Unconsolidated Soil Research Articles

Optimization of pre-grouting construction and evaluation of grouting effect in a deeply buried silt-filled shield tunnel

Controlling strata deformation during shield tunneling beneath unconsolidated soil layers poses a significant challenge in engineering construction. Limited research exists on optimizing pre-grouting mechanisms for shield tunnels in unconsolidated soil layers and controlling strata deformation. Therefore, conducting on-site optimization experiments for pre-grouting is crucial for controlling strata deformation. The paper employs crushed stone aggregate as a basis for modifying the shield jacket material. The primary method of verifying grout strength involves direct detection of foundation bearing capacity using a heavy-duty probe inside the tunnel. The feasibility of the comprehensive evaluation scheme is further confirmed through a combination of multi-point core sampling, five-point water pressure tests, and on-site shield monitoring data. The research results indicate that this technology effectively enhances the stability of deep-buried weak strata. By improving the physical and mechanical properties of backfill soil through a combination of crushed stone-cement slurry-soil skeleton, the self-stabilizing ability of surrounding rock is enhanced, and strata deformation is controlled. Additionally, a set of pre-grouting reinforcement and evaluation techniques suitable for deep-buried weak strata is proposed, providing valuable references for similar projects.

A Practicable Guideline for Predicting the Thermal Conductivity of Unconsolidated Soils

For large infrastructure projects, such as high-voltage underground cables or for evaluating the very shallow geothermal potential (vSGP) of small-scale horizontal geothermal systems, large-scale geothermal collector systems (LSCs), and fifth generation low temperature district heating and cooling networks (5GDHC), the thermal conductivity (λ) of the subsurface is a decisive soil parameter in terms of dimensioning and design. In the planning phase, when direct measurements of the thermal conductivity are not yet available or possible, λ must therefore often be estimated. Various empirical literature models can be used for this purpose, based on the knowledge of bulk density, moisture content, and grain size distribution. In this study, selected models were validated using 59 series of thermal conductivity measurements performed on soil samples taken from different sites in Germany. By considering different soil texture and moisture categories, a practicable guideline in the form of a decision tree, employed by empirical models to calculate the thermal conductivity of unconsolidated soils, was developed. The Hu et al. (2001) model showed the smallest deviations from the measured values for clayey and silty soils, with an RMSE value of 0.20 W/(m∙K). The Markert et al. (2017) model was determined to be the best-fitting model for sandy soils, with an RMSE value of 0.29 W/(m∙K).

The evolution of gully erosion in the Rift Valley of Kenya over the past 50 years

Gullies are common in areas of unconsolidated deposit soil, and relatively steep-sided erosion that spread quickly in depth and width over short periods may occur during heavy or extended rainfall and. Soil erosion has been recognized as the major cause of land degradation worldwide, especially in the East African Rift Valley of Kenya where thick layers of volcanic ash have been deposited. This paper reports the results of studying the evolutionary process of gully erosion and types of gullies in the East African Rift Valley in Kenya over the last 50 years using remote sensing images, field investigations, and UAV (Unmanned Aerial Vehicle) aerial photography. Forward expansion, backward expansion, new gullies, and road culvert gullies were classified according to their morphological evolution characteristics and then identified throughout the history of the valley over the past 50 years. The erosion length increase from forward expansion was the largest of the four categories, followed by backward expansion, new gullies, and road culvert gullies. Human activity and rainstorms are the main factors of gully erosion in the study area. Additionally, four types of gullies were also categorized according to their causes of formation via field investigation and testing: physically-induced gullies, artificially-induced gullies, pipe erosion-induced gullies, and fissure-induced gullies, and artificially-induced and fissure-induced gullies were the most common type of gully in the study area. The evolution of gullies poses a serious threat to the ecological environment since it can lead to grassland degradation, segmentation of landscape ecology, and the erosion of the survival environment of wildlife. In this regard, man-made and fissure-caused gullies are the most severe and should be investigated further.

