Ground Strain Research Articles

Ground strains induced by the 2022 Hunga-Tonga volcanic eruption, observed by a 1500-m laser strainmeter at Kamioka, Japan

In this study, we detected the horizontal ground strains induced by the atmospheric Lamb wave emitted from the 2022 eruption of the Tonga–Hunga Ha’apai undersea volcano, at an underground observatory in Kamioka, Japan. The observed strains were in the range of {10}^{-11}–{10}^{-10} and were measured precisely using a 1500-m laser strainmeter with a high resolution in the order of {10}^{-12}. This was one of the first observations of a Lamb wave using a laser strainmeter. The strainmeter was constructed in a tunnel of the KAGRA gravitational-wave telescope. Our observations demonstrate that strain and atmospheric pressure were clearly correlated, resulting in a regression coefficient of - left(2.3-3.7right)times {10}^{-10} strain/hPa. This finding was compared with the responses under regular pressure conditions and the estimations obtained using the local deformation and traveling wave models. The observed coefficients for the Lamb wave exhibited smaller magnitudes than those observed under regular conditions and take values between that of the two theoretical models. These results reflect the intermediate scale of the pressure distribution of the Lamb wave between the assumptions of the simple models. The strain variations were also found to have started earlier than the corresponding pressure changes at the observation site with characteristic time lags ranging from 25 to 155 s. In addition, several aspects related to the mechanism that created the time lags are discussed.Graphical

Clarification of Deterioration Mechanism and Seismic Performance of Telecommunication Steel Conduit

This study evaluates the seismic response of conduits considering the aging deterioration of steel-pipe threaded joints for communication. To model the displacement-load characteristics of the aged steel-pipe threaded joint, fracture experiments were conducted using specimens with a burial period of 30 to 50 years. The obtained results showed that the maximum tensile load tended to decrease as the burial period became longer and as the internal corrosion became severe. The deterioration of steel pipe threaded joints was represented by a model in which the yield load and maximum load decrease as the pipe thickness decreases in proportion to the 0.5th power of the burial period t due to corrosion. The seismic response of the system is investigated by modeling the pipe with beam elements and the deteriorated joints as well as the pipe-soil interaction with spring elements. It is shown that joints with a burial period of more than 20 years are plasticized with a ground strain of 0.3%, and joints with a burial period of 50 years are destroyed with a ground strain of 0.5%. As a result, the effect of joint deterioration on the seismic performance of the steel pipe conduits was quantitatively clarified.

Quantifying the Surface Strain Field Induced by Active Sources with Distributed Acoustic Sensing: Theory and Practice.

Quantitative dynamic strain measurements of the ground would be useful for engineering scale problems such as monitoring for natural hazards, soil-structure interaction studies, and non-invasive site investigation using full waveform inversion (FWI). Distributed acoustic sensing (DAS), a promising technology for these purposes, needs to be better understood in terms of its directional sensitivity, spatial position, and amplitude for application to engineering-scale problems. This study investigates whether the physical measurements made using DAS are consistent with the theoretical transfer function, reception patterns, and experimental measurements of ground strain made by geophones. Results show that DAS and geophone measurements are consistent in both phase and amplitude for broadband (10 s of Hz), high amplitude (10 s of microstrain), and complex wavefields originating from different positions around the array when: (1) the DAS channels and geophone locations are properly aligned, (2) the DAS cable provides good deformation coupling to the internal optical fiber, (3) the cable is coupled to the ground through direct burial and compaction, and (4) laser frequency drift is mitigated in the DAS measurements. The transfer function of DAS arrays is presented considering the gauge length, pulse shape, and cable design. The theoretical relationship between DAS-measured and pointwise strain for vertical and horizontal active sources is introduced using 3D elastic finite-difference simulations. The implications of using DAS strain measurements are discussed including directionality and magnitude differences between the actual and DAS-measured strain fields. Estimating measurement quality based on the wavelength-to-gauge length ratio for field data is demonstrated. A method for spatially aligning the DAS channels with the geophone locations at tolerances less than the spatial resolution of a DAS system is proposed.

