Large Diameter Research Articles

Heat transfer performance and optimal design of shallow coaxial ground heat exchangers

The heat transfer performance of coaxial ground heat exchangers (GHEs) can be strongly influenced by their structure parameters and improved by the optimal design. To improve the heat transfer efficiency, this study proposed a coaxial GHE with large pipe diameters and thick inner pipe insulation for shallow ground source heat pump systems, which had heat transfer rates of more than 120 W/m in 12 h during both heat injection and extraction experiments. The validated three-dimensional CFD model was used to numerically investigate the influence of various structural parameters on the heat transfer efficiency considering the thermal short-circuiting effect. The thermal short-circuiting effect could be alleviated with thicker inner pipe insulation, while the decreasing annular space occupied by the insulation would reduce the borehole heat transfer rates, thus, an inner pipe with a 35 mm-thick insulation obtained the optimal heat transfer rate. The inner pipe diameter increase contributed to a more severe thermal short-circuiting and poor heat transfer performance. Increasing the outer pipe diameter improved the heat transfer efficiency and an optimal outer pipe diameter of 155 mm existed when considering the heat transfer performance and its efficiency. Therefore, increasing the inner pipe insulation thickness and outer pipe diameters can be regarded as an efficient method to improve the thermal performance of coaxial GHEs.

Determining a Reliability Centered Maintenance (RCM) analysis model for large diameter prestressed concrete water pipelines

Which maintenance task to perform on an asset is generally known but the schedule of when to perform the task may not be well defined. If the task is performed early, while it may benefit the asset, it may also be expending resources that could be better used elsewhere. If the task is not performed soon enough, the asset may fail, or the asset may require more extensive maintenance be performed. Reliability Centered Maintenance (RCM) is an analysis process used to determine the most effective maintenance strategies. RCM analysis can help an agency establish the most cost effective maintenance strategies for an asset and help establish the best schedule for implementing those strategies. The ultimate goal of an RCM is to determine the required function of an asset with the required reliability at the lowest operation and maintenance costs by identifying revealing indicators of potential failures to establish a condition based strategy; essentially, predicting failures and identifying procedures to minimize the risk of the failure. This paper reviews potential models for predicting the progression of distress of prestressed concrete pipe segments for use in an RCM analysis and proposes a regression model operators can use to forecast when to perform maintenance activities. The paper further considers the condition of the drinking water infrastructure in the United States, developing the case for evaluating predictive models to forecast when a pipeline may reach a specified limit state. The results of this study suggest that RCM analyses for large diameter water pipelines can improve reliability, reduce maintenance costs, and extend the useful life of a pipeline regardless of age or material. Further, using a regression style model with gathered data can be used to forecast when specific maintenance thresholds may be reached, prompting predictive maintenance actions.

Prognostic factors for surgical treatment of radiation-induced scleral necrosis after brachytherapy for uveal melanoma.

Radiation-induced scleral necrosis (RISN) is a less frequent complication of brachytherapy for uveal melanoma, and may require surgical treatment in selected cases. We aimed to identify the prognostic factors for RISN treatment. All patients with brachytherapy for uveal melanoma treated at our institution between 01/1999 and 12/2016 who developed RISN were followed until 02/2021. Various parameters were evaluated through univariable and multivariable Cox regression analysis. The surgical intervention due to RISN was the principal outcome event of this study. Of 115 patients in the final cohort, 51 individuals (44%) underwent RISN treatment (conjunctival revision [n = 2], patching [n = 46] or enucleation [n = 3]) at median 1.80 months after RISN occurrence. Significant RISN characteristics were summarized into a novel RISN severity scale - Grade I: largest diameter ≤ 5 mm and no progression; Grade II: largest diameter > 5 mm or any progression during the follow-up; Grade III: presence of uveal prolapse; and Grade IV: leakage through open eyewall perforation. In the multivariable analysis, the RISN severity scale (aHR = 2.37 per grade increase, p = 0.01) and the time between brachytherapy and RISN occurrence (<15 months, aHR = 6.33, p < 0.0001) were independently associated with the study endpoint. The RISN severity scale showed high diagnostic accuracy for prediction of RISN treatment (AUC = 0.869). In our series, about the half of RISN cases underwent surgical treatment. The presented novel severity scale for RISN might become a helpful tool for clinical management of individuals with RISN. We recommend external validation of the diagnostic accuracy of the presented scale.

