Wall Collapse Research Articles

Study on Nano Composite Cement Slurry System Suitable for Low Temperature Formation

In order to solve the problems of borehole wall collapse and well leakage during drilling in low temperature formation, a new nano-composite cement-based grouting material system suitable for low-temperature formations has been developed. The effect of nano-Al2O3 on the performance and process of low-temperature silicate-thioaluminate composite cement slurry was studied by combining macroscopic test and microscopic analysis. Through the synergistic hydration effect induced by mixing ordinary Portland cement with sulphoaluminate cement, together with nano-Al2O3, antifreeze agent (EG), water reducing agent (JS-1), early strength agent (TEOA), a new composite cement slurry (NAC) was developed, an integrated analysis of scanning electron microscopy, X-ray diffraction and exotherm was used to observe and analyze the patterns of the low temperature process of NAC. The experiment concluded, at a low temperature of –9 ℃, the nano-composite cement cement (NAC) had good initial fluidity, with a pumpable period of 57 min, and 24 h compressive strength of 6.9 MPa. Research shows that NAC has the effect of 'right angle thickening' and the performance is superior at low temperature, which can meet the performance requirements of borehole wall protection and plugging in low temperature formation drilling.

Laboratory experiment of fire spread between two informal settlement dwellings

Fire spread between informal settlement dwellings (ISD) is a primary concern for large scale informal settlements conflagrations. Globally, approximately one billion people live in informal settlements and are exposed to these fires. This paper presents a fire spread experiment between two dwellings, built with ISO 9705 dimension as an approximation of an ISD and separated by 1 m. The fire development and fire spread mechanisms within and between the ISDs were investigated and benchmarked against an independent single dwelling experiment with identical boundary conditions. Parameters, such as mass loss rate of fuel, total heat release rate, gas temperatures, wall and roof temperatures, and gas velocity at the openings were measured, as well as external incident heat fluxes. A comparison between the single and double dwelling experimental results are made. It was established that the existence of the adjacent dwelling, which changes the dynamics of initial burning stage of the wood cribs in dwelling, delayed the flashover of the burning dwelling by more than 150 s (Dwelling 1). The fire spread from dwelling to dwelling that is perpendicular to the plane of the openings is hypothetically concerned with wall collapse or large flame ejections from the burning cardboard linings, rather than the radiation from the heated metal wall, with recorded fluxes of 35, 20, and 5 kW/m2, respectively. Due to the very thin-walls with high conductivity and natural leakage in ISDs, current theories for temperatures, heat release rates, flame shapes, and flashover conditions, based on thermally thick-walled dwellings, do not replicate the data well. A new fire spread model between dwellings, based on accumulated energy, is proposed in this work and conservatively under-predicts the time to ignition by 9 % for this experiment.

Horizontal well drilling technology for super-long horizontal section with small hole in Changqing Oilfield

In order to solve the problems such as the difficulty of borehole trajectory control, low drilling encounter rate, high risk of downhole engineering, low mechanical drilling rate, collapse of wellbore wall and loss of well in the construction of super-long horizontal well in Changqing Oilfield, we analyze the reasons, and through the application of rotary steered intelligent well trajectory control technology to accurately control the trajectory, near-bit azimuth gamma imaging technology to improve the penetration rate of the reservoir, engineering parameter monitoring technology to ensure downhole safety, combined with the field optimization of bit selection to improve the mechanical drilling rate, the experimental selection of nano film sealing water-based drilling fluid to improve the performance of drilling fluid. Well Tao XX, constructed in Changqing Oilfield, applied the rotary steering technology, and completed the construction tasks of 4466 meters of horizontal section, 8008 meters of total well depth and the reservoir penetration rate was 96.6% in a safe and efficient way, which set a new record of the deepest well depth in Changqing Oilfield and the longest horizontal section on land in the Asia-Pacific region. The practical construction results of this well show that the rotary steering technology is feasible and effective in the construction of slim-hole super-long horizontal wells.

Upper airway collapse characteristics in adult patients with OSA and previous tonsillectomy.

