Loss Of Suction Research Articles

Field monitoring of soil-moisture to understand the hydrological response of a road-cut slope

Rainfall and slope-cutting for road construction are two key landslide causative factors in Nepal, but how they interact to cause failures is poorly understood. To improve understanding of the effects of cut slopes during rainfall, geotechnical investigations and field monitoring were conducted in a mountainous district, Sindhupalchowk, located in central Nepal. This paper presents the results of the field-investigations and the measurements of volumetric water content obtained from the sensors installed in the study-site. Field-based evidence suggests that the slope that was cut for road construction during the dry period remained stable due to the presence of soil suction, which imparted additional strength to the soil. At the start of the monsoon, infiltration of rainwater caused saturation of the soil at shallow depth, consequently causing loss of suction and reduction of the soil strength. The presence of the road-cut in the hillslope resulting in steeper slopes then promoted the failure. These observations suggest that the presence of road-cuts in the hillslopes can cause landslides even during non-exceptional rainfall events.

Coupled hydro-mechanical modelling of a 1995 Hong Kong landslide

The paper deals with the modelling of the instability mechanism induced by rainfall in an unsaturated cut-slope. A large-sized landslide occurred in 1995 in Hong Kong (the so-called “Fei Tsui Road landslide”). It was here analysed because it was characterized by unusual dimensions and very large runout distance for the study area. The slope failure was attributed to a decrease in soil shear strength due to the rise of a perched water table above a weak kaolin-rich layer, together with the loss of suction caused by water infiltration during a heavy rainfall event. The hydro-mechanical coupled analyses made through the commercial software Plaxis 2D aimed to investigate the relations between the hydrological variables (i.e., rainfall infiltration, suction, saturation) and the slope response in terms of changes in soil resistance and soil plastic deformations. The study demonstrates that the evaluation of the hydro-mechanical coupling effects on the hydraulic slope response as well as on the stability of the whole slope is a crucial issue to well capture the mechanical behaviour of the unsaturated cut-slope. Different failure scenarios have been also considered in order to match the field observations and to back-analyse the initial condition of the slope before landslide.

Complications of small incision lenticule extraction.

The procedure of small incision lenticule extraction (SMILE) was introduced in 2011, and since then there has been an increase in the number of cases undergoing this procedure worldwide. The surgery has a learning curve and may be associated with problems in the intraoperative and postoperative periods. The intraoperative problems during SMILE surgery include the loss of suction, the occurrence of altered or irregular opaque bubble layer and black spots, difficulty in lenticular dissection and extraction, cap perforation, incision-related problems, and decentered ablation. Most of the postoperative problems are similar as in other laser refractive procedures, but with decreased incidence. The identification of risk factors, clinical features, and management of complications of SMILE help to obtain optimum refractive outcomes.

Assessment of plant-induced suction and its effects on the shear strength of rooted soils

Shallow landslides, either on bare or vegetated slopes, can be triggered after a rainfall event due to loss of suction. An extensive laboratory programme was performed in this study to assess the relationships between water content, plant-induced suction, root biomass and shear strength parameters. Root-permeated soils, planted with combinations of different species, were tested in an inclinable large-scale direct shear apparatus. The effects of mycorrhizal fungi were also investigated with inoculated specimens. The results suggested that the root biomass, as well as root/shoot ratio, was an indicator of plant-induced suction and shear strength of root-permeated soils tested under laboratory conditions. Longer plant growth duration and more species yielded higher mean values of matric suction and normalised shear stress. Mycorrhizal fungi were found to be beneficial in improving the plant functions related to water uptake.

Durability of silty soil stabilized with recycled lignin for sustainable engineering materials

Lignin is an industrial waste derived from the paper plant, which poses a potential threat to the surrounding environment without proper disposal. The present study aims to evaluate the durability performance of recycled lignin stabilized silty soil subjected to different adverse environments. A series of laboratory experiments were conducted to determine unconfined compressive strength (qu), moisture stability coefficient (Kr), mass loss (Sm) and pH value of the stabilized silt exposed to water soaking and wetting-drying cycles. The results showed that the strength and durability of natural silt were obviously improved with the inclusion of lignin. Lignin cementation and matrix suction played important roles in the strength behavior of the unsaturated stabilized silt. The compressive strength suffered a dramatic drop after 1 day of soaking due to the dissolution of cementing materials and the loss of suction. Lignin stabilized silt possessed a higher Kr than that of quicklime stabilized one, indicating its superiority in durability. After 28 days of standard curing, 12% lignin stabilized silt had an ability to resist 4 cycles of wetting-drying, resulting in the cumulative mass loss (Cm) of approximately 20%. Soil pH value presented a decreasing trend with wetting-drying cycles, and an exponential correlation of pH with Cm was found by data fitting. Scanning electron microscope analysis revealed that the lignin-based cementing materials are gradually lost during the process of wetting-drying cycles. Additional research is encouraged to explore an effective method to prevent the deterioration of mechanical properties of lignin stabilized soils in practical projects.