Evaluation of the impact of transition from porous to fractured rock media on 3D field-scale DNAPLs contamination

A 3D high-resolution subsurface characteristic (HSC) numerical model to assess migration and distribution of subsurface DNAPLs was developed. Diverse field data, including lithologic, hydrogeologic, petrophysical, and fracture information from both in situ observations and laboratory experiments were utilized for realistic model representation. For the first time, the model integrates hydrogeologic characteristics of both porous (unconsolidated soil (US) and weathered rock (WR)) and fractured rock (FR) media distinctly affecting DNAPLs migration. This allowed for capturing DNAPLs behavior within US, WR, and FR as well as at the boundary between the media, simultaneously. In the 3D HSC model, hypothetical 100-year DNAPLs contamination was simulated, quantitatively analyzing its spatiotemporal distributions by momentum analyses. Twelve sensitivity scenarios examined the impact of WR and FR characteristics on DNAPLs migration, delineating significant roles of WR. DNAPLs primarily resided in WR due to low permeability and limited penetration into FR through sparse inlet fractures. The permeability anisotropy in WR was most influential to determine the DNAPLs fate, surpassing the impacts of FR characteristics, including rock matrix permeability, fracture aperture size, and fracture + rock mean porosity. This study first attempted to apply the field-data-based multiple geological media concept in the DNAPLs prediction model. Consequently, the field-scale effects of WR and media transitions, which have been often overlooked in evaluating DNAPLs contamination, were underscored.

Assessing the liquefaction potential of seabed soils based on ocean ambient noise in the Yellow River Delta

Seabed soils can undergo liquefaction under cyclic loading, resulting in a rapid decrease in strength and stiffness, which may lead to the destruction of offshore structures. Therefore, the assessment of seabed soil liquefaction will become an important factor in disaster prevention and risk analysis in coastal and offshore engineering construction. In this study, the ocean ambient noise with low-frequency, long-wavelength, and wide-band characteristics was used to conduct and analysis noise based on the horizontal-to-vertical spectral ratio method. The shear wave velocity of the seabed soil was obtained by inverting the ocean ambient noise dataset. Then, we proposed a shear wave velocity threshold that can be used for liquefaction assessment of Holocene unconsolidated fine-grained soils by statistical analysis, and the liquefaction potential of the soils was evaluated according to 1-D shear wave velocity structures and 2-D shear wave velocity profiles. The results showed that the distribution of the shear wave velocity obtained by inverting ocean ambient noise was generally consistent with the measured shear wave velocity in the field, indicating that the inversion results have a certain degree of accuracy. A shear wave velocity threshold of 200 m/s was proposed for liquefaction assessment, determining that the soils within 0-10 m depth in the coastal area of Yellow River Delta have liquefaction potential. This result is in accordance with the assessment based on the critical shear wave velocity, indicating that this threshold is applicable to the assessment of seabed soil liquefaction in the Yellow River Delta. The in-situ observations of ocean ambient noise provide a more convenient, economical, and environmentally friendly method, which can help to investigate marine geology disasters and serve marine engineering construction.

Seasonal Variations of Soil Thermal Conductivity at the InSight Landing Site

AbstractThe heat flow and physical properties package measured soil thermal conductivity at the landing site in the 0.03–0.37 m depth range. Six measurements spanning solar longitudes from 8.0° to 210.0° were made and atmospheric pressure at the site was simultaneously measured using InSight's Pressure Sensor. We find that soil thermal conductivity strongly correlates with atmospheric pressure. This trend is compatible with predictions of the pressure dependence of thermal conductivity for unconsolidated soils under martian atmospheric conditions, indicating that heat transport through the pore filling gas is a major contributor to the total heat transport. Therefore, any cementation or induration of the soil sampled by the experiments must be minimal and soil surrounding the mole at depths below the duricrust is likely unconsolidated. Thermal conductivity data presented here are the first direct evidence that the atmosphere interacts with the top most meter of material on Mars.