Mindlin solution on ground deformation caused by the trench excavation during installation of concrete diaphragm wall panels

Concrete diaphragm walls (CDWs) are widely used as support of deep excavation in soft ground in urban areas. Ground deformation occurs during the excavation of trenches for the installation of the CDW panels due to ground stress release. This paper investigates the ground deformation during slurry trenching using Mindlin solution. The pressure of slurry used to protect the trench stability during excavation is simulated as a triangularly distributed load on the trench walls, the soil stress state is solved using Mindlin solution, and the horizontal and vertical ground displacement are obtained through integral transformation of ground strain. The rationality of the solution is verified through comparison between the analytical solution and field measurement. Sensitivity analyses are performed on soil elastic modulus, Poisson's ratio, trench excavation depth and panel length. Simplified formulation is proposed for the prediction of horizontal ground deformation. The impact of excavation stages and adjacent panels on the ground deformation is explored. The study finds that the Mindlin solution is able to provide an approximate solution on the ground deformation during slurry trenching, and the simplified formulation can be used to provide a fast estimate of the horizontal ground movement in engineering practice.

Checking the site categorization criteria and amplification factors of the 2021 draft of Eurocode 8 Part 1\u20131

In this paper the site categorization criteria and the corresponding site amplification factors proposed in the 2021 draft of Part 1 of Eurocode 8 (2021-draft, CEN/TC250/SC8 Working Draft N1017) are first introduced and compared with the current version of Eurocode 8, as well as with site amplification factors from recent empirical ground motion prediction equations. Afterwards, these values are checked by two approaches. First, a wide dataset of strong motion records is built, where recording stations are classified according to 2021-draft, and the spectral amplifications are empirically estimated computing the site-to-site residuals from regional and global ground motion models for reference rock conditions. Second, a comprehensive parametric numerical study of one-dimensional (1D) site amplification is carried out, based on randomly generated shear-wave velocity profiles, classified according to the new criteria. A reasonably good agreement is found by both approaches. The most relevant discrepancies occur for the shallow soft soil conditions (soil category E) that, owing to the complex interaction of shear wave velocity, soil deposit thickness and frequency range of the excitation, show the largest scatter both in terms of records and of 1D numerical simulations. Furthermore, 1D numerical simulations for soft soil conditions tend to provide lower site amplification factors than 2021-draft, as well as lower than the corresponding site-to-site residuals from records, because of higher impact of non-linear (NL) site effects in the simulations. A site-specific study on NL effects at three KiK-net stations with a significantly large amount of high-intensity recorded ground motions gives support to the 2021-draft NL reduction factors, although the very limited number of recording stations allowing such analysis prevents deriving more general implications. In the presence of such controversial arguments, it is reasonable that a standard should adopt a prudent solution, with a limited reduction of the site amplification factors to account for NL soil response, while leaving the possibility to carry out site-specific estimations of such factors when sufficient information is available to model the ground strain dependency of local soil properties.

Simulation of near-fault ground strains and rotations from actual strike-slip earthquakes: case studies of the 2004Mw 6.0 Parkfield, the 1979Mw 6.5 Imperial Valley and the 1999Mw 7.5 Izmit earthquakes

SUMMARYPrevious studies have demonstrated that finite-fault simulations of actual or hypothetical earthquakes using deterministic, physics-based simulation techniques constitute an effective tool for characterizing near-fault ground strains and rotations in the low-frequency range. The characteristics of these motions are further investigated in this study by performing forward ground-motion simulations of three well-documented strike-slip earthquakes (i.e. 2004 Mw 6.0 Parkfield, 1979 Mw 6.5 Imperial Valley and 1999 Mw 7.5 Izmit) using models of the seismic source and crustal structure available in the literature. Time histories of ground strains and rotations are numerically generated at near-fault stations and at a dense grid of observation points extending over the causative fault. This is achieved by finite differencing translational motions simulated at very closely spaced stations using a kinematic modelling approach. The simulation results show that the three strike-slip earthquakes produce large-amplitude pulse-like shear strain and torsion in the forward direction of rupture propagation. The time histories of specific components of displacement gradient, strain and rotation at near-fault stations can be estimated from those of ground velocities using a phase velocity, whereas peak ground torsions in the near-fault region can be reasonably estimated from peak horizontal ground velocities using a scaling factor. However, both the phase velocity and the scaling factor exhibit significant variability in the near-fault region of the considered earthquakes. The concept of isochrones is also utilized to associate fault rupture characteristics with near-fault ground strains and rotations. The results indicate that the seismic energy radiated from the high-isochrone-velocity region of the fault—which encompasses areas of large slip locally driven by high stress drop—arrives at a near-fault station in a short time interval that coincides with the time window of the large-amplitude pulse-like shear strain and torsion.

