calculated by the effective earth pressure is closer to measured value. The calculation methods and related conclusions proposed in this paper can provide a valuable guide for pipe jacking in fractured rock mass.

Diffusion characteristics and reinforcement effect of cement slurry on porous medium under dynamic water condition considering infiltration

Grouting methods are known to effectively remediate the groundwater inrush in tunnels with weak water-rich sand layers. However, the diffusion characteristic of cement slurry flowing in rock and soil media with flowing water is one of the many critical issues that still remain unsolved. The cement-based grouting material diffusion characteristics of water in rock, considering four grouting parameters of water-cement ratio, water flow speed and fractal dimension of particle mass, were researched through a series of experiments such as cement particle filtration, nuclear magnetic resonance and diffusion test. Then compressive strength, scanning electron microscope(SEM) and mercury intrusion porosimetry(MIP) were performed on consolidated specimens to examine physico-chemical bonding mechanisms characteristics. The results indicate that 1) The viscosity of the effluent at the test point varies with the increase of water discharge velocity with different water cement ratio. When the water cement ratio is low, the viscosity of effluent increases first and then decreases with the increase of water flow rate. For high water cement ratio, the viscosity of the same test point decreases with the increase of water velocity. 2) The porosity of the consolidation with a low water velocity is lower than that of the media with a high water velocity within 4 m of the injection site. However, when it exceeds 4 m, the porosity has the opposite trend. 3) In the range of 0.3 ∼ 0.4 m, the grouting pressure at middle and low velocity is higher than that of high velocity. Beyond this range, the trend is reversed. 4) When cement slurry flows in particles, its pressure attenuation law is not affected by the state of dynamic water and is only related to the fractal dimension of particles. Its pressure attenuation decreases sharply with the increase of distance, when cement slurry flows in the particle mass with higher fractal dimension. Nevertheless, the flow pressure of cement slurry decreases slowly with the increase of distance at low fractal dimension. 5) The compressive strength of the consolidated body of cement and sand decreases with the increase of water-cement ratio and distance. Microstructural changes in sand fabric indicate that cement grouting material modified the porous network of consolidated sand. The pores were filled and particles were bonded by hydration product of cement.

Experimental Investigation on Flow Behavior of Paste Slurry Transported by Gravity in Vertical Pipes

In order to dispose of large quantities of mineral tailings, paste backfill is proposed and widely adopted. Paste backfill, which has high concentration and yield stress and behaves as a non-Newtonian fluid, is prepared at the surface plant and then transported underground. Vertical pipelines are more likely to suffer various failures, such as pipe breaks, wear and plugging, during the transport process. Few present studies focus on the flow behavior of paste slurry flowing in vertical pipes. In this work, two L-shaped pipeline systems with internal diameters (ID) of 40 mm and 65 mm with electrical resistance tomography (ERT) were manufactured to visualize flow regimes and measure the axial velocity and pipe pressure of slurry flowing in the upper and lower zones of vertical pipes. Flow regimes were extracted from ERT-reconstructed images stacked by time-series. Based on this, four typical flow regimes were summarized, and the characteristics of velocity and pressure change with vertical pipe depth were discussed.

Numerical Investigation of Slurry Fracturing during Shield Tunneling under a Reservoir