A Soft Pneumatic Actuator as a Haptic Wearable Device for Upper Limb Amputees: Toward a Soft Robotic Liner

Object manipulation and fluid, goal-directed, movements require sensory information for effective execution. Amputees lose this intrinsic feedback when controlling their artificial limbs and must instead rely on visual information to compensate. Here, we describe an application for providing touch and kinesthetic information to amputees. We report on a soft robotic pneumatic actuator approach that can be incorporated into a prosthetic limb as the silicone suction socket liner itself. This approach alleviates many problems inherent to rigid tactors such as poor trim lines from external mounting, electromyography (EMG) signal contamination, and loss of limb fixation suction due to holes in the liner to pass touch and vibration to the residual limb. We analyzed two soft materials and different chamber geometries to generate a prototype. We characterized the static and dynamic properties of this prototype during operation obtaining a maximum force of 12.5 N at 70 kPa, free displacement of 4.5 mm at 50 kPa, and a bandwidth near 70 Hz. We presented an analytical model that fits well with the experimental data and provided a comparison between this soft pneumatic actuator and other rigid tactor devices. The results of testing the prototype in able-bodied participants and one amputee individual demonstrated that this soft pneumatic actuator achieved good performance at frequencies of 5 and 70 Hz at 60 kPa. In sequential days of training with the prototype participants reported perceptions of wrist flexion/extension and demonstrated learned associations between tapping and hand closing.

Stability analysis of an unsaturated expansive soil slope subjected to rainfall infiltration

Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P53. Management of pressure injury with a novel negative pressure device (NPD) in people with spinal cord injury (SCI)

BACKGROUND CONTEXT Treatment of pressure injury (PI) is an ongoing clinical challenge particularly in people with SCI in developing countries where socioeconomic conditions often dictate treatment modalities. When negative pressure wound therapy (NPWT) was introduced, there were a series of devices (V.A.C., KCI, San Antonio, TX) manufactured. These devices for NPWT are costly and hard to afford by patients in developing countries like India and others. Commercially available devices are typically rented and require costly consumables. This study focuses on a novel, bellows-powered negative pressure device (NPD) that is easy to apply and does not require electricity. PURPOSE The purpose of this study was to evaluate wound-healing outcome measures (length, width, and depth, exudate amount, and tissue type) in PIs of spinal cord-injured patients treated with NPWT using a novel negative pressure device versus PI treated with wet-moist gauze (conventional wound care). STUDY DESIGN/SETTING Randomized controlled clinical trail (RCT) Department of Orthopaedic Surgery, King George's Medical University, Lucknow, India. This RCT was registered and approved by our institutional ethics committee. PATIENT SAMPLE Thirty-four (34) spinal cord injury subjects resulting traumatic paraplegia. OUTCOME MEASURES The outcome measures were surface area (length X width) and depth of PI, granulation tissue formation, exudates, microorganisms and cost effectivenes sat week 0, 3, 6 and week 9. METHODS Conventional therapy in our facility comprises wet to moistgauze dressings, and this intervention was used for comparison to the experimental intervention (NPWT via bellows enhanced vacuum device). The NPD dressing was changed weekly or more often if the dressing became saturated or loss of suction occurred. RESULTS Significantly reduced length of PI in NPWT group was observed at week 6 (p=.04) which further reduced at week 9 (p=.001) as compared to conventionally treated group. Similarly significant reduction of width and depth of PI was observed in NPWT at week 9 (p CONCLUSIONS NPWT by our locally constructed indigenized novel NPD is better wound care procedure and cost effective for management of pressure injury. We also found that the NPD reduced wound exudate, cleared slough, and accelerated the formation of red granulation tissue. Improving basic knowledge of NPWT in the management of PIs may help clinicians and wound care researchers identify and proactively intervene in an effort to minimize the time and cost associated with PI healing in SCI patients.