Microsphere-assisted hyperspectral imaging: super-resolution, non-destructive metrology for semiconductor devices

As semiconductor devices shrink and their manufacturing processes advance, accurately measuring in-cell critical dimensions (CD) becomes increasingly crucial. Traditional test element group (TEG) measurements are becoming inadequate for representing the fine, repetitive patterns in cell blocks. Conventional non-destructive metrology technologies like optical critical dimension (OCD) are limited due to their large spot diameter of approximately 25 μm, which impedes their efficacy for detailed in-cell structural analysis. Consequently, there is a pressing need for small-spot and non-destructive metrology methods. To address this limitation, we demonstrate a microsphere-assisted hyperspectral imaging (MAHSI) system, specifically designed for small spot optical metrology with super-resolution. Utilizing microsphere-assisted super-resolution imaging, this system achieves an optical resolution of 66 nm within a field of view of 5.6 μm × 5.6 μm. This approach effectively breaks the diffraction limit, significantly enhancing the magnification of the system. The MAHSI system incorporating hyperspectral imaging with a wavelength range of 400–790 nm, enables the capture of the reflection spectrum at each camera pixel. The achieved pixel resolution, which is equivalent to the measuring spot size, is 14.4 nm/pixel and the magnification is 450X. The MAHSI system enables measurement of local uniformity in critical areas like corners and edges of DRAM cell blocks, areas previously challenging to inspect with conventional OCD methods. To our knowledge, this approach represents the first global implementation of microsphere-assisted hyperspectral imaging to address the metrology challenges in complex 3D structures of semiconductor devices.

Bending forming of lightweight large diameter thin-walled aluminum alloy aviation tube

To improve the forming quality of lightweight aviation tubes, the influence of different tube specifications, forming requirements and process parameters on bending forming of large diameter thin-walled (LDTW) LF2M aluminum alloy tubes (AATs) was studied. A finite element analysis model for LDTW AAT bending was established and verified. The results show that with the increase of mandrel extension length [Formula: see text], the wall-thinning ratio tends to increase. With the increase of [Formula: see text], the overall wall-thickening ratio decreases. With the increase of [Formula: see text], the ovality decreases first and then increases. The bending radius has a great influence on wall thickness variation. It has great significance to guide the bending forming of lightweight LDTW aluminum alloy aviation tube.

Complications associated with loop ileostomy: analysis of risk factors.

Loop ileostomy is a common surgical procedure but is associated with complications such as outlet obstruction (OO), parastomal hernia (PH), and high-output stoma (HOS). This study aimed to identify risk factors for these complications, as well as their causal relationships. The study included 188 consecutive patients who underwent loop ileostomy between April 2016 and September 2021. Clinical factors and postoperative stoma-related complications (OO, HOS, and PH) were analyzed retrospectively. Stoma-related factors were evaluated using specific measurements from computed tomography (CT) scans. The incidence, clinical course, and risk factors for the stoma-related complications were investigated. OO was diagnosed in 28 cases (15.7%), PH in 60 (32%), and HOS in 57 (31.8%). A small longitudinal stoma diameter at the rectus abdominis level on CT and a right-sided stoma were significantly associated with OO. Creation of an ileostomy for anastomotic leakage was independently associated with HOS. Higher body weight and a large longitudinal stoma diameter at the rectus abdominis level on CT were significantly associated with PH. There was a significant relationship between the occurrence of OO and HOS. However, the association between OO and PH was marginal. This study identified key risk factors for OO, HOS, and PH as complications of loop ileostomy and their causal relationships. Our findings provide insights that may guide the prevention and management of complications related to loop ileostomy.

