Uniaxial Compressive Strength Research Articles

The Effect of Freeze-thaw on Mechanical and Ultrasonic Properties of Hungarian Oolitic Stones

The freeze-thaw process is a weathering phenomenon that occurs in rocks and stones when water enters small cracks and pores within the stone. When the temperature drops below freezing, the water inside the rock expands as it freezes, exerting pressure on the rock from within. In this study the effect of freeze thaw on mechanical parameter uniaxial compression strength (UCS) and ultrasonic pulse velocity (UPV) of 47 oolitic samples were considered. At first, capillary absorption for cylindrical and prismatic oolitic samples were measured and then freeze-thaw experiment with 23 cycles were applied to the samples. UPV of samples before and after freeze-thaw was analysed by two ultrasonic devices including Geotron and Pundit. It was observed that freeze thaw decreases primary velocity (Vp) and secondary velocity (Vs) by around 20 and 7% respectively. However, average UCS of 1.6 MPa indicates strength decrease of samples, which represent negative effect of pore expansion due to freeze thaw on strength parameter of samples.

Study on the influence of rock bridge angle on the size effect of rock uniaxial compression.

As a basic parameter of rock, the rock bridge angle plays an important role in maintaining the stability of rock masses. To study the size effect of rock bridge angle on the uniaxial compressive strength of rocks, this paper adopts the principle of regression analysis and combines numerical simulation to carry out relevant research. The research results indicate that: (1) the uniaxial compressive strength decreases with the increase of the rock bridge angle, showing a power function relationship; (2) The uniaxial compressive strength decreases with the increase of rock size and tends to stabilize when the rock size is greater than 350 mm, showing a significant size effect. (3) The fluctuation coefficient of compressive strength increases with the increase of rock bridge angle and decreases with the increase of rock size; When the rock size is 350 mm, the fluctuation coefficient is less than 5%; (4) The characteristic compressive strength and characteristic size both increase with the increase of the rock bridge angle.

Influences of bedding angle and soaking time on the mechanical behaviour of silty mudstone: laboratory testing and theoretical modelling

Silty mudstone is highly susceptible to the influence of hot and humid environments, leading to the deterioration of its mechanical properties presenting a geohazard and even resulting in geological disasters. Accurately characterizing the effects of bedding and water–rock interaction on the mechanical behaviour of silty mudstone is a crucial prerequisite for the protection and reinforcement of silty mudstone slopes. To this end, uniaxial compression tests and Brazilian splitting tests were conducted to examine the mechanical properties of bedded silty mudstone. Based on the test results, the effects of bedding angle and soaking time on mechanical properties such as tensile strength, uniaxial compressive strength and elastic modulus of bedded silty mudstone were revealed. The test results showed that the tensile strength increased exponentially with increasing bedding angle. The observed split failure patterns of bedded silty mudstone encompassed splitting–pulling damage, shear damage and splitting damage. The uniaxial compressive strength of silty mudstone exhibited a U-shaped variation with an increase in bedding angle. The specimen with a bedding angle of 45° had the lowest uniaxial compressive strength at 7.64 MPa. Furthermore, the elastic modulus of silty mudstone was positively correlated with the bedding angle. The failure patterns of bedded silty mudstone under uniaxial compression included splitting-tension damage, shear-slip damage and splitting-shear damage. The saturated tensile strength, uniaxial compressive strength and elastic modulus of bedded silty mudstone exhibited an exponential decrease with increasing soaking time. The test data confirmed the applicability of the Jaeger equation to the uniaxial compressive strength of bedded silty mudstone. Subsequently, a modified Hoek–Brown failure criterion was derived by combining fracture mechanics theory and test results and introducing a softening factor. The parameters A , D and m in the above failure criterion decreased exponentially with increasing soaking time and an empirical Hoek–Brown failure criterion considering the soaking time was established. Compared with previous theoretical models, this model is more adaptable to the actual engineering situation, which results in more accurate calculations.

