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Cracks, broadly defined as compliant discontinuities, are a major cause of elastic anisotropy. However, few models are available for quantifying crack properties relevant to anisotropy. We developed a rock-physics model to quantify crack angular distribution and normal-to-tangential compliance ratio from pressure-dependent acoustic velocities measured in the laboratory. Our model uses a rectangular function of variable width and amplitude to extract the maximum dip angle of cracks, which is a direct quantification of crack alignment relative to the bedding plane. We tested the model on an organic-rich shale data set and confirmed that crack alignment and compliance ratio strongly impact Thomsen anisotropy parameters, thus demonstrating the model as a useful tool for better understanding how cracks affect elastic anisotropy.

From geochemical reactions to proppant emplacement, hydraulic fracturing induces various chemomechanical fracture alterations in shale reservoirs. Hydraulic fracturing through the injection of a vast amount and variety of fluids and proppants has substantial impacts on fluid flow and hydrocarbon production. There is a strong need to improve our understanding on how fracture alterations affect flow pathways within the stimulated rock volume and develop monitoring tools. We have conducted time-lapse rock-physics experiments on clay-rich (carbonate-poor) Marcellus shales to characterize the acoustic velocity and permeability responses to fracture acidizing and propping. Acoustic P- and S-wave velocities and fracture permeability were measured before and after laboratory-induced fracture alterations along with microstructural imaging through X-ray computed tomography and scanning electron microscopy. Our experiments indicate that the S-wave velocity is an important geophysical observable, particularly the S-wave polarized perpendicular to fractures because it is sensitive to fracture stiffness. The acidizing and propping of a fracture decrease its elastic stiffness. This effect is stronger for acidizing, so it is possible that proppant monitoring will be masked by chemical alteration except when propping is highly efficient (i.e., most fractures are propped). However, fracture permeability is undermined by the softening of fracture surfaces due to acidizing, while being greatly enhanced by propping. These contrasting effects on fluid flow in combination with similar seismic attributes indicate the importance of experiments to improve existing rock-physics models, which must include changes to the rock frame. Such improvements are necessary for a correct interpretation of seismic velocity monitoring of flow pathways in stimulated shales.

The transition to a low-carbon future involves every component of our productive life — from the energy we use, to the buildings we construct, to the materials we use in our daily lives. Realistically, the shift onto a low-carbon path cannot happen instantly but requires adopting short- and long-term solutions while assessing whether the solutions work in the physical world in which we live. In the short term, incremental technological improvements, such as transitioning to energy sources like natural gas, have the potential to yield immediate benefit to air quality and pollution. In the mid and long term, however, more far-reaching decarbonization technologies must be pursued to achieve game-changing outcomes. In the geosciences realm, leading technologies span from cleaner energy solutions to exploring alternative earth-inspired materials and processes. These include CO2 storage in geologic disposal sites along with its reuse for material manufacturing, the development of enhanced geothermal systems expanding the use of geothermal energy, and adapting subsurface processes to engineer greener processes and materials through geomimicry. In this landscape, experimentation and rock physics are at the crux of understanding rock-fluid processes and are the premise and foundation of decarbonizing our future. All of these applications require experimentation for wider public acceptance to avoid hasty solutions that are counterproductive. The cross-disciplinary nature of each endeavor is pivotal in assessing how processes induced by fluids, their chemistry, and thermal capacity affect the physical and mechanical properties of treated environments. This paper provides an account of the role that rock physics will play in leveraging knowledge across the nanosciences to underpin our path to a decarbonized future through chemical and thermal stimulation practices, solid-CO2 reactions, and engineering processes that manipulate geology to produce materials with functional properties.

