Bottom Of Pit Research Articles

Study on the Influence of Excavation Unloading on Pile Depth in Sandy Soil

With the development of urban construction, uplift pile has been widely used in underground structure bearing buoyancy. The pile is buried deep underground, and the foundation pit is excavated on the pile foundation, the stress redistribution of the soil after the foundation pit excavation will reduce the lateral stress of the pile at the bottom of the pit, resulting in the reduction of friction resistance, but this effect is limited to a certain depth at the bottom of the foundation pit. Referring to the unloading influence depth corresponding to the vertical unloading coefficient in the spring back calculation of foundation pit and introducing the unloading influence depth corresponding to the horizontal unloading coefficient, it is deduced that the relationship between the horizontal unloading coefficient and the vertical unloading coefficient is based on the friction angle. Based on the bearing capacity control and numerical simulation, it is determined that the corresponding depth when the horizontal unloading coefficient is 0.95 is the unloading influence depth. The depth to width ratio of excavation has a great influence on unloading influence depth, and the internal friction angle of soil has little influence on unloading influence depth, while the influences of pile diameter and pile-soil friction coefficient can be ignored. The formula of unloading influence depth is derived in this paper. Comparing the unloading influence depth of sand and soft soil, the unloading influence depth of sand is greater than that of soft soil.

Failure Mechanism and Stability Control Technology of Slope during Open-Pit Combing Underground Extraction: A Case Study from Shanxi Province of China

With the development of society, the demand for mineral resources is gradually increasing, and the current situation of decreasing total resources dictates the inevitable interaction between open-pit combing underground extraction (OPUG) in time and space. In this research, we took the Anjialing coal mine in Shanxi Province of China as a case study, and tested the physical and mechanical properties of coal rocks in the laboratory. The similarity criterion was used to build a similar experimental model for the deformation evolution of the slope of the open-pit mine section; the digital scattering method was used to test the influence of the underground mining process parameters on the deformation evolution of the open-pit slope. The results showed that there was an obvious distribution of “three zones” above the mining goaf, namely, a collapse zone, fracture zone, and slow subsidence zone. When the mining face was continuously advanced towards the bottom of the open pit, the supporting stress of the mining face transferred to the side of the open-pit slope. Additionally, large displacement and stress concentration were observed on the slope near the stoping line, which caused the slope body to move along the uppermost part of the slope first, and thereafter along the lower part. Various techniques for slope stability control are discussed, including the optimization of spatial and temporal relationships between open-pit and underground mining, the optimization of mining plans, and the use of monitoring and early warning systems. The results can provide a guide for slope stability control of similar open-pit mines in the process of mining coal resources.

Experimental investigation on damage evolution and failure mechanism of pre-corroded AA7075-T6 under multiaxial fatigue loading

To investigate the tension–torsion fatigue failure of pre-corroded AA7075-T6, fatigue damage accumulation, macro-crack formation and propagation are quantitatively characterized through 3D-DIC based strain maps and damage severity curves, micro-cracking characteristics are further examined by SEM, TEM, and EBSD observation. Experimental results show that corrosion pit induces fatigue macro-cracks formation, and the identified nucleation time, amount, and location are diverse for different loading conditions. Four dominated fatigue micro-crack initiation forms and corresponding mechanisms were analyzed, namely, pit bottom, sidewall dis-continuous surface, corrosion micro-feature (micro-pits/jut-ins), and pit subsurface, which depends on multi-factors involving corrosion macro-morphology, corrosion micro-morphology, loading condition and underlying microstructure.

Clinicopathological characteristics of signet-ring cell carcinoma derived from gastric fovelar epithelium.