Microzooplankton and phytoplankton of Ross Sea polynya areas and potential linkage among functional traits

The Ross Sea is characterized by a series of subsystems with different characteristics making it an extremely productive area. To understand whether species composition and functional traits of the plankton community can be used as biological tracers, we have analyzed the composition of phytoplankton and microzooplankton, and their potential relationships, in two different polynyas of the Ross Sea during the austral summer 2017. Sampling activities were carried out near Terra Nova Bay, between Cape Washington and the northern shore of the Drygalski Ice Tongue, and in the South-Central Ross Sea. We investigated the phytoplankton and microzooplankton structure using the phytoplankton body size classes and the tintinnids lorica oral diameter as functional traits, speculating on the relationship between the two plankton communities and their use as biological indicators in a changing Southern Ocean. Our data showed significant differences in terms of plankton composition and related functional traits between the two areas, suggesting the existence of distinct ecological dynamics despite the similar total carbon content. In Terra Nova Bay, heterotrophic dinoflagellates were the most abundant microzooplankton, in association with a large phytoplankton biomass mainly represented by diatoms and nano- and micro-phytoplankton. Tintinnids with large lorica oral diameters were abundant in Central Ross Sea, where phytoplankton was dominated by Phaeocystis antarctica and by the micro size class. Among microzooplankton, Protoperidinium defectum, P. applanatum and P. incertum were the most abundant dinoflagellates species, while Codonellopsis gaussi, C. gaussi forma cylindroconica, Laackmanniella prolongata and Cymatocylis drygalskii were the most abundant tintinnids. The phytoplankton was dominated by diatoms Pseudo-nitzschia subcurvata, Fragilariopsis cylindrus, F. curta and by the haptophyte P. antarctica. Our data indicate that beyond physical and chemical features defining distinct sectors of the Ross Sea, both species composition and functional traits of phytoplankton and microzooplankton represent a valid monitoring tool, especially with the ongoing global warming and its effects on Antarctic food webs.

A modified Nonlinear Foundation Beam model for half-rigid monopiles with Timoshenko representation and compatible soil springs in sand

There is a large number of monopile foundations for offshore wind turbines falling in the type of half-rigid pile, and are recommended to be analyzed by the p-y method in design. However, the p-y method currently adopted in oil and gas industry for slender piles has proved to be inapplicable for monopile-soil interaction, with overestimated ultimate lateral resistance and underestimated initial stiffness predicted. Thus, factoring in the bending resistance provided by shaft friction and end bearing forces for large diameter monopiles, a modified Nonlinear Foundation Beam (NFB) method is proposed in this paper to predict the monopile response in sand, where a beam element considering sectional shear stress is adopted, and another three sets of soil springs are incorporated with the p-y soil spring. Unified relationships of the proposed soil springs are also proposed with varying sand and pile properties. The modified NFB method is validated by published test results with diameters ranging from 2 m to 6 m, and L/D ratios from 5.08 to 8.29, proving its applicability for analysis of half-rigid monopiles.

The efficacy and safety of additional pulmonary vein antrum substrate ablation after cryo-ablation in patients with persistent atrial fibrillation

