Lateral Ground Research Articles

Propulsion in hexapod locomotion: how do desert ants traverse slopes?

The employment of an alternating tripod gait to traverse uneven terrains is a common characteristic shared among many Hexapoda. Because this could be one specific cause for their ecological success, we examined the alternating tripod gait of the desert ant Cataglyphis fortis together with their ground reaction forces and weight-specific leg impulses for level locomotion and on moderate (±30deg) and steep (±60deg) slopes in order to understand mechanical functions of individual legs during inclined locomotion. There were three main findings from the experimental data. (1) The hind legs acted as the main brake (negative weight-specific impulse in the direction of progression) on both the moderate and steep downslopes while the front legs became the main motor (positive weight-specific impulse in the direction of progression) on the steep upslope. In both cases, the primary motor or brake was found to be above the centre of mass. (2) Normalised double support durations were prolonged on steep slopes, which could enhance the effect of lateral shear loading between left and right legs with the presence of direction-dependent attachment structures. (3) The notable directional change in the lateral ground reaction forces between the moderate and steep slopes implied the utilisation of different coordination programs in the extensor-flexor system.

Rapid degradation of permafrost underneath waterbodies in tundra landscapes—Toward a representation of thermokarst in land surface models

AbstractWaterbodies such as lakes and ponds are abundant in vast Arctic landscapes and strongly affect the thermal state of the surrounding permafrost. In order to gain a better understanding of the impact of small‐ and medium‐sized waterbodies on permafrost and the formation of thermokarst, a land surface model was developed that can represent the vertical and lateral thermal interactions between waterbodies and permafrost. The model was validated using temperature measurements from two typical waterbodies located within the Lena River delta in northern Siberia. Impact simulations were performed under current climate conditions as well as under a moderate and a strong climate‐warming scenario. The performed simulations demonstrate that small waterbodies can rise the sediment surface temperature by more than 10°C and accelerate permafrost thaw by a factor of between 4 and 5. Up to 70% of this additional heat flux into the ground was found to be dissipated into the surrounding permafrost by lateral ground heat flux in the case of small, shallow, and isolated waterbodies. Under moderate climate warming, the lateral heat flux was found to reduce permafrost degradation underneath waterbodies by a factor of 2. Under stronger climatic warming, however, the lateral heat flux was too small to prevent rapid permafrost degradation. The lateral heat flux was also found to strongly impede the formation of thermokarst. Despite this stabilizing effect, our simulations have demonstrated that underneath shallow waterbodies (<1 m), thermokarst initiation happens 30 to 40 years earlier than in simulations without preexisting waterbody.

PVCO Pipeline Performance Under Large Ground Deformation

Technological advances have improved pipeline capacity to accommodate large ground deformation associated with earthquakes, floods, landslides, tunneling, deep excavations, mining, and subsidence. The fabrication of polyvinyl chloride (PVC) piping, for example, can be modified by expanding PVC pipe stock to approximately twice its original diameter, thus causing PVC molecular chains to realign in the circumferential direction. This process yields biaxially oriented polyvinyl chloride (PVCO) pipe with increased circumferential strength, reduced pipe wall thickness, and enhanced cross-sectional flexibility. This paper reports on experiments performed at the Cornell University Large-Scale Lifelines Testing Facility characterizing PVCO pipeline performance in response to large ground deformation. The evaluation was performed on 150-mm (6-in.)-diameter PVCO pipelines with bell-and-spigot joints. The testing procedure included determination of fundamental PVCO material properties, axial joint tension and compression tests, four-point bending tests, and a full-scale fault rupture simulation. The test results show that the performance of segmental PVCO pipelines under large ground deformation is strongly influenced by the axial pullout and compressive load capacity of the joints, as well as their ability to accommodate deflection and joint rotation. The PVCO pipeline performance is quantified in terms of its capacity to accommodate horizontal ground strain, and compared with a statistical characterization of lateral ground strains caused by soil liquefaction during the Canterbury earthquake sequence in New Zealand.

Effect of vertical ground motion on earthquake-induced derailment of railway vehicles over simply-supported bridges

The running safety of railway vehicles on bridges can be negatively affected by earthquake events. This phenomenon has traditionally been investigated with only the lateral ground excitation component considered. This paper presented results from a numerical investigation on the contribution of vertical ground motion component to the derailment of vehicles on simply-supported bridges. A full nonlinear wheel–rail contact model was used in the investigation together with the Hertzian contact theory and nonlinear creepage theory, which allows the wheel to jump vertically and separate from the rail. The wheel–rail relative displacement was used as the criterion for derailment events. A total of 18 ground motion records were used in the analysis to account for the uncertainty of ground motions. The results showed that inclusion of vertical ground motion will likely increase the chance of derailment. It is recommended to include vertical ground motion component in earthquake induced derailment analysis to ensure conservative estimations. The derailment event on bridges was found to be more closely related to the deck acceleration rather than the ground acceleration.

