Burial Depth Research Articles

Development and prediction of scour around offshore wind turbine monopile foundations in ebb and flow tides

Monopile foundations are commonly used to support offshore wind turbines (OWTs) in nearshore shallow waters, where the periodic ebb and flow of tides can cause severe seabed erosion around these foundations. Accurately predicting the progression of scour depth under these tidal conditions is crucial for the safety of OWTs. While a few empirical formulas for equilibrium scour depth in periodic tides have been proposed, they often overlook the backfilling effects during their derivation. Consequently, these methods fail to predict the progression of scour depth characterized by recurring scouring and backfilling processes. In this study, the scour progression under different tidal patterns, including square tides, symmetrical sinusoidal tides, and asymmetrical sinusoidal tides with various periods, is investigated using numerical methods. It is indicated by the results that deeper scour depths are produced by symmetrical tides compared to asymmetrical tides, while the highest scour depth is observed under square tides, potentially slightly exceeding that under unidirectional currents. Additionally, asymmetric scour depths at the front and back sides of the pile can result from the asymmetry of tides. Although scour progression is affected by tide periods, their impact on the equilibrium scour depth is limited. Furthermore, a new concept called normalized cumulative effective flow intensity is introduced, which plays a primary role in governing equilibrium scour depth. Based on this concept, prediction methods for both equilibrium scour depth and scour progression under sinusoidal tides, which closely resemble natural tidal patterns, are proposed. The accuracy of these methods is validated by experimental data from previous studies. These findings not only provide a method to optimize the design of monopile burial depth but also aid in the development of appropriate maintenance measures to prevent scour-induced damage to OWT foundations over their long lifespans.

Investigation into the variation characteristics and influencing factors of coalbed methane gas content in deep coal seams

Gas saturation is a critical parameter for the selection and development of coalbed methane, as well as a key indicator reflecting the challenges in coalbed methane development and productivity evaluation of coalbed methane wells. As one of the significant factors influencing gas saturation, gas content plays a vital role in comprehensively investigating coal pore properties to fully comprehend the process and conditions of methane adsorption and desorption. In this study, 3# and 15# coals from Qinshui Basin, China was selected as research subjects. The experimental evaluation encompassed an examination of composition, pore characteristics, permeability characteristics of coal, rock mechanical parameters while discussing the impact of temperature and pressure on coal's adsorption and desorption capacity. The mineral characteristics analysis revealed that vitrinite is the main component with varying percentages and reflectance values in both 3# and 15# coal seams. The gas content and methane concentration in the 15# coal seam are higher than those in the 3# coal seam. The relationship between gas content within a coal seam and burial depth depends on achieving a balance between positive pressure effects caused by overburden stress exertion on gases trapped within pores under high pressures during burial history versus negative temperature effects due to cooling during geological processes over time. Predictions were made regarding deep-coal gas content which holds significant implications for accurately understanding variations in desorption behavior along with optimizing fracturing engineering.

Germination characteristics associated with nicosulfuron resistance in Amaranthus retroflexus L.

Nicosulfuron-resistant biotype (R) and -sensitive biotype (S) Amaranthus retroflexus L. seeds were subjected to different temperature, light, salt, osmotic potential, pH value and burial depth treatments. The difference in germination response of two populations to the above abiotic environmental factors was used to study the fitness cost of nicosulfuron-resistance evolution in A. retroflexus. The aim is to find a powerful tool for weed control in the presence of evolutionary resistance selection. The results of this experiment showed that the germination rate and germination index in S population were generally higher than that in R population. When the salt stress was 80 mM, the water potential was -0.1 Mpa ~ -0.4 Mpa, and under strong acid and alkali conditions, the germination index in S population was prominently higher than that in R population (p<0.05). The delayed seed germination in R population indicated that its nicosulfuron resistance may be linked to seed biochemical compositions that altered seed germination dynamics. The resistant and sensitive biotype of A. retroflexus had differently favourable adaptability in diverse environments. Salt, osmotic potential and pH value are not the major constraints for A. retroflexus germination, however, A. retroflexus are strongly responsive to temperature, light and burial depth. Considering that seeds of A. retroflexus are unable to reach the soil surface beyond the depth of 6 cm, deep inversion tillage before sowing may be an effective and economical weed management tool for the control of nicosulfuron resistant A. retroflexus.