Increasing engine efficiency at part load with the exhaust valve control: a simplified modelling approach

In this study, a new, innovative system based on variable regulation of the exhaust valves in the spark ignited engine was described and analysed. The efficiency of standard spark ignited engines decreases during partial load compared to full load, due to increased losses in the exchange of working medium, precisely, loss of suction. The simplified model of the new system has been developed and a comparison was made between the standard engine, regulated with a valve on the intake system, and an engine that is regulated by dual opening of the exhaust valves. Research was carried out on the model of a four cylinder Otto engine with direct injection into the cylinder. The main results showed a significant improvement over the standard engine with a fixed intake geometry. Specific consumption is reduced between 3.83% and 4.23%, and losses of cylinder gases exchange have decreased between 85% and 87%.

Increasing engine efficiency at part load with the exhaust valve control: a simplified modelling approach

In this study, a new, innovative system based on variable regulation of the exhaust valves in the spark ignited engine was described and analysed. The efficiency of standard spark ignited engines decreases during partial load compared to full load, due to increased losses in the exchange of working medium, precisely, loss of suction. The simplified model of the new system has been developed and a comparison was made between the standard engine, regulated with a valve on the intake system, and an engine that is regulated by dual opening of the exhaust valves. Research was carried out on the model of a four cylinder Otto engine with direct injection into the cylinder. The main results showed a significant improvement over the standard engine with a fixed intake geometry. Specific consumption is reduced between 3.83% and 4.23%, and losses of cylinder gases exchange have decreased between 85% and 87%.

Numerical evaluation of reinforced slopes with various backfill-reinforcement-drainage systems subject to rainfall infiltration

This paper presents a numerical study investigating the hydraulic response and stability of geosynthetic-reinforced soil slopes subject to rainfall. A series of numerical simulations of unsaturated slopes with various backfill–reinforcement–drainage systems subject to rainfall infiltration was performed by comprehensively considering the combined effect of backfill (i.e., sand, silt, and silty clay), reinforcement type (i.e., geogrid or nonwoven geotextile), and rainfall intensity (350 and 500 mm/day). The backfills were modeled using three soil–water characteristic curves (SWCCs) representing the general suction range associated with sand, silt, and clay. The influence of sand cushions in improving the stability of reinforced clay slopes was also assessed. The numerical results reveal that the loss of matric suction and development of a capillary barrier effect within clay backfills could have adverse impacts on both the global and local stabilities of the reinforced clay slopes. The contribution of matric suction in enhancing slope stability was initially high for reinforced clay slopes; however, the global stability of the reinforced clay slope substantially decreased due to the loss of matric suction as the rainfall infiltration proceeded. The local instability of the geotextile-reinforced clay slope occurred due to the capillary barrier effect at the geotextile–clay interface. The reinforced marginal soil slopes cannot effectively drain the infiltrating water under torrential rainfall. Free drainage conditions may not be assumed for these slopes if the drainage is not properly considered. Both the global and local factors of safety (FS) of the reinforced sand slope were minimally influenced by the loss of matric suction induced by rainfall infiltration. The required reinforcement tensile strengths for the reinforced silt and clay slopes to maintain FS = 1.3 were, respectively, approximately 3 and 4 times larger than that for reinforced sand slopes. Numerical results also indicated that the inclusion of sand cushions, which provide both strength and drainage functions, can effectively enhance the slope stability. An optimal sand cushion thickness of 15 cm (replacing 20% of marginal backfill with sand) was determined in this study.