We aimed to investigate the immunophenotype, differential diagnosis, and clinicopathological characteristics of signet-ring cell carcinoma (SRCC) derived from gastric foveolar epithelium. Clinical characteristics, endoscopic findings, histopathological features, and follow-up data of seven cases of SRCC derived from gastric foveolar epithelium with small intramucosal lesions were analyzed. Seven patients with a mean age of 38.3 years were diagnosed with SRCC derived from gastric foveolar epithelium and small intramucosal lesions, all of them were negative for CDH-1 germline mutation. The glands proliferated and expanded, and then morphologically transformed into signet-ring cells and formed clonal hyperplastic SRCC, which expanded laterally along the gastric foveolar cells to a length of 3-6 mm. Periodic acid Schiff staining was positive, while CK7 and MUC6 were negative, in all cases. Ki-67-positive cells ranged 37%-60%. During a follow-up period of 6-30 months, no patients experienced tumor recurrence or metastasis. SRCC derived from gastric foveolar epithelium is originated from the proliferative region of the bottom of the gastric pit and gland neck. It is easily missed diagnosed or misdiagnosed as it grows laterally along the gastric foveolar cells. Biological behavior, genetics, and etiology of such SRCC, as well as the clinicopathological characteristics, need to be further studied.

Deformation Stability Response of Adjacent Subway Tunnels considering Excavation and Support of Foundation Pit

Abstract Since the safety and stability of the original tunnel structure are easily affected by the adjacent foundation pit excavation, it is strongly necessary to study the deformation evolution of tunnels during the adjacent foundation pit excavation. With regard to the two cases that tunnel is adjacently located at the right and bottom of foundation pit, the influence of different supporting methods, including pile support, bolt support, pile-bolt support, and shotcrete-bolt support, on the tunnel stability was investigated on the basis of the whole excavation process numerical simulation of deep foundation pit for determining the best foundation pit supporting beneficial to the stability of adjacent tunnel. The results indicate that both one-step excavation and multistep excavation have great influences on the displacement of adjacent tunnels, wherein the influences on the tunnel located at the right of foundation pit are greater than those at the bottom of foundation pit. Multistep excavation is recommended for the foundation pit adjacent to shallow tunnel. In the case of the tunnel located on the bottom of the foundation pit, the maximum stress generated around the tunnel is small, the maximum stress area is limited, and the displacement of tunnel monitoring points is also small. For the tunnel located at the right of the foundation pit, the pile-bolt supporting can effectively limit the displacement of soil between the tunnel and the foundation pit, reduce the maximum stress and the maximum stress distribution area, and effectively control the tunnel displacement.

The Influence of 20Kh13 Steel Specimen Surface Pitting Damage on the Growth of Fatigue Cracks

The damage to the surface of steam turbine rotor blades by pitting reduces significantly their fatigue resistance and can lead to fracture resulted from the development of fatigue cracks. To determine the service life of blades or the probability of their breakage, it is necessary to have data that allow one to assess how the degree and nature of damage to their surface affects their fatigue resistance. If the rotor blade has passed, in an off-design operation mode, the zone of increased stress amplitudes, then, given the known number of cycles, the measure of fatigue damage to the blade material can be estimated. If the stress amplitudes did not exceed the endurance limit (taking into account the safety factor and the loading cycle asymmetry value), the fatigue cracks which could lead to blade failure did not appear in the blade material. If the stress amplitudes and the corresponding number of cycles are in the zone to the left of the French line, irreversible fatigue damage did not occur in the blade material. Determination of the lengths of fatigue cracks appearing at the pit bottom as a function of stress amplitude and number of operating cycles is a topical issue. This will make it possible to evaluate the size of the damaged layer and to restore the blade fatigue resistance by removing this layer. The results from studies of crack resistance under fatigue loading of specimens made of 20Kh13 blade steel with artificially created pitting damage to the surface are presented. The possibility of using the calculated dependences for evaluating the French line for samples with initial pitting damage has been confirmed, and an assessment of the damaged metal layer at the pit bottom depending on the stress amplitude and number of operating cycles has been obtained. The length with which the crack must be removed to restore the blade system service life has been determined.