Abstract Background Cryo-ablation for persistent atrial fibrillation (PeAF) has been reported to be safe and comparable to radiofrequency (RF) ablation, but the outcome was not satisfactory. AF drivers mapping after pulmonary vein isolation (PVI) was reported to be widely identified in left atrium (LA). On the other hand, extensive drivers ablation is considered to have limited durability of PVI compared to cryo-ablation. Purpose This study sought to investigate the efficacy and safety of additional PV antrum substrate ablation after PVI by cryo-ablation in patients with PeAF. Methods A total of 122 consecutive patients (90 men, 32 women) who underwent ablation between January 2021 and July 2023 for PeAF, except for patients with long standing ≥10years AF, or large LA diameter ≥55mm, or low left ventricular ejection fraction (LVEF) ≤35% with organic heart disease, were divided into three groups; cryo-ablation alone (Cryo group; 30 patients), RF ablation alone guided by AF drivers mapping (RF group; 52 patients), or cryo-ablation plus RF for AF drivers (Cryo+RF group; 40 patients). AF drivers mapping was performed by real-time phase mapping system or complex fractionated electrograms (Figure1). The outcome of freedom from atrial tachy-arrhythmia lasting longer than 30 seconds without anti-arrhythmic drugs after three months blanking period of a single procedure was compared among groups. Results Baseline characteristics of patients (68±9.2 years old, LVEF 57±9.9 %, LA diameter 43±5.4 mm, persistent AF duration 9.4±18 months, long standing ≥1year AF 17 patients) were similar in three groups. The incident of recurrence of atrial tachy-arrhythmia in Cryo+RF group was significantly lower compared with Cryo group (15% vs. 37%; p=0.014) and RF group (15% vs. 25%; p=0.28) (Figure2). There was no serious complication in three groups. Conclusion Additional drivers RF ablation after cryo-ablation for PeAF is safe and associated with a significant reduction in atrial tachy-arrhythmia recurrence.Figure 1Figure 2

Intelligent circumferential deformation prediction of structures in PCCP-E with a large diameter under internal water overpressure based on prototype experiments and Inception-ResNet-LSTM

Prestressed Concrete Cylinder Pipe (PCCP) is extensively employed in long-distance water transmission projects, owing to its notable pressure-bearing capacity and durability. Nonetheless, the operation under overpressure conditions poses a risk of structural damage and functional failure to PCCP during its service life. Consequently, accurate prediction of the deformation characteristics of overpressure operation with the structural deformation data under standard water pressure is of great importance for ensuring the safety and reliability of the project. However, it is a challenge to obtain spatiotemporal features for traditional algorithms. As a consequence, a novel deep learning model, i.e. Inception-ResNet-LSTM, is put forward to forecast PCCP deformation. It integrates the Inception, ResNet, and Long Short-Term Memory (LSTM). Based on the prototype experiments, the monitoring was undertaken on the deformations of the inner and outer concrete layers, the steel cylinders, and the prestressed steel wire under internal water pressures of 0 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa, and 1.15 MPa. In the case study, the deformation data of different structures are input into Inception-ResNet-LSTM to establish a model. For all the structures, the R2 (coefficient of determination) of the Inception-ResNet-LSTM model exceeds 0.97. Based on the results, it is demonstrated that the model has captured the spatiotemporal features from the monitoring data. In comparison to models based on DL and ML algorithms, Inception-ResNet-LSTM demonstrates superior performance, exhibiting heightened accuracy and enhanced generalization capabilities. It provides a new method for PCCP deformation estimation under overpressure.

Influence of shale reservoir properties on shale oil mobility and its mechanism

Given the tremendous potential for continental shale oil in China, many oilfields in the central and eastern parts of the country are involved in the exploration and development of shale oil resources. Besides engineering factors, shale oil mobility is the key to determining its commercial viability. This study explores the Hetaoyuan Formation in the Biyang Depression as an example to determine the influence of reservoir properties on the movable oil volume and its mechanisms. Multiple techniques were used, including displacement nuclear magnetic resonance (NMR), low-temperature nitrogen adsorption (LTNA), X-ray diffraction (XRD) bulk mineral analysis, and scanning electron microscopy (SEM), and the results suggest that large average pore diameter, high throat to pore ratio, single pore morphology, and small specific surface area can weaken the boundary layer effect and reduce the amount of adsorbed oil. Our observations reveal that compared to the dissolution pores and intergranular pores in brittle minerals, the intercrystalline pores in terrigenous clastic clay minerals are more affected by compaction. Furthermore, authigenic clay minerals notably block the intergranular pores in the interbedded sandstones. Clay minerals are identified as the main contributor to the specific surface area, with high clay mineral content enhancing the pore heterogeneity of the reservoir. Thus, positive shale oil mobility occurs in shale with a weak boundary layer effect, which is attributed to the high brittle mineral content, large average pore diameter, small specific surface area, single pore morphology, and reservoir homogeneity.