The Jinan Jiluo Road Crossing the Yellow River Tunnel North Extension Project will intersect the Queshan reservoir, which currently supplies 60% of the domestic water in Jinan City. During the excavation process of the large-diameter slurry type shield used in this project, it may lead to slurry fracturing of the stratum in front of the excavation face and slurry blow-out from the surface if the slurry support pressure is too high. The leakage of shield slurry will pollute the reservoir water, and the safety of domestic water in Jinan will be threatened. Shield slurry blow-out may also lead to water inrush accidents. It is difficult to prevent slurry blow-out during shallow shield tunnel construction due to an insufficient understanding of the shield slurry fracturing mechanism. The initiation and extension of shield slurry fracturing are very complex and difficult to observe in the stratum. Currently, there is no effective method to study the slurry fracturing mechanism of shield tunneling. This paper presents a numerical simulation method of shield tunneling slurry fracturing based on the extended finite element method (XFEM). The risk of slurry blow-out in shield tunnel crossing reservoir engineering is analyzed. The advantages of the XFEM for simulating crack propagation are fully exploited. Considering the coexistence of tensile and shear failures in soft soils, embedding the combined tensile and shear failure criterion is realized in the XFEM by the secondary development of the ABAQUS extended finite element. Compared with the slurry fracturing test of blind-hole clay samples, the rationality of the simulation method for slurry fracturing in cohesive soil is verified. Through the establishment of the slurry fracturing extension model, the slurry fracturing process of shield tunneling in cohesive soil layer is simulated. The variation law of slurry pressure in the process of fracture extension is studied, and the influence of shield slurry support pressure, overburden thickness, formation shear strength, and slurry viscosity on fracture extension pressure and extension path is analyzed. Based on this numerical simulation method, the risk of slurry blow-out is analyzed in the shield tunneling intersecting the Queshan Reservoir of the Jinan Jiluo Road Crossing the Yellow River Tunnel North Extension Project.

Mechanism and preventive measures of slurry leakage at shield tail brushes under abnormal shutdown condition—A case study

Based on an underwater shield tunnel project, this study introduces the phenomenon of abnormal shutdown and the measures designed to mitigate problems in construction. On the strength of the analysis of the slurry leakage causes during re-tunneling, the mechanism of slurry leakage induced by jack retraction was studied, and treatment measures of leakage at shield tail brushes were elaborated upon. The results show that the sudden change of stratum leads to an abnormal shutdown, and a sharp increase in the slurry pressure at the shield cut location leads to the slurry penetrating the gap between the outer wall of the shield shell and the soil, increasing the risk of instantaneous breakdown at shield tail brushes. The radial displacement of the outer wall of the segments caused by retractions of three jacks and a single jack along the circumferential direction distinctly shows three regions and four regions, respectively. The radial shrinkage of the outer wall of the segments at the jack retraction position decreases the tightness between the shield tail brushes and the outer wall of the segments. The expansion of the outer wall of the segments at the surrounding position, especially at the lower position, increases the slurry level to the radial shrinkage position of the segments, which increases the risk of slurry leakage. Furthermore, when the shield machine faces an abnormal shutdown, re-tunneling, and assembly of segments, the jack can be gradually retracted from top to bottom. The slurry leakage degree can be observed when retracting, and the corresponding measures can be taken for timely plugging. According to the leakage degree, it can be determined whether to replace the shield tail brushes to reduce the risk of large-scale leakage accidents.

The Characteristics of Spiral Pipe Increasing Resistance and Reducing Pressure and the Amendment Equation of Stowing Gradient

To solve the high slurry pressure and severe wear at some sections in backfilling pipelines, this study investigates the solution of using an auxiliary pipe to increase the resistance and reduce the pressure of the mine backfilling pipeline. Using computational fluid dynamics, three auxiliary pipe models, a Z-shaped pipe, a S-shaped pipe and a spiral pipe were constructed and the velocity and pressure distribution characteristics of the filling slurry in the auxiliary pipes were analyzed. The function of friction loss in spiral pipes with different pitches and spiral diameters was established, and the amendment equation for calculating the effective stowing gradient was studied when using spiral pipes to increase resistance and reduce pressure. The results show that, compared with the Z-shaped pipe and the S-shaped pipe, the velocity and pressure in the spiral pipe change continuously and steadily, and there is no obvious sudden change in the local velocity and pressure. Therefore, it is difficult to burst the pipe. When the velocity is 2.5 m/s and the vertical height of the pipe is 2.5 m, the friction loss of the filling slurry in the spiral pipe can reach 3.87~21.26 times that in the vertical pipe, indicating that the spiral pipe can effectively play the role of increasing resistance and reducing pressure. The relationship between the friction loss and spiral diameter is a linear function, and the relationship between the friction loss and pitch is a quadratic function. The three are binary quadratic function relationships. The equation for calculating the effective stowing gradient is obtained, which provides a convenient method for engineering applications and industrial design.