Study on Slump and Compressive Strength of Gangue Based on Aggregate Size Gradation

In order to solve the ecological environment pollution caused by a large amount of coal gangue accumulation and the problems of poor conveying performance and low support strength of paste filling materials. Based on the standard slump test and uniaxial compressive strength test, the slump and compressive strength (post-coagulation) of gangue paste under different aggregate size aggregations were obtained through orthogonal experiments in this study. The results show that the slump of the gangue filling paste with four types of aggregate size gradations is negatively correlated with the mass fraction, and the slump of the filling paste with a coarser aggregate content is more obviously affected by the mass fraction The increase of fine aggregate content has a significant impact on the compressive strength of the filling paste, which shows a trend of first increasing and then decreasing. When the mixing ratio of coarse aggregate and fine aggregate is 5:5, the compressive strength of the paste reaches the best. In addition, different proportions of aggregate mixing cause the filling paste to form different skeleton structures, including the skeleton void structure at 7:3 or 6:4, the skeleton dense structure at 5:5, and the skeleton suspension structure at 4:6, which are decisive for the final performance of the paste. By analyzing the experimental results of the compressive strength and slump of the gangue filling paste, it was found that the relationship between the compressive strength and slump of the gangue filling paste is a power index function. Through data fitting, it was found that the regression coefficient of the fitting function is no less than 0.97, and the fitting effect is good for evaluating the strength of the filling paste under the aggregate size grading.

THE MECHANICAL PROPERTIES AND FAILURE MODE OF SIMULATED LUNAR ROCK BY IN SITU TEMPERATURE REAL-TIME ACTION OF LUNAR-BASED

To achieve in situ condition-preserved coring of the lunar surface and deep lunar rocks and a return mission, it is necessary to explore the mechanical properties and failure modes of simulated lunar rocks that have physical and mechanical properties approximately equivalent to those of mare basalt under simulated lunar temperature environments ([Formula: see text][Formula: see text]C to 200[Formula: see text]C). To this end, real-time uniaxial compression tests were conducted on simulated lunar rocks under corresponding in situ temperature conditions, and the mechanical properties, deformation characteristics, micromorphology, and failure modes were analyzed. Based on the macroscopic analysis, as the environmental temperature decreases, the uniaxial compressive strength, peak strain, and peak strain duration of simulated lunar rocks exhibit a nonlinear increasing trend, with maximum increases of 33.00[Formula: see text], 36.16[Formula: see text], and 49.25[Formula: see text] from those at room temperature, respectively. Based on microscopic analysis, the intergranular fractures run through the entire samples under the environmental temperature. As the environmental temperature increases, intergranular and transgranular fractures coexist, and layered fractures appear at high temperatures. At the same time, some samples exhibit undulating and stepped morphologies caused by shear stress. For the fractal dimension of a simulated lunar rock main fracture surface, the fractal dimension of the actual angle and the corrected angle increase first and then decrease with increasing environmental temperature, and the maximum error of the two is only 1.84[Formula: see text]. The overall fractal dimension ranges from 2.02 to 2.28, and the fractal dimension under real-time high-temperature conditions is higher than that under real-time low-temperature conditions. In addition, the failure mode of the simulated lunar rocks under real-time in situ temperature changes is a combined tensile–shear failure mode with shear failure (primary) and tensile failure (secondary). The above research results are expected to be applied to in situ condition-preserved coring in extreme lunar environments and provide a scientific basis for the design and development of in situ condition-preserved coring robot systems for the extreme environment of deep space.

Experimental study on the punching failure model of soft red rock subgrade by BPT-BVM methods and it’s assessment of the load bearing capacity