To analyze upper airway (UA) collapse patterns through drug-induced sleep endoscopy (DISE) in adult patients withobstructive sleep apnea (OSA) who previously underwent tonsillectomy. This was a retrospective study on patients withOSA who underwent DISE between June 1, 2013 and July 30, 2017 at Stanford Hospital. Subjects who had prior tonsillectomy history were classified into the tonsil0 group, whereas others were classified into the tonsil1 and tonsil2/3/4 group based on tonsil grade. UA collapse characteristics were recorded and analyzed among groups according to Velum, Oropharynx, Tongue base and Epiglottis (VOTE) classification. A total of 205 individuals were included, 38 in tonsil0 group, 104 in tonsil1 and 63 in tonsil2/3/4. The tonsil0 group had a higher percentage of anterior-posterior (AP) velum (58%) and tongue base (45%) collapse compared with the tonsil2/3/4 group (22%, P = 0.0003 and 22%, P = 0.02, respectively) but less oropharyngeal lateral wall collapses (29% vs 53%, P = 0.02). Most of the tonsil0 group (70%) showed multi-sites collapse pattern, the percentage of combined obstruction in both palatopharyngeal and hypopharyngeal region was higher (50% vs 29%, P = 0.03). The difference of velum complete AP collapse remained significant after adjusting for age and BMI (Odds Ratio = 0.33, 95% CI 0.12-0.86, P = 0.02). No significant differences were found between the tonsil0 and tonsil1 groups. Compared with individuals with larger tonsils (grade 2 to 4), those with previous tonsillectomy and OSA were susceptible to the velum AP configuration collapse. Diversity of multi-sites obstruction and combined collapse in both palatopharyngeal and hypopharyngeal level was the main characteristic.

Trans-hyoid hyoidthyroidpexy: A modified technique for selected cases of obstructive sleep apnea

ObjectiveHypopharyngeal collapse (HC) considered a challenge in surgery of obstructive sleep apnea (OSA). Several procedures were presented to deal with HC indirectly via providing support to the lateral walls of the hypopharynx preventing transverse collapse but hyoidthryoidpexy had gained more popularity. The procedure aimed to fix the mobile hyoid bone to a rigid mid-line neck structure, thus preventing the bone and its attached muscles from collapsing during sleep with the negative intrathoracic pressure on inspiration. Study designA prospective case series study. MethodsFrom April 2018 to January 2020, A Modified Technique of Trans hyoid hyoidthyroidpexy was applied for all included patients (24) patients with symptoms of OSA showing predominant lateral wall collapse of the hypopharynx (with retro-palatal collapse) with other OSA surgery. Results6–8 months postoperatively, the Apnea Hypopnea index dropped from 43.75 ± 8.44 to 16.28 ± 7.35 (P < 0.0001; t = 10.6988). 14 patients (58.33%) were reported as successful while 7 patients (29.17%) were considered responders and three patients (12.5%) were considered non responders. The mean lowest oxygen desaturation elevated from 77.56 ± 5.64 to 92.38 ± 6.25 (p < 0.0001). Epworth Sleepiness Scale improved (P < 0.0001) from 16.85 ± 4.23 to 5.17 ± 3.89. ConclusionTrans-hyoid hyoidthyroidpwxy is a modified technique of hyoidthyroidpexy. The procedure reported good outcomes in treating OSA. It is a simple, cost-effective and less traumatic technique. It could be combined with other multilevel surgical procedures.

Microstructural and mechanical properties of Al2O3 and ZTA foams prepared by thermo-foaming technique

Alumina and zirconia toughened alumina foams were fabricated through a thermo-foaming method using varying amounts of powder to sucrose weight ratio. All the fabricated foams were characterized for their compressive strength, bending strength, and fracture toughness under static loading conditions. The compressive strength increases with an increase in a weight ratio from 0.4 to 1.2. The maximum compressive strength values were found to be 1.9 MPa, and 1.8 MPa for alumina and zirconia toughened alumina foams, respectively. Further increase in powder to sucrose weight ratio led to a decrease in the compressive strength due to the partial collapse of the cell walls during the foaming process. The 3-point bend test results revealed an improvement of bending strength and fracture toughness values of zirconia toughened alumina foams compared to alumina foam, which can be attributed to the transformation toughening mechanism.