Why Excavation of a Small Air Shaft Caused Excessively Large Displacements: Forensic Investigation

AbstractAny deficiency in excavation design or construction could lead to excessively large retaining wall and ground displacements, usually accompanied by damage to adjacent structures or facilities. This paper documents a case history of a small air shaft excavation in Shanghai soft clay. Its maximum lateral wall displacement and ground settlement were twice and three times the local deformation control criteria and 3 and 14 times those of one adjacent air shaft excavation featuring similar subsurface conditions, geometric size, and supporting system. To identify probable causes pertaining to its poor performance, a comprehensive investigation was carried out in both design (propping element, supporting system stiffness, wall penetration ratio, and jet grouting of basal soils) and construction (excavation duration, excavation width, exposed wall length, and management of heavy-duty truck and stockpile of construction materials). The investigations show that there were several major contributory factors,...

Application of an Enhanced Anisotropic Bounding Surface Model in Simulating Deep Excavations in Clays

AbstractFinite-element simulations are conducted to assess the capability of an anisotropic bounding surface model in simulating ground response due to deep excavations. The model assumes a nonassociative flow rule that allows for the simulation of not only strain-hardening, but also strain-softening response. It can be degenerated into anisotropic and isotropic forms of the bounding surface model employing associative flow. After integrating the model into a commercial finite-element code, two deep excavation case histories were simulated. The simulation results are compared with published field measurements and with those obtained using the anisotropic Sekiguchi-Ohta and MIT-E3 models. Satisfactory agreement between finite-element simulations and field measurements in terms of lateral wall deflections and ground surface settlements was realized. The difference in results between the nonassociative and associative versions of the anisotropic bounding surface model was found to be rather small given the f...

Field studies of a technique to mitigate ground settlement of operating highways

In the eastern coastal region of China, many operating highways built over soft ground are vulnerable to severe post-construction settlement. In this study, a technique using jet grouted piles is developed to mitigate post-construction settlement. The piles are installed by drilling boreholes throughout the embankment. The principal stages of the construction process are described, and two field tests in China, on the Lianyan and Linhai highways, are presented. The results revealed that ground heaves of up to 219 mm and 337 mm induced during a short construction period were able to mitigate the settlement of the embankment. The average settling rate was significantly reduced from 60 mm/y to 9 mm/y on the Lianyan highway. Lateral ground displacement on the Linhai highway increased with time during construction, but after construction showed a slight reduction associated with the dissipation of excess pore water pressure. An analytical method was adopted to describe the ground heave due to the jet grouted piles. The ground heave increased with grout pump pressure, but decreased as the embankment load and distance from the pile center increased.

Field Observation of Soil Displacements Resulting Due Unsupported Excavation and Its Effects on Proposed Adjacent Piles

Soil movement resulting due unsupported excavation nearby axially loaded piles imposes significant structural troubles on geotechnical engineers especially for piles that are not designed to account for loss of lateral confinement. In this study the field excavation works of 7.0 m deep open tunnel was continuously followed up by the authors. The work is related to the project of developing the Army canal in the east of Baghdad city in Iraq. A number of selected points around the field excavation are installed on the ground surface at different horizontal distance. The elevation and coordinates of points are recorded during 23 days with excavation progress period. The field excavation process was numerically simulated by using the finite element package PLAXIS 3D foundation. The obtained analysis results regarding the displacements of the selected points are compared with the field observation for verification purpose. Moreover, finite element analysis of axially loaded piles that are presumed to be existed at the locations of the observation points is carried out to study the effect of excavation on full scale piles behaviors. The field observation monitored an upward movement and positive lateral ground movement for shallow excavation depth. Later on and as the excavation process went deeper, a downward movement and negative lateral ground movement are noticed. The analyses results are in general well agreed with the monitored values of soil displacements at the selected points. It is found also that there are obvious effects of the nearby excavation on the presumed piles in terms of displacements and bending moments.

