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Microscale mechanical forces can determine important outcomes ranging from the site of material fracture to stem cell fate. However, local stresses in a vast majority of systems cannot be measured due to the limitations of current techniques. In this work, we present the design and implementation of the CdSe-CdS core-shell tetrapod nanocrystal, a local stress sensor with bright luminescence readout. We calibrate the tetrapod luminescence response to stress and use the luminescence signal to report the spatial distribution of local stresses in single polyester fibers under uniaxial strain. The bright stress-dependent emission of the tetrapod, its nanoscale size, and its colloidal nature provide a unique tool that may be incorporated into a variety of micromechanical systems including materials and biological samples to quantify local stresses with high spatial resolution.

Rough surfaces known as stylolites are common geological features that are developed by pressure solution, especially in carbonate rocks, where they are used as strain markers and as stress gauges. As applications are developing in various geological settings, questions arise regarding the uncertainties associated with quantitative estimates of paleostress using stylolite roughness. This contribution reports for the first time a measurement of the temperature at which pressure solution was active by applying clumped isotopes thermometry to calcite cement found in jogs linking the tips of the stylolites. This authigenic calcite formed as a redistribution of the surrounding dissolved material by the same dissolution processes that formed the extensive stylolite network. We compare the depth derived from these temperatures to the depth calculated from the vertical stress inversion of a bedding parallel stylolite population documented on a slab of the Calcare Massiccio formation (early Jurassic) formerly collected in the Umbria-Marches Arcuate Ridge (Northern Apennines, Italy). We further validate the coevality between the jog development and the pressure solution by simulating the stress field around the stylolite tip. Calcite clumped isotopes constrain crystallization to temperatures between 35 and 40 °C from a common fluid with a δ18O signature around −1.3‰ SMOW. Additional δ18O isotopes on numerous jogs allows the range of precipitation temperature to be extended to from 25 to 53 °C, corresponding to a depth range of 650 to 1900 m. This may be directly compared to the results of stylolite roughness inversion for stress, which predict a range of vertical stress from 14 to 46 MPa, corresponding to depths from 400 to 2000 m. The overall correlation between these two independent depth estimates suggests that sedimentary stylolites can reliably be used as a depth gauge, independently of the thermal gradient. Beyond the method validation, our study also reveals some mechanisms of pressure solution and the associated p,T conditions favouring their development in carbonates.

Pile tip grouting is an important technique for improving the bearing capacity of cast-in-place bored piles. This paper presents a field experimental study on the effects of tip post-grouting in an enlarged head cast-in-place bored pile. The bearing data of the pile before and after the grouting were obtained through two load tests. The settling rod method was used to monitor the settlement at three critical sections, including the pile bottom during loading, while the method of rebar stress gauge was employed to monitor the strain of the pile shaft. The study results indicate that post-grouting at the pile tip significantly enhanced the bearing capacity of the pile and helped control the settlement at the pile top. A comparison between the measured and calculated settlement values at critical sections demonstrates the applicability of the settlement rod method and strain gauge method. Post-grouting at the pile toe effectively improved the side friction of the pile, resulting in smaller axial forces in the lower part of the grouted pile under equivalent loads.

Hydraulic fracturing (HF) technology has been widely used in the coal mining industry. This technology can effectively increase the permeability coefficient of low-permeability coal seams, thereby enhancing the gas drainage efficiency and increasing the safety of coal mining. To study the correlation between the fluid injection pressure (FIP) and the unit fluid injection quantity (UFIQ) during hydraulic fracturing and considering the limitations of laboratory and numerical simulation methods, this study employs a field engineering experiment at the 1703 mining working face of Jin’zhong Coal Mine in Sichuan Province as the test site. Through the monitoring and analysis of the FIP and the UFIQ during the whole HF process of coal seam drilling, it is found that there is a certain correlation between the FIP and the UFIQ, the FIP will appear obvious “decreases-recovery” phenomenon when the coal cracks and cracks propagation. And in this process, the UFIQ will appear the corresponding “rise-recovery” phenomenon. At the same time, the fracturing process is divided into three stages according to the variation law of UFIQ in the HF process: liquid filling stage, energy storage and coal cracking cycle stage, and stop cracking stage. In addition, through the arrangement of holes stress gauges around the fracturing hole, it is found that the transfer of disturbance stress formed in the coal mass due to HF behavior is mainly attenuation, and its change stage in the whole HF process is mainly divided into the original stress stage, the stress response stage, and the stress stabilization stage. These results inform the design and optimization of fracturing parameters in hydraulic fracturing processes and aid in understanding the mechanisms of earthquake induction by HF.

The technology of continuously welded rails (CWRs) is important in modern railway track structures. To measure rail stress, resistance strain gauges are preferred due to their good stability, sensitivity, and resistance to external interference. Based on the bi-directional strain method, we present a new method for measuring longitudinal rail stress using resistance strain gauges and develop a monitoring device for rail stress to realize long-term and multi-point measurement. Also relevant experimental verification and analysis are conducted. Results indicate that under various constraints the rail stress–strain values can be calculated just with the measured total longitudinal strain and total vertical strain. Considering the measurement error caused by sectional feature of sensors, we put forward a correction equation applicable to different stress conditions. Although the temperature values of the four full-bridge stress gauges can offset each other, the measurement error caused by rail flexural strain can also be eliminated to a certain extent at the same time, the non-uniform distribution of rail cross section temperature and unbalanced flexural strain still affect the measurement error. The experimental results also show that the developed rail-stress-monitoring sensor is suitable for measuring rail stress with reliable working performance.

