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The basic principle of the three-dimensional stress state test is deduced based on the relationship between the normal stress and the conventional stress state, and the relationship between the total stress state and the effective stress state is given based on Terzaghi’s effective stress principle. On this basis, we made a three-dimensional earth...
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This study investigated the resilience of traditional concrete dams compared to 3D printed concrete dams (3DPC) when subjected to debris flow. Three types of dams, namely check dams, arch dams, and curve dams, were numerically analyzed using a three-dimensional Coupled Eulerian-Lagrangian (CEL) methodology. The research focused on critical factors...
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... This earth pressure cell comprised a pressure cell, a pressure sensor, an oil chamber, two pressure-bearing membranes, a connecting pipe, and a shielded cable. When pressure acted on the pressurebearing membrane of the pressure cell, it underwent slight flexible deformation, causing the liquid in the oil chamber to become pressurized [3,5,41]. The liquid pressure, generated by the incompressible property of the liquid, was transmitted to the pressure-bearing membrane of the pressure sensor through the connecting pipe, thereby altering the vibration frequency of the sensor. ...
... The physicomechanical properties of samples at different buried depths within the loess profile are illustrated in to Q 1 strata, there was an overall increasing trend in the dry density of both loess and paleosol, with the dry density of paleosol notably exceeding that of the underlying loess. Particularly, from the Q 4 to Q 2 strata, the dry density of loess increased from 1.42 to 1.63 g/cm 3 , while that of paleosol increased from 1.44 to 1.74 g/cm 3 , showing substantial variations. In the Q 1 2 strata, the dry density of loess increased marginally from 1.66 to 1.69 g/cm 3 , and that of paleosol increased from 1.76 to 1.79 g/cm 3 , indicating slight variations. ...
During the construction of tunnels in the Chinese Loess Plateau, the primary focus has traditionally been on the loess surrounding the tunnel. However, the swelling of paleosol and the low mechanical strength of loess in thick paleosol strata elevate the risks associated with tunnel construction. The distribution of loess and paleosol significantly influences tunnel stability. In this paper, we monitored the surrounding rock displacement and support structure pressure of a tunnel built within the thick paleosol strata. The thermal–mechanical coupling model was employed to simulate and calculate the swelling of paleosol, and the impact of loess and paleosol distribution on tunnel stability was thoroughly discussed. The results confirm the reliability of the thermal–mechanical coupling numerical model. At the vault and spandrel, where the interface lies between the thick paleosol strata and thick loess strata around the tunnel, the surrounding rock displacement initially increases and then decreases with the decrease in tunnel depth. However, the surrounding rock pressure exhibits an inverse variation, reaching a minimum when the interface is at the bottom of the lower bench. In areas with a thin loess layer around the tunnel, the surrounding rock displacement decreases, while the surrounding rock pressure increases with the reduction in the height of the thin loess layer. Furthermore, in comparison with surrounding rock with a full paleosol section, the displacement safety factor is 0.39–0.40 smaller, but the pressure safety factor is 1.21–1.24 larger when the interface is at the bottom of the lower bench. Simultaneously, the pressure safety factor is 0.17–0.41 larger, but the displacement safety factor is only 0.08–0.09 smaller with the thin loess layer in the upper bench. These findings provide a valuable theoretical reference for the construction of tunnels in thick paleosol strata and multi-strata environments with swelling soil and weak mechanical strength soil.
... At this stage, numerous newly formed micro-cracks would gradually derive, develop, nucleate and even coalesce under the actions of external loads, and gradually formed the dominant seepage channels. According to Griffith strength theory [51], numerous newly developed micro-crack tips were easy to form the high-stress concentration zone, which was accompanied by significant energy accumulation. Therefore, U P e raised rapidly (2.77 kJ·m −3 →42.69 kJ·m −3 ). ...
Rock burst is easy to occur in the water-rich roadway of coal mines, which is closely related to the energy dissipation and fracture mechanism of rocks under coupled hydro-mechanical (H-M) unloading. Therefore, in combination with the triaxial loading and unloading process and H-M coupling effect, the mechanical test of layered sandstones under coupled hydro-mechanical unloading (TLUTP) was conducted. The energy dissipation and fracture mechanism were revealed. The results show that: (1) The influence of layered angles on the peak volumetric strain is more sensitive than that of confining pressure under conventional triaxial loading with H-M coupling (CTLTP). On the contrary, the influence of confining pressure on the peak volumetric strain is more sensitive than that of layered angles under TLUTP. (2) With increasing layered angles, the peak elastic energy density under CTLTP shows the "W" shaped evolution characteristic, while that of under TLUTP shows the "N" shaped evolution characteristic. (3) The "Energy Flow" chain is proposed. Meanwhile, combined with the domino effect and the structural evolution theory, the energy dissipation and fracture mechanism of layered sandstones under coupled hydro-mechanical unloading are both revealed. The conclusions obtained can provide certain fundamental theoretical references for the effective prevention of rock burst in a layered water-rich roadway.