The recommended bearing capacity of medium weathering mudstone foundation is less than the capacity of the rock structure to withstand loads in Southwest China. A comprehensive failure characterization of medium weathering mudstone in Chengdu has been performed including bearing plate test (BPT), binocular vision measurement (BVM) test, uniaxial compressive strength test, trial trench test of shallow rock surface and 3D imaging in this paper. Failure behavior of rock has been modeled with 3D imaging algorithm that utilizes Zhang’s calibration method in BVM system combination with trial trench test of shallow rock surface. The bearing capacity of medium weathering mudstone foundation were extracted from uniaxial experiments and BPT-BVM test by fitting relevant material properties to the data. The results revealed that: Bearing capacity of medium weathering mudstone of layered isotropic in Chengdu is undervalued. Specifically, the characteristic load carrying value is in the range 1500–2500 kP, that is 50% higher than in the local standard system. Failure process is different from Hoek–Brown Failure Criterion, presenting a wave peak transfer phenomenon of the increment displacement into the distance. Thus, it can be reduced to that of punching failures for thin bedded structures of Moudstone foundations. Compressive strength of soft rock proves to be main factor limiting the bearing capacity, a clear correlation between the uniaxial compressive strength reduction coefficient and the bearing capacity has been used to establish, leading to the proposal of a load bearing capacity prediction model.

Comparison of perlite and pumice effects on the geotechnical properties of saline silty soil

ABSTRACT This research mainly sought to evaluate the sediments of the Urmia lake bed to prevent their erosion and the possibility of improving the problematic saline fine soils in the region by the geo-polymerisation process. For this purpose, perlite and pumice materials, with pozzolanic properties and weight percentages of 3, 5, and 7, were separately mixed with soil, along with the calcium hydroxide (Ca(OH)2) solution as a catalyst with 2%, 5%, and 7%. Then, the samples were cured for one day. Uniaxial compressive strength (UCS), direct shear, and consolidation tests were performed to assess the geotechnical properties of improved soil compaction. The results revealed that, compared to pumice, perlite could improve the behavioural properties of the studied soil. The inclusion of perlite and pumice, along with calcium hydroxide, increased the flexibility of the stabilised soil, as indicated by the brittleness index. Similarly, combining 3% perlite with 2% Ca(OH)2 could increase UCS at failure by 3.27 times. In addition, the mixture of 5% perlite with 7% Ca(OH)2 could enhance the shear strength by 3.3 times. Finally, combining 3% perlite with 5% calcium hydroxide reduced the swelling of the improved soil by 82%, and the consolidation settlement was decreased by 64% on average.

An Experimental Study on the Mechanical Properties and Microstructure of the Cemented Paste Backfill Made by Coal-Based Solid Wastes and Nanocomposite Fibers under Dry-Wet Cycling.

The mechanical properties and microstructure of the cemented paste backfill (CPB) in dry-wet cycle environments are particularly critical in backfill mining. In this study, coal gangue, fly ash, cement, glass fiber, and nano-SiO2 were used to prepare CPB, and dry-wet cycle tests on CPB specimens with different curing ages were conducted. The compressive, tensile, and shear strength of CPB specimens with different curing ages under different dry-wet cycles were analyzed, and the microstructural damage of the specimens was observed by scanning electron microscopy (SEM). The results show that compared with the specimens without dry-wet cycles, the uniaxial compressive strength, tensile strength, and shear strength of the specimens with a curing age of 7 d after seven dry-wet cycles were the smallest, being reduced by 40.22%, 58.25%, and 66.8%, respectively. After seven dry-wet cycles, the compressive, tensile, and shear strength of the specimens with the curing age of 28 d decreased slightly. The SEM results show that with the increasing number of dry-wet cycles, the internal structure of the specimen becomes more and more loose and fragile, and the damage degree of the structural skeleton gradually increases, leading to the poor mechanical properties of CPB specimens. The number of cracks and pores on the specimen surface is relatively limited after a curing age of 28 d, while the occurrence of internal structural damage within the specimen remains insignificant. Therefore, the dry-wet cycle has an important influence on the both mechanical properties and microstructure of CPB. This study provides a reference for the treatment of coal-based solid waste and facilitates the understanding of the mechanical properties of backfill materials under dry-wet cycling conditions.