Effective water and nitrogen (N) management strategies are critical for sustainable agricultural development. Lysimeter experiments with two deep percolation rates (low percolation and high percolation, i.e., LP and HP: 3 mm d−1 and 5 mm d−1) and five N application levels (N0~N4: 0, 60, 135, 210 and 285 kg N ha−1) were conducted to investigate the effects of controlled drainage on water productivity (WP) and N use efficiency (NUE) in water-saving irrigated paddy fields. The results demonstrated that NH4+-N and NO3−-N were the major components of total nitrogen (TN) in ponded water and leachate, accounting for more than 77.1% and 83.6% of TN, respectively. The risk of N leaching loss increased significantly under treatment of high percolation rates or high N application levels. High percolation loss required greater irrigation input, thus reducing WP. In addition, N uptake increased with increasing N application, but fertilization applied in excess of crop demand had a negative effect on grain yield. NUE was affected by the amount of N applied and increased with decreasing N levels. Water and N application levels had a significant effect on N uptake of rice, but their interaction on N uptake or NUE was not significant. For the LP and HP regimes, the highest N uptake and WP were obtained with N application levels of 285 kg ha−1 and 210 kg ha−1, respectively. Our overall results suggested that the combination of controlled drainage and water-saving irrigation was a feasible mitigation strategy to reduce N losses through subdrainage percolation and to provide more nutrients available for rice to improve NUE, thus reducing diffuse agricultural pollution. Long-term field trials are necessary to validate the lysimeter results.

Excess soluble salts in the soil and irrigation water creates difficulties for plant growth and lowers nutrient availability in the soil. Organic ameliorants such as biochar are believed to be one ...

Salt rock is a polycrystalline material of interest for geostorage because of its low permeability and potential to self-heal by pressure solution at favorable stress and temperature conditions. It is often assumed that microcrack propagation and healing lead to isotropic stiffness changes. The goal of this study is to check this assumption and to gain a fundamental understanding of the mechanisms that control the accumulation of damage and irreversible deformation. Cyclic axial loading tests are performed under a confining pressure of 1 MPa on synthetic salt rock generated by thermal consolidation. The stress–strain curves and the microstructure images taken at key stages of the cycles reveal the formation of a complex system of sliding and wing microcracks, the orientation of which is loading dependent. We interpret the mechanisms that control the coupled evolution of crack families by a discrete wing crack elastoplastic damage (DWCPD) model. Crack propagation is controlled by Mode I and Mode II fracture mechanics criteria. Sliding “main” cracks grow if a cohesive frictional criterion is met, while the wing cracks propagate in tension. Displacement jumps at crack faces are related to the deformation of the rock representative elementary volume (REV). The DWCPD model can capture the nonlinear stress–strain relationship and the degradation of stiffness during the loading cycles. Simulations show that microcracks occur following two stages: (1) wing cracks initiate and main cracks do not propagate; (2) wing cracks and main cracks then propagate simultaneously. Higher friction at the crack faces leads to higher strength. With a larger cohesion, salt rock strength increases, damage development is delayed and exhibits a stick-slip evolution. At higher confinement, the initiation of wing cracks is delayed, which results in an increase of strength. The damage rate is higher in specimens that are damaged prior to compression than in the ones that are not. The proposed DWCPD model can be extended to any polycrystalline semi-brittle material, and can be applied to understand the formation of crack patterns in geostorage facilities.

Understanding salinity and fertilizer interaction is of great importance to improve crop production and fertilizer use efficiency in saline areas. To evaluate the interactive effects of different soil salinity levels and nitrogen (N) applications rates on the sunflower photosynthetic characteristics of N uptake and N use efficiency, a two-year field experiment was conducted in Hetao Irrigation District, China. The experiment consisted of three initial salinity (IS) levels expressed as the electrical conductivity of a saturated soil extract (ECe) (S0: 1.72–2.61 dS/m; S1: 4.73–5.90 dS/m; S2: 6.85–9.04 dS/m) and four N rates (45, 90, 135, and 180 kg/ha), referred as N0–N3, respectively. The results indicated that the net photosynthetic rate (Pn) of sunflowers treated with S0 and S1 levels both had a significant decrease in the bud stage, and then reached their maximum at anthesis. However, during the crop cycle, the Pn at S2 level only had small fluctuations and still remained at a high level (>40 μmol CO2/(m2 s)) at the early mature stage. When increasing IS levels from S0 to S1, the plant N uptake (PNU) under the same N rates were only decreased by less than 10% at maturity, whereas the decline was expanded to 17.2–45.7% from S1 to S2. Additionally, though applying the N2 rate could not increase sunflower PNU at the S0 and S1 levels, its N use efficiency was better than those under N3. Meanwhile, at the S2 level, the application of the N0 rate produced a higher N productive efficiency (NPE) and N uptake efficiency (NUPE) than the other N rates. Therefore, our study proposed recommended rates of N fertilizer (S0 and S1: 135 kg/ha, S2: 45 kg/ha) for sunflowers under different saline conditions.