Geophysical performance of subsurface characterization for site suitability in construction purpose

Geophysical investigations are indirect methods of characterization of subsurface materials. Detailed information about the underlying subsurface is essential in preventing foundation failure and comprehending ground conditions. Seismic refraction is the most commonly used method for site characterization. Most researchers use this method with borehole data to investigate the subsurface. However, it is not adequate to rely on one method. To achieve an optimum result, it is best to apply different techniques and, as far as possible, integrate their results. The research aims to identify the shallow subsurface using geophysical techniques, correlate the results with the borehole data, estimate the rippability of rocks based on seismic velocity, and recommend a suitable foundation depth. 2D resistivity and seismic refraction methods were employed. Results show two resistivity zones. The lower resistivity zone (1–700 Ωm) comprises the loose and weathered zone, and the higher resistivity zone (700–4000 Ωm) indicates a more competent and compacted zone. The seismic interpretation reveals three subsurface layers. The first layer has an average velocity of 300–1600 m/s, indicating loose and unconsolidated soil with low N-values. The second layer (1600–2900 m/s) is interpreted as a stiffer and more competent layer. The third layer (2900–3800 m/s) is the most competent layer characterised by its high stiffness, and high N-values. The depth of rippable materials changes across sections, ranging from subsurface to a depth of 5 m. A marginal zone between rippable and non-rippable materials exists at a depth of 5–13 m. Non-rippable materials are below the depth of 13 m. The combined approaches' findings indicate that the area has the sufficient bearing capacity and is acceptable for construction; this will be considered when designing and constructing structures.

GIS-based landslide susceptibility zonation and risk assessment in complex landscape: A case of Beshilo watershed, northern Ethiopia

Landslides necessitate comprehensive prediction of susceptible zones for timely intervention to mitigate any disaster. Present study at Beshilo-watershed in Amhara Regional State of Ethiopia was attempted to prepare landslide susceptibility zonation (LSZ) map and to carry out risk assessment. GIS-based multi-criteria decision analysis was adopted by considering factors; land-use/land-cover, slope, elevation, aspect, drainage-density, rainfall, lithology, lineament/fault density, soil depth, and texture. Factor weights were determined through Analytical Hierarchy Process (AHP) and the factor classes rating were assigned through logical judgment. Landslide susceptibility indices were determined based on a continuous numerical scale developed for this purpose. Very high and high susceptibility zones were found to spread in 1215.28 km2 and 2279.87 km2, respectively in the eastern and north-eastern parts that are characterized by high lineament/fault density, barren lands, shrubs, bushes, grassland, or croplands mostly having unconsolidated soils with shallow depth. The Receiver Operating Characteristics (ROC) curve showed acceptable results. Further, risk assessment indicated that populations in high to very high-risk zones need timely attention of the local authorities to avert any unwanted happenings.

Infiltration Assessments on Top of Yungang Grottoes by Time-Lapse Electrical Resistivity Tomography

Water plays a vital role in the weathering process of grottoes. Precipitation is a main water source in the grotto hosting mountain rock. In this study, time-lapse electrical resistivity tomography was adopted to track the movement of infiltrated water in a profile in the Yungang Grottoes. Our one-year monitoring data indicated a good resistivity response to rainfall in the shallow unconsolidated soil layers. There were only resistivity decreases in the near surface 5 m across the whole monitoring profile, and resistivity values quickly returned to a neutral state after the rain stopped. Based on the analysis of a typical rainfall event during the rainy season, we found that the infiltrated water cannot continuously move downwards to recharge local groundwater. It moves horizontally to a nearby gully due to the existence of a hydraulic conductive fine sand layer and low permeable mudstone and sandstone base rocks. An artificial infiltration experiment was carried out to further verify the fate of infiltrated water. Based on mass balance analysis, with 10 m3 of infiltrated water, it only saturated dry soil in the top 1.36 m soil layer on average and this was roughly consistent with our field borehole wetting front verifications at 1.2 and 1.3 m. There were limited horizontal expansions from the infiltrated water. Therefore, based on our monitoring data and analysis, infiltrated water was not the main source of the water involved in the weathering process of the Yungang Grottoes.