Nitric Oxide-Releasing Nanoparticles Are Similar to Efinaconazole in Their Capacity to Eradicate Trichophyton rubrum Biofilms.

Filamentous fungi such as Trichophyton rubrum and T. mentagrophytes, the main causative agents of onychomycosis, have been recognized as biofilm-forming microorganisms. Nitric oxide-releasing nanoparticles (NO-np) are currently in development for the management of superficial and deep bacterial and fungal infections, with documented activity against biofilms. In this context, this work aimed to evaluate, for the first time, the in vitro anti-T. rubrum biofilm potential of NO-np using standard ATCC MYA-4438 and clinical BR1A strains and compare it to commonly used antifungal drugs including fluconazole, terbinafine and efinaconazole. The biofilms formed by the standard strain produced more biomass than those from the clinical strain. NO-np, fluconazole, terbinafine, and efinaconazole inhibited the in vitro growth of planktonic T. rubrum cells. Similarly, NO-np reduced the metabolic activities of clinical strain BR1A preformed biofilms at the highest concentration tested (SMIC50 = 40 mg/mL). Scanning electron and confocal microscopy revealed that NO-np and efinaconazole severely damaged established biofilms for both strains, resulting in collapse of hyphal cell walls and reduced the density, extracellular matrix and thickness of the biofilms. These findings suggest that biofilms should be considered when developing and testing new drugs for the treatment of dermatophytosis. Development of a biofilm phenotype by these fungi may explain the resistance of dermatophytes to some antifungals and why prolonged treatment is usually required for onychomycosis.

Dynamic sleep MRI in obstructive sleep apnea: a systematic review and meta-analysis.

PurposeThe objective of this study is to systematically review the international literature for dynamic sleep magnetic resonance imaging (MRI) as a diagnostic tool in obstructive sleep apnea (OSA), to perform meta-analysis on the quantitative data from the review, and to discuss its implications in future research and potential clinical applications.Study designA comprehensive review of the literature was performed, followed by a detailed analysis of the relevant data that has been published on the topic.MethodsClinical key, Uptodate, Ovid, Ebscohost, Pubmed/MEDLINE, Scopus, Dynamed, Web of Science and The Cochrane Library were systematically searched. Once the search was completed, dynamic sleep MRI data were analyzed.ResultsNineteen articles reported on 410 OSA patients and 79 controls that underwent dynamic sleep MRI and were included in this review. For meta-analysis of dynamic sleep MRI data, eight articles presented relevant data on 160 OSA patients. Obstruction was reported as follows: retropalatal (RP) 98%, retroglossal (RG) 41% and hypopharyngeal (HP) in 5%. Lateral pharyngeal wall (LPW) collapse was found in 35/73 (48%) patients. The combinations of RP + RG were observed in 24% and RP + RG + LPW in 16%. If sedation was used, 98% of study participants fell asleep compared to 66% of unsedated participants.ConclusionsDynamic sleep MRI has demonstrated that nearly all patients have retropalatal obstruction, retroglossal obstruction is common and hypopharyngeal obstruction is rare. Nearly all patients (98%) who are sedated are able to fall asleep during the MRI. There is significant heterogeneity in the literature and standardization is needed.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00405-021-06942-y.

Experimental study on unsteady characteristics of the transient cavitation flow

The characteristics of unsteady cavitation flow under different cavitation numbers are investigated experimentally. An optical test rig is designed to visualize the cavitation flow and the cavity length is defined based on high-speed camera technology. The development of cavitation flow can be divided into inception and fusion region, expansion region and collapse region. Due to the interaction between the re-entrant jet and the cavity interface, the cavitation bubbles near the solid wall collapse earlier than them in the downstream. The cavitation number is also the important factor determining the cavity length pulsation. Further analysis shows that the smaller the cavitation number, the smaller the frequency of cavity length fluctuations and the larger the mean cavity length. The cavitation intensity is stronger at lower cavitation number. Meanwhile, the cycle collapsing frequency of cavitation is around 220–320 Hz. With the decrease of cavitation number, the amplitude of cavitation pulsation increases while the corresponding collapsing frequency decreases.