Settlement control investigation of high fill subgrade in karst section with tunnel slag filling

In this paper, based on the Kaihua section of the G205 (China) national highway reconstruction project, the construction area of the K4+550-K4+940 section was chosen to conduct settlement control research on the high-fill roadbed of the karst section within the construction area. The viability of using clayey gravel and tunnel slag as roadbed fill was evaluated through laboratory soil tests. The construction technology of grouting is used to manage the substructure of the karst section. After installing pre-stress anchors on the top of the foundation, a “layered” filling scheme was utilized to fill the tunnel slag and clayey gravel. The FLAC3D simulation software contrasted the deformation curves of key nodes on unanchored and anchored roadbeds. The test results indicate that the California Bearing Ratio test (CBR) test satisfies the requirements of the specification and that the uniaxial compression strength of the tunnel slag satisfies the requirements of the specification when the clayey gravel is near the optimal moisture content and dry density, and when the compaction is controlled to within 94%. The use of pre-stress anchors can strengthen the foundation’s rock and soil layers, and reduce the plastic zone’s distribution. This article provides a corresponding engineering experience for the treatment of high-fill roadbeds in karst areas.

Experimental research on influence of curing environment on mechanical properties of coal gangue cementation

Abstract To investigate the impact of curing environments on the mechanical properties of coal gangue cementation (CGC), various curing methods were established, including standard bag curing, standard curing, natural sealing curing, natural curing, water curing, and varying curing ages. By examining the uniaxial compressive strength (UCS) and stress–strain relationship of CGC by applying axial loads, the influence mechanism was analyzed in terms of both physical and chemical reactions. Furthermore, a mechanistic structural model was established to illustrate the impact of the curing environment on the mechanical properties of CGC. The primary substances and reasons affecting the mechanical properties of CGC were analyzed through the use of scanning electron microscopy and X-ray diffraction techniques. Evaluation of influence factors on CGC mechanical properties by grey correlation degree. The findings indicate that curing temperature, humidity, and carbonization are the principal factors influencing the UCS. Maintaining constant temperature and humidity while isolating CO2 is conducive to improving the UCS. The hydration products, such as needle-like ettringite and white fibrous calcium silicate hydrogel, fill the internal voids of CGC and are the primary substances affecting UCS. The hydration products formed during standard curing and natural curing of CGC can undergo carbonation with CO2 to form CaCO3, which interacts with ettringite and hydrated calcium silicate to provide strength support for CGC. However, beyond a certain age, CO2 will progressively diminish the UCS; the larger the contact area and the longer the exposure time to the gel materials in CGC, the faster the UCS decreases.

Performance evolution of alkali-activated phosphorus slag paste filling material: Effect of hemihydrate phosphogypsum content

The stockpiling issues of phosphorus slag (PS) and hemihydrate phosphogypsum (HPG) have become vital technical obstacles limiting the economic development of enterprises. The synergistic substitution of PS and HPG for ordinary Portland cement in preparing alkali-activated phosphorus slag paste filling material (AAPS-PM) is essential to realize the high-value utilization of PS and HPG and reduce carbon emissions. HPG was selected as a sulfate activator for this research due to its metastable qualities and chemical composition benefits. The effect of HPG on the properties of AAPS-PM was systematically investigated by setting time, fluidity, strength development, water resistance, and pore solution pH experiments. The evolution of hydration products and pore size characteristics was elaborated employing X-ray diffractometer (XRD), scanning electron microscopy (SEM) and low-field nuclear magnetic resonance (NMR). The results demonstrated that the addition of HPG displayed remarkable procoagulant thickening characteristics on AAPS-PM. Additionally, HPG was conducive to developing early uniaxial compressive strength (UCS), whereas 90% content of HPG had a negative impact on the enhancement of later UCS. The softening coefficient and water absorption exhibited duality with 80% HPG content as the critical point, obtaining a maximum value of 0.73 and a minimum value of 6.63%, respectively. It is noteworthy that the decrease in pore solution pH was primarily correlated with the acidity carried by HPG. Herein, the alkali activator accelerated the depolymerization of PS vitreous and generated H3SiO4- and H3AlO42- and Al(OH)63-. Furthermore, the active ions combined with Ca2+ and SO42- supplied by HPG, which contributed to the formation of dihydrate gypsum, ettringite and C-(A)-S-H gels. Encouragingly, microscopic analysis confirmed the macroscopic performance changes of AAPS-PM. The gel network created by the interweaving of hydration products refined the pore structure and improved the microstructure morphology, which is the primary source of mechanical strength. Nevertheless, the high content of HPG provided a driving force for the development of capillary pores, resulting in a rapid reduction in later strength. Overall, this research can contribute new ideas to the large-scale integrated disposal of solid waste.