Effect of concreting pressure on ground response caused by installation of diaphragm wall panels

The ground response during diaphragm wall panel installation is strongly affected by the support slurry pressure, and by the subsequent lateral pressures during the tremie placement and set-up of wet concrete. The support slurry pressure can be reliably assumed as hydrostatic within the excavated trench, whereas the lateral concreting pressure is much more complex due to the stiffening effect of wet concrete. This paper reviews the measurements of wet concrete pressures from a series of instrumented diaphragm wall panels which show that lateral pressures in the concrete slurry increase as the tremie displaces bentonite slurry and reach a maximum condition about 1 h after placement, while conditions over the longer term closely approximate the hydrostatic pressure of the bentonite-filled trench. The maximum increase of pressure varies at different heights of the same trench, and also varies for two separate panels in the same project, reflecting the varying velocity of concreting. Model tests of concreting pressure on formwork also demonstrate that the lateral pressure reduces from hydrostatic wet concrete pressure a few hours after casting. A time-dependent lateral concreting pressure model is developed to represent these measurements more realistically. This proposed model is implemented into a finite-element program to investigate its effects on the ground response due to the concreting process. Computed results from a reference case can capture the progressive variations of ground movement, earth and pore water pressure in the soil adjacent to the trench during and shortly after the concreting process, which is consistent with the reported measurements.

Quantitative determination of the hydrostatic pressure of oil-well cement slurry using its hydration kinetics

This study investigated the hydration kinetics and microstructure of oil-well cement slurry in the early hydration stage using calorimetry, X-ray powder diffraction, thermogravimetry, scanning electron microscopy, and X-ray computed tomography to reveal the hydrostatic pressure reduction mechanism and the quantitative relationship between the hydration kinetics and hydrostatic pressure of the cement slurry. The results showed that the time-varying characterisation of the hydrostatic pressure of the cement slurry was in accordance with the Arrhenius equation. During the hydrostatic pressure reduction of the cement slurry, its microstructure developed from “suspension particles” to a “particles framework,” and the “framework” bonded to external interfaces. The hydration products strengthened the “framework” and decreased the porosity, pore size, and connectivity of the cement slurry, leading to the gravity of the entire cement slurry being supported by external interfaces and the slurry lost hydrostatic pressure. Hydration kinetics indicated that the cement slurry hydrostatic pressure changed linearly with hydration heat increments. Using hydration heat increments, a prediction method which successfully predicted the hydrostatic pressure of oil-well cement slurry was developed.

Three-dimensional tunnel face stability considering slurry pressure transfer mechanisms

In slurry-shield tunneling, the bentonite slurry tends to infiltrate into the soil skeleton ahead of the tunnel face, causing a forward seepage flow associated with excess pore pressures in the ground. Both the slurry infiltration and the forward seepage flow significantly impact the tunnel face stability. In the present paper, a kinematic approach of limit analysis with the classical three-dimensional discretized rotational failure mechanism is employed to assess the face stability of a slurry-shield-driven tunnel. Three situations of slurry infiltrations that influence the face pressure transfer mechanisms were considered: a full filter cake, a penetration zone, and pure groundwater flow without a filter cake or a penetration zone. The pore pressure distributions surrounding the tunnel face were firstly obtained using numerical calculations. Afterward, the incorporation of numerically obtained pore pressure distributions into the work rate calculations allows considering a three-dimensional forward seepage flow ahead of the tunnel face, which provides a rigorous upper-bound estimation to the tunnel face safety factor determined by the strength reduction technique. The proposed method is validated by comparing the calculated results with those provided by previously published literature. The effects of excess slurry pressures, hydraulic conditions, pressure drop coefficients, and soil shear strength were investigated. Several design charts are given for practical application.