Ansa cervicalis stimulation increases pharyngeal patency in patients with obstructive sleep apnea.

Hypoglossal nerve stimulation (HNS) is an alternative treatment option for obstructive sleep apnea (OSA) that reduces pharyngeal collapsibility, but HNS nonresponders often demonstrate continued retropalatal and lateral pharyngeal wall collapse. Recent evidence suggests that caudal pharyngeal traction with sternothyroid muscle contraction via ansa cervicalis stimulation (ACS) can also stabilize the pharynx, but the underlying mechanisms have not been elucidated. Our objective was to evaluate the effect of ACS on pharyngeal patency during expiration when the airway is most hypotonic. Eight participants with OSA underwent sustained ultrasound-guided fine-wire stimulation of the medial branch of the right hypoglossal nerve with and without transient stimulation of the branch of the ansa cervicalis nerve plexus innervating the right sternothyroid muscle during drug-induced sleep endoscopy. Airway cross-sectional area and expiratory airflow (V̇e) were measured from endoscopy video with ImageJ and pneumotachometry, respectively. ACS significantly increased retropalatal cross-sectional area (CSARP) to 211% [159-263] of unstimulated CSARP (P < 0.05). Adding ACS to HNS increased CSARP from baseline by 341% [244-439] (P < 0.05), a 180% [133-227] increase over isolated HNS (P < 0.05). ACS increased V̇e from baseline by 177% [138-217] P < 0.05). Adding ACS to HNS increased V̇e by 254% [207-301], reflecting decreases in pharyngeal collapsibility. Combining ACS with HNS increased retropalatal cross-sectional area and increased expiratory airflow, suggesting decreases in pharyngeal collapsibility. Our findings suggest that ACS exerts caudal traction on the upper airway through sternothyroid muscle contraction and that it may augment HNS efficacy in patients with OSA.NEW & NOTEWORTHY Ansa cervicalis stimulation (ACS) is a recently proposed neurostimulation mechanism for generating caudal pharyngeal traction that may benefit patients with obstructive sleep apnea. Here, we document endoscopic findings with ACS during drug-induced sleep endoscopy and additionally detail the effects of ACS on expiratory airflow, when the pharynx is known to be most hypotonic.

Excision of Lower Lip Mucocele Using Injection of Hydrocolloid Dental Impression Material in a Pediatric Patient: A Case Report

Oral mucocele is a benign cystic exophytic lesion affecting the minor salivary gland and is especially present in pediatric patients (3% under 14 years). It is characterized by an extravasation or retention of fluid or mucus in the submucosal tissue of the minor salivary glands. Several surgical techniques have been proposed over the years, including the excision of the mucocele by using the injection of a hydrocolloid impression material in the light of the cyst to prevent the collapse of the cystic wall and solidify the lesion, resulting in a better cleavage plan. The combined clinical approach between the combination of Shira’s technique and the surgical excision of the cystic lesion results in a conservative surgical removal of the lesion. Here, we reported the removal of a labial mucocele in a 14-year-old male patient, using the injection of a hydrocolloid impression material. At a 12 months follow up, the patient showed complete healing of the surgical site, showing a pinkish lip lining mucosa without scarring or recurrence of the primary lesion. The combined therapeutic approach between Shira’s technique and surgical excision allows a safe and predictable excision of the labial mucocele, minimizing the risk of recurrence.

A comparison of an absorbable nasal implant versus functional rhinoplasty for nasal obstruction