Casing deformation is the most significant problem while developing Longmaxi shale gas formation in Sichuan Basin, southwest China. In one of the operating acreages with 72 horizontal wells, 38 wells encountered casing deformation problems after several stages of hydraulic fracturing treatments. Tremendous lateral lengths were affected, among which some of them were treated with diversion technology during fracturing and some others were simply abandoned. Previous research explores this problem from perspectives of cementing, casing strength and etc. However, after combining all the data, we found that it is likely due to formation slip. In this research, we summarized all the casing deformation positions happened in the area of interest. We then project these positions into the ant-tracking plot. It is found that most of the deformed positions correspond to the fault positions in the ant-tracking plot. Further, we run caliper logs for some of the wells. From the images of the deformed positions, it can be inferred that the casing deformation is due to the formation shear. Based on what we found, we set up a model for fault slip potential. This model is based on Mohr-Coulomb (MC) failure criteria. We use this model to analyze the natural fractures observed from an FMI log. It is found that the increase of pore pressure from hydraulic fracturing jobs can cause natural fractures to slip. However, it cannot cause beddings to slip, which some of the previous research has suggested. The data and analysis in this research confirm that casing deformation in Longmaxi shale formation is caused by fault slip. Other reasons, like voids in cement bond, lithological layers, are not detrimental to this problem. In the end, we presented a method for continuing treatment when casing deformation happens. This method has been utilized in field, and significant downtime is reduced.

Summary The extremely low permeability of many tight formations has required hydraulic and acid fracturing which introduce both geochemical and mechanical alterations to reservoir rock. There is an increasing need to effectively monitor those changes in situ for both economic and environmental considerations. We have been conducting engineering geophysics experiments to enhance the interpretation of hydraulic fracturing by characterizing acoustic velocity of propped and acidified fractures as well as acoustic emissions occurring upon chemo-mechanical rock deformation. Our experiments show that P- and S-waves are affected differently, with S-wave velocity being particularly prone to geochemically altered and propped fracture zones. Acoustic emission accounts only for a small portion of the total energy released from rock fracturing process.

The coupled operation of fracture, diffusion, and intracrystalline-plastic micromechanisms during semibrittle deformation of rock is directly relevant to understanding crustal processes such as ear...

The consolidation coefficient is the most basic parameter to calculate the consolidation rate of soil layer, and the horizontal consolidation coefficient controls the radial water flow into the drainage well. Based on the background of the soft soil in Shantou, Guangdong Province, a series of experimental studies on the consolidation characteristics were carried out by using the modified consolidation instrument. And the concept of the composite consolidation coefficient of the drained water body was put forward. The composite consolidation coefficient reflects the consolidation characteristics of soft soil with drainage water, The test results showed that: 1) The consolidation test with drainage plate is basically consistent with the load compression curve, but its consolidation rate is fast, which is reflected by the composite consolidation coefficient. 2) In the consolidation test of water bodies with drainage, the vertical consolidation coefficient and radial consolidation coefficient are calculated by “three-point method”, and then the composite consolidation coefficient is obtained. The composite consolidation coefficient decreases with the increase of drain spacing ratio, effective drainage diameter and drainage height, which is basically consistent with the theoretical formula. 3) The vertical consolidation coefficient and radial consolidation coefficient decrease with the increase of the diameter of the sample, and the difference is obvious when the load is large. The large-size model with a diameter of 100 mm and a height of 100 mm is about 1.35 times of the vertical consolidation coefficient of the conventional consolidation test.