In this paper, a static load test and a multiparameter statistical analysis method are used to study the value of pile side friction in different soil layers in a loess region. Currently, static load testing is the most commonly used method to determine the bearing capacity of pile foundation. During the test, a vertical load is applied at the top of the pile, the data under each load level are recorded, and a Q-S curve is drawn to obtain the ultimate bearing capacity of a single pile. Reinforcement stress gauges are installed at different sections of the pile body, and then the axial force and the pile side friction of each section are calculated. Few studies have investigated the calculation of pile side friction in different soil layers using the multiparameter statistical analysis method. Obtaining accurate results using this method will provide an important supplement to the calculation of pile side friction and will also be conducive to the development of theoretical calculation of pile side friction. Therefore, taking Wuding Expressway project in loess region as an example, the lateral friction resistance of six test piles is studied through static load testing and multiparameter statistical analysis. The multiparameter statistical analysis method is compared with the static load test results, and the error is controlled within 20%. The results show that the calculation results of multiparameter statistical analysis essentially fulfill engineering requirements.

Two sets of shock compression tests (i.e. conventional and reverse impact) were conducted to determine the shock response of two rock materials using a plate impact facility. Embedded manganin stress gauges were used for the measurements of longitudinal stress and shock velocity. Photon Doppler velocimetry was used to capture the free surface velocity of the target. Experimental data were obtained on a fine-grained marble and a coarse-grained gabbro over a shock pressure range of approximately 1.5-12 GPa. Gabbro exhibited a linear Hugoniot equation of state (EOS) in the pressure-particle velocity (P-up) plane, while for marble a nonlinear response was observed. The EOS relations between shock velocity (US) and particle velocity (up) are linearly fitted as US = 2.62 + 3.319up and US = 5.4 85 + 1.038up for marble and gabbro, respectively. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’.

Double-cutting top-retention mining is one of the important directions for sustainable coal development, and its mining-induced overburden fissure evolution law determines the response of unloading gas extraction projects. This paper used physical analog modeling experiments to compare and analyze the overburden fissure evolution laws induced by double-roof-cutting and conventional mining methods. The results show that double-cutting roof alley mining has a significant controlling effect on roof decompression, settlement, and fissure development, and the basic roof subsidence of the interlayer after cutting the roof is small, with the maximum subsidence of 9.85 mm; the rock layer after the roof collapse in conventional mining is more fragmented, and the range of fissure development is larger than that in double-roof-cutting with retained roadway conditions, having the maximum subsidence of 13.65 mm. The latter achieves a more uniform overall settlement by decompressing the roof and making the angle of collapse, fissure development height, and width smaller than under conventional mining. The double-roof-cutting mining reduces the degree of stress concentration in the surrounding rock, promotes the settlement of the roof and the time of the first pressure, improves the stability of the roadway, and forms an effective gas transport channel through the roof slit. Highlights The characteristics of overlying rock breaking movement after double-roof-cutting retaining roadway mining and conventional mining are studied, and the differences of overlying rock caving characteristics are analyzed. The stress evolution of roof and coal seam is monitored by stress gauge, and the stress evolution law caused by roof settlement in mining process is analyzed. Digital speckle technique is used to characterize the subsidence of overburden after mining. The distribution characteristics of fracture network in mining overburden rock are analyzed qualitatively and quantitatively by using fracture number and fractal dimension. The extraction parameters of directional goaf with high and low placement of filling lane in 4502 working face of Shaqu No. 1 Coal mine are tested, and the experimental conclusions are verified.

This study takes three roadways with similar burial depths in different strata in Xieqiao Mine of Huainan as its research object. This study involves the observation and analysis of borehole stress gauge data under the influence of mining pressure. The observation data show that: (1) under the influence of mining, the high-wall vertical stress increases as the distance from the roadway surface increases, and the peak point is at 6 m. The increment value of vertical stress at the low side has a maximum value at 8 m and a peak value at 14 m. The increase value of horizontal stress of the high side has two peaks, which are 4 m and 6 m, respectively. The increment of horizontal stress in low walls is also about 8 m. (2) The mining influence range of working face mining is about 150 m. Mining influence distance can be divided into three stages: 0–25 m, 25–60 m, and beyond 60 m. The increase of vertical and horizontal stress caused by mining increases sharply within 25 m from the working face. (3) The buried depth of the roadway has an influence on the range of mining influence and the increase of mining stress caused by working face mining. The more the buried depth of the roadway increases, the greater the range of mining influence and the increased value of mining stress. (4) After roadway excavation, the surface deformation of roadway surrounding rock reduces the increase of mining stress near the roadway surface. The mutual verification between the analysis results and theoretical calculation results is helpful to roadway support design and advanced support design of the working face.

Concrete stress is an important item of dam safety monitoring. The stress of dam body can be mastered and the safety degree of dam can be estimated through systematic monitoring and analysis of the stress and strain of concrete. Non-stress gauge, as well as a strain gauge group, is used to monitor the stress and strain of concrete dams. The stress-free strain of concrete can be obtained by utilizing a non-stress gauge, which is the basis for stress analysis. Results of stress-free monitoring are influenced by surrounding environments, instrument structure, and installation method. Finite element numerical simulation and meso-mechanical methods are used to study factors, such as non-uniform temperature field around the gauge, stiffness of a bucket, and aggregate state of concrete. Results show that the stiffness of bucket and non-uniform temperature field slightly influence the results of non-stress strain measurements. In addition, when the aggregate content is the same, the influence of the aggregate distribution is less. However, extra-large aggregate removal method significantly influences the monitoring results. The influence of the removal method on the stress analysis to monitor the data of the strain gauge group is evaluated using an example. Recommendations to deal with extra-large aggregate in the installation of non-stress gauges are presented.