Adsorption behavior of helium in quartz slit by molecular simulation

Due to the multiple influences of unique physicochemical properties of helium, petrographic characteristics and temperature and pressure conditions, little is known about the helium adsorption behaviors in minerals and rocks at geological conditions. Based on the grand canonical Monte Carlo simulations, this study revealed the adsorption characteristics of pure helium and the competitive adsorption of binary mixtures with different proportions of methane and helium under geological temperature and pressure conditions in quartz slit model. Molecular simulation of pure helium shows that physical adsorption of helium exists in mineral surfaces, which indicates a preservation mechanism of helium in helium source rocks. Binary mixtures simulations indicate that the adsorption capacity of methane in quartz is stronger than that of helium, and the competitive adsorption of methane increases with decreasing burial depth. This means that during the upwards migration processes of natural gas, the adsorbed helium that distributed in the migration pathway will be gradually displaced by methane, then concentrate in the hydrocarbon gases and subsequently accumulate together in favorable traps to form helium-rich natural gas reservoirs. Our results provide a molecular-scale insight into the preservation and accumulation of helium in helium source rocks and are significant for assessing the helium resource potential.

Field monitoring and numerical simulation for force characteristics of pipe jacking in deep buried moderately weathered slate

Understanding the force characteristics of pipe jacking in rock formations is crucial for ensuring the stability of the structure and construction safety during construction. Yet, very little is explored about its characteristics in rock formations of pipe jacking. This paper presents a case study of constructing a deeply buried moderately weathered slate sewage pipeline using pipe jacking method in Changsha, China. To this end, we propose a novel method to combine field monitoring and numerical simulation representation in an efficacious way. Field monitoring was conducted to investigate the spatial distribution characteristics of jacking force, axial stress, and hoop stress in moderately weathered slate. Numerical simulation methods were employed to discuss the influences of several factors on pipe stress: the pipe-rock contact area, contact relationships at pipe joint interfaces, the height of the jacking force position, and the depth of pipe burial. The results show that hand shield is influenced by the excavation technology, and the distribution of jacking force exhibits a stepped or oscillating upward pattern in moderately weathered slate. The maximum axial stress occurs at the mid-span position of the arched roof of pipe at 30 MPa. Hoop stresses are dominated by compressive stresses with the maximum at-8 MPa. As the pipe burial depth increases, so does the axial stress on the pipe. Lower positioning of the jacking force heightens this stress effect. A larger pipe-rock contact area correlates with reduced axial stress levels. The weakening of the contact interface between pipe joints minimally affects axial stress, as stress primarily transmits through non-weakened areas. To ensure the reliability of the data, automatic monitoring and measuring instruments calibrated for on-site monitoring are used. The results of this study can provide beneficial guidance for the design and construction of pipe jacking.

Study on the burial depth calculation method for AC submarine cable based on the surface optical fiber monitoring temperature

AbstractThe partial exposure of submarine cable may cause damage to the metal sheath, which will affect its safe and stable operation. Existing detection methods for burial depth of submarine cables are difficult to implement and have a long detection period. In this contribution, a method is proposed to calculate the burial depth of alternating current (AC) submarine cable based on surface optical fiber monitoring temperature. According to the functional relationship between the transient temperature rise of submarine cable outer sheath above the ambient temperature and the burial depth (in the IEC‐60853 standard), the burial depth of submarine cables is calculated. The optical fiber temperature, electric load and meteorological temperature data are used for 30 consecutive days in September 2020 to calculate the change of burial depth of AC 500 kV oil‐filled submarine cable. The calculation results are basically consistent with the detection conclusion of side‐scan sonar, which shows that the method can accurately calculate the burial depth of submarine cables and locate the exposed position. This provides a theoretical basis for the intelligent operation and maintenance of AC submarine cables.