Evaluating seismic beamforming capabilities of distributed acoustic sensing arrays

Abstract. The versatility and cost efficiency of fibre-optic distributed acoustic sensing (DAS) technologies facilitate geophysical monitoring in environments that were previously inaccessible for instrumentation. Moreover, the spatio-temporal data density permitted by DAS naturally appeals to seismic array processing techniques, such as beamforming for source location. However, the measurement principle of DAS is inherently different from that of conventional seismometers, providing measurements of ground strain rather than ground motion, and so the suitability of traditional seismological methods requires in-depth evaluation. In this study, we evaluate the performance of a DAS array in the task of seismic beamforming, in comparison with a co-located nodal seismometer array. We find that, even though the nodal array achieves excellent performance in localising a regional ML 4.3 earthquake, the DAS array exhibits poor waveform coherence and consequently produces inadequate beamforming results that are dominated by the signatures of shallow scattered waves. We demonstrate that this behaviour is likely inherent to the DAS measurement principle, and so new strategies need to be adopted to tailor array processing techniques to this emerging measurement technology. One strategy demonstrated here is to convert the DAS strain rates to particle velocities by spatial integration using the nodal seismometer recordings as a reference, which dramatically improves waveform coherence and beamforming performance and warrants new types of “hybrid” array design that combine dense DAS arrays with sparse seismometer arrays.

A methodology based on strain analysis for identifying potential discontinuous deformation zones in sublevel caving mines

Underground mining operations using the sublevel caving method often result in discontinuous ground deformations involving surface cracks. Determining the limit of the discontinuous deformation zone is important for the relocation of neighbouring residential areas, mining infrastructure, and the planning of underground mining operations. The limit of the discontinuous deformation zone is characterised by the outermost surface crack, which is a tensile crack when it occurs and is correlated with the horizontal ground tensile strain. In this study, a mathematical procedure combining the horizontal displacement, as periodically monitored by total station and GPS, multiquadric radial basis function (MQ-RBF) interpolation, and continuum mechanics is provided to calculate the strain state at any point on the ground. Then the relationship between a new tensile crack and horizontal ground tensile strain is studied to determine the criterion representing the presence of a new tensile crack. This means that, when the criterion at any point on the ground is satisfied, the point will have the potential to crack. Based on this, the potential discontinuous deformation zone where surface cracks may occur can be identified, potential break angles at representative sections can then be determined. A case study is presented to illustrate the results given by the above methodology. The result shows that when major principal horizontal ground strain ε1 at any point on the ground reaches the potential cracking major principal strain, PCMPS (6 mm/m in this case study), the point will have the potential to crack. Subsequently, the area within the outermost contour of the PCMPS can be defined as the potential discontinuous deformation zone. Moreover, the approximate matching of the limits of potential discontinuous deformation zones and surface cracks verifies the reliability of the mathematical procedure and the rationality of the PCMPS in identifying the discontinuous deformation zone. Additionally, in this case study, the potential break angles at two respective sections are significantly different, indicating that the break angles should be further studied and care taken in design of works in these two zones, respectively.