Corrosion behaviours of B + F dual-phase X80 pipeline steel in simulated near neutral and acidic soil solution

ABSTRACT Slow strain rate tensile corrosion (SSRT), immersion corrosion and polarisation behaviours of B + F dual-phase X80 pipeline steel in simulated near-neutral and acidic soil solutions were compared. The stress corrosion of X80 steel in acidic soil solution is more sensitive, whose mechanism is intergranular fracture induced by pitting. Crack nucleates at the bottom of corrosion pit and propagates along the weak path–grain boundary. In near-neutral soil solution, the crack is originated from a corrosion pit and propagated mainly transgranular. The parabolic velocity constant in immersion test and corrosion current of X80 steel in acidic soil solution is much higher, 40 and 2.7 times of those in near-neutral soil solution respectively. Dual-phase X80 steel has poor corrosion resistance in acidic soil solution. X80 steel in near-neutral soil solution corrodes in the form of an irregular corrosion pit at the bainite area, or a round corrosion pit near inclusions.

Effects of Pit-Bottom-Soil Reinforcement on the Deformation of Subway Deep Foundation Pits Based on an Improved Model

Reinforcement of pit bottom soil has been utilized in subway deep foundation-pit engineering in soft-soil areas. This study proposes an improved foundation-pit excavation model to better investigate the effect of soil reinforcement at the bottom of a pit on the deformation of a subway’s deep foundation pits. The strength parameters of the reinforced soil utilized in the improved model could be obtained through a cone penetration test before and after the pit-bottom-soil reinforcement. The results show that the enveloped structure’s lateral displacement and the surface settlement outside the pit were reduced by 37% and 23% after soil reinforcement, respectively. The uplift suppression in the centre of the base exhibited a significant effect, and the uplift suppression exceeded approximately 50%. Thus, the foundation reinforcement could effectively reduce the subway foundation-pit support structure’s horizontal deformation, ground settlement, and the pit bottom soil’s uplift deformation. The bending moment of the diaphragm wall was mainly affected near the excavation surface at the bottom of the pit. The closer the support position to the surface, the smaller the effect on the axial force.

Deformation Characteristics of Soil Layers and Diaphragm Walls during Deep Foundation Pit Excavation: Simulation Verification and Parameter Analysis

The research on the deformation of soil mass and ground connection walls is not sufficiently thorough due to the huge risk of deep excavation in soft soil areas. In this paper, finite element software is used to numerically simulate a symmetrical foundation pit in Suzhou, and the reliability is verified by on-site measured data. The purpose of this study is to investigate the deformation mechanism of the enclosure structure and surrounding soil during the excavation of soft soil foundation pits, and to carry out sensitivity analysis. The results show that the maximum subsidence of the surface is 21.25 mm, the maximum horizontal displacement of the underground diaphragm wall is 9.45 mm, and the maximum uplift of the pit bottom is 21.46 mm. By changing the soil layer properties (the elastic modulus, cohesion, and internal friction angle) and the insertion ratio of the diaphragm wall, the maximum horizontal displacement of the diaphragm wall is more easily affected than the maximum settlement of the surface. Based on different research results, the maximum land subsidence and maximum horizontal displacement of the support structure are 0.313–0.060% and 0.070–0.250% of the maximum excavation depth, respectively. Finally, the simulation may have some applicability to other foundation pit excavations.

Influence of corrosion pit geometry on stress distribution within a single artificial pit

ABSTRACT A lower pitting severity produces a shallower corrosion pit shape on a corroded ballast tank. Pit distributions of corroded specimens have a probability model for the non-Gaussian surface. Therefore, the present work focuses on the numerical study of stress distribution within the corrosion pit area, while considering different corrosion pit geometries. Accordingly, 45 dog bone-shaped finite element models with a single corrosion pit are investigated. The geometrical parameters of the corrosion pit are analyzed with quantitative correlations at different sizes, shapes, and different levels of enlargement. Additionally, a corrosion pit alteration scenario is proposed, with a narrow deep, hemispherical, and final shallow wide form. Results show that the stress concentration factor remains relatively constant at the pit edge and increases toward the pit bottom. Furthermore, stress declines on the pit bottom and shallower corrosion pit form, which conforms to the polynomial trendline.