PurposeAn absorbable nasal implant for the treatment lateral nasal wall collapse was approved for use in patients with nasal obstruction. It remains to be seen whether this treatment is equivalent to open techniques for the treatment of nasal valve incompetence from collapsibility. Materials and methodsTwo groups were analyzed for the study. One group had surgery which included the implant, septoplasty, and inferior turbinate submucous reduction and the other group had a variety of functional rhinoplasty techniques for lateral wall insufficiency in addition to septoplasty and inferior turbinate submucous reduction. NOSE and SNOT-22 were used to demonstrate pre and post-operative changes. ResultsNinety total patients were identified. Fifty patients underwent insertion of an absorbable nasal implant and 40 underwent a traditional open technique to stabilize the LNW. For the implant group the mean NOSE score was 63.4 (SD 24) and post-operative was 22.9 (SD 19.9), in addition, the SNOT-22 score was 38.8 (SD 19.8) and post-operative was 18.5 (SD 15.2). For the open rhinoplasty group, the mean NOSE score was 57.9 (SD 23.2) and post-operative was 17.6 (SD 16.4). The SNOT-22 score was 33.6 (SD 14.9) and post-operative score was 11.5 (SD 15.2) The delta between pre and post-operative NOSE and SNOT-22 test were not different at an average of 3.95 months post-operatively between the groups (NOSE, P = 0.94 and SNOT-22, p = 0.53). ConclusionIn patients with multiple structural causes of nasal obstruction, including lateral wall insufficiency, insertion of an absorbable nasal implant, to support the LNW, seems to be equally effective as functional rhinoplasty techniques over a 4 month timeframe.

Comparison of Physical and Numerical Model on Dam Break Flood Wave Propagation in Horizontal Channel

This paper presents experimental results and the development of a numerical model for simulating dam break flood wave propagation. Floods caused by dam breaks have special flow characteristics due to potential energy caused by upstream and downstream elevation differences, and very high flow rates, from the collapse of the dam wall. The physical model is built on a horizontal channel, with 10 meters length and 1-meter width. The reservoirs used are upstream and downstream. Channels used are made of steel materials with negligible friction. The building used is made from wood with a volume of 10x10x40 cm. Flood wave propagation is modelled as a flash flood due to the mass movement of water in large quantities with the sudden opening of water gates. As the initial conditions, the door will be closed. On the upstream of the door, given the initial conditions of water level. Physical models result is used as calibration of numerical models. The developed numeric model is open foam that produces 3D modeling. The result of the physical model and numerical model show the highest flow velocity and good agreement of the pattern of flow velocity profiles during the first 3 seconds. The comparison of the Numerical model and Physical Model indicates whether the numerical model is feasible for use in dam-break modeling. For better results, it is necessary to develop a further model. Solutions to this physical and numerical model can be part of the mitigation effort in case the disaster phenomenon occurs.

Analysis and Application of Optimal and Fast Drilling Technology in Gaoshangpu Block of Jidong Oilfield

The Gaoshangpu block of Jidong Oilfield is a hot block for increasing production and storage in Jidong Oilfield. High-quality and efficient drilling and completion can shorten the operation time and have huge economic and social benefits. Aiming at the problems of large well depth, complex geological conditions, poor stratum drillability, low drilling machinery efficiency, and long drilling cycle in the Gaoshangpu block of Jidong Oilfield, this paper optimizes its drill bits, speed-up tools, drilling parameters, and drilling fluid performance. Through bit optimization, a PDC bit optimization template is formed. A single S1942 PDC and BTM159AR PDC bit can solve the problem of poor formation drillability, improve drilling efficiency, shorten completion time and optimize speed-up tools in the study area. For glutenite developed stratum (bottom of Guantao Formation), we use shock-absorbing thruster, and for gray mudstone (Shahejie Formation), we use shock-absorbing thruster + curved screw. 1% organic silicon polymer can be added to the three-open drilling fluid to improve the drilling fluid performance. The adding of the compound (PLH: KPAM: ammonium salt = 1: 1: 2) can inhibit mud making, and the 2% anti-collapse agent before drilling into basalt can solve the well wall collapse of Shahejie Formation and Guantao Formation. The liquid with density of 1.44-1.45 can prevent well overflow. The research results provide guidance for high-quality and efficient drilling in the Gaoshangpu block of Jidong Oilfield and ensure the safety of drilling operations.

Constitutive Modeling of the Densification Behavior in Open-Porous Cellular Solids.