Physical and mechanical characteristics deterioration and crack evolution of sandy mudstone in an open-pit mine under multiple freeze–thaw cycles

In open-pit mines located in cold regions north of the 38°N latitude, there are significant freeze–thaw phenomena in slope rocks. This study conducted freeze–thaw cycle tests, considering the number of freeze–thaw cycles and the freezing temperature, on sandy mudstone commonly found in the slopes of open-pit mines. The investigation focused on the effects of freeze–thaw cycles on the physical and mechanical properties and acoustic emission (AE) characteristics of sandy mudstone. The results show that, with an increase in the number of freeze–thaw cycles and a decrease in freezing temperature, the sandy mudstone specimens exhibit nonlinear exponential changes in mass loss rate, P-wave velocity loss rate, peak strain, uniaxial compressive strength (UCS) and elastic modulus, and the amplitude of these changes gradually decreases. The stress–strain curves of specimens shift gradually from apparently brittle to plastic. Simultaneously, the microstructure changes from dense to loose, the micro surface transitions from flat to rough, and cracks and pore defects gradually develop. The peak AE ringing counts, cumulative AE ringing counts, crack initiation stress, and crack damage stress of the specimens all decrease with an increase in the number of freeze–thaw cycles and a decrease in freezing temperature. This suggests a shift from brittle failure to ductile failure. However, the ratio of crack initiation stress and crack damage stress to peak stress does not vary significantly with the number of freeze–thaw cycles and freezing temperature.

Research on Slurry Flowability and Mechanical Properties of Cemented Paste Backfill: Effects of Cement-to-Tailings Mass Ratio and Mass Concentration.

The flowability and mechanical properties are increasingly crucial in the filling process of deep metal mines with mining depths exceeding 1000 m. The rheological properties of filling slurry in the pipeline were analyzed through rheological tests, L-tube self-flow tests, and semi-industrial loop tests. The results revealed that with an increase in the cement-to-tailings mass ratio (c/t ratio) and mass concentration, the slurry exhibited a higher flow resistance and decreased stowing gradient. During slurry transportation, the pressure loss in the straight pipe was positively correlated with the slurry flow rate, c/t ratio, and mass concentration. A uniaxial compressive strength (UCS) test was conducted to analyze the mechanical properties of the cemented paste backfill containing BMC (CCPB) in both standard and deep-underground curing environments. The UCS of the CCPB showed an increasing trend with the rise in curing age, mass concentration, and the c/t ratio. The comprehensive analysis concluded that when the c/t ratio is 1:4, and the mass concentration is approximately 74%, and parameters such as the slump, bleeding rate, and flowability of the filling slurry meet the criteria for conveying and goaf filling, resulting in a high-strength filling body.

Study and Application of Rock Drilling Resistance Characteristics in the Jiyang Depression Formation

In response to the unclear drilling resistance characteristics of rocks in the Ji’yang Depression, low drilling efficiency of PDC drill bits, and difficulties in drill bit selection, this study selected rock samples from different depths in the area for indoor drilling resistance analysis testing. Based on logging data, a prediction model was established for drilling resistance characteristics parameters of the strata in the area, and a graph of drilling resistance characteristic parameters of the rocks in the area was drawn. The study showed that the uniaxial compressive strength of the strata rocks was 50–110 MPa, with a hardness of 500–1300 MPa, a plasticity coefficient ranging from 1 to 2, a rock drillability grade of 8–20, and an abrasiveness index of 5–20. Combining the analysis of on-site drilling bit failures, PDC drill bits adapted to the strata in the area were selected, and the mechanical drilling speed of the selected bits reached 12.58 m/h, successfully drilling through the target layer. The above research results are of guiding significance for understanding the reasons for the difficulty of drilling into the Jiyang Depression strata and for improving mechanical drilling speed and drill bit selection in this area.