Using InSAR Time Series to Monitor Surface Fractures and Fissures in the Al-Yutamah Valley, Western Arabia

Western Arabia routinely experiences geophysical phenomena that deform the surface of the earth in a variety of ways. These phenomena include earthquakes, volcanic eruptions, sinkholes, and earth fissuring and fracturing. We perform a time-series analysis of interferometric synthetic aperture radar (InSAR) observations derived from the ESA Sentinel-1 radar satellite constellation to map regional surface displacements in western Arabia as a function of time. We rely on InSAR products generated by the JPL-Caltech ARIA project to detect regions with short wavelength anomalies, and then manually reprocess InSAR products at a higher resolution for these regions to maximize spatial and temporal coverage. We post-process InSAR products using MintPy workflows to develop the InSAR time series. We report short wavelength anomalies localized within alluvial valleys across western Arabia and find a 5 cm/year line-of-sight surface displacement within the Al-Yutamah Valley. Part of the observed subsidence is correlated with surface fractures that developed in conjunction with severe rainfall events in regions characterized mainly by alluvial sediments at the surface. Regions of observed subsidence that are not associated with any surface fractures or fissures are correlated with the presence of basalt layers at the surface. Both regions are subject to groundwater exploitation. The observed subsidence is inferred to be driven by groundwater withdrawal perhaps modulated by the presence of a preexisting depositional environment (e.g., paleo-lake deposits) that promotes unconsolidated soil compaction.

Pluri-decennial erosion rates using SUM/ISUM and sediment traps survey in the Mercurey vineyards (Burgundy, France)

Vineyards are often considered to be among the agricultural lands most sensitive to erosion. We used the Stock Unearthing Measurement/Improved Stock Unearthing Measurement (SUM/ISUM) method and sediment traps volume measurements to assess the pluri-decennial erosion rates on a sub-catchment of the Mercurey vineyards in Burgundy, France. The measured erosion rates were compared to local environmental conditions (such as slope, soil type, age of vines, etc.) to discuss the role of driving factors. We found that the mean erosion rate was 21.4 ± 3.1 t.ha−1.yr−1 on vine plots (from −3.2 ± 1.5 t.ha−1.yr−1 to 53 ± 5.8 t.ha−1.yr−1), while sediment accumulation rates in traps varied from 16.6 ± 5.9 (upslope) to 0.13 ± 0.05 (downslope). The measurements were characterized by variable error margins (from 7% to 43% of the measured value) that are directly correlated with erosion rates. Both slope (USLE-LS factor) and age of vines were identified as driving factors of soil erosion. Runoff is the main modality of erosion. The higher erodibility of soil during the first years after plantation (unconsolidated and bare soil); and the regular (every 15 to 20 years) backfilling of eroded plots with soil collected in downslope sediment traps can explain the effect of the age of vines on erosion. In spite of erosion control strategies, the measured rates remain higher than what can be tolerated for sustainable development of agriculture. Therefore, we suggest that the current erosion mitigation strategy should be complemented with other techniques that maintain soils on plots (e.g., grass strips on the interrows, mulching).

Rainfall and Landslide Susceptibility in Hakha Environ in Northern Chin State, Myanmar

This research emphasizes the cause of landslides that occur in Hakha Town and its environ. The main aim is to investigate the distinct phenomena that result in a landslide and to provide suggestions that can reduce the risk of landslide in its prone area. Regarding the two phenomena, natural and man-made, the data on soil, steep slope, monsoon rainfall, pine forest areas, water sources, motor-car road area, population, and houses were collected by field survey, observation, and questionnaires. The collected data were processed and analyzed by using remote sensing methods, qualitative and quantitative methods, and Geographic Information System. According to the results, major causes of the landslides in the study area are found to be due to location lying between 1,830 meters (6,000 ft) and 2,440 meters (8,000 ft) above sea level and establishing of the settlements on steep slopes, receiving plenty of rainfall under the mountain climate with the extremely cold winter season, the existence of unstable and unconsolidated soil and lithology, extending construction of new roads and expansion of the existing roads, population growth and settling of more people in the urban area, and collapsing of big old pine trees. In conclusion, landslides in the study area are found resulting from combined activities of physical factors and human impacts.