Channel-flow triple electrode for simultaneous in situ detection of platinum and copper dissolution

• In situ method for monitoring dissolution of Pt–Cu alloys was developed. • Established method enables Pt and Cu detection with high time resolution. • Pt and Cu dissolved independently from Pt–75 at% Cu alloy under potential cycling. • The dissolution behavior of Pt–75 at% Cu was unaffected by the scan rate. A channel-flow triple electrode (CFTE) was constructed for in situ monitoring of the dissolution of Pt–Cu alloys during electrochemical measurements. In the CFTE, Cu 2+ ions dissolved from upstream Cu or Pt–Cu alloy electrodes were quantitatively detected by electrochemical reduction of Cu 2+ to Cu on the downstream detection electrode. The dissolution behaviors of Cu-rich Pt–Cu alloys in 0.5 M H 2 SO 4 during anodic polarization and potential cycling were investigated using CFTE. The level of Pt dissolution was below the detection limit, and Pt could not be detected during the anodic polarization of Pt–Cu alloys. However, the dissolution of both Pt and Cu was detected under potential cycling for a Pt–75 at% Cu alloy (Pt 25 Cu 75 ). The dissolution of Cu as Cu 2+ from Pt 25 Cu 75 occurred continuously at the pit bottoms through the thick Pt-enriched layer at potentials above 0.7 V vs the standard hydrogen electrode during potential cycling. In contrast, Pt dissolved mainly from the Pt-enriched layer. The potential cycling scan rate did not affect the mechanism of Cu dissolution from Pt 25 Cu 75 . The high time-resolution of detection by the CFTE enables dissolution peaks to be distinguished under potential cycling at a high scan rate. The CFTE therefore provides an excellent method for monitoring the dissolution of Pt–Cu alloys.

Effect of Size on the Stability of Narrow Foundation Pits

The traditional design method for narrow foundation pits ignores size effects. Engineering practice shows that this is too conservative and causes large‐scale waste. In this study, with the help of ABAQUS finite element software, retaining‐structure models in semi‐infinite and infinite elastic space are used to simulate the mechanical performances of pile‐supported structures under different combinations of excavation depth, retaining pile‐embedded depth, and excavation width. Furthermore, based on antioverturning stability theory and circular slip theory, the intrinsic relationship among these variables and their effects on the stability of excavation is analysed. Finally, based on the restraint effect of retaining structures on the soil below the pit bottom under actual working conditions, critical width is determined and used to classify foundation pits. Moreover, the applicability of existing codes is discussed. These results can improve the design and construction of narrow excavations, benefitting the construction industry and society in general.

Numerical Simulation and Field Monitoring Analysis for Deep Foundation Pit Construction of Subway Station

To investigate the effect of deep foundation pit excavation on the stability of retaining structure, a subway station in the city of Jinan was selected as a project, and a FLAC3D-based three dimensional model was developed for numerical simulation. The horizontal displacement of the retaining structure, the axial force of the support, and the vertical displacement of the column were studied and compared to the collected data from the field. The findings indicate that when the foundation pit is excavated, the maximum deformation of the retaining structure progressively decreases from the top, the distortion of the retaining structure gradually rises, and the final maximum deformation is around 17 meters deep. In each layer of support, the largest axial force support is located in the first reinforced concrete support; the uplift of the pit bottom caused by soil unloading plays a primary role in the vertical displacement of the column, and the column exhibits an upward trend under all construction conditions. When compared to the measured data, the generated findings are comparable and the fluctuation trend is extremely consistent. The findings of this article may give technical direction for the development of subway stations with a comparable engineering basis.

Flow accelerated corrosion and erosion\u2212corrosion behavior of marine carbon steel in natural seawater

In this work, flow accelerated corrosion (FAC) and erosion−corrosion of marine carbon steel in natural seawater were electrochemically studied using a submerged impingement jet system. Results show that the formation of a relatively compact rust layer in flowing natural seawater would lead to the FAC pattern change from ‘flow marks’ to pits. The increase of the flow velocity was found to have a negligible influence on the FAC rate at velocities of 5−8 m s−1. The synergy of mechanical erosion and electrochemical corrosion is the main contributor to the total steel loss under erosion−corrosion. The increase of the sand impact energy could induce the pitting damage and accelerate the steel degradation. The accumulation of the rust inside the pits could facilitate the longitudinal growth of the pits, however, the accumulated rusts retard the erosion of the pit bottom. The erosion and corrosion could work together to cause the steel peeling at the pit boundary. The steel degradation would gradually change from corrosion-dominated to erosion-dominated along with the impact energy increasing.