Comparative analysis of strain parameter acquisition based on Cave strain and GPS observation

A set of three-component extensometers are installed on the Xibozi Seismic Station in Yanqing District, Beijing. The layout of the extensometers is an isosceles triangle, and the observation is the amount of expansion and contraction of each side, which is then converted into the strain value of each side. In this paper, the regional crustal strain parameters were calculated based on the observations of the extensometers and the continuous GPS observations around Xibozi Sesimic Staion. From two aspects of observation at the same site and different scales, the ground strain information reflected by the two observation methods is compared and analyzed. From the strain parameters calculated by a single point (extensometers) and the strain parameters calculated by the triangular surface observation (GPS) with different specifications, the overall Beijing area is in the context of tensile strain. However, there is a gap of several orders of magnitude between the two results, which may be related to the artificial operation of the pre-processes such as zero drift and step removal of the instrument’s strain observation data.

New insights from the Ölfus case study concerning the seismic performance of buried concrete wastewater pipes in the vicinity of a severe earthquake

The correlation of earthquake damage to underground wastewater (sewage and drainage) pipelines and measured intensity measurements is described in this paper. The study is based on pipelines consisting primarily of segmented concrete pipes in Hveragerði, Iceland. This town experienced a Mw 6.3 earthquake on 29 May 2008, originated in its near field. Subsequently, the interior conditions of all the pipelines were thoroughly investigated by a robot camera. All the pipeline damage detected was analysed and documented. While damage in segmented pipelines is assumed to occur primarily at the joints due to axial ground strains, the predominant damage in Hveragerði was circular cracks at the centre zone of the pipe barrels. This suggests that (1) ground curvature plays a greater role in the seismic response of the pipelines, and (2) the stiffness and strength of the pipe barrel should be considered in a seismic analysis. The pipe damage observed in the sewage lines, close to the engineering bedrock, was half as much as the damage observed in the drainage lines resting on a thicker backfill material. A relationship between non-minor damage rates and the intensity measurements was observed for the drainage pipeline only, where the best overall correlation results were obtained for peak ground velocity. The commonly used fragility curves greatly underestimate the damage rate observed in the study area. This may apply to the potable water systems, where the majority of segmented pipelines consist of brittle pipes of cast iron, asbestos or concrete (HAZUS, NIBS 2003).

TIME-DEPENDENT BEHAVIOUR OF PILED RAFT FOUNDATIONS ON SATURATED CLAY: EXPERIMENTAL INVESTIGATIONS

When designing a piled raft foundation (PR) on clay, it is necessary to understand the timedependent behaviour of the foundation because stresses and strains in clayey ground will change for a long time after the construction, due to consolidation processes of the ground. This paper, therefore, aims to investigate the long-term behaviour of PRs through small-scale physical modelling. In the experiments, the model ground was prepared by consolidating a slurry mixture of Kasaoka clay and silica sand. The model foundations consisted of a square raft having a width of 125 mm and 4 or 9 piles having a length of 150 mm. For the loading test of PR, vertical load was increased by multiple steps and each load step was maintained to observe the long-term behaviour. The experimental results show that the piles effectively suppress the foundation settlement for relatively smaller loads. In the primary consolidation stage, the pile resistance increases with elapsed time while the raft resistance decreases. This is caused by the dissipation of pore water pressure and the corresponding increase of effective stresses of soils below the raft base. In the secondary consolidation stage, for the case of 4-pile PR, the resistances of both the raft and piles are stable although creep settlement continues. For the secondary consolidation stage of 9-pile PR, pile load reduces slightly under smaller applied loads and stable under larger applied loads. In general, the 9-pile PR reduces the foundation settlement significantly under smaller applied loads, compared to the 4-pile PR.