Undrained creep behavior of CO2 hydrate-bearing sand and its constitutive modeling considering the cementing effect of hydrates

A technique for carbon dioxide (CO2) capture and storage using CO2 hydrates where CO2 is stored as solid hydrates in the seabed ground, is attracting attention. Shallow sediments may be the most suitable seabed ground for CO2 hydrate storage because these unconsolidated soil sediments satisfy the limitation for the low-temperature condition. Hence, the deformation properties and long-term stability of gas hydrate-bearing sediments during and after gas storage must be investigated. In this study, a series of undrained triaxial creep tests were conducted on artificially made CO2 hydrate-bearing sand specimens to study the fundamental time dependent property of hydrate-bearing sediment. We extended an elasto-viscoplastic constitutive model by introducing a cohesion component and its degradation on surfaces and applied the proposed model to creep tests on gas hydrate-bearing sand.Three findings were obtained from the experiments and modelling. First, CO2 hydrate-bearing sand specimens showed accelerated creep behavior, which was characterized by the creep stress ratio level, regardless of the hydrate saturation. Second, creep accelerated under undrained conditions before the stress reached the critical state line obtained from the monotonic loading tests, and the stress ratio at the occurrence of acceleration creep was higher for specimens with a higher hydrate saturation. Third, the elasto-viscoplastic constitutive model which considered the cementing effect of hydrates was able to well reproduce the undrained creep behavior of hydrate-bearing sand with different hydrate saturations under relatively high creep stress levels.

Surface‐Wave Dispersion in Partially Saturated Soils: The Role of Capillary Forces

AbstractImproving our understanding of the relation between the water content and the seismic signatures of unconsolidated superficial soils is an important objective in the overall field of hydrogeophysics. Current approaches to constrain the water content in the vadose zone from seismic data are based on computing the ratio between compressional and shear wave velocities Vp/Vs. While this allows for the detection of pronounced changes in saturation, such as the groundwater table, it is essentially insensitive to variations in the saturation‐depth profile. Conversely, evidence shows that surface waves are sensitive to both the location of the water table and the saturation‐depth profile. Classic rock physics models are unable to explain the corresponding observations. We propose to estimate surface‐wave signatures accounting for capillary suction effects. We extend the Hertz‐Mindlin model using Bishop's effective stress definition, thus accounting for stiffness changes associated with capillary stresses acting on the soil's frame. We then compute the elastic properties of the partially saturated medium using the Biot‐Gassmann‐Wood model. Considering a 1D unconsolidated porous medium under steady‐state saturation conditions, as given by Richards' equation, we simulate body‐wave travel times and surface‐wave dispersion characteristics for different water table depths and overlying soil textures. Our results illustrate that surface‐wave phase velocity dispersion curves are remarkably sensitive to capillary effects in partially saturated soils, exhibiting velocity changes of up to 20% in the 10–100 Hz frequency range. These effects, which are particularly important in medium‐to fine‐grained soils, are virtually nonexistent in the corresponding Vp/Vs profiles.

A Carica papaya L. genotype with low leaf chlorophyll concentration copes successfully with soil water stress in the field