Pressure propagation mechanism of open-cell aluminium foam within a pipe under hypervelocity impact

Low-density open-cell aluminium (Al) foam exhibits a different deformation mode under hypervelocity impacts compared to being subjected to medium-low speed and quasi-static compression. In this case, material flows between cells in the form of metal jets and propagates forward. This paper establishes the open-cell Al foam model based on Voronoi tessellation. Using numerical methods, one-dimensional hypervelocity constant velocity impact experiments of 1–6 km/s inside a closed pipe are conducted on Al foam with different internal structure parameters (average cell diameter: 2–3.5 mm; ligament width: 0.251–1 mm). Propagation mechanism of pressure waves in foams and the key factors affecting the propagation velocity are investigated. Three zones are divided according to the condition of jet distribution along the impact direction: unaffected zone, jet influence zone, and particle accumulation zone. The variation of the length of different zones with impact velocity is discussed: higher velocities result in longer jet influence zones but shorter particle accumulation zones. Meanwhile, length of zones is closely related to the width of Al foam ligament and cell pore diameter: the larger the diameter of cell pores and the smaller the width of ligaments, the longer the length of the jet influence zone. Time dependence is exhibited in the length of jet influence zone for the large cell pore diameter specimens(≥0.03 cm). Particle pressures are extracted using the one-dimensional averaging method, which propagates forward significantly lower than in dense materials. Dominant factors affecting the pressure wave propagation of open-cell Al foam, i.e., the internal unloading space, are obtained by combining two-dimensional hypervelocity impact simulation experiments with different boundary conditions. A strong correlation between metal jet distribution and particle pressure propagation is observed.

Lessons Learned from Failures and Design Improvements for Large Diameter Seals

Large diameter seals are used in Prototype Fast Breeder Reactor (PFBR) to prevent the escape of radioactive argon cover gas through wide annular gaps. The design of these seals shall address different challenges than normal seals. The large tolerances needed on the width of annulus, achievable tolerances on rubber, clearances in the seal holder, etc., influence the seal performance. The paper discusses analytical and experimental work done to develop robust large diameter seals. The contours of the present study are based on the feedback from the testing and qualification of small size model seals. Various permutations of geometry for seal and its holder are numerically investigated. The study mainly highlighted the influence of seal holder on the seal performance. Various sensitivity studies done on selected seal and seal holder demonstrated robustness of the design solutions.Graphical

Design and development of a novel multirotor configuration with counter-rotating coaxial propellers

In this study, a novel multirotor configuration has been developed, which utilizes a coaxial counter-rotating propeller with a large diameter at the center and four propellers with smaller diameters on four arms in an X configuration. The research pursues two main objectives. The first objective is to establish a development method for multirotors based on the well-known V-method approach in system development. The proposed method enables the design team to analyse and evaluate the multirotor at each stage of the design process, from the system to the component level, and improve the design with greater speed and accuracy. Additionally, the proposed approach can be integrated with various optimization methods, if necessary, to achieve an optimal design. The second objective is to provide the proof-of-concept of the novel multirotor configuration. This objective is pursued across different evaluation sections, from evaluating individual components to fully evaluating the multirotor, to assess the performance of this novel configuration and identify its advantages and disadvantages. The results of various evaluations demonstrate the proposed development process's practicality and proves that the novel configuration is operational and competitive with conventional multirotors in various applications.