A Parametric Investigation of Near‐Fault Ground Strains and Rotations Using Finite‐Fault Simulations

AbstractAlthough previous studies have performed finite‐fault simulations of actual or hypothetical earthquakes to generate time histories of near‐fault ground strains and rotations, no systematic attempt has been made to assess the sensitivity of these motions to variations in seismic source parameters (e.g., fault type, magnitude, rupture velocity, slip velocity, hypocenter location, burial depth). Such a parametric investigation is presented in this article by generating time histories of ground strains and rotations at near‐fault stations and at a dense grid of observation points extending over the causative fault for a suite of hypothetical strike‐slip and dip‐slip earthquakes. The simulation results show that strike‐slip earthquakes produce large shear strain and torsion, whereas dip‐slip earthquakes generate large axial strain and rocking. The time histories of specific components of displacement gradient, strain, and rotation at near‐fault stations may be estimated from those of ground velocities using a simple scaling relation, whereas peak rotational motions in the near‐fault region may be reasonably estimated from peak translational motions using a properly selected scaling factor. The parametric analysis results show that near‐fault ground strains and rotations exhibit strong sensitivity to variations in rupture velocity, slip velocity, and burial depth, whereas a change in hypocenter location significantly alters the spatial distributions of peak ground strains (PGSs) and rotations (PGRs). The presence of a low‐velocity surface layer increases the amplitude and duration of ground strains and rotations, whereas their static offsets are also amplified. Distinct attenuation characteristics are observed for PGSs and PGRs depending on the component of interest, the earthquake magnitude, and the rupture distance. Finally, the spatial distributions of PGSs and PGRs obtained from a stochastically generated variable slip distribution are overall similar to those obtained from a tapered uniform slip distribution, whereas the spatial distributions of the respective static offsets differ significantly.

Effect of seismic and soil parameter uncertainties on seismic damage of buried segmented pipeline

Abstract Pipeline is one of the critical infrastructures in today civilisation and spreads over a large area with varying soil conditions. The failure in pipe network causes significant economy losses to asset owners and environmental impact to the society. Therefore, it is important to ensure the safe operation of a pipe network during its lifetime. The structural performance (i.e., static and dynamic) of the buried pipeline largely depends on the pipe-soil interaction along the pipe segments. The soil shear strength properties (i.e., soil cohesion, density and friction angle) and its variability have been widely recognised as critical factors, which control the seismic performance of buried pipeline. These parameters are frequently considered independently in many studies, but in natural soil, the parameters are most likely to have strong dependency, which have significant influence in the seismic performance of buried pipe. Additionally, pipe seismic performance is also influenced by variability in ground motion parameters (e.g., wave propagation length, ground particle velocity, phase velocity of wave, etc). Thus, this study aims to stochastically evaluate the influence of soil uncertainties and variability in seismic parameters on seismic performance of buried segmented pipeline. Bivariate random field is used to probabilistically sample the cross-correlated soil parameters via Monte Carlo Simulations. The nonlinear finite element (FE) models are developed to simulate the axial joint-failure of segmented cast-iron (CI) pipelines with lead-caulked joint. The probabilistic seismic demand model (PSDM) is developed between repair rate (RR) per km to maximum ground strain by considering seismic wave with various wave propagation lengths. Furthermore, the effect of soil variabilities and seismic wave propagation lengths in seismic demand parameters are presented. Finally, for the PSDM can be implemented for rapid seismic damage estimate for buried pipe.

Segmented pipeline damage predictions using liquefaction vulnerability parameters

Past observations showed that pipeline damages in liquefaction zones are significantly higher than the damages in areas where there was no liquefaction. Existing vulnerability relationships for the pipelines in liquefaction zones utilize parameters such as ground displacement, horizontal ground strain, angular distortion or both. These relationships are particularly useful in performance or risk assessment of pipeline systems. However, prediction of these parameters for pipeline damage estimates is difficult to perform and highly variable with current procedures. This paper proposes new correlations of asbestos cement (AC), cast iron (CI) and polyvinyl chloride (PVC) pipeline damage, expressed as repairs/km, with three different liquefaction parameters: liquefaction severity number (LSN), one-dimensional volumetric reconsolidation settlement (SV1D), and liquefaction potential index (LPI). The pipeline damage data from 22 February 2011, Mw = 6.2 Christchurch earthquake and geotechnical information pertaining to liquefied area in Christchurch are utilized herein. Cone penetration test (CPT) based Boulanger and Idriss [1] liquefaction triggering procedure with 15th, 50th and 85th percentile cyclic resistance ratio (CRR) curves (corresponding to probabilities of liquefaction, PL, equal to 15%, 50%, and 85%) was used to calculate the parameters. It is shown that the relationships between AC, CI and PVC pipeline damages and LSN, SV1D and LPI are strong, except for the correlation for AC pipeline damage versus LPI. Considering CI and PVC pipelines, both LSN and LPI correlations are comparable and slightly better than SV1D correlations. Use of different probabilities of liquefaction triggering does not have significant effect on correlations with LSN and SV1D whereas the same is not true for LPI correlations. Regarding the resilience of pipelines, PVC and AC pipelines performed the best and worst, respectively in all cases with CI pipelines in the middle. The correlations have the potential for use with existing or new liquefaction hazard maps for prediction of pipeline damage from future earthquakes.