Theoretical Research on Grouting in Deep Loose Layers Based on the Cylindrical Diffusion Model of Radial Tube Flow

Grouting in deep, loose layers are a complex process in which many modes such as infiltration, splitting, and compaction coexist. It is of great significance to establish a realistic, simplified physical model to study the law of slurry diffusion. Herein, a cylindrical diffusion model of radial tube flow is established, and the control differential equations of both the Bingham slurry diffusion velocity in a single tube and the diffusion velocity of the radial tube flow are deduced. Additionally, the calculation formulas for the diffusion radius and slurry pressure distribution function are obtained. The rationality of the theory is verified by combining our results with those of the field grouting test of the Guotun coal mine. The results show that the cylindrical diffusion model of radial tube flow can successfully characterize the slurry diffusion law of grouting in a deep, loose layer. The slurry pressure attenuation shows distinguishable stages: within the first 30% of the diffusion radius, the slurry pressure decreased sharply by approximately 70%, and the slurry pressure decreases slowly in the later stages. Furthermore, the diffusion radius has a nonlinear, negative correlation with the height of the grouting section and the comprehensive injection rate of formation; the change rate is relatively more gradual, and there are no distinguishable stages. The research results provide a theoretical basis for reasonably determining the grouting parameters of deep, loose layers in the future.

Theoretical Research on Sand Penetration Grouting Based on Cylindrical Diffusion Model of Tortuous Tubes

The penetration paths of grouts in sand layers are tortuous, and there is no reasonable penetration grouting theory at present. By employing tortuous circular tubes as the internal penetration pore channels of the sand layer, the cylindrical diffusion model is established for sand-layer penetration grouting. First, the permeability of porous media and average penetration velocity of Bingham slurry were deduced by considering tortuosity. Second, based on the penetration continuity equation, the active steady-state penetration differential equation of Bingham slurry and the pressure distribution function of slurry in the diffusion region were obtained. Finally, combined with the indoor penetration grouting test results, the attenuation law of slurry pressure and the influencing factors of diffusion radius were discussed. The results show that the cylindrical diffusion model of tortuous tubes can better characterize the diffusion process of penetration grouting in the sand layer. The stop condition for diffusion during penetration grouting is the reduction of the pressure gradient of the slurry to its starting value. The slurry pressure attenuation has obvious stages. The slurry pressure attenuation is faster in the area close to the grouting tube. At 50% of the maximum diffusion radius, the pressure attenuation is 70.01~75.41% of the total pressure attenuation within the diffusion region. Increasing the grouting pressure and permeability coefficient and reducing the slurry viscosity ratio can greatly increase the slurry diffusion radius. These results provide a theoretical basis for determining sand grouting parameters in the future.

The effect of process parameters on chemical mechanical polishing of quartz glass

The effects of polishing pressure, polishing speed and pH value of the polishing slurry on the chemical activity of quartz glass, the material removal rate (MRR) and surface roughness (Ra) of the workpiece were studied. Using MRR and Ra as evaluation indexes, three factors and four levels of the orthogonal test were used to perform chemical mechanical polishing on quartz glass. By measuring the contact angle between the polishing slurry and workpiece, the influence of different polishing slurries on the chemical activity of quartz glass surface was studied. The processing mechanism of CMP quartz glass was analyzed. The order of important factors affecting MRR of quartz glass was: pressure [Formula: see text] rotation speed [Formula: see text] pH value; the order of significant factors affecting Ra of quartz glass was: pressure [Formula: see text] pH value [Formula: see text] rotation speed. The optimum polishing process parameter combination of the MRR was: pressure 27.58 kPa, rotation speed 85 rpm, pH value 12; the optimum polishing process parameter combination of the Ra was: pressure 13.79 kPa, rotation speed 85 rpm, pH value 12. The MRR and Ra of the workpiece are evaluated from the mechanical action of pressure and speed and the chemical action of polishing slurry on the workpiece. The results proved that the effect of the alkaline polishing solution on MRR and Ra of quartz glass is more significant than that of the acidic polishing slurry.