Geodynamic controls on clastic-dominated base metal deposits

Abstract. To meet the growing global demand for metal resources, new ore deposit discoveries are required. However, finding new high-grade deposits, particularly those not exposed at the Earth's surface, is very challenging. Therefore, understanding the geodynamic controls on the mineralizing processes can help identify new areas for exploration. Here we focus on clastic-dominated Zn–Pb deposits, the largest global resource of zinc and lead, which formed in sedimentary basins of extensional systems. Using numerical modelling of lithospheric extension coupled with surface erosion and sedimentation, we determine the geodynamic conditions required to generate the rare spatiotemporal window where potential metal source rocks, transport pathways, and host sequences are present. We show that the largest potential metal endowment can be expected in narrow asymmetric rifts, where the mineralization window spans about 1–3 Myr in the upper ∼ 4 km of the sedimentary infill close to shore. The narrow asymmetric rift type is characterized by rift migration, a process that successively generates hyper-extended crust through sequential faulting, resulting in one wide and one narrow conjugate margin. Rift migration also leads to (1) a sufficient life span of the migration-side border fault to accommodate a thick submarine package of sediments, including coarse (permeable) continental sediments that can act as source rock; (2) rising asthenosphere beneath the thinned lithosphere and crust, resulting in elevated temperatures in these overlying sediments that are favourable for leaching metals from the source rock; (3) the deposition of organic-rich sediments that form the host rock at shallower burial depths and lower temperatures; and (4) the generation of smaller faults that cut the major basin created by the border fault and provide additional pathways for focused fluid flow from source to host rock. Wide rifts with rift migration can have similarly favourable configurations, but these occur less frequently and less potential source rock is produced, thereby limiting potential metal endowment. In simulations of narrow symmetric rifts, the conditions to form ore deposits are rarely fulfilled. Based on these insights, exploration programmes should prioritize the narrow margins formed in asymmetric rift systems, in particular regions within several tens of kilometres from the paleo-shoreline, where we predict the highest-value deposits to have formed.

Burial of a sand sea: Heterogeneous compaction and cementation of the jurassic Etjo Formation, Namibia and what it tells

Aeolian sandstones are capable of forming excellent reservoir rock due to their textural and compositional maturity. Often spanning across large areas, such formations may however experience spatial variability in burial and temperature exposure potentially leading to a heterogeneous diagenesis and subsequent reservoir quality. To assess such potential variability, this case study focusses on the diagenesis of the aeolian units of the Lower Jurassic Etjo Formation in Namibia, exposed at three key localities lying >100 km apart from each other. The Etjo Formation has experienced two major burial phases controlled by the emplacement of (I) Jurassic Karoo and (II) Lower Cretaceous Paraná-Etendeka volcanic rocks separated by an intervening exhumation phase. Petrographic analysis reveals very different rock properties between the localities with respect to intergranular volumes (IGV), intensity of quartz cementation, and preserved porosities. Average IGV and quartz cement values are 30.7 % and 24.3 % at Gamsberg, 23.7 % and 6.5 % at Waterberg and 19.7 % and 15.4 % at Mt. Etjo. Point-counted intergranular porosity values are on average 2.6 % (Gamsberg), 10.8 % (Waterberg), and 1.5 % (Mt. Etjo). Waterberg samples had an on average 72 % larger nucleation surface area available for quartz cement growth than samples from Mt. Etjo. The higher quartz cement volumes at Mt. Etjo therefore argue for a higher thermal exposure than at Waterberg. This is supported by kaolinite-to-illite transformation only occurring at Mt. Etjo. We attribute the higher temperature signature to the proximity of Mt. Etjo to the center of lower Cretaceous Paraná-Etendeka volcanism and related elevated thicknesses of the lava pile or heat flow increase. At Gamsberg, there is evidence for a quartz cement generation that formed during the Jurassic. This earlier cement stabilized the grain framework and preserved the IGV during the following Etendeka burial event. The Etjo Formation provides an exceptional example for the wide range of very low to very high degrees of compaction and cementation that can occur within an otherwise homogeneous, texturally and compositionally mature sandstone formation. This study underscores the importance of accounting spatial variations in burial depths and temperatures when predicting the diagenetic properties of reservoir rocks.