Experimental study on I/II/III mixed mode fracture characteristics of a combined rock mass under creep loading

I/II/III mixed mode fractures of intersecting joint fissures often occur in natural rock masses, and jointed rock masses are prone to rockbursts in deep underground engineering when subjected to long-term crustal stresses. However, most studies of the mechanical mechanisms of these intersected joints have been conducted by simplifying two-dimensional joint model tests. Furthermore, the fracture mechanisms of two-dimensional intersected joints under tension and compression are completely different from those of three-dimensional joints. This paper presents a novel prefabricated specimen with combinations of intersecting joints capable of detecting the failure behaviours of rock I/II/III mixed mode fractures under creep loading. Uniaxial compression and multistage creep tests are performed on prefabricated sandstone specimens with intersecting joints of 0°/0°, 0°/30°, 0°/60°, and 0°/90°. The experimental results show that with the increase in the number of prefabricated intersecting joints, the uniaxial compressive strength and elastic modulus values of the sandstone specimens gradually decrease. In addition, the sandstone specimens experience relatively few AE events and minor axial strain variations in the first creep stage and the second creep stage of the multistage creep test. The axial strain increases sharply due to the sharp increase in the number of AE events in the third creep stage. The 0°/60° sandstone specimen undergoes accelerated creep failure, resulting in mixed X-shaped tensile‒shear rupture. The RA value is high based on the quantification of the creeping cracks using the acoustic emission parameters of the rise angle (RA) and average frequency (AF). The AF values of the 0°/0°, 0°/30°, and 0°/90° sandstone specimens are high. The experimental results show that a larger joint intersection angle leads to greater mutual restraints and greater effects of prefabricated crack propagation in the rock specimens, thus increasing the final failure strength. Finally, based on the acoustic emission count, a characteristic variable D suitable for characterizing the creep damage evolution of a joint rock mass is established. The findings of this paper can facilitate an effective understanding of the creep effect of I/II/III mixed mode fracture and its micromechanism. The research results will have a certain reference value for the detection and risk mitigation of instantaneous and time-delayed rockbursts.

Petrographic and Mechanical Analysis of Grano-Diorite Deposits in the Qala Region, Dikundi Province, Afghanistan

This research paper offers a detailed investigation into the petrographic composition and physical-mechanical properties of granodiorites in the Qala area of Dikundi Province. It starts with a geological overview of the region. It examines macroscopic and microscopic petrographic characteristics, paragenetic mineral composition, and critical physical-mechanical properties such as bulk density, water absorption, and uniaxial compressive strength. XRF analysis was also employed for accuracy. The research approach is purely investigative, with samples collected from the Qala area and tests conducted by international standards. These granodiorites' uniaxial compressive strength was approximately 94.02 Mega Pascals, signifying their exceptional structural durability. Additionally, these granodiorites exhibit a specific gravity of 2.57, considered high, and a water absorption rate of about 0.29%, making them highly suitable for construction. In summary, this academic research comprehensively analyses granodiorites within the Qala region, Dikundi Province. These findings are essential for evaluating the suitability of these granodiorites for various applications, particularly in the construction industry, contributing significantly to our understanding of this geological resource. The research recommends the need for government investment in the granodiorite mining sector, particularly in the Qala deposit. Detailed geological investigations are imperative to harness the full potential of this resource, generate employment opportunities, reduce dependency on stone imports, and explore international markets.

Advancing Rock-Socketed Pile Design with a Unified Interface Shear Strength Framework for Soft Rocks