Numerical Simulation of the Diffusion of Fissure Slurry at High Temperature

Deep-buried tunnel at high-ground temperature is prone to the sudden surge of water when crossing the water-rich formation, resulting in casualties and economic losses. Slurry injection is a common and effective method of governance for addressing this issue. However, there has been little research into pulping at high-ground temperature, with most of the existing research focusing on room temperature conditions. We studied two kinds of slurry commonly used in grouting, cement slurry and cement-sodium silicate slurry. Indoor testing was used in this paper to clarify the effect of temperature on slurry viscosity, and numerical simulation was used to study slurry diffusion in flat cracks at different temperatures. The results showed that in a hydrostatic environment, the spread rate of slurry was independent of temperature and type of slurry. For the same kind of slurry, the higher the temperature, the greater the maximum slurry pressure. The higher the temperature in a flow environment, the faster the slurry diffusion. As the temperature rised, the grouting pressure required for crack sealing decreased at first then rises. In a flow environment, the sealing effect of cement-sodium silicate slurry was superior to that of cement slurry.

Modeling Hydraulic Fracturing and Blow-Out Failure of Tunnel Face During Shield Tunneling in Soft Soils

A common conflict of objectives for shield tunneling is to provide sufficient support pressure to maintain the stability of the tunnel face while avoiding blow-out of the tunnel face. Slurry-induced hydraulic fracturing, which is an important cause of blow-out failure in slurry-type shield tunneling, is investigated in this study. A fracture initiation mechanism for soft soils is developed and the fracturing pressure is described using a combined shear and tensile failure criteria within the cavity expansion theory framework. A slurry-induced fracture propagation model, coupled with the fracture initiation mechanism, is then proposed for predicting the fracture length and growth rate in front of tunnel face. The model is successfully applied to test data from the literature, and used in a parametric analysis. The results show that a fracture may easily extend to the ground surface when tunneling in ground with low strength parameters or shallow depth, and hydraulic fracture can be mitigated by using a high-density slurry. Finally, some design charts are provided to guide engineers in selecting a reasonable range of slurry pressure during shield tunneling, thus mitigating the risks of blow-out as well as maintaining face stability.

Numerical Investigation of Slurry Pressure Drop at Different Pipe Roughness in a Straight Pipe Using CFD

Slurry flow (water–glass beads) through a horizontal pipe of diameter, 0.0549 m and length, 3.8 m with two particle sizes, i.e., 125- and 440-micron, has been numerically modeled and investigated based on the kinetic theory of slurry transportation. The effect of particles interaction on the pipe flow characteristics such as velocity profile, wall shear stress, vector regime, granular pressure and temperature has been evaluated at different solid concentration and flow velocity range. It is well established that the pressure drop is the key parameter for the design of efficient slurry pipeline system, which is influenced by factors such as flow velocity, slurry viscosity, solid concentration, pipe material and pipe geometry. However, to best of our knowledge, the estimation of pressure drop at different pipe roughness height and a concentration range of 40–60% is not yet established. Therefore, in the present work, the numerical simulation is carried out for slurry flow through a horizontal pipeline at different roughness heights (Rh = 10–50 micron) and Prandtl numbers, i.e., 1.34, 2.14, 3.42 and 5.83. The kinetic parameters are calculated at a flow velocity (Vm) of 1–5 ms−1 and solid concentration (Cw) range of 40–60%. The results and procedure of the current simulation are validated against the available experimental results in the literature. The outcomes of the present work reveals that pressure drop increases with increase in pipe roughness height for the chosen velocity and solid concentration range. In addition, the larger particle is found to have more influence on the pressure, velocity, temperature distribution for the entire range of flow velocity and solid concentration. Furthermore, settling velocity and specific energy consumption are also predicted and discussed through the slurry pipeline. The findings show that the settling velocity of particle increases with increase in particle size at different Prandtl number. The energy efficiency for solid transportation through pipeline at different Prandtl numbers and particle size are also evaluated. Based on the results, it is concluded that specific energy efficiency varies with solid concentration and particle size, i.e., higher concentration and larger particle size demonstrates higher energy consumption. Furthermore, fluid at low Prandtl number exhibits higher energy consumptions. In order to design the efficient slurry pipeline system, it is recommended that the slurry must be transported at low velocity and high Prandtl number.