Study on Grouting Repair and Reinforcement Technology of soft Foundation of large diameter Highway Tunnel

Taking the uneven settlement of the foundation of a two-way eight-lane large diameter highway tunnel as the engineering background, the joint grouting reinforcement technology of miniature steel pipe pile and steel sleeve valve pipe is put forward. based on the field measured settlement data and foundation core samples, the effectiveness of repair and reinforcement is analyzed. The research results show that the combined grouting of miniature steel pipe pile and steel sleeve valve pipe can effectively control the settlement of tunnel foundation, and significantly improve the RQD (Rock Quality Designation) value of tunnel foundation, which provides technical reference and basis for the construction of similar projects.

Research and Application of High Efficiency Pressure Relief Technology for Ultra-high Pressure Hydraulic Slotted Coal Seam

In order to solve the technical problem of efficient pressure relief of the impact coal seam, the principle of ultra-high pressure hydraulic slit relief and anti-impact technology is expounded, and the ultra-high pressure hydraulic slit device with working pressure up to 100MPa is selected as the pressure relief equipment of coal seam. The field test of high-efficiency pressure relief by ultra-high pressure hydraulic slotting in impact coal seam was carried out. The test showed that the slotting radius of No.3 coal in Tangkou Mine could reach 1.5m under the condition of 100MPa slotting pressure. The stress variation in seam area and large diameter drilling area is compared and analyzed. The stress in seam area decreases significantly by 40%. The stress of bolt (cable) and the deformation of surrounding rock in the slit area are investigated. Compared with the large-diameter pressure relief area, the increase value of bolt is lower and the increase value of cable is significant in the hydraulic slit test area. The technical benefits of hydraulic slotting and large-diameter drilling are summarized and compared. The engineering quantity of drilling with ultra-high pressure hydraulic slotting is reduced by 60%, and the coal output is 2.5 times of that of large-diameter drilling. The large-diameter drilling provides limited pressure relief space for coal seam, but the ultra-high pressure hydraulic slotting technology can effectively increase the deformation space in the coal body and reduce the elastic energy stored in the coal pillar, so as to achieve a good pressure relief effect. The field test shows that compared with large diameter drilling, ultra-high pressure hydraulic slotting technology has remarkable effects of pressure relief, shock absorption and shock prevention.

Influence of precast microbial reinforcement on lateral responses of monopiles

Microbially Induced Calcium Carbonate Precipitation (MICP) provides an environmentally friendly solution for reinforcing large diameter monopiles for offshore wind turbines (OWTs). This study presents an investigation into the lateral responses of monopiles with precast microbial reinforcement using a low-pH one-phase method. Both static and cyclic loading tests were carried out. The results of static loading tests show that the failure mode of the bio-reinforced monopile was an overall overturn failure. The lateral bearing capacity was increased by 50% and the bending moment was reduced by about 25% with the bio-reinforcement. Further investigation was conducted on the secant stiffness, damping ratio, and accumulated deformation of the bio-reinforced monopile under various cyclic loadings. With the bio-reinforcement, the accumulated deformation under one-way cyclic loading can be reduced by 30%–60%. The influences of cyclic loading parameters and loading sequence on pile stiffness were clarified. The growth ratio of pile stiffness due to bio-reinforcement under one-way loading was between 1.65 and 2.82, and decreased with increasing load amplitude. The ratio was smaller under two-way loading. Three competing factors on pile stiffness were identified: cyclic compaction of the unreinforced sandy soil, weakening of the bio-reinforced soil and soil subsidence around the bio-reinforced soil.