Study on the detectability of CSRMT in archaeological exploration: taking the ancient city wall remains as an example

Although electromagnetic methods have made significant advances in archaeological exploration, there remains a lack of a method that offers both high operating efficiency and high resolution. This study introduces a novel approach derived from the Controlled Source Radio Magnetotelluric (CSRMT) method. The CSRMT method combines the efficient configuration of the Controlled Source Audio-magnetotelluric (CSAMT) method with enhanced resolution capabilities. To evaluate the efficacy of the new method in archeological exploration, we designed a series of models based on existing references related to ancient city wall remains. Using the 3D contraction integral equation method, we numerically simulated the high-frequency component of the CSRMT method, and then on, the Laterally Constrained Inversion technique is used to invert the data. The effectiveness of the method was assessed qualitatively and quantitatively through analysing the electromagnetic field and apparent resistivity of models with varying widths, heights, top burial depths, and resistivity. Our analysis revealed that models with shallower burial depth and greater height of the underground city wall exhibited higher resolution. The findings demonstrate that the CSRMT method can efficiently and accurately identify buried remains, making it a highly promising tool for archaeological exploration and warranting further development.

Coupling effects of stress, seepage and damage during reconstruction and excavation of abandoned deep water-rich roadways

A stress–seepage–damage coupling model considering the long-term creep of a deep rock mass was established to study the mechanism of evolution of stability of the surrounding rock during reconstruction and excavation of abandoned deep water-rich roadways in a mine. The research shows that the maximum compressive stress in a circular cavern is significantly lower than that in a horseshoe-shaped cavern. Stress is distributed more uniformly in the circular cavern, and appropriately enlarging the size of the reconstructed excavation site can improve the stability of the surrounding rock. As the creep duration for abandoned roadways increases from 1 to 9 years, the growth rates for vault settlement and horizontal clearance convergence remain constant and the roadway undergoes steady-state creep. With increasing burial depth of the abandoned roadway (200–400 m), a pressure arch is gradually formed in the roadway roof in the reconstruction and mining process. The surrounding rock forms a ‘self-bearing structure’ with arch mechanical characteristics and a load transfer mechanism to maintain its own stability, and the overall bearing capacity of the surrounding rock is greatly improved. However, once the burial depth exceeds 400 m, the effect of the pressure arch begins to diminish with further increases in burial depth. Furthermore, porewater pressure significantly weakens the surrounding rocks.

Longevity and persistence of arrowleaf sida seeds in soil and emergence modeling using thermal and hydrothermal time models

Arrowleaf sida (Sida rhombifolia L.) is a weed that has a fibrous stem, aggressive root system and waxy leaves that can hinder herbicide absorption. Based on knowledge of the environmental requirements for germination of this species, it is possible to predict emergence to assist in integrated management. The aim of this investigation was to characterize the air temperature and soil water potential requirements for arrowleaf sida germination, to model the emergence in the field using thermal and hydrothermal time models and to evaluate the longevity of the arrowleaf sida seed bank. Laboratory experiments were conducted to determine the temperature and water potential for seed germination by testing eight temperatures (10, 15, 20, 25, 30, 35, 40, and 45 °C) and 10 water potentials (0, −0.05, −0.1, −0.2, −0.4, −0.6, −0.9, −1.2, −1.5, and −2.0 MPa). Field experiments were conducted between 2014 and 2018 to model the emergence using three sampling times (starting on 10/20, 11/10, and 12/01), during which soybean seeds were sown. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted, in which the first factor included three burial depths (0, 3, and 6 cm) and the second factor included five collection times (0, 1, 4, 10, and 16 months) after seed burial. The base, optimal and maximum temperatures for arrowleaf sida germination were 10.0, 24.8, and 42.5 °C, respectively, and the base water potential was −1.20 MPa. It is possible to predict the emergence of arrowleaf sida in the field by hydrothermal and thermal time models under different environmental conditions. In addition, this species has a persistent seed bank, with 30% of seeds being viable after 16 months of burial.