Performance of a Deep Excavation and Its Effect on Adjacent Tunnels in Shanghai Soft Clay

AbstractA 267-m-long, 54-m-wide, and 14.9–16.4-m-deep multipropped deep excavation with three cross walls in Shanghai soft clay was constructed at a side of an existing metro station. To investigate the performance of this deep excavation and the effect of this deep excavation on adjacent metro station and shield tunnels, the ground deformation and structure responses were extensively monitored. Based on the field observations, the deflections and vertical movements of diaphragm walls, surface settlements, vertical and horizontal displacements of the up track and the down track within the station and nearby shield tunnels, as well as tunnel convergence were extensively analyzed. By adopting cross walls, jet grouting and large dimension concrete struts, the measured maximum lateral wall deflection and ground deformation were much smaller than those at other sites without installing cross walls in Shanghai soft clay. The maximum excavation-induced lateral wall movements and ground settlement behind the reta...

DEM modeling of cantilever retaining excavations: implications for lunar constructions

PurposeRetained excavation is important for future lunar exploratory missions and potential human colonization that requires the construction of permanent outposts. Knowledge in excavation obtained on the Earth is not directly applicable to lunar excavation because of the low lunar gravity and the non-negligible adhesive van der Waals interactions between lunar regolith grains. This study aims at revealing how the gravity level and lunar environment conditions should be considered to extend the knowledge in Earth excavation response to lunar excavation.Design/methodology/approachTwo-dimensional Discrete Element Method (DEM) simulations were carried out to investigate the respective effect of gravity level and lunar environment conditions (high vacuum and extreme temperature) on retained excavation response. A novel contact model was employed with a moment – relative rotation law to account for the angularity of lunar soil particles, and a normal attractive force to account for the van der Waals interactions.FindingsThe simulation results showed that the excavation response is non-linearly related to the gravity level. Van der Waals interactions can increase the dilatancy of lunar regolith and, surprisingly as a consequence, significantly increase the bending moment and deflection of the retaining wall, and the ground displacements. Based on the simulation results, a parabola model was proposed to predict the excavation induced lateral ground movements on the Moon.Originality/valueThis study indicates that an unsafe estimate of the wall response to an excavation on the Moon would be obtained if only the effect of gravity is considered while the effect of van der Waals interactions is neglected.

Finite element modeling of lateral pipeline–soil interactions in dense sand

Finite element (FE) analyses of pipeline–soil interaction for pipelines buried in dense sand subjected to lateral ground displacements are presented in this paper. Analysis is performed — using the Arbitrary Lagrangian–Eulerian (ALE) method available in Abaqus/Explicit FE software — in the plane strain condition using the Mohr–Coulomb (MC) and modified Mohr–Coulomb (MMC) models. The MMC model considers a number of important features and properties of stress–strain and volume change behaviour of dense sand including the nonlinear pre- and post-peak behaviour with a smooth transition and the variation of the angle of internal friction and dilation angle with plastic shear strain, loading conditions (triaxial or plane strain), density, and mean effective stress. Comparing FE and experimental results, it is shown that the MMC model can better simulate the force–displacement response for a wide range of lateral displacements of the pipe for different burial depths, although the peak force on the pipe could be matched using the MC model. Examining the progressive development of zones of large inelastic shear deformation (shear bands), it is shown that the mobilized angle of internal friction and dilation angle vary along the length of the shear band; however, constant values are used in the MC model. A comprehensive parametric study is also performed to investigate the effects of pipeline diameter, burial depth, and soil properties. Many important aspects in the force–displacement curves and failure mechanisms are explained using the present FE analyses.

Analysis of Knee Joint Line Obliquity after High Tibial Osteotomy.

The aim of this study was to evaluate which lower extremity alignment (knee and ankle joint) parameters affect knee joint line obliquity (KJLO) in the coronal plane after open wedge high tibial osteotomy (OWHTO). Overall, 69 knees of patients that underwent OWHTO were evaluated using radiographs obtained preoperatively and from 6 weeks to 3 months postoperatively. We measured multiple parameters of knee and ankle joint alignment (hip-knee-ankle angle [HKA], joint line height [JLH], posterior tibial slope [PS], femoral condyle-tibial plateau angle [FCTP], medial proximal tibial angle [MPTA], mechanical lateral distal femoral angle [mLDFA], KJLO, talar tilt angle [TTA], ankle joint obliquity [AJO], and the lateral distal tibial ground surface angle [LDTGA]; preoperative [-pre], postoperative [-post], and the difference between -pre and -post values [-Δ]). We categorized patients into two groups according to the KJLO-post value (the normal group [within ± 4 degrees, 56 knees] and the abnormal group [greater than ± 4 degrees, 13 knees]), and compared their -pre parameters. Multiple logistic regression analysis was used to examine the contribution of the -pre parameters to abnormal KJLO-post. The mean HKA-Δ (-9.4 ± 4.7 degrees) was larger than the mean KJLO-Δ (-2.1 ± 3.2 degrees). The knee joint alignment parameters (the HKA-pre, FCTP-pre) differed significantly between the two groups (p < 0.05). In addition, the HKA-pre (odds ratio [OR] = 1.27, p = 0.006) and FCTP-pre (OR = 2.13, p = 0.006) were significant predictors of abnormal KJLO-post. However, -pre ankle joint parameters (TTA, AJO, and LDTGA) did not differ significantly between the two groups and were not significantly associated with the abnormal KJLO-post. The -pre knee joint alignment and knee joint convergence angle evaluated by HKA-pre and FCTP-pre angle, respectively, were significant predictors of abnormal KJLO after OWHTO. However, -pre ankle joint parameters were not significantly associated with abnormal KJLO after OWHTO.