Effect of Geocomposite Layers on Slope Stability Under Rainfall Condition

Slope instability and associated loss of matric suction under rainfall condition is a serious global issue, and deserves special attention. The objective of the present paper is to investigate the effect of inclusion of a special variety of geosynthetic material, referred to as geocomposite (or dual-function hybrid geosynthetic) within slopes subjected to rainfall. In this regard, centrifuge based physical modelling was performed on a model silty-sand slope having 7.2 m height (prototype scale) and 2V:1H inclination at 30 gravities using the 4.5 m radius centrifuge facility available at IIT Bombay, India. A rainfall simulating assembly was designed and developed for the above study, capable of producing fine mist at a uniform rate during in-flight testing using specially designed pneumatic nozzles (intensity range: 2 mm/h to as high as 80 mm/h). The surface settlements, displacement profile, strain experienced by reinforcement layers, and pore water pressure profiles developed during rainfall were investigated in the unreinforced and reinforced slope models. It was observed that, the unreinforced slope model experienced excessive settlement and increasing phreatic levels with rainfall, leading to catastrophic failure. On the contrary, the geocomposite reinforced slope was stable under rainfall condition, and experienced negligible deformation with progress of rainfall, the maximum peak strain value being as low as 8.01%. Further, the inclusion of geocomposite layers provided preferential drainage channels within the slope, and resulted in reduction of pore water pressure values by almost 47%, thereby indicating the importance of coupling the functions of reinforcement and drainage simultaneously within low-permeability slopes subjected to rainfall. The above finding facilitates the use of locally available low-permeable soils in construction of reinforced soil walls/slopes, thereby economizing the project. Further, use of marginal soils in combination with geocomposites (or hybrid geosynthetics) can prevent the unsustainable mining of natural sand deposits for construction purposes, while catering to the problem of scarcity of good quality permeable granular materials in recent times.

Experimental investigation on cohesionless sandy bank failure resulting from water level rising

In the last decade, sediment replenishment forming cohesionless sandy banks below dams has become an increasingly common practice in Japan to compensate for sediment deficits downstream. The erosion process of the placed cohesionless sediment is a combination of lateral toe-erosion and the following mass failure. To explore cohesionless bank failure mechanisms, a series of experiments was done in a soil tank using a compacted sandy soil mass exposed to an increasing water level. Two types of uniform sand (D50 = 0.40mm and 0.17mm) and two bank heights (50cm and 25cm) were used under the condition of a constant bank slope of 75°. The three dimensional (3D) geometry of the bank after failure was measured using a handheld 3D scanner. The motion of bank failure was captured using the particle image velocimetry (PIV) technique, and the matric suction was measured by tensiometers. The compacted sandy soil was eroded by loss of matric suction accompanying the rise in water level which subsequently caused rotational slide and cantilever toppling failure due to destabilization of the bank. The effect of erosion protection resulting from the slumped blocks after these failures is discussed in the light of different failure mechanisms. Tensile strength is analyzed by inverse calculation of cantilever toppling failure events. The tensile strength had non-linear relation with degree of saturation and showed a peak. The findings of the study show that it is important to incorporate the non-linear relation of tensile strength into stability analysis of cantilever toppling failure and prediction of tension crack depth within unsaturated cohesionless banks.

Analysis of design choices for a slope stability scenario in the humid tropics

Prediction of the conditions under which landslides may occur is essential for designing sustainable risk-mitigation measures and cost-effective geotechnical structures. Slope stability analyses typically account for slope geometry, soil mechanical properties and groundwater conditions to determine the performance of a slope with respect to a specified factor of safety. These properties vary both spatially and over time; geotechnical design codes require the use of factored design parameter values to account for possible worst-case conditions. Furthermore, standard geotechnical analyses typically exclude the dynamic hydrological processes of rainfall infiltration and loss of matric suction that often trigger landslides. Slope stability assessment is particularly challenging in developing countries with limited resources for acquiring slope data, meeting conservative design standards and mitigating landslide risk. This study applied a combined slope hydrology and stability model to address these issues for a residual soil slope in the tropics. This paper presents a method for maximising stability information from limited data, disaggregating the effects of three different design parameter sets and factor of safety threshold choices, as well as diagnosing the dominant geotechnical and dynamic landslide-triggering factors. This modelling approach provides a more transparent basis for sustainable slope-management decisions.

Large (9 mm) Deep Anterior Lamellar Keratoplasty with Clearance of a 6-mm Optical Zone Optimizes Outcomes of Keratoconus Surgery