Using tire derived aggregates (TDA) as infill material for wave barriers

Ground-borne vibrations caused by construction activities and highway and railway traffic may disturb adjacent structures and sensitive machines. Thus, studies on isolating this type of vibrations have accelerated in recent years. Few experimental work investigated the use of rubber-soil mixtures as infill material for vibration mitigation. However, despite its high damping capacity, almost no experimental work has been conducted to evaluate the use of Tire Derived Aggregates (TDA) as infill material for trench barriers. This paper aims to investigate the use of TDA trenches as a wave barrier. Also, the performance of buried TDA trenches was considered in this work. A series of vibration tests were conducted in a steel tank with dimensions of 2.75 m long, 2.25 m wide, and 1.80 m deep. The trench depth and frequency varied from 0.2 to 0.6 m and 100–200 Hz, respectively. The results showed that TDA trenches had a superior performance compared to open trenches. TDA trenches could reduce the vertical vibration amplitude by up to 30 % more than open trenches. Also, open and TDA trenches performed better in mitigating the vertical vibrations compared to the other directions. Furthermore, for optimum design of open and TDA trenches, the normalized trench depth should be between 1 and 1.3 D. Covering TDA trenches with soil was found to decrease their vibration isolation significantly at normalized burial depth larger than 0.15.

Advancing Sustainable Geothermal Energy: A Case Study of Controlled Source Audio-Frequency Magnetotellurics Applications in Qihe, Shandong

Geothermal energy is a key part of sustainable and renewable energy strategies, especially for clean heating in northern regions. This study focuses on Qihe County in Shandong Province, applying a controlled source audio-frequency magnetotellurics (CSAMT) method to investigate deep karst geothermal reservoirs. This research addresses the complex geological conditions and electromagnetic interference in the region, aiming to improve sustainable geothermal resource development. The findings indicate that the geothermal reservoir in the study area primarily consists of Ordovician limestone, characterized by moderate burial depth, high water volume, and elevated water temperature. Integrating CSAMT with vertical electrical sounding (VES) and radiometric surveying has clearly defined the deep aquifer layers and major water-controlling fault structures. Drilling verification results demonstrate the significant effectiveness of the integrated geophysical methods employed, providing reliable technical support for deep geothermal exploration in similar regions. This study makes a significant contribution to the scientific and technical foundation necessary for the sustainable development and utilization of geothermal resources, supporting the broader goals of environmental sustainability and renewable energy.

Research on the Twin-Link Stepping Temporary Support Mechanism and the Repeatable Supportability of the Roof in the Underground Excavation Roadway of Coal Mine

The coal mine’s underground heading roadway suffers from a lack of effective temporary support, which contributes to low efficiency and inadequate safety in excavation operations. This paper presents a novel approach for roadway excavation, support, and anchoring, utilizing the twin-link stepping temporary support method. To address the stability requirements of the roadway roof in this support method, a numerical model of the excavation face was developed using the BBM (Bonded Block Model) method in 3DEC 7.0 software. Through numerical simulation, the repeatability of the twin-link stepping temporary support process was assessed for various roadway roof rock types, thicknesses, and burial depths. By considering aspects such as roof fragmentation, roof convergence, and relative displacement between the direct roof and the bedrock, the range of roadway roof repeatability was determined. The proposed twin-link stepping temporary support process, along with its applicable roof conditions, establishes a theoretical foundation for implementing the parallel operation mode in coal mine underground heading roadways, thereby significantly enhancing safety and efficiency.

Full-scale test on the mechanical behavior of longitudinal joints of NC-UHPC composite segments under compression-bending load

The performance of longitudinal joints in shield tunnel segments is crucial for ensuring structural stability and durability. This study presents an innovative segment structure combining normal concrete (NC) and ultra-high performance concrete (UHPC) (hereafter called NC-UHPC composite segment). Full-scale joint tests were conducted to analyze the mechanical response and failure characteristics of longitudinal joints in these segments. Compared to reinforced concrete (RC) segment joints, NC-UHPC composite segment joints exhibited a significant increase in initial cracking load by 197.93% under sagging moments and 435.3% under hogging moments. The ultimate load-bearing capacity increased by 55.71% and 67.10%, and the initial bending stiffness improved by 20.57% and 10.59% under sagging and hogging moments, respectively. Furthermore, NC-UHPC composite segment joints exhibited smaller crack distribution areas and fewer cracks, indicating superior crack resistance. No cracks or damage were observed at the NC-UHPC interface. Evaluation of joint toughness and ductility indices further highlighted the favorable performance of NC-UHPC composite segment joints. Finally, a refined numerical model was established to compare the deflection and bending stiffness of RC segment joints with NC-UHPC composite segment joints under varying axial forces. The findings suggest that NC-UHPC composite segments are more suitable for tunnel engineering with greater burial depth, higher water pressure, and larger axial forces.