... With the increase in burial depth, the stress conditions of coal rocks become more complex, resulting in the decline of CBM permeability [5], gas protrusion [6,7], and rock explosion [8,9], which probably enhances the difficulty of CBM exploration. Therefore, it is important to understand the initiation and evolution of the fracture network of coal rocks under different stress conditions, which is vital for exploiting CBM [10] and engineering safety [11,12]. ...
Understanding the evolution of pore-fracture networks in coal during loading is of paramount importance for coalbed methane exploration. To shed light on these dynamic changes, this study undertook uniaxial compression experiments on coal samples collected from the eastern edge of the Ordos Basin, complemented by μ-CT scanning to obtain a 3D visualization of the crack network model. The compression process was divided into three stages, namely, micro-crack compaction, linear elasticity, and peak failure. An increase in stress resulted in greater concentration and unevenness in fractal dimensions, illustrating the propagation of initial cleats and micro-cracks in the dominant crack direction and the ensuing process of crack merging. These results provide valuable insights into the internal structure and behavior of coal under stress, informing more efficient strategies for coalbed methane extraction.
... et al. proved that cyclic injection can help reduce the breakdown pressure by using cylindrical dry-hot rock samples [11]. Other studies have been valuable for the protection of energy and environmental security [12][13][14][15]. Zhou et al. carried out cyclic hydraulic fracturing tests on rectangular concrete samples with multiple perforation clusters, and the results showed that more cracks could be produced by injecting the perforation cluster through the cyclic pump [16]. ...
Sandstone oil–gas reservoirs in the Junggar Basin, China have great development potential. However, their ultra-deep formation depth leads to high crustal stress and high breakdown pressure. Therefore, in this research, we studied the cyclic hydraulic fracturing of tight sandstone with different combinations of “high-pressure duration + low-pressure duration” under high-stress conditions. Through laboratory experiments, the pump pressure curves, hydraulic fracture morphology, acoustic emission counts, and peak frequency of the samples were obtained. The results showed that: (1) Compared with conventional hydraulic fracturing, the breakdown pressure of cyclic hydraulic fracturing was reduced by more than 30%, the minimum threshold of cyclic pump pressure required for sample breakdown was between 60%Pb and 70%Pb, and cyclic hydraulic fracturing more easily formed complex and diverse hydraulic fractures. (2) In cyclic hydraulic fracturing, under the same upper limit of cyclic pump pressure, the shorter the high-pressure duration, the fewer the cycles required for sample breakdown. (3) Under the same “high-pressure duration + low-pressure duration” condition, the lower the upper limit of the cyclic pump pressure, and the greater the number of cycles required for sample breakdown. (4) The AE cumulative counts curves fluctuated greatly during cyclic hydraulic fracturing, rising in an obvious step-wise manner and the AE peak frequency was banded and mainly divided into three parts: low frequency, medium frequency, and high frequency.
... Some researchers have since proposed several empirical regression methods to predict the compressive strength of concrete for a given mix ratio [8][9][10]. However, the components of concrete do not show a simple linear relationship with concrete strength but rather a strongly non-linear relationship, which makes it extremely difficult to summarise the exact regression expressions directly [11,12]. In recent years, with the rapid development of artificial intelligence, the method of machine learning has been widely used in major research areas in structural engineering, such as structural system identification [13], structural element design [14][15][16][17][18] and concrete compressive strength prediction [19][20][21][22][23][24]. ...
Accurate prediction of the compressive strength of concrete is of great significance to construction quality and progress. In order to understand the current research status in the concrete compressive strength prediction field, a bibliometric analysis of the relevant literature published in this field in the last decade was conducted first. The 3135 journal articles published from 2012 to 2021 in the Web of Science core database were used as the database, and the knowledge map was drawn with the help of the visualisation software CiteSpace 6.1R2 to analyse the field at the macro level in terms of spatial and temporal distribution, hotspot distribution and evolutionary trends, respectively. Afterwards, we go into the detail and divide concrete compressive strength prediction methods into two categories: traditional and machine-learning methods, and introduce the typical methods of each. In addition, a boosting-based ensemble machine-learning algorithm, namely the gradient boosting regression tree (GBRT) algorithm, is proposed for predicting the compressive strength of concrete. 1030 sets of concrete compressive strength test data were collected as the dataset, of which 60% were used to train the model, 20% to validate the model and 20% to test the trained model. The coefficient of determination (R2) of the GBRT model was 0.92, the mean square error (MSE) was 22.09 MPa, and the root mean square error (RMSE) was 4.7 MPa, which is an excellent prediction accuracy compared to prediction models constructed by other machine-learning algorithms. In addition, a five-fold cross-validation analysis was carried out, and the eight input variables were analyzed for their characteristic importance.