Retaining Technology for Deep Foundation Pit Excavation Adjacent to High-Speed Railways Based on Deformation Control

Considering the deep foundation pit of a car dumper room close to the Beijing–Baotou railway, the countermeasures of the foundation pit design are analyzed according to the surrounding environment and stratum conditions. Through Midas GTS software as well as field measured results, the construction effect on the adjacent railway subgrade is discussed. Therefore, the deformation characteristics of the foundation pit as well as the retaining structure, including the railway subgrade, caused by the excavation process, are revealed. The results show that the five-sided water-stop structure formed by cement piles around and at the bottom of the pit avoids the consolidation settlement of the adjacent railway subgrade caused by deep dewatering and also reduces the lateral displacement (i.e., in a horizontal direction) and the heave of the pit bottom. As a result, the lateral displacement near the railway side is larger than that of the retaining structure on the other side due to the subgrade on the pit side. The cross-lot bracing across the foundation pit will transfer the bias pressure of the subgrade to the retaining structure far away from the railway, while the transfer effect of the knee bracing is not obvious. The deformation of the railway subgrade and its evolution rate caused by the removal of internal bracing is significantly greater than the subgrade deformation and the change rate of deformation caused by excavation. The research results provide useful guidance for the deep foundation pit design.

GRAVES OF THE SCYTHIAN AMAZONS: TYPOLOGY AND DESIGN FEATURES

Types of burial structures are one of the most reliable ethno-differentiating criterion. They are commonly due to local natural and economic factors that were accepted by the newcomer population along with main characteristics of their own ritual.
 As for the shape, the graves of Scythian warriors are arbitrarily divided into 11 types with options, which in general make up three main groups: simple pits and more intricate variable chamber constructions such as undercut and catacombs.
 303 graves of women with weapons from 267 barrows are known in the territory of European Scythia. More than half of them (55 %) have not been looted. By territorial principle they can be divided into five main groups: 1) Lower Dnipro steppe (or Steppe); 2) Crimea Foothills; 3) Danube-Dnister steppes (or Transnistria); 4) Forest Steppe Dnipro area (or Forest Steppe); 5) Don region (Steppe and partly Forest Steppe).
 In total, among graves of the Amazons of European Scythia the undercut (alcove) graves are the most represented — 104, inferior to them are catacombs — 99 and pit graves — 80, undefined — 20. However, the indicators for some groups differ significantly.
 We can mention the following design features of the graves: ground steps and hollow in the bottom of entrance pit, separation of entrance to dromos or chamber etc.
 Some specific features are also present in the arrangement of internal space of the graves (nishes, wall and ceiling design, floor decoration, arrangement of a funeral bed etc.).
 So, burial complexes of the female warriors correspond to Scythian regulations, that is, the design of ground and underground elements does not stand out in the burial ground. Here, we are dealing only with regional features typical for community members who lived there.

Hydrodynamics, sediment transport, and water quality of two contrasting dredge pits on the Louisiana shelf

Sediment is needed for coastal restoration in Louisiana and is often excavated offshore from mud-capped and sandy dredge pits. To better understand the post-dredging effects on hydrodynamics, sediment transport, and water quality, two tripods were deployed at sandy Caminada pit and mud-capped Sandy Point pit in summer 2018 and 2019, respectively, and profiling data were collected during a total of 34 casts in 2018 and 2019. The results reveal similarities and differences between pit and adjacent waters and are used to compare two pits. Tropical storm events were observed during each deployment which provided insight concerning the effects these storms have on dredge pits. Water masses inside Caminada pit were relatively stable and sluggish which resulted from the pit's deep depth and location. Sandy Point dredge pit was highly impacted by the Mississippi River plume due to its proximity, which effectively stratified the water column in summer 2019, affecting ventilation near the seabed. Strong winds, taller waves, higher shear stresses, elevated turbidity and increased dissolved oxygen were generally found during the passages of tropical storms over both pits. Comparing with outside tripod station, the inside station of Caminada pit experienced a longer duration of low dissolved oxygen in bottom waters. Water mass movements and oxygen consumption from resuspension of pit bottom are likely key mechanisms driving oxygen dynamics. Our results provide observational data for future studies on post-dredging morphologic change, marine communities, and oxygen dynamics of dredge pits on the Louisiana shelf and other coastal dredge areas worldwide.