Ground response and grout distribution by field soil grouting

Generally, grout extent and ground deformation are of great concern in soil grouting practice. In this paper, the ground behaviour, injection mechanism and grout distribution relating to field grouting in soils are discussed. It is found that the mechanisms of injection comply with generally accepted groutability requirements based on particle size ratio, where suspension grouts fracture clayey soils and solution grout permeates sandy soils. Ground heaving is affected by the sealing effect of grouts in upper soil layers. This study shows ground heave increases with the depth of grouting. The final heave volume reaches about 22% of the total grout injected. Lateral ground expansion is influenced by the hydraulic fracturing of grouts. Hydraulic fractures, which are nearly vertically formed in soils, produce lateral movements of the ground. The final lateral expansion of the ground, within 1 m radial zone of the grout hole, is approximately 12% of the total grout injected. A three-dimensional grout distribution is postulated based on the mapped grout traces in soils. The observed vertical grout fractures, with apertures of less than 15 mm and lateral extents of 1~4 m, confirm that the site soil strata are normally consolidated.

영구지반변형이 매설된 하수도관로 성능에 미치는 영향

In recent years, the earthquake sequence in Christchurch, New Zealand (NZ) was unprecedented in terms of repeated earthquake shocks with substantial levels of ground motion affecting modern infrastructure, and in particular, broad and precise reports for liquefaction-induced permanent ground deformation (PGD) and repairs of wastewater (WW) pipelines were collected. In this study, a geographical information system (GIS) and linear regression analysis were performed using data for the length and repair points of earthenware (EW) and concrete (CONC) wastewater pipelines acquired after the MW 6.2 February 22, 2011 earthquake. The repair rates (repairs/km) for the EW and CONC wastewater pipelines were evaluated inside the areas of PGD, and both angular distortion of ground and lateral ground strain were calculated from the high resolution LiDAR data acquired before and after the seismic event. The research results showed that both pipelines have similar trends of damage but the CONC wastewater pipeline with higher stiffness showed less damage. The results of linear regression analyses can be used to predict the repair rates for EW and CONC wastewater pipelines inside the areas of PGD induced by future earthquakes.

Optimum design of reinforced concrete cantilever retaining walls with particle swarm optimization

In this study, a Particle Swarm Optimization (PSO) based algorithm is used for optimum design of reinforced concrete cantilever retaining walls. Besides vertical loads, both active and static lateral ground pressures are considered for design. Reinforced concrete design rules defined in TS-500 and checking procedures about sliding, overturning and bearing capacity failures defined in TS-7994 are taken into account as constraints of the optimization problem. In order to evaluate the relationship between optimum design results and values of PSO solution parameters, a sensitivity analysis is performed. Results show that, PSO based solution algorithm may be used as an efficient tool for optimum design of reinforced concrete cantilever retaining walls by satisfying all considered constraints.

Principal component analysis in ground reaction forces and center of pressure gait waveforms of people with transfemoral amputation.

The alterations in gait pattern of people with transfemoral amputation leave them more susceptible to musculoskeletal injury. Principal component analysis is a method that reduces the amount of gait data and allows analyzing the entire waveform. To use the principal component analysis to compare the ground reaction force and center of pressure displacement waveforms obtained during gait between able-bodied subjects and both limbs of individuals with transfemoral amputation. This is a transversal study with a convenience sample. We used a force plate and pressure plate to record the anterior-posterior, medial-lateral and vertical ground reaction force, and anterior-posterior and medial-lateral center of pressure positions of 12 participants with transfemoral amputation and 20 able-bodied subjects during gait. The principal component analysis was performed to compare the gait waveforms between the participants with transfemoral amputation and the able-bodied individuals. The principal component analysis model explained between 74% and 93% of the data variance. In all ground reaction force and center of pressure waveforms relevant portions were identified; and always at least one principal component presented scores statistically different (p < 0.05) between the groups of participants in these relevant portions. Principal component analysis was able to discriminate many portions of the stance phase between both lower limbs of people with transfemoral amputation compared to the able-bodied participants. Principal component analysis reduced the amount of data, allowed analyzing the whole waveform, and identified specific sub-phases of gait that were different between the groups. Therefore, this approach seems to be a powerful tool to be used in gait evaluation and following the rehabilitation status of people with transfemoral amputation.

