Study on mudcake disintegration in clayey strata during shield tunneling : effects of dispersants and bentonite slurry

While tunnel boring machines (TBMs) tunneling in clayey strata, the adhered excavated soil on the cutterhead and cutting tools tends to form mudcake after compaction and consolidation. Mudcake can obstruct the cutterhead openings and rendering the cutting tools ineffective, leads to a substantial reduction in advance rate. Dispersants are recognized as an effective method for the disintegration of mudcakes. A novel set of equipment, comprising a mudcake compression device and a mudcake disintegration apparatus, is developed for assessing mudcake disintegration properties. The results showed that mudcakes underwent a tripartite disintegration process in water, including an initial stage, a rapid disintegration stage, and a stable stage. In the initial stage, the mudcakes absorbed water before disintegration, resulting in marginal changes in the weight of the disintegrated mudcakes. In the rapid disintegration stage, the weight of the disintegrated mudcakes increased quickly. During the stable stage, the weight of the disintegrated mudcakes remained relatively constant. The submersion of mudcakes in a dispersant solution substantially increased the rate of disintegration. Greater dispersant concentration corresponded to an increase in the disintegration rate. No weight gain was observed in mudcakes during the initial disintegration stage. When mudcakes disintegrated in a bentonite slurry, the weight of the disintegrated mudcakes initially decreased and then stabilized. The weight of the disintegrated mudcakes turned negative, indicating an increase in the weight of mudcakes. This suggested that bentonite significantly hindered mudcake disintegration

Moisture Transfer and Formation of Separate Ice in the Freezing Process of Saturated Soils

The formation and layer of ice lenses during the freezing of soil in cold regions is closely related to frozen heave and moisture immigration. The purpose of the paper is to explain the physical mechanisms pertaining to ice lens formation, which were analyzed and verified using numerical simulation results. Based on a few assumptions, the formation and layers of ice lenses are illuminated in the following steps: the initial stage of freezing, formation of the first layer of ice lens, formation of the second layer of ice lens, and formation of the final layer of ice lens. Compared with the numerical results of coupled thermo–hydro–mechanical simulations of one-side freezing of soil columns in an open system, the proposed analysis method of the formation and layers of ice lenses is verified to be reasonable, and it is demonstrated that the classical criterion for the formation of ice lens in freezing saturated soil is only suitable for the final layer of ice lens. Finally, a new criterion, in terms of flux rate, for the formation of ice lens is proposed

Mechanical Properties and Binary-Medium-Based Constitutive Model for Coral-Reef Limestone Samples Subjected to Uniaxial Loading

The mechanical and deformation mechanism of coral-reef limestone is vital for the stability and safety of infrastructures built on the ground composed of those materials. Upon loading, strain softening behavior of the coral-reef limestone occurs, usually due to the nonuniform cementation distribution, and the cementation within the samples may break up gradually and reduce the bearing capacity. In order to study their mechanical features, uniaxial compression tests were carried out in this study, and, based on the test results, a binary-medium-based constitutive model was formulated, in which, the sample was idealized, respectively, as the bonded and frictional elements. The bonded elements are composed of strong cementation and may gradually break up to transform into the frictional elements, both of which bear the external loading conjointly. In the new model, the parameters determination method was adopted based on uniaxial compression testing, and comparisons were made between the tested and computed results, which demonstrate that the model can reflect the salient features of coral-reef limestone samples, such as the strain softening and bonding breakage during the loading process. The study can provide a basis for the basic design of coral-reef limestone

Mechanical Properties and Binary-Medium-Based Constitutive Model for Coral-Reef Limestone Samples Subjected to Uniaxial Loading

The mechanical and deformation mechanism of coral-reef limestone is vital for the stability and safety of infrastructures built on the ground composed of those materials. Upon loading, strain softening behavior of the coral-reef limestone occurs, usually due to the nonuniform cementation distribution, and the cementation within the samples may break up gradually and reduce the bearing capacity. In order to study their mechanical features, uniaxial compression tests were carried out in this study, and, based on the test results, a binary-medium-based constitutive model was formulated, in which, the sample was idealized, respectively, as the bonded and frictional elements. The bonded elements are composed of strong cementation and may gradually break up to transform into the frictional elements, both of which bear the external loading conjointly. In the new model, the parameters determination method was adopted based on uniaxial compression testing, and comparisons were made between the tested and computed results, which demonstrate that the model can reflect the salient features of coral-reef limestone samples, such as the strain softening and bonding breakage during the loading process. The study can provide a basis for the basic design of coral-reef limestone

Clogging Prevention of Slurry–Earth Pressure Balance Dual-Mode Shield in Composed Strata with Medium–Coarse Sand and Argillaceous Siltstone

The slurry–earth pressure balance dual-mode shield has an earth pressure balance (EPB) and slurry shield functions. Based on a shield tunnel project of Guangzhou Metro Line 12 in China, this study investigates the clogging prevention of a slurry–earth pressure balance dual-mode shield in a composed stratum with medium–coarse sand and argillaceous siltstone. The results show that the slurry mode was not applicable to the composed stratum with medium–coarse sand and argillaceous siltstone. The excavated soil accumulated easily in the slurry chamber, causing shield clogging. The total thrust force of the shield increased significantly, the tunneling speed gradually decreased to 0, and the torque of the cutterhead increased slightly after the slurry shield was clogged. The fluctuation in the total thrust force, the cutterhead torque, and the tunneling speed also increased significantly. The EPB mode is recommended for composed strata with medium–coarse sand and argillaceous siltstone. The dispersible foam agent and water needed to be used for soil conditioning. The injection amount of foam and water was determined according to the status of the mud discharged by the screw conveyor. Water absorption can be used to characterize the water absorption capacity of particles larger than 0.15 mm. The ideal soil state was that the consistency index of the particles smaller than 0.15 mm was less than 0.5 to prevent the EPB shield from clogging. The water absorption of soil with a particle larger than 0.15 mm should be removed when calculating the consistency index