In the context of increasing drought frequencies, water sensitive plant species need to have defined irrigation thresholds. One such species is papaya (Carica papaya L.), with a current demand for the selection of drought tolerance genotypes. The aim of this study was to evaluate the growth, leaf gas exchanges, sap flow and chlorophyll (Chl) fluorescence in two papaya genotypes (pale-green leaf ‘Golden’ - G and dark-green leaf ‘Aliança’ – AL) under soil water deficit (Ψsoil) conditions. The experiments were carried out in the field, in an unconsolidated alluvial sediment soil type. The two papaya genotypes, contrasting in their leaf Chl contents, were grown under irrigated (I, Ψsoil of -12 kPa), and non-irrigated (NI, Ψsoil gradually diminished from - 23 to -311 kPa) conditions for 41 days. Leaf gas exchanges, xylem sap-flow, green intensity (SPAD index), plant height, trunk diameter and leaf area were measured five times, following Ψsoil decreases. At the lowest Ψsoil (-311 kPa), the Chl photochemistry and fruit number measurements were performed. Intrinsic water use efficiency was higher in the GNI than in the ALNI genotype. Leaf temperature and photochemical efficiency was not affected by soil water restrictions in GNI and ALNI. The water deficit effect on growth traits was linked to whole canopy assimilation, due to the higher leaf area in ALI than GI, or in ALNI than in GNI, once the leaf assimilation rate was similar between those treatments. The ψsoil of ca. -30 kPa can be considered as a threshold for papaya irrigation for the soil type studied here. Soil water stress did not affect the number of fruits in GNI, whilst this was reduced by 83% in ALNI compared to irrigated plants, indicating that pale-green leaf papaya genotypes are an alternative to cope with water stress.

Generalized predictive framework for lateral break-out resistance of submarine pipelines considering nonlinear seabed geometry and consolidation

The ultimate capacity of submarine pipelines under combined vertical and horizontal loading, so-called lateral break-out resistance, is influenced by the change in seabed geometry due to the installation process and subsequent drainage with associated gain in soil shear strength due to consolidation. The majority of existing solutions in the literature and the current design practices for the assessment of lateral break-out resistance are based on small-strain geometry assumptions and the unconsolidated undrained soil response, i.e. without considering the change in seabed geometry due to installation or improvement in shear strength of the surrounding soil due to post-installation consolidation. In this paper, the effects of installation and subsequent consolidation on the combined load carrying capacity of on-bottom pipelines in a soft clay seabed are investigated and quantified in a systematic manner. A large deformation finite element approach coupled with the Modified Cam Clay plasticity model is adopted to simulate the installation of pipelines, and a series of coupled small strain finite element analyses are performed to study the consolidation and break-out response. A comprehensive range of normalised pipe installation depth, preload level and consolidation time period is considered. Results are interpreted using a critical state framework, and expressed in terms of generalized equations for ease of application in engineering design. A predictive methodology is developed for the estimation of combined load capacity of submarine pipelines in soft clay, including the influences of installation, drainage and consolidated strength.

Rainfall-triggered debris flows: triggering-propagation modelling and application to an event in Southern Italy

Debris flows are high-speed and unpredictable phenomena, considered among the main sources of hazard worldwide, since they can affect structures, the economy, and human lives. Rainfall typically triggers these events, causing the flowing of the unconsolidated soil downslope. This work focuses on debris-flow events characterized by multiple triggering areas, which are extremely complex since they involve a spatial sequence of numerous triggers in a relatively small portion of the slope. Numerical modelling of this type of phenomenon can contribute to hazard and risk assessment, which is key to designing effective mitigation structures. In this article, two different models are applied for triggering and propagation, respectively. The former computes the transient pore-pressure changes and the consequent factor of safety variation caused by rainfall infiltration, inducing the triggering of the event. The latter is a depth-averaged numerical model that simulates the event runout, and whose parameters are calibrated through back-analysis. The applicability of the two combined approaches is tested through modelling of an historical event in Southern Italy, which was characterized by large mass releases from multiple triggering zones. Residential areas were hit, suffering serious consequences. Two rheologies are compared to individuate the most suitable propagation model for the study case and obtained results are commented.