A three-dimensional human walking model

A three-dimensional human bipedal walking model with compliant legs is presented in this paper. The legs are modeled with time-variant dampers, and the model is able to characterize the gait pattern of an individual using a minimal set of parameters. Feedback control, for both the forward and lateral movements, is implemented to regulate the walking performance of the pedestrian. The model provides an improvement over classic invert pendulum models. Numerical studies were undertaken to investigate the effects of leg stiffness and attack angle. Simulation results show that when walking at a given speed, increasing the leg stiffness with a constant attack angle results in a longer step length, a higher step frequency, a faster walking speed and an increase in both the peak vertical and lateral ground reaction forces. Increasing the attack angle with a constant leg stiffness results in a higher step frequency, a decrease in the step length, an increase in the total energy of the system and a decrease in both the peak vertical and lateral ground reaction forces.

Development of a Regression Model for the Treadmill Ground Reaction Force Components

Treadmills allow for collecting multiple steps in a small area, and continuous testing for a long period of time with multiple speeds. These factors prove to be useful for biomechanics research laboratories that are usually equipped with floor embedded platforms. Acquiring instrumented treadmills with a built in force plate(s) – may not be financially feasible for many general purpose biomechanics laboratories; additionally instrumented treadmills only measures the vertical component of ground reaction force. The purpose of this study was to examine the components of Ground Reaction Force (GRF) in treadmill walking which were measured by placing a treadmill over floor-mounted force plates and to develop a set of regression equations to be used in associating treadmill’s GRF components with GRF components obtained during overground walking. The GRF measured during the treadmill walk was compared to GRF measured in overground walking. A total of twelve male subjects participated in this study. The analysis of the data did not reveal statistical differences in the anterior-posterior component of the GRF (APGRFP1 and APGRFP2) and in the early-stance and mid-stance peaks of the vertical GRF (VGRFP1 and VGRFP2) between treadmill and overground walking. Statistical differences between treadmill and overground walking were found during latestance for vertical ground reaction force (VGRFP3) and medial lateral ground reaction force (MLGRFP2) (p<0.05). During push-offoccurring in late-stance-vertical ground reaction force peaks (VGRFP3) were less in treadmill walking than in overground walking by 5-6% (p<0.05). The Medial-lateral ground reaction forces peaks (MLGRFP2) were also less in treadmill walking than in overground walking by 1-2% (p<0.05). In addition, five regression equations were developed for treadmill’s GRF.

A novel CB ACS-fed dual band antenna with truncated ground plane for 2.4/5 GHz WLAN application

A novel conductor backed asymmetric coplanar strip (CBACS) fed dual band antenna which is suitable for wireless local area network is presented in this paper. The proposed antenna is composed of inverted L-shaped exciting strip, a lateral ground plane and a modified truncated ground plane on the backside with overall dimension of about 25mm×17.5mm×1.6mm. The proposed design comprises monopole patch with asymmetric coplanar ground plane with conductor backing exhibit dual band of response with measured bandwidth of return loss ≤−10dB is 2.30–2.55GHz and 4.06–6.65GHz which cover all the WLAN bands (2.4/5.2/5.8GHz). The parametric studies indicate that operating frequencies and wider bandwidth are determined by the dimension of the ground plane at the top and bottom. The proposed antenna covers IEEE 802.11a/b/HYPERLAN-2/RFID band with good radiation characteristics. The measurement of proposed antenna that has been printed on an FR4 substrate with dielectric constant 4.4 yields good conformity between simulated results. The proposed structure is simulated using the method of moment based electromagnetic solver IE3D version 15.10.

뉴질랜드 크라이스트처어치 지진에 의해 발생된 영구지반변형과 매설된 상수도관 성능평가

In this study, the performance of underground water pipeline system affected by earthquakes is examined by using data acquired after MW 6.2 February 22, 2011 earthquake in Christchurch, NZ. Water pipeline repair rates, expressed as repairs/km, for different types of pipe are evaluated inside the areas of which liquefaction induced by permanent ground deformation was observed and assessed relative to differential settlement and lateral ground strain, calculated from high resolution LiDAR data acquired before and after each seismic event. The earthquake performance of underground water pipeline systems associated with permanent ground deformation is summarized in this paper. The results show that highly ductile polyethylene water pipelines has a high earthquake performance.