Clogging Prevention of Slurry–Earth Pressure Balance Dual-Mode Shield in Composed Strata with Medium–Coarse Sand and Argillaceous Siltstone

The slurry–earth pressure balance dual-mode shield has an earth pressure balance (EPB) and slurry shield functions. Based on a shield tunnel project of Guangzhou Metro Line 12 in China, this study investigates the clogging prevention of a slurry–earth pressure balance dual-mode shield in a composed stratum with medium–coarse sand and argillaceous siltstone. The results show that the slurry mode was not applicable to the composed stratum with medium–coarse sand and argillaceous siltstone. The excavated soil accumulated easily in the slurry chamber, causing shield clogging. The total thrust force of the shield increased significantly, the tunneling speed gradually decreased to 0, and the torque of the cutterhead increased slightly after the slurry shield was clogged. The fluctuation in the total thrust force, the cutterhead torque, and the tunneling speed also increased significantly. The EPB mode is recommended for composed strata with medium–coarse sand and argillaceous siltstone. The dispersible foam agent and water needed to be used for soil conditioning. The injection amount of foam and water was determined according to the status of the mud discharged by the screw conveyor. Water absorption can be used to characterize the water absorption capacity of particles larger than 0.15 mm. The ideal soil state was that the consistency index of the particles smaller than 0.15 mm was less than 0.5 to prevent the EPB shield from clogging. The water absorption of soil with a particle larger than 0.15 mm should be removed when calculating the consistency index

Study on Mudcake disintegration in clayey strata during shield tunneling: Effects of dispersants and bentonite slurry

While tunnel boring machines (TBMs) tunneling in clayey strata, the adhered excavated soil on the cutterhead and cutting tools tends to form mudcake after compaction and consolidation. Mudcake can obstruct the cutterhead openings and rendering the cutting tools ineffective, leads to a substantial reduction in advance rate. Dispersants are recognized as an effective method for the disintegration of mudcakes. A novel set of equipment, comprising a mudcake compression device and a mudcake disintegration apparatus, is developed for assessing mudcake disintegration properties. The results showed that mudcakes underwent a tripartite disintegration process in water, including an initial stage, a rapid disintegration stage, and a stable stage. In the initial stage, the mudcakes absorbed water before disintegration, resulting in marginal changes in the weight of the disintegrated mudcakes. In the rapid disintegration stage, the weight of the disintegrated mudcakes increased quickly. During the stable stage, the weight of the disintegrated mudcakes remained relatively constant. The submersion of mudcakes in a dispersant solution substantially increased the rate of disintegration. Greater dispersant concentration corresponded to an increase in the disintegration rate. No weight gain was observed in mudcakes during the initial disintegration stage. When mudcakes disintegrated in a bentonite slurry, the weight of the disintegrated mudcakes initially decreased and then stabilized. The weight of the disintegrated mudcakes turned negative, indicating an increase in the weight of mudcakes. This suggested that bentonite significantly hindered mudcake disintegration

Experimental and Numerical Analysis of Pile–Rock Interaction Characteristics of Steel Pipe Piles Penetrating into Coral Reef Limestone

In order to study the characteristics of pile–rock action of steel pipe driven pile in coral reef limestone stratum, coral reef limestone at the China–Maldives Friendship Bridge site was selected to carry out indoor physical and model tests with red sandstone as the control group. The test outcomes indicate the following: (1) when substantial deformation is permitted, the coral reef limestone has a considerable strength dispersion, a low post-peak stress decrease rate, and a high residual strength, roughly 30% of the peak strength; (2) when the steel pipe pile penetrates the coral reef limestone, the pile top load shows an obvious sawtooth shape, and with the increase in penetration depth, the pile end load of the high-porosity rock sample gradually decreases, and the pile end load of the low-porosity rock sample gradually increases; (3) when the steel pipe pile is penetrated, the strain value of the red sandstone is about twice that of the coral reef limestone at the same position from the steel pipe pile. These findings indicate that the high porosity and heterogeneity cementation characteristics of the coral reef limestone make the extrusion effect during piling significantly less than that of the red sandstone. In addition, the steel pipe pile penetration process is numerically simulated using a four-dimensional discrete spring model method based on the multi-body damage criterion. The numerical simulation results further demonstrate that the pile-side rock fragmentation during steel pipe pile penetration is the primary reason for the lower bearing capacity of steel pipe piles in coral reef limestone stratums. This method provides a novel approach for studying the mechanical properties of reef limestone. The findings can serve as a guide for the design and construction of steel pipe piles in the reef limestone stratum

Potential relationship between inadequate response to DNA damage and development of myelodysplastic syndrome

Hematopoietic stem cells (HSCs) are responsible for the continuous regeneration of all types of blood cells, including themselves. To ensure the functional and genomic integrity of blood tissue, a network of regulatory pathways tightly controls the proliferative status of HSCs. Nevertheless, normal HSC aging is associated with a noticeable decline in regenerative potential and possible changes in other functions. Myelodysplastic syndrome (MDS) is an age-associated hematopoietic malignancy, characterized by abnormal blood cell maturation and a high propensity for leukemic transformation. It is furthermore thought to originate in a HSC and to be associated with the accrual of multiple genetic and epigenetic aberrations. This raises the question whether MDS is, in part, related to an inability to adequately cope with DNA damage. Here we discuss the various components of the cellular response to DNA damage. For each component, we evaluate related studies that may shed light on a potential relationship between MDS development and aberrant DNA damage response/repair