Use of X-ray computed tomography for studying the desiccation cracking and self-healing of fine soil during drying–wetting paths

Managed aquifer recharge is an efficient approach using surface water for groundwater recharge. However, soil clogging in the infiltration systems represents a critical problem that reduces the efficiency of recharge systems. In recent years, much research has been conducted to investigate clogging in subsurface and surface soil (cake). Cake prevents infiltration into the water table and can drastically reduce the recharge rate. In arid and semi-arid areas, alternation of humid and dry seasons has an effect on cake cracking. In the present research, the propagation of desiccation cracking and self-healing of unconsolidated soil (cake), placed in Plexiglas columns, was investigated using X-ray computed tomography (CT) during drying–wetting (DW) paths. The results showed that during the drying path, cracks initiated at the base of the soil by friction with the bottom of the column and then propagated to the top surface of the cake. As the drying time increased, evaporation at the top surface led to more cracks growing from the surface than from the bottom of the cake. However, the cracks at the bottom tended to stabilize because the water content was greater than at the top surface. The initiation, propagation, and expansion of the cracks developed in the saturated condition of the cake. During the wetting path, some cracks were closed while others appeared. The cracks tended to close progressively with wetting time, highlighting the self-healing phenomenon, probably due to the high plasticity index of cake soil. The results showed that cake swelling is mainly related to an increase of the void ratio due to a decrease in suction between particles. The results demonstrate the capacity of the X-ray CT technique to investigate the evolution of cracks during DW paths.

A Novel Method for Fracture Pressure Prediction in Shallow Formation During Deep-Water Drilling

Abstract Large numbers of deep-water drilling practices have shown that more than 60% of deep-water wells have complex leak-off during the drilling process, which poses great difficulties and challenges for the safety and operation time of deep-water drilling. The purpose of this article is to establish a method for predicting the fracture pressure in shallow formations. In this study, the deep-water shallow formation was divided into the upper unconsolidated soil layer, and the lower diagenetic rock layer according to the geotechnical distribution characteristics of the deep-water shallow formation. The location of the transition soil/rock layer zone was determined using the upper soil layer density trend line, and the lower rock layer density log data regression trend line. The deep-water shallow fracture pressure prediction model was established based on the soil/rock transition zone. The shear failure criterion was used above the transition zone, and the tensile failure criterion is used below the transition zone. The shallow fracture pressure of six drilled exploratory wells in the X block from the South China Sea was calculated using this new method and the calculation errors were all less than 3.18%. Moreover, the shallow fracture pressure body in this block was established using the Kriging interpolation method based on six drilled exploratory wells data. This shallow fracture pressure body established here was used to predict nine development wells shallow fracture pressure with a predictive error of less than 1.7% and there were no drilling accidents. The case study demonstrates that the new model can significantly improve the prediction accuracy has good prospects for popularization and application.

Biogeochemical Coring and Preservation Method for Unconsolidated Soil Samples

AbstractDeveloping an accurate conceptual site model (CSM) is an important process before a decision can be made regarding effective remedial actions. A critical aspect of an accurate CSM is thoroughly understanding the biogeochemistry occurring at the site in the area of concern. To collect media samples that accurately preserve the in situ biogeochemistry, a new Rotosonic core barrel and core preservation protocol was developed. The new biogeochemical core barrel (BCB) successfully isolated and preserved the in situ biogeochemical conditions of the soil core and minimized the soil core's exposure pathways to air. The BCB's success was achieved by a modified Rotosonic core barrel, a specialized drive shoe, an internal BCB core barrel piston, hydraulic extrusion of the soil core into a stainless core tube with an internal piston, and specialized core tube sealing, handling, and subsampling methods. Detailed subsampling of 65‐foot (nominally 20 m) soil core in 2‐inch (nominally 51 mm) increments within a specialized anaerobic glovebox confirmed the presence of five biogeochemical redox transition zones within the soil core. The BCB also allowed for split soil core samples for detailed mineralogical and live microbiological studies. Success of the BCB method is further evidenced by the presence of the highly redox‐sensitive surface bound iron sulfide mineral mackinawite. The BCB allowed detailed analysis of the soil core including Fe and S concentration gradients, oxidation–reduction potential gradients, volatile organic compound analysis, and live microbiological assessments.