The macroscopic mechanical behavior of open-porous cellular materials is dictated by the geometric and material properties of their microscopic cell walls. The overall compressive response of such materials is divided into three regimes, namely, the linear elastic, plateau and densification. In this paper, a constitutive model is presented, which captures not only the linear elastic regime and the subsequent pore-collapse, but is also shown to be capable of capturing the hardening upon the densification of the network. Here, the network is considered to be made up of idealized square-shaped cells, whose cell walls undergo bending and buckling under compression. Depending on the choice of damage criterion, viz. elastic buckling or irreversible bending, the cell walls collapse. These collapsed cells are then assumed to behave as nonlinear springs, acting as a foundation to the elastic network of active open cells. To this end, the network is decomposed into an active network and a collapsed one. The compressive strain at the onset of densification is then shown to be quantified by the point of intersection of the two network stress-strain curves. A parameter sensitivity analysis is presented to demonstrate the range of different material characteristics that the model is capable of capturing. The proposed constitutive model is further validated against two different types of nanoporous materials and shows good agreement.

2-Hydroxychalcone as a Potent Compound and Photosensitizer Against Dermatophyte Biofilms.

Dermatophytes, fungi that cause dermatophytosis, can invade keratinized tissues in humans and animals. The biofilm-forming ability of these fungi was described recently, and it may be correlated with the long treatment period and common recurrences of this mycosis. In this study, we evaluated the anti-dermatophytic and anti-biofilm activity of 2-hydroxychalcone (2-chalcone) in the dark and photodynamic therapy (PDT)-mediated and to determine its mechanism of action. Trichophyton rubrum and Trichophyton mentagrophytes strains were used in the study. The antifungal susceptibility test of planktonic cells, early-stage biofilms, and mature biofilms were performed using colorimetric methods. Topographies were visualized by scanning electron microscopy (SEM). Human skin keratinocyte (HaCat) monolayers were also used in the cytotoxicity assays. The mechanisms of action of 2-chalcone in the dark and under photoexcitation were investigated using confocal microscopy and the quantification of ergosterol, reactive oxygen species (ROS), and death induction by apoptosis/necrosis. All strains, in the planktonic form, were inhibited after treatment with 2-chalcone (minimum inhibitory concentration (MIC) = 7.8-15.6 mg/L), terbinafine (TRB) (MIC = 0.008–0.03 mg/L), and fluconazole (FLZ) (1–512 mg/L). Early-stage biofilm and mature biofilms were inhibited by 2-chalcone at concentrations of 15.6 mg/L and 31.2 mg/L in all tested strains. However, mature biofilms were resistant to all the antifungal drugs tested. When planktonic cells and biofilms (early-stage and mature) were treated with 2-chalcone-mediated PDT, the inhibitory concentrations were reduced by four times (2–7.8 mg/L). SEM images of biofilms treated with 2-chalcone showed cell wall collapse, resulting from a probable extravasation of cytoplasmic content. The toxicity of 2-chalcone in HaCat cells showed higher IC50 values in the dark than under photoexcitation. Further, 2-chalcone targets ergosterol in the cell and promotes the generation of ROS, resulting in cell death by apoptosis and necrosis. Overall, 2-chalcone-mediated PDT is a promising and safe drug candidate against dermatophytes, particularly in anti-biofilm treatment.

Role of transpalatal advancement pharyngoplasty in management of lateral pharyngeal wall collapse in OSA

IntroductionNon-response to palatal surgery for OSA is a problem. Residual lateral wall hypopharyngeal collapse is the proposed mechanism of failure. ObjectiveThis study aims to evaluate the role of transpalatal advancement pharyngoplasty in non-responders to primary palatal surgery with residual lateral wall hypopharyngeal collapse. MethodsThis is a retrospective study that was conducted on patients who underwent transpalatal advancement pharyngoplasty for residual lateral wall hypopharyngeal. Inclusion criteria were age greater than 18-years, OSA proved by the polysomnography with apnea hypopnea index >15, lateral wall collapse at the level of hypopharynx as proved by drug-induced sleep endoscopy and had a previous tonsillectomy or previous palatal surgery for OSA. Exclusion criteria were those with no history of tonsillectomy or any other surgery for OSA and those with a missed followup. Data of included patients were collected and included gender, age, polysomnographic data like the apnea hypopnea index, oxygen desaturation and the calculated preoperative Epworth sleepiness scale. The early outcome included symptom improvement as measured by Epworth sleepiness scale score and lateral pharyngeal wall evaluation by nasopharyngoscopic examination in the first postoperative month. Late outcome measurement was performed by the 6-month postoperative polysomnography. Data were analyzed using SPSS program. ResultsThe study included 37 patients with a mean age of (40.43 ± 6.51). The study included 26 men and 11 women. There was a statistically significant improvement of apnea hypopnea index from 37.8 ± 9.93 to 9.9 ± 2.55. In addition, a statistically significant improvement of lowest oxygen saturation from 78.9 ± 3.39 to 83.3 ± 3.31 was encountered. The patients improved clinically, and this improvement was measured by statistically significant improvement of Epworth sleepiness scale score and snoring visual analogue scale. ConclusionTranspalatal advancement pharyngoplasty widens the retropalatal airway and has a great role in the management of the vertical palate phenotype. In addition, it can have a role in the management of lateral walls, especially lateral wall hypopharyngeal collapse.

