Deformation monitoring of long-span railway bridges based on SBAS-InSAR technology

The deformation monitoring of long-span railway bridges is significant to ensure the safety of human life and property.The interferometric synthetic aperture radar(In SAR)technology has the advantage of high accuracy in bridge deformation monitoring.This study monitored the deformation of the Ganjiang Super Bridge based on the small baseline subsets(SBAS)In SAR technology and Sentinel-1A data.We analyzed the deformation results combined with bridge structure,temperature,and riverbed sediment scouring.The results are as follows:(1)The Ganjiang Super Bridge area is stable overall,with deformation rates ranging from-15.6 mm/yr to 10.7 mm/yr(2)The settlement of the Ganjiang Super Bridge deck gradually increases from the bridge tower toward the main span,which conforms to the typical deformation pattern of a cable-stayed bridge.(3)The sediment scouring from the riverbed cause the serious settlement on the bridge’s east side compared with that on the west side.(4)The bridge deformation negatively correlates with temperature,with a faster settlement at a higher temperature and a slow rebound trend at a lower temperature.The study findings can provide scientific data support for the health monitoring of long-span railway bridges.

Combining Thermochronology and Geochronology to Constrains Orogenic Processes in the Alps and Tibet

Deciphering the kinematics of deformation is key to understand the crustal evolution.In the last decades several techniques have been developed to help constraining the timing of deformation.On one side geochronology techniques allow the dating of a wider range of minerals with higher spatial resolution.On the other side thermochronology,with the help of numerical simulations(PeCube,QTQt…),help to constrain the rock exhumation history that is often linked to the vertical component of deformation.In both cases the deformation timing can accurately be discussed only together with a serious structural analysis.

Present-day deformation of Agung volcano,Indonesia, as determined using SBAS-InSAR

Based on ALOS PALSAR images, time series deformation fields of the Agung w^lcann area were obtained using SBAS-InSAR in 2007 -2009. The time series deformation showed obvious inflation around the Agung volcano area, which was positively correlated with time. We modeled the cumulated deformation interferogram based on Mogi point source and vertical prolate spheroid source. The deformation model indicated that the vertical prolate spheroid model fit the observed deformation reasonably well. The magma chamber was loc, ated beneath the eenter of the volcano at a depth of approximately 5 km beneath the summit.

Mechanism of deformation around northern Hejin,China,observed by InSAR

Interferometric synthetic aperture radar （InSAR） images reveal deformation around northern Hejin, Shanxi Province. The small baseline subset （SBAS） approach for InSAR-derived deformation indicates that the observed deformation pattern can be characterized by the sum of two phenomena： background subsidence from December 2003 to February 2009 with a cumulative displacement of approximately 5 cm and uplift from Febru- ary 2009 to November 2010 with a cumulative displacement of approximately 2.5 cm. Deformation modeling indicates that the local deformation was caused by the closing and opening of a sill beneath northern Hejin. The modeled sill which is approximately 5 km long, 2 km wide, is centered at 1.5 km depth. The deformation was caused by the withdrawal and influx of subsurface water.

Identify Landslide Precursors from Time Series InSAR Results

Landslides cause huge human and economic losses globally.Detecting landslide precursors is crucial for disaster prevention.The small baseline subset interferometric synthetic-aperture radar(SBAS-InSAR)has been a popular method for detecting landslide precursors.However,non-monotonic displacements in SBAS-InSAR results are pervasive,making it challenging to single out true landslide signals.By exploiting time series displacements derived by SBAS-InSAR,we proposed a method to identify moving landslides.The method calculates two indices(global/local change index)to rank monotonicity of the time series from the derived displacements.Using two thresholds of the proposed indices,more than 