To evaluate the outcomes of a 9-mm deep anterior lamellar keratoplasty (DALK) with removal of the deep stroma limited to the central 6-mm optical zone. Prospective, noncomparative, interventional case series. A total of 80 consecutive keratoconic eyes without deep stromal scarring, with at least 1 postoperative examination 1 month after complete suture removal. A standardized DALK was performed, including (1) deep trephination of the recipient bed 450 to 550 μm in depth and 9 mm in diameter; (2) pneumatic dissection; (3) debulking of approximately 80% of the anterior stroma; (4) removal of the deep stroma (bubble roof) from a central 6-mm optical zone; and (5) transplantation of a 9-mm anterior corneal lamella cut by microkeratome-assisted dissection (400-μm head) and sutured with a double running 10-0 nylon suture. Success rate and type of pneumatic dissection obtained; best spectacle-corrected visual acuity (BSCVA), refractive astigmatism (RA), and topographic astigmatism (TA), central corneal thickness (CCT) and endothelial cell density 12 months postoperatively; and intraoperative and postoperative complications. Pneumatic dissection created a "big bubble" in 67 of 80 eyes (83.7%), all of them but 1 (1.5%) being of type 1 according to the classification by Dua etal. After complete suture removal, BSCVA averaged 0.09±0.72 logarithm of the minimum angle of resolution (logMAR) and was ≥20/20 in 28 eyes (35%), ≥20/25 in 54 eyes (67.5%), and ≥20/40 in 76 eyes (95%); RA averaged 3.10±1.30 diopters (D), with 73 eyes (91%) within 4.5 D and none above 6 D; regular TA was detected in 72 eyes (90%); mean CCT was 492±62.10 μm; postoperative endothelial cell density averaged 2026±397cells/mm2 with a mean cell loss of 11.2%. Intraoperative complications included loss of suction (n= 1) and perforation (n= 4). No conversion to penetrating keratoplasty was necessary. After surgery, double anterior chamber was observed in 2 cases (2.5%), both managed successfully by air filling of the anterior chamber. Stromal rejection was observed in 6 eyes (7.5%) and was reversed with topical steroids in all cases. In keratoconic eyes without deep stromal scars, the combination of a graft larger than conventional ones with limited removal of deep stroma can improve visual and refractive outcomes of DALK, while minimizing the rate of complications.

Preventing Seal Leak During Negative Pressure Wound Therapy Near External Fixators: A Technical Tip

Negative pressure wound therapy is an effective tool for the treatment of open wounds. Occasionally these wounds are associated with injuries or procedures that require treatment with an external fixator. This article shows how a simple, inexpensive, and commercially available product can be used to prevent loss of suction around external fixator pins within the negative pressure wound treatment area.

Effect of infiltration on the performance of an unsaturated geotextile-reinforced soil wall

A full-scale geotextile-reinforced soil wall was built in order to assess the characteristics of water infiltration and its effect on the structure performance. Nonwoven geotextiles were selected as inclusions in order to provide not only reinforcement, but also internal drainage to the fine-grained soil used as backfill material. The structure was built in a laboratory setting, which facilitated implementation of a thorough instrumentation plan to measure volumetric water content changes of soil, suction, facing displacements and reinforcement strains. An irrigation system was used to simulate controlled rainfall events. The monitoring program allowed the evaluation of the advancement of infiltration and internal geosynthetic drainage. Evaluation of the effect of the hydraulic response on the overall performance of the structure included assessment of the development of capillary breaks at soil-geotextiles interfaces. Capillary breaks resulted in water storage above the geotextile reinforcements and led to retardation of the infiltration front in comparison to the infiltration that would occur without the presence of permeable reinforcements. After breakthrough, water was also found to migrate along the geotextiles, suggesting that the reinforcement layers ultimately provided in-plane drainage capacity. While generation of positive pore water pressures was not evidenced during the tests, the advancing infiltration front was found to affect the performance of the wall. Specifically, infiltration led to increasing reinforcement strains and facing displacements, as well as to the progressive loss of suction. While the accumulation of water due to the temporary capillary break also resulted in an increased backfill unit weight, its effect on deformation of the wall was not possible to be captured but it is intrinsic on the overall behavior observed in this study. Correlations between reinforcement strains/face displacement and the average of suction in the backfill soil, as measured by tensiometers in different locations within the backfill mass, point to the relevance of the suction as a representative indicator of the deformability of the geotextile-reinforced wall subjected to water infiltration. Reinforcement strains and face displacements were found to reduce more significantly with reduction of suction until a certain value of suction from which the rate of decreasing declines.