Analysis of reinforced retaining wall failure based on reinforcement length

Reinforced retaining walls are structures constructed horizontally to resist earth pressure by leveraging the frictional force imparted by the backfill. Reinforcements are employed because they exhibit excellent safety and economic efficiency. However, insufficient reinforcement can lead to collapse, and excessive reinforcement reduces economic efficiency. Therefore, it is important to select the appropriate type, length, and spacing of reinforcements. However, in actual sites, although the stress and fracture mechanisms in the straight and curved sections of reinforced soil retaining walls differ, the same amount of reinforcements are typically installed. Such an approach can lead to wall collapse or reduce economic feasibility. Therefore, in this study, the behaviours of straight and curved sections fortified with reinforcements of various lengths (1, 3, 5, and 7 m) are predicted through a three-dimensional numerical analysis. The retaining walls are of the same height, but the reinforcement variations in the aforementioned sections influence the wall behaviour differently. Based on the results, the optimum reinforcement lengths for the straight and curved parts were selected. By installing reinforcements of different lengths in these sections, the maximum reinforcing effect with minimum reinforcement was derived. This study further found that the curved section of the wall required more reinforcements, and the reinforcement lengths for the curved and straight sections should be separately optimized.

The role of the hold-down in the capacity model of LTF and CLT shear walls based on the experimental lateral response

Cross Laminated Timber (CLT) and Light Timber Frame (LTF) shear walls are widespread constructive technologies in timber engineering. Despite the intrinsic differences, the lateral response of the two structural systems may be quite similar under specific connection layouts, boundary constraints, and size of the shear walls. This paper compares the experimental cyclic responses of CLT and LTF shear walls characterized by the same size 250×250cm, and loaded according to the EN 12512 protocol. The rigid-body rotation of the shear walls prevails over the deformation and rigid-body translation in the post-elastic displacement range. As a consequence, a capacity model of the two systems based on the sole hold-down response accurately seizes the observed cyclic response, despite ignoring the other resisting contributions. The authors examine the differences exhibited by the CLT and LTF shear walls and the related error corresponding to a capacity model based on the sole hold down restraints. Additionally, it is assessed the overstrength of the CLT panel and LTF sheathing to the shear walls collapse due to the hold-down failure. The estimated overstrength factor is the most meaningful difference between the two structural systems in the considered experimental layouts.

Simulating the failure of masonry walls subjected to support settlement with the combined finite-discrete element method

Masonry walls are usually built with individual blocks, and they are highly discontinuous and nonlinear. Therefore, it is very difficult to simulate their failure behavior with typical finite element methods. A combined finite-discrete element method (FDEM) is employed in this paper to examine the failure of dry-joint masonry walls subjected to uneven support settlement. With finite elements incorporated into discrete elements, both the deformation of masonry blocks and the interaction between them can be predicted accurately. Additionally, a cohesive fracture model is implemented to account for the potential rupture of masonry blocks. Examples are validated with data from experimental and numerical sources, indicating that the FDEM is able to simulate the collapse of masonry walls well. Further simulations with the consideration of floor load and block fractures reveal that the existence of floor load will decrease the support settlement capacity of masonry walls. Once the dominant fracture damage occurs, the structures collapse quickly with very small support settlement.