Conceptual engineering designs on resumption of mining operations and flooding protection in Mir Mine

Selection of a geotechnology for underground mining in Mir Mine, in challenging hydrogeological conditions has been the point under hot discussion for a few decades. An associate issue is protection of underground excavations from flooding. The latter problem is critical at interfaces of kimberlite and freely soluble host rock salt. After termination of surface mining operations, out of two variants of underground mining systems with cemented backfill or with bulk caving, the scenario with backfilling and with dry conservation of the open pit was selected. Dry conservation means fill of dolerite layer on the pit bottom, placement of water-proof film on this layer and outlet of all inflows via a drainage day drift and vertical boreholes. No other activities on protection of the mine from halite-undersaturated brine inflows from the pit were provided by the adopted design solutions. In the chosen scenario, above the impermeable film, a water body generated had varied volume subject to the ratio of water inflows in the pit and flow rate of discharge boreholes. Water inflows in the mine resulted in uncontrollable growth of salt karst at the kimberlite–rock salt interface, and in the subsequent degradation of the interface due dissolution of salt in the contact zone and owing to filling of fractures with dissolved salt inside the ore body. Based on the implemented research, the authors assess prospects for the resumption of operations in the mine by stoping with caving. Such technology seems to be most advisable in the given hydrogeological conditions. In this case, it is required to start with catchment of ground water inflows in the pit by means of arrangement of internal and external drainage loops.

Изменения атмосферного давления как неблагоприятный фактор работы в глубоких карьерах

The need in considering changes (including sharp) of the atmospheric pressure during the operation of deep open pits as one of the unfavorable factors is substantiated. It is believed that the atmospheric pressure in a particular region varies slightly-within 30–40 mm Hg per year. But at the present time, when only in Russia there are five open pits with a depth of 500 m and more, it is impossible to ignore changes in the atmospheric pressure in relation to workers moving, for example, by motor transport, from the surface to the bottom of the open pit and back. In this case, it can change by 50 or more mm Hg in half an hour. To solve the related problems, it is required to find out how atmospheric pressure affects the blood pressure of the open pit workers. The experience of the Dead Sea Clinic located in Israel at the Dead Sea at a depth of more than 400 m below the sea level is taken as a basis. Long-term measurements of the blood pressure in patients of the clinic revealed a tendency to decrease it by an average of 10–20 mm Hg. To prevent the adverse effect of a sharp change in the atmospheric pressure on people working in deep open pits, it is required to provide for appropriate measures of a different nature: technological (provide for changes in the characteristics of the open pit roads to ensure smoother descents and ascents of the dump trucks); technical (use of the conveyor and combined transport); organizational (including changes in the work and rest regimes of the working employees); regulatory (amendments to the relevant safety rules and other normative documents). To apply the results obtained in the open pit mining, it is necessary to conduct appropriate research in the operating deep open pits.

Effects of corrosive media on the localized corrosion forms of Mg-3Zn alloy

Mg-3Zn alloy presents filiform corrosion in NaCl solution but pitting corrosion in Na2SO4 solution. The mechanisms for those different localized corrosion forms were investigated using SEM, XPS and electrochemical measurements. It is found that surface films and different features of Cl– and SO42– determine the corrosion forms of Mg-3Zn alloy. The surface film formed in NaCl solution is porous, and Cl– ions are enriched in the filament heads, resulting in propagation of corrosion along the horizontal direction to form filiform corrosion. However, the surface film formed in Na2SO4 solution is compact, and SO42– anions are aboundant at the bottom of corrosion pits, resulting in the propagation of corrosion along the vertical direction to form pitting corrosion. Corrosive media play a key role in the initiation and propagation of corrosion, further resulting in the different corrosion forms of Mg alloys.