Enhancement on PDC bit based on Archimedean spiral control method

The Longmaxi Formation shale in the Sichuan Basin has a large burial depth, narrow horizontal windows, and stringent requirements for controlling well deviations. When PDC bits are used for drilling, the cutting structure experiences significant challenges in terms of stability and rock-breaking efficiency. The secondary design cycle of PDC bits is lengthy, and the cost of engineering trials is high. Thus, bit development relies on strong empirical knowledge. Additionally, the spiral degree of the blades has not been uniformly defined, and there was a lack of quantitative studies about its effect on the rock-breaking performance of PDC bits. In this study, thus Archimedean spiral was used as the quantitative control equation for the spiral degree of the blades. The cutting depth control distance ΔL2 (or designed depth of cutting, designed DOC) and the level of different track (LODT) were used to adjust the radial cutting section of the interaction process between the bit and shale. An orthogonal coupling study was conducted on the rock-breaking efficiency and stability of 8 1/2ʺ PDC bits with six spiral span angles θspan, six cutting depth control distances ΔL2, and six LODTs as design parameters. The results indicated that using the triaxial compressive strength under the liquid column pressure as the mechanical specific energy (MSE) benchmark, the shear failure mode reduced the mechanical specific energy below this benchmark when cutting depth control distance ΔL2 of the front and rear elements exceeded 1.0 mm. However, increasing the cutting depth control distance ΔL2 led to an increase in torque and circumferential vibration amplitude. In addition, compared to straight blade designs, spiral blade designs significantly reduced the axial/circumferential vibrations, with reductions in circumferential vibration amplitude ranging from 37.87% to 48.33%. The spiral blade designs had a suppressive effect on axial vibrations only when the spiral span angle θspan was between 12 and 36° or 60°, reducing the axial vibration amplitude by approximately 20.09–25.69%. Different ΔL2 must be considered in conjunction with cutter material properties when selecting the spiral span angle based on the simulation results. When the ΔL2 exceeded 1.0 mm, LODT of 3/6 could maximize the reduction in the mechanical specific energy. Using MSE as the objective function, this study provided several PDC bit enhancement design schemes suitable for the Longmaxi Formation. The research results contributed to a quantitative understanding of the coupling effects between spiral span angle θspan and cutting sections on the rock-breaking efficiency and stability of PDC bits.

Key indicators of caprock sealing assessment with consideration of faults in potential CO2 geological storage sites in Subei Basin, China

Good caprock sealing is crucial for ensuring the long-term safety and security of carbon dioxide (CO2) geological storage. However, concealed faults within caprocks and reservoirs can impact the transport and accumulation of CO2 plumes. Due to the uncertainties associated with the geometric structure, physical properties, and combined relationships among reservoir, caprock and fault, accurately evaluating caprock sealing is challenging. To address the challenge of identifying key indicators for caprock sealing considering faults, this study focuses on the one potential CO2 geological storage field in the Subei Basin, China. First, this study establishes a hydraulic-mechanical (HM) coupled finite element model considering a combination of caprock, reservoir and fault. Then, 22 research indicators, including fault offset, fault dip, caprock thickness, burial depth, permeability and mechanical properties, are analysed to evaluate their influence on caprock sealing via the tornado analysis and response surface methods. Finally, key indicators are determined based on evaluation criteria, such as pore pressure increment (ΔPP) and Coulomb failure stress (CFS), in the fault plane. The research results indicate that fault dip, fault offset, fault permeability, burial depth, and reservoir permeability are key indicators. The caprock thickness, caprock permeability, and caprock Young's modulus significantly influence the caprock sealing capacity. The ΔPP and CFS increase with increasing fault dip and offset. When the fault dip exceeds 45°, the ΔPP and CFS reach maximum values at the interface between the reservoir and caprock. Fault permeability has a greater impact than reservoir permeability and caprock permeability. The research results may provide guidance for the evaluation of caprock sealing capacity for CO2 geological storage.