Every year, a large amount of silt is generated by river dredging. For the characteristics of dredging silt, such as high moisture content, low strength and high compressibility, the traditional solidification method can no longer better solve this kind of silt problem. This paper mainly studies the fluidized solidification treatment of high water content sludge, not only makes the silt soil achieve a good solidification effect, but also the project cost is lower, the construction method is more environmentally friendly and green. The influencing factors of the solidified soil are mainly investigated by the unconfined compression test and the fluidity test. The experiment result shows 1)When the cement to sludge mass ratio (RCS) is 0.09 - 0.16 and the fly ash to cement mass ratio (RFC) is 0.35 - 0.80, as the amount of RFC increases, the flow rate of the solidified soil gradually decreases. With the increase of time, the liquidity is significantly reduced, and the influence of cement on the fluidity is greater than that of fly ash. 2) When RCS = 0.09 - 0.16, the strength of the sludge solidified soil at 28 d age increased by 4.5 - 6 times. 3) When RCS = 0.09 - 0.16 and RFC = 35% - 80%, the intensity of 14 d increased by 1.23 times than that of 7 d, and the intensity of 28 days increased by 1.29 times than that of 14 d. This experiment can provide the mix ratio design of solidified materials for different needs of the project, which can better provide a basis for engineering application and strength prediction.

In order to explore the effects of moisture content and plasticity index on Duncan-Chang model parameters K,n, C and Rf, we selected 8 groups of soft soil with water content of 69.1% - 94.3% and plasticity index of 32.2 - 54.1 for triaxial unconsolidated undrained shear test. The results show that Cuu, K and n values all showed a downward trend, and Rf variation was not obvious with the increase of moisture content. The variation rule of each parameter is not obvious with the increase of plasticity index. When moisture content is constant, Cuu and n values do not change much, K increases with the increase of plasticity index within the range of 70% - 80% moisture content, and does not change much with the increase of plasticity index when moisture content is greater than 80%, Rf has no obvious rule. When the plasticity index is constant, Cuu, Kand n decrease with the increase of moisture content, Rf has no obvious rule. The maximum value of Cuu is 20.18 kPa, the minimum is 3.72 kPa, and the maximum to minimum ratio is 5.42. The maximum value of K is 0.517, the minimum is 0.022, and the maximum to minimum ratio is 23.5. The maximum value of n is 1.198, the minimum is 0.150, and the maximum to minimum ratio is 7.99. The maximum value of Rf is 0.872, the minimum is 0.679, and the maximum to minimum ratio is 1.28.

Parallel and orthogonal tests are used to explore the influence law of the dosage and age of curing agent on the strength of solidified sludge. The test results show that: 1) The strength of solidified sludge is mainly related to the cement content and dry soil content, and presents a good linear relationship. The influence of gypsum content is not significant. As the age increases, the strength is greatly affected by the cement content. 2) At different ages, the unconfined compression strength of solidified sludge presents a linear relationship, and the change law of later strength can be predicted by early strength. 3) Degree of influence of curing agent dosage: cement dosage > gypsum dosage > dry soil dosage. The optimal mixture ratio is 8% of cement content, 30% of gypsum content (proportion of cement content), and 4 times of dry soil content (multiple of cement content).

In order to solve the brittle failure of cement flowing solidified sludge, basalt fiber and cement are mixed to prepare flowing solidified sludge. The fluidity and unconfined compressive strength tests of fluid solidified sludge with different cement and fiber content have been carried out. The results show that mixing basalt fiber into cement solidified fluid sludge will reduce its fluidity and increase its unconfined resistance Compressive strength; there is an optimal amount of basalt fiber, and its optimal amount is affected by the amount of cement; with the increase of curing age, the compressive strength of the sludge solidified with fiber cement increases gradually; the solidified sludge is unconfined for 14d and 28d The unconfined compressive strength has a linear relationship with the 7d unconfined compressive strength.