... Consequently, the crack propagation behavior in inter-salt shale reservoirs tends to be contrary to predictions. It is particularly important to understand the mechanical properties of deep rock, soil, and crack propagation [10][11][12]. ...
Hydraulic fracture morphology and propagation mode are difficult to predict in layers of the various lithological strata, which seriously affects exploitation efficiency. This paper studies the fundamental mechanical and microscopic properties of the two main interfaces in inter-salt shale reservoirs. On this basis, cement-salt combination samples with composite interfaces are prepared, and hydraulic fracturing tests are carried out under different fluid velocities, viscosity, and stress conditions. The result shows that the shale bedding and salt-shale interface are the main geological interfaces of the inter-salt shale reservoir. The former is filled with salt, and the average tensile strength is 0.42 MPa, c = 1.473 MPa, and φ = 19.00°. The latter is well cemented, and the interface strength is greater than that of shale bedding, with c = 2.373MPa and φ = 26.15°. There are three basic fracture modes for the samples with compound interfaces. Low-viscosity fracturing fluid and high-viscosity fracturing fluid tend to open the internal bedding interface and produce a single longitudinal crack, respectively, so properly selecting the viscosity and displacement is necessary. Excessive geostress differences will aggravate the strain incompatibility of the interface between different rock properties, which makes the interfaces open easily. The pump pressure curves' morphological characters are different with different failure modes.
... Engineered fills such as tailings deposits allow the positioning of a measurement probe, such as a total stress cell, before depositing the tailings, thus eliminating the need for disturbance to make the measurement (e.g. Chen et al. 2021). However, even in this case, the effect of the relative stiffness of the stress cell and the soil results in the measurement of lateral stresses not being straightforward (Clayton and Bica, 1993 where emax and emin are the maximum and minimum void ratios determined using standard laboratory testing techniques and e is the void ratio of interest (e.g. the in-situ void ratio Therefore, a min emax). ...
The paper is a State of the Art paper on tailings, prepared and presented at the 20th International Conference on Soil Mechanics and Geotechnical Engineering, held in Sydney in May 2022.
... These reaction products enveloped the soil particles and strengthened the soil. In addition, the formation of several stable gel reactants likely increased the bulk density of the soil [41,42]. The SEM analysis results were consistent with those reported by Ltififi et al. [43]. ...
Granite residual soil is widely distributed in southeastern China. Notably, this soil easily softens when exposed to water and is easily damaged when subjected to stress, and these characteristics are not conducive to engineering construction and underground space development. In this study, computed tomography(CT), mercury intrusion tests, XRD and SEM techniques are used to examine the improvement of granite residual soil in the Shenzhen area through the addition of cement. The soil micropore structure, saturated permeability coefficient and soil strength characteristics for improved soil specimens with different cement contents (2%, 4%, 6% and 8%) and curing durations (3 d, 5 d and 8 d) are examined. The results show that the pore distribution of granite residual soil has a bimodal structure. In the cement-improved soil, the large pores are eliminated, connectivity of pores is decreased, and number of isolated pores increases. Moreover, the unconfined compressive strength of the improved soil is higher than that of the granite residual soil. The introduction of cement contents of 6% can effectively increase the strength of granite residual soil while decreasing the permeability.
... This device can only monitor normal stress in three directions but cannot obtain shear stress and principal stress. Chen et al. [18] performed research on 3D stress monitoring, which provides a reference for 3D stress monitoring. The research mentioned little about the direction of principal stress. ...
... The stress state of a point in the soil can be represented by the stress component [18]. Considering the symmetry of shear stress, the stress state at a point can be represented by σx, σy, σz, σxy, σyz, and σzx. ...
... This is mainly because in the triaxial test, the loading is mainly in the vertical and radial directions, where σx, σy, and σz represent three principal stresses. The principal plane and principal stress do not vary with the coordinate system [18], so the measurements of σx, σy, and σz in the three loading paths are less affected by rotation. To verify the applicability of the 3D stress device, compare the normal stresses σx, σy, σz, and shear stresses σxy, σyz, σzx measured by the 3D stress device with the reference values provided by the triaxial loading system. ...
The stress state is the basis for evaluating soil deformation and strength. To study the three-dimensional (3D) stress state of the soil, a 3D stress device based on fiber Bragg grating (FBG) and Micro Electro Mechanical System (MEMS) was designed to measure the 3D stress state, principal stress, and direction of principal stress. First, the FBG one-dimensional earth pressure cell is developed and calibrated. Based on the calculation relationship between normal stress and the 3D stress state, and considering the device rotation, the 3D stress device was developed and verified in the large-scale triaxial test. The results show that the range of the one-dimensional earth pressure cell is 1 MPa, and the linearity is within 2.5% FS. The device can effectively measure soil’s 3D stress, principal stress, and direction. The measured results are consistent with the reference and theoretical results. The device provides a new method for effectively measuring 3D stress in soil.