Numerical modelling of upheaval buckling of offshore pipelines with unstressed and stressed initial imperfections

Buried offshore pipelines transporting hydrocarbon at high temperatures and pressures might experience upheaval buckling. Although pipelines are designed to remain in place, field evidence shows that the buried pipeline might displace a significantly large distance in the upward direction. In the present study, the pre- and post-buckling behaviour of offshore pipelines buried in sand is investigated considering the degradation of uplift soil resistance with the upward displacement of the pipe. The soil resistance degradation models are implemented in a finite element program, and the analyses are performed for large upward displacements even when a buckled section moves above the seabed. The simulation results show that the capacity of the pipeline to carry the load generated from an increase in pressure and temperature reduces significantly if post-peak degradation of uplift soil resistance is considered. The effects of the internal pressure modelling approach, uplift soil resistance degradation model, burial depth and pipe dimensions (diameter and thickness) on upheaval buckling for varying initial imperfections are investigated. Based on a simplified model for developing initial stresses in a pipeline during installation, it has been shown that initial stresses primarily affect the upheaval buckling at lower ranges of upward displacement of the pipe.

ALEM-FEM-BEM coupling for response analysis of pile group in laminated fluid-saturated geomaterials induced by tunnel excavation

This paper proposes a two-stage analytical methodology for predicting the response of pile groups in layered fluid-saturated soils induced by tunnel excavation. The Loganathan analytical approach is adopted for estimating the free-field response induced by tunneling. At the second phase, the solution to the surrounding soil of pile groups is employed as the kernel function based on the analytical layer-element method (ALEM). Subsequently, the analysis of soil-structure interaction is presented using the boundary element method (BEM). The Timoshenko-beam model is utilized to simulate each monopile combined with finite element method (FEM). Finally, the responses of adjacent pile groups are derived by the coordination conditions and coupling of BEM and FEM. Comparisons are made between the presented analytical solutions and existing experimental and numerical results. Parametric analyses are performed to evaluate the influence of soil permeability, material stratification, tunnel-pile distance, tunnel buried depth, and pile slenderness ratio on the mechanical behavior of grouped piles. The results show that the pile group in hard top and soft bottom saturated soils demonstrates better load-bearing capacity than that in soft upper and hard lower soils. Then, with the increment of tunnel-pile distance, the displacement and bending moment are reduced by 22.2 %-50 % and 41.2 %-66.7 %, respectively, and the increased rate of mechanical response over time slows down. Moreover, increasing the burial depth reduces the displacement by 8.6 %-33.3 % and the bending moment by 33.4 %-50 %, respectively, and the locations of peak responses increase from 0.6 times the pile length to 0.8 times the pile length.

Prediction of tight sandstone reservoirs by multiwave joint prestack inversion technology: A case study of the Qiulin area in the Sichuan Basin

The Shaximiao (SXM) Formation of the Middle Triassic in the central Sichuan Basin is a river-lake sedimentary system with an average burial depth of 2800 m. The channel sand bodies of the SXM Formation in the Qiulin area are developed with large lateral variation and high- and medium-porosity sand. This leads to great differences in the seismic response and difficulty in predicting the sand bodies and reservoirs using P-wave data. We carry out well-log analysis for different types of sand bodies. The no. 8 sand body of high porosity can be effectively identified using P-wave impedance (PI). Whereas for the no. 7 sand body of relatively lower porosity (mainly due to the higher shale content in the no. 7 sand compared with the no. 8 sand), sandstone and mudstone can be distinguished using S-wave impedance (SI), and reservoirs can be recognized by the P- to S-wave velocity ratio ([Formula: see text]/[Formula: see text]). Based on the PP wave and the P-to-S converted wave (PS wave) (after matching) angle-stacked data, a prestack inversion of multicomponent data is performed. Multiwave joint inversion results (SI and [Formula: see text]/[Formula: see text]) have better accuracy and stronger stability than the PP-wave inversion in practical application. In addition, the PI of the joint inversion more clearly describes the distribution and boundaries of the channel sand and better matches the prediction and drilling data in sand 8. The SI of the joint inversion can identify subtle sand bodies (weak PI contrast) that are difficult to be detected by PP-wave inversion. The distribution of the reservoir predicted by the [Formula: see text]/[Formula: see text] of the joint inversion is clearer (the no. 7 sand body) and better than that by the PP-wave inversion. This study demonstrates the advantage of the multiwave joint inversion technology in tight sand identification.