This paper takes the construction of a foundation pile project in Wenzhou as an example. Through indoor experiments, the law of squeezing soil stress with time and space and the dissipation of pore water pressure during the process of pile driving are studied. The test results show that (1) the static pressure of pipe pile driving has a good exponential increase relationship with the pile penetration depth; (2) the pile bottom pressure and radial squeezing soil pressure have a linear relationship with the pile penetration depth; (3) the radial earth pressure increases with the static pressure on the top of the pile during pile sinking, while decreases during unloading; the increment of radial earth pressure decreases with the increase of the distance between the pile and the measuring point, and the radial squeezing range can be determined according to the increase ratio of the radial earth pressure; (4) the ratio of the excess pore water pressure to the distance from the measuring point to the pile diameter decreases exponentially.

This article is based on a pile foundation project in Wenzhou City, combined with construction site monitoring data, and established a finite element model to analyze the soil squeezing displacement caused by the construction of PHC pipe piles in deep silt sites, as well as the displacement of different sizes of digged holes on the surface impact. When the distance from the pile position to monitoring point is 35 times of the pile diameter, the field test results show that the horizontal displacement and velocity change of the soil caused by the pile foundation construction decrease with the buried depth, and the main influence range is within the buried depth of 0-14 m. Numerical simulation results show that: (1)without digged hole, the main influence range of the main soil squeezing displacement is about 8 times of pile diameter; (2)the larger the diameter of the digged hole, the smaller the displacement and the influence range of the affected soil on the surface; (3)The ground squeeze displacement caused by the pile construction attenuates in a power function with the distance from the pile position to the measuring point.

Based on the treatment of dredger fill soft soil foundation in Eastern Shantou, Guangdong Province, consolidation theory and numerical simulation based on composite consolidation coefficient are used to study the consolidation characteristics of dredger fill soft soil, and the results are compared with the field monitoring results. The calculation results show that the theoretical consolidation degree of the site is 93.4%, which is basically consistent with the final consolidation degree of field monitoring. In the first two stages of surcharge loading, field monitoring is faster than theoretical calculation. The field monitoring value of the final settlement is 1342 mm, which is about 10% less than the theoretical value. The final average consolidation degree of the two models is 97.9%, which is 4.7% more than the field monitoring value. The results show that the pore water pressure law is obvious, the dissipation rate is about 16% higher than the field monitoring value, and the consolidation effect is more obvious. The numerical simulation of the composite coefficient model has certain applicability and can be used to guide the design and construction of similar projects.

Based on an example of a project in Tangshan, the high-rise buildings are built in karst area and mined out affected area which is treated by high pressure grouting, and foundation is adopted the form of pile raft foundation. By long-term measured settlement of high-rise buildings, It is found that foundation settlement is linear increase with the increase of load before the building is roof-sealed, and the settlement increases slowly after the building is roof-sealed, and the curve tends to converge, and the foundation consolidation is completed. The settlement of the foundation is about 80% - 84% of the total settlement before the building is roof-sealed.Three layer BP neural network model is used to predict the settlement in the karst area and mined affected area.Compared with the measured data, the relative difference of the prediction is 0.91% - 2.08% in the karst area, and is 0.95% - 2.11% in mined affected area. The prediction results of high precision can meet the engineering requirements.

As urban land use is relatively tight, the rational use of sludge landfills has become a problem that must be solved. Because the sludge has the characteristics of high water content, poor permeability, strong flocculation, high combined water content, and high organic matter content, the traditional vacuum preloading method, stacking preloading method and other curing methods are too inefficient and can not meet engineering requirements. In this paper, an indoor electroosmosis drainage consolidation test was designed for sludge in a sludge landfill area in Shenzhen. The test results show that the reasonable drainage method, stacking method and shortening the electrode spacing increase the strength of solidified sludge by 1.1 times, 1.6 times and 2.8 times. The water content is reduced by 19.8%, 25.5% and 55.6%.The drainage rate is linear with the current.