AbstractThe shaft resistance of rock-socketed piles (RSPs) is primarily influenced by the interactions between the pile, rock and any soft interface materials. This study presents a fundamental experimental and numerical investigation to predict the shaft resistance of model RSPs in soft rocks through a comprehensive shear strength framework incorporating the major variables such as roughness and smear fabric. By calibrating the Discrete Element Method (DEM) results with the experimental outcomes, this study evaluates the load-resistance attributes of RSPs in three different soft rocks for a wide range of roughness and smear configurations. The interface roughness effect of the RSPs in terms of the friction coefficient was correlated with the ultimate shaft resistances, uniaxial compressive strength and Young’s modulus of the rock. The study then incorporated the effect of smear fabric (placement, thickness and area proportion) in the shear strength framework of clean shafts. Comprehensive review of the DEM results revealed that the socket roughness effect diminishes at a critical roughness factor $$({\text{RF}})$$ ( RF ) of 0.4, beyond which the smear predominantly influences the shaft capacity. Following this, the effects of roughness and smear fabric were incorporated into a single equation representing the interface shear strength of RSPs, where the existence of smear results in a maximum reduction of up to 75% of the ultimate shaft resistance. The distinctive feature of this unified interface shear strength framework lies in its integration of the new smear fabric parameter and the linkage to the mechanical properties of soft rocks, which is the limitation of the earlier studies. It thereby sets a strong base for future studies aimed at advancing the pile-rock interface models.

Application of Relationship model for the Measurement While Drilling Data to Predict Rock Uniaxial Compressive Strength for Tunneling

Application of Relationship model for the Measurement While Drilling Data to Predict Rock Uniaxial Compressive Strength for Tunneling

Study on the Influence of Contact Surface Characteristics on Strength and Fracture Evolution of Layered Cemented Backfill (LCB)

The stability of backfill plays a crucial role in the process of mine operation. In this study, author combined indoor experiments, surface fitting, numerical simulation, and theoretical derivation to investigate how the filling times (FTs), cement tailings ratio (CTR), and minimum CTR filling position (MCFP) affect the uniaxial compressive strength (UCS) and fracture evolution behavior of LCB. The findings demonstrate that an augmentation in FTs reduces the UCS of LCB. Moreover, the highest strength ratio resulting from diverse MCFP amounts to 2.25 times. When once filling, backfill sustain damage as a result of cracks penetrating, whereas LCB that are filled multiple times first encounter damage at the layered contact surface, followed by the gradual spread of cracks until penetrate the LCB. Through an interactive regression model, it is evident that FTs, CTR, and MCFP significantly affect the UCS. Additionally, the interaction between CTR and MCFP has a considerable impact on the UCS. Based on numerical simulation, an increase in FTs results in a wider large displacement area generated by the backfill, leading to greater horizontal and vertical displacement. The MCFP has a significant impact on the lateral displacement and maximum stress of the backfill. Theoretical derivation verifies that MCFP at the top or middle layer results in an increase in the UCS, which is consistent with the experimental findings and numerical simulation. This paper elaborates on the mechanical mechanism behind the interaction between CTR and MCFP. These findings can provide a foundation for assessing the durability and stability of LCB in subsequent stages.

Influence of frost heave with confining pressure under seepage on compressive strength of frozen silt in artificial ground freezing

Artificial ground freezing (AGF) is used for constructing subway cross passages in coastal areas. The continuous construction of complex projects (cross-sea or cross-river tunnels) has resulted in freezing environments with high groundwater seepage velocities. Seepage cannot provide an open system in soil freezing for moisture migration, resulting in large amount of frost heave owing to segregated ice compared to close freezing system. The influence of frost heave under seepage on the compressive strength of frozen silt during artificial ground freezing must be studied to ensure AGF construction safety. Thus, a unidirectional freezing device that can control seepage and confining pressure conditions during freezing was designed to prepare frozen silt samples under different seepage velocities with confining pressures and to measure the relevant segregation frost heave. Subsequently, uniaxial compression tests were performed. The compressive strength of frozen silt under the influence of frost heave and seepage conditions was analyzed. The frost heave rate, uniaxial compressive strength, and elastic modulus of frozen silt in an open freezing system were measured. The seepage velocity during freezing increased the frost heave rate of the silt; the uniaxial compressive strength and elastic modulus of the frozen silt increased subsequently. The effective confining pressure suppressed frost heave of silt and reduced the uniaxial compressive strength and elastic modulus of the frozen silt. The test results were analyzed considering the segregation frost heave formation mechanism, and a theoretical improvement model of the uniaxial compressive strength and elastic modulus of frozen silt related to the content of segregated ice was proposed. This research is significant for ensuring the AGF construction safety in cross-river or ocean tunnel engineering under seepage conditions.