Preliminary Analysis on Matric Suction for Barren Soil

Most research conducted on slope failures can broadly be attributed to the convergence of three factors, i.e. rainfall, steepness of slope, and soil geological profile. The mechanism of the failures is mainly due to the loss of matric suction of soils by rainwater. When rainwater infiltrates into the slopes, it will start to saturate the soil, i.e., reduce the matric suction. A good understanding of landslide mechanisms and the characteristics of unsaturated soil and rock in tropical areas is crucial in landslide hazard formulation. Most of the slope failures in unsaturated tropical residual soil in Malaysia are mainly due to infiltration, especially during intense and prolonged rainfall, which reduces the soil matric suction and hence decreases the stability of the slope. Therefore, the aim of this research is to determine the matric suction for barren soil and to model an unsaturated slope with natural rainfall to evaluate the effects of matric suction on rainfall intensity. A field test was carried out using the Watermark Soil Moisture Sensor to determine the matric suction. The sensor was connected to a program called SpecWare 9 Basic which also used Data Logging Rain gauge Watermark 1120 to measure the intensity and duration of rainfall. This study was conducted at the Research Centre for Soft Soil which is a new Research and Development (R & D) initiative by Universiti Tun Hussein Onn Malaysia, Parit Raja. Field observation showed that the highest daily suction was recorded during noon while the lowest suction was obtained at night and early morning. The highest matric suction for loose condition was 31.0 kPa while the highest matric suction for compacted condition was 32.4 kPa. The results implied that the field suction variation was not only governed by the rainfall, but also the cyclic evaporation process. The findings clearly indicated that the changes in soil suction distribution patterns occurred due to different weather conditions.

Impact of Suction Loss During Small Incision Lenticule Extraction (SMILE).

To evaluate the clinical results of suction loss in eyes during small incision lenticule extraction (SMILE). This prospective paired-eye case study enrolled 8,490 eyes of 4,296 patients, of which 35 eyes experienced suction loss during the SMILE procedure while being treated for myopia or myopic astigmatism. The eyes with suction loss were re-treated with SMILE, femtosecond laser-assisted LASIK (FS-LASIK), or pseudo SMILE, and the fellow eyes were treated with SMILE. Patients were examined before surgery and at 1 day, 1 week, and 1 and 3 months postoperatively. Corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA), manifest refraction, higher order aberrations (HOAs), and morphologic modifications of corneal architecture were evaluated. At 3 months, patients were asked if they preferred the vision in either eye. High-contrast CDVA was worse in the eyes that suffered loss of suction than in the fellow eyes at 1 week postoperatively (two-tailed paired t tests, P = .04), but not at 1 and 3 months. There was no statistical significance between the two treatments in the safety and efficacy indices or the 3rd and 4th order aberrations at 3 months postoperatively (two-tailed paired t tests, all P > .05). No apparent abnormalities were observed in the corneas by frequency-domain optical coherence tomography. Re-treatment with femtosecond laser for incomplete SMILE was safe, predictable, and effective, and the patients did not perceive a difference in vision. [J Refract Surg. 2016;32(10):686-692.].

Characteristics of landslides in unwelded pyroclastic flow deposits, southern Kyushu, Japan

Abstract. We investigated 184 landslides that occurred in unwelded pyroclastic flow deposits (Shirasu) on southern Kyushu Island, Japan, that included detailed data on the rainfall characteristics and the timing of slope failure. Localized rainfall intensity, antecedent precipitation index (API), and topography affected the hydrologic processes that triggered landslides. API (adjusted for evapotranspiration losses) for large ( > 200 mm) storms that triggered landslides was much lower than for smaller ( ≤ 200 mm) storms. Mean storm intensity and 7-day API (API7) thresholds of > 5 mmh−1 and ≤ 30 mm (or API30 ≤ 60 mm), respectively, were useful to identify landslides triggered by rapid pore water pressure response, especially for shorter ( < 20 h) duration events. During smaller storms with lower intensity, landslides are likely affected by a combined increase in soil weight and loss of suction when API30 ≥ 150 mm; simulations indicated that these weight and suction changes due to rainfall accumulation decreased the factor of safety in steep Shirasu slopes, but did not necessarily trigger the landslides. Most of the landslides that were plotted below a general rainfall intensity–duration threshold for landslide initiation occurred during smaller storms with API30 values > 200 mm, indicating that they were highly influenced by the combined effects of the accumulated weight of rainfall and loss of suction. Our findings show that both event rainfall characteristics and API affect the hydrogeomorphic processes that trigger different types of landslides in Shirasu. This knowledge and the thresholds we have identified are useful for predicting the occurrence of different types of landslides in unwelded Shirasu deposits and improving sediment disaster prevention practices, including real-time warning systems.