AHP-FSE-Based Risk Assessment and Mitigation for Slurry Balancing Shield Tunnel Construction.

Slurry balancing shield construction is a method in which slurry pressure and groundwater pressure are balanced to achieve stability of excavation working face. It is widely used in tunnel construction due to its safety and high-efficiency characteristics. At present, research on safety risk management of slurry balancing shield construction is relatively lacking, and most scholars still mainly focus on technical research. In this paper, based on system engineering theory and from the perspective of whole construction process, a comprehensive evaluation index system for shield construction risk analysis is built by taking “human-machine-material-method-environment” as assessment dimensions. This paper modifies the existing analytic hierarchy process (AHP), combines AHP with fuzzy synthetic evaluation to build a risk analysis model, and quantifies the construction risk by evaluation set and matrix. Combined with case study, the effectiveness of the proposed model is verified, and measures to mitigate safety risks of slurry shield construction are proposed from perspectives of management, economy, and technology. This paper evaluates the overall risk level of project from a systematic perspective, which is an extension of traditional technology-oriented research.

Accelerated Weathering and Carbonation (Mild to Intensified) of Natural Canadian Silicates (Kimberlite and Wollastonite) for CO2 Sequestration

Canada’s mineral reserves can play a very important role in curbing climate change if natural alkaline minerals are used for the process of mineral carbonation. In this work, the potential of using two Canadian natural silicates for accelerated carbonation is experimentally assessed: kimberlite mine tailing (Mg0.846Al0.165Fe0.147Ca0.067SiO3.381) from the Northwest Territories, and mined wollastonite ore (Ca0.609Mg0.132Al0.091Fe0.024SiO2.914) from Ontario. The aim of this work was to evaluate the weathering reactivity and CO2 uptake capacity via carbonation of these two comminuted rocks, both of which are made up of a mixture of alkaline minerals, under process conditions that spanned from milder to intensified. Research questions addressed include: does kimberlite contain a sufficient amount of reactive minerals to act as an effective carbon sink; is dehydroxylation necessary to activate kimberlite, and to what extent does it do this; do secondary phases of wollastonite hinder its reactivity; and can either of these minerals be carbonated without pH buffering, or only weathered? Incubator, slurry, and pressurized slurry methods of accelerated weathering and carbonation were used, and the effect of the process parameters (temperature, solid-to-liquid ration, reaction time, CO2 level, pH buffer) on the CO2 uptake and crystalline carbonates formation is tested. The reacted samples were analyzed by pH test, loss-on-ignition test, calcimeter test, and X-ray diffraction analysis. Results showed that wollastonite ore (rich in fast-weathering CaSiO3) is more suitable for accelerated carbonation than kimberlite tailing (containing slow-weathering hydrated magnesium silicates and aluminosilicates) when only its capability to rapidly form solid carbonates is considered. Incubator and pressurized buffered slurry methods proved to be most effective as under these conditions the precipitation of carbonates was more favorable, while the unbuffered slurry reaction conditions were more akin to accelerated weathering rather than accelerated carbonation.

Numerical Simulations for Analysis of Face Stability of Tunnelling

The aim of this paper is to evaluate numerical procedures that are used for analysis of face stability of a tunnelling. Two-dimensional (2D) and threedimensional (3D) Finite Element (FE) modelling of the Second Heinenoord Tunnel in Netherlands were done by using PLAXIS programs. The models were simulated the tunnel boring machine (TBM) with shell element and the slurry pressure with applied face pressure that measured in the site from the literature. Two methods were used to determine the situation of face failure. The first method was done by reducing the applied face pressure until the failure of the face was occurred, so the minimum required face pressure was determined. The second one was done by reducing the shear strength of the soil until the face failure, so the safety factor was determined. Both methods were applied for 2D and 3D FE-modelling. The results were presented and discussed. Also, the results of the minimum required support pressure were compared to the result of the centrifugal test model for the Second Heinenoord Tunnel found in literature. It was found that, the reducing applied face pressure method is much better than the reducing shear strength method. Also, the result of 3D FE-modelling gave better prediction when comparing with the experimental result .