Increased growth rate and amikacin resistance of Salmonella enteritidis after one-month spaceflight on China's Shenzhou-11 spacecraft.

China launched the Tiangong‐2 space laboratory in 2016 and will eventually build a basic space station by the early 2020s. These spaceflight missions require astronauts to stay on the space station for more than 6 months, and they inevitably carry microbes into the space environment. It is known that the space environment affects microbial behavior, including growth rate, biofilm formation, virulence, drug resistance, and metabolism. However, the mechanisms of these alternations have not been fully elucidated. Therefore, it is beneficial to monitor microorganisms for preventing infections among astronauts in a space environment. Salmonella enteritidis is a Gram‐negative bacterial pathogen that commonly causes acute gastroenteritis in humans. In this study, to better understand the effects of the space environment on S. enteritidis, a S. enteritidis strain was taken into space by the Shenzhou‐11 spacecraft from 17 October 2016 to 18 November 2016, and a ground simulation with similar temperature conditions was simultaneously performed as a control. It was found that the flight strain displayed an increased growth rate, enhanced amikacin resistance, and some metabolism alterations compared with the ground strain. Enrichment analysis of proteome revealed that the increased growth rate might be associated with differentially expressed proteins involved in transmembrane transport and energy production and conversion assembly. A combined transcriptome and proteome analysis showed that the amikacin resistance was due to the downregulation of the oppA gene and oligopeptide transporter protein OppA. In conclusion, this study is the first systematic analysis of the phenotypic, genomic, transcriptomic, and proteomic variations in S. enteritidis during spaceflight and will provide beneficial insights for future studies on space microbiology.

Evaluation of seismic behavior of box culvert buried in the ground through centrifuge model tests and numerical analysis

Japan has yet to establish a seismic design for road box culverts (RBCs) because past major earthquakes did not damage them. In recent years, structures with enlarged sectional dimensions (the purpose of which is to optimize the internal space in RBCs) have become common. However, the unknown seismic strength of such large RBCs makes RBC seismic designs increasingly necessary. Several seismic design methods have been developed for and applied to rectangular underground structures, e.g., cut-and-cover tunnels, which are structurally similar to RBCs. Although these methods are applicable to RBCs, it is uncertain whether they can be applied directly because there are currently no evaluation results from model tests on RBCs, which have unique structural features, e.g., no haunch at the bottom of the sidewalls. Therefore, we verify a seismic behavior of an RBC and develop a method for evaluating it in order to establish a seismic design for RBCs. We conducted centrifuge model tests subjected to seismic force and a numerical analysis using an elastoplastic finite analysis method, in addition, we validated this analysis by comparing the test and analytical results. The test results show RBCs will most likely develop rocking rotation when the ground strain exceeds approximately 0.08%. A comparison of the numerical and experimental results shows that this analysis can estimate the shear deformation behavior with approximately 90% accuracy in square cross-section cases. Meanwhile, this analysis has tendency to underestimate the axial forces in each case and to overestimate the bending moments of some members in the case of wide cross-sections.