Relationship Between Diameter and Pelvic Vein Reflux

Introduction: Diameter has been a complementary measurement in the evaluation of venous valvular insufficiency of superficial veins of the lower extremity. Small veins with reflux or large veins without reflux may indicate alternative treatments. Awareness of pelvic vein reflux is increasing. The pelvic vein diameter-reflux relationship was investigated. Methods: Findings of lower extremity ultrasound (US) and/or clinical conditions—pelvic pain, dyspareunia and dysmenorrhoea—were indications for pelvic/abdominal venous US. Complete US examination included renal, internal iliac and gonadal/ovarian veins. Diameters of the largest right or left pelvic veins were compared with presence of reflux. Intravaginal US was completed in 104 women, age 46 ± 11 (standard deviation) (range 25-76) years old. Pelvic symptoms were reported by 30 (29%) patients. The other patients had pelvic-related recurrent varicose veins or suspected pelvic source of lower extremity venous reflux. Positive and negative predictive values (PPV, NPV) and other statistics at the 90-95% level were calculated relating diameter to pelvic vein reflux. Results: Pelvic vein reflux was detected in 54 (52%) women. Pelvic vein diameters were larger in refluxing, 8.4 ± 1.9 (5.1-14.0) mm, than in nonrefluxing veins, 5.2 ± 1.0 (3.4-8.3) mm ( P &lt; .001 by t test). Diameters ≥6.3 mm had 91% (49/54) sensitivity and 92% (49/53) PPV. Diameters ≤6.3 mm had 94% specificity (47/50) and 89% (47/53) NPV. All veins with diameter ≥8.4 mm ( n = 21) had reflux. All veins with diameter ≤5.0 mm ( n = 27) did not have reflux. Conclusions: Probabilities of pelvic vein reflux were estimated based on diameters. Diameter-reflux agreement solidifies diagnosis. An explanation for contradiction between small diameter and reflux or large diameter and no reflux is recommended.

Harnessing fuzzy logic for building structural health during large diameter tunnelling in urban area

Building structural health is constantly jeopardized by tunnel construction, which thus is in a sustained demand for holistic risk assessment and management approaches. In this study, we propose an enhanced consulting fuzzy model with limited information losses to evaluate the static and dynamic risks of building health deterioration during tunnelling. The model integrates three main strategies including, (i) reducing influence of experts’ bias in the ranking processes; (ii) expanding the space of uncertainties in fuzzy environment, and (iii) controlling risk aversion settings through the prospect theory. The construction of the largest diameter (15.3 m) tunnel in China is adopted as a case study to demonstrate the application of the proposed model in assessing the risk statuses of surrounding buildings. Through the proposed model, the risk index can indicate beneficial or detrimental effects of tunnelling and the degree of risk factors delineates priority actions for risk management. The results enable the development of operational risk abatement procedures to enhance the state of practice of large diameter tunnel construction in complex geological conditions.

The effectiveness of minimally invasive surgical techniques for treating patients with chronic venous insufficiency in the stage of trophic disorders: comparative study

Introduction. Despite the active introduction of minimally invasive techniques into modern phlebology, the problem of surgical treatment of chronic venous insufficiency (CVI) in the stage of trophic disorders is still far from being finally resolved, especially problems of horizontal reflux. Aim. Тo comparatively evaluate the results of using various tactics of minimally invasive surgical treatment in patients with lower extremitiesʹs CVI in the stage of trophic disorders.Materials and methods. A study at 139 patients with CVI at the stage of trophic disorders was carried out. Group 1 (n = 79) included patients who underwent endovasal laser coagulation of the trunks of the great and small saphenous veins (GSV and SSV) with microfoam sclerotherapy of varicose perforating veins. In group 2 (n = 60) – method of intervention was determined by the diameter of Cockettʹs perforants.Results. Indicators of the early postoperative period in the study groups were comparable. After 2 months, no cases of relapse in the GSV and SSV were registered. Recurrence of horizontal reflux was observed only in 6 (7.6%) people in group 1. In long-term postoperative follow-up, decrease in the severity of the disease according to the VCSS scale was found in both groups (p &lt; 0.001). The persistence of pathological reflux along was observed in 16 (22.5%) patients of group 1. Moreover, in 62.5% and 68.75% cases of relapses, the perforants had, respectively, a large diameter and high blood flowʹs speed.Discussion. In general, minimally invasive techniques used demonstrated comparable clinical results and high efficiency. At the same time, the importance of preoperative assessment and taking into account the properties of perforants has been proven.Conclusion. The claimed method should be considered as an effective and safety method of obliteration of incompetent perforating veins at severe forms of CVI.