Valley amplification of horizontal ground strain

It is recognized that seismic damages to segmented buried pipelines depend in part upon transient ground strain due to seismic wave propagation. Such wave propagation damage seems to be larger at sites with variable subsurface conditions, because of drastic changes in seismic wave characteristics as they propagates in heterogeneous rock and soil layers. This paper intends to investigate the amplification of horizontal ground strains in a valley subjected to vertically incident SH waves. A 2D model with an inclined soil-rock interface is established to simulate conditions of the valley subject to seismic wave propagation. A procedure for evaluating the ground strain amplification is developed by consideration of travel path effects. Three amplification/de-amplification mechanisms are specifically considered, the ground velocity amplification, ground strain amplification due to the change in the propagation direction, and de-amplification due to a lack of total reflection at the soil-rock interface. The analysis results show that the maximum amplification factor is mainly affected by the interface inclination angle and shear wave velocity ratio between the valley soil and the base rock. For a given number of wave cycles, the amplification factor grows with the increment of the inclination angle and declines with the growth of shear wave velocity ratio. The de-amplification at inclined interface is likely to nullify the amplification generated by travel path effects.

Comparison of Observed and Synthetic Near‐Fault Dynamic Ground Strains and Rotations from the 2004 Mw 6.0 Parkfield, California, Earthquake

Comparison of Observed and Synthetic Near‐Fault Dynamic Ground Strains and Rotations from the 2004 Mw 6.0 Parkfield, California, Earthquake

VULNERABILITY ASSESSMENT OF SURIGAO METRO WATER DISTRICT UNDER SEISMIC HAZARD

Earlier this year, Surigao Del Norte, a province in the Philippines experienced a 6.7 magnitudeearthquake. The severe ground movement caused some of the buried pipelines to be pulled-out from theirsupports. This type of failure occurs when the ground strain during extreme seismic excitation exceeds thestrain capacity of the buried pipe. The failure of the pipes resulted in the loss of water that was vital for post-earthquake recovery efforts. In this regard, there is a need to re-assess the vulnerability of the buried pipes ofthe water network. In this paper, a probabilistic seismic hazard analysis (PSHA) was employed to estimatethe seismic hazard within the concession area. Past seismic data that can significantly affect the targetstructure is used for this purpose. The buried water lifeline system of Surigao Metro Water District (SMWD)was chosen as the target lifeline. An appropriate ground motion prediction equation (GMPE) was used todevelop the uniform hazard response spectra for the site. To assess the vulnerability of the pipes threedamage states were considered: major, moderate and minor. The probability of major, moderate and minordamage to each pipe was determined using Monte Carlo simulation. Subsequently, fragility curves wereobtained.

Comparison of horizontal ground displacements in Avonside area, Christchurch from air photo, LiDAR and satellite measurements regarding pipeline damage assessment

Recent earthquakes show that pipeline damage is severe in the areas where permanent ground deformations (e.g., liquefaction zones) occur. Ground movement hazard to pipeline systems can be assessed by using ground displacement measurements around the location of pipelines. There are many different ways of measuring ground displacements after an earthquake occur. This paper compares displacements measured in Avonside area, Christchurch, NZ, by using four different ways with respect to their effects on pipeline damage assessments. They are air photo, satellite, high resolution light detection and ranging (LiDAR) surveys data presented at 4- and 56-m grids acquired before and after the Mw6.2 22 February 2011 earthquake. Avonside area was in the liquefaction zones of the 22 February 2011 earthquake. Where possible, benchmark measurements were also included in the comparisons. In this study, the focus was on asbestos cement and cast iron water pipelines as the length of the pipelines and the number of damages in the study area was much higher compared to other pipe materials, providing sufficient repair rate data passing the screening criteria to develop linear regressions. The correlations between pipeline damage and lateral ground strains were developed by calculating the horizontal strains from these four different type displacements. The comparisons show that satellite imagery is good for estimating total movements but not so good for estimating lateral strains and conversely LiDAR surveys are not so good for estimating total movements, but much better for estimating lateral strains. Hence, pipeline damage correlations with LiDAR calculated strains provide higher determination coefficient (r2) value. The results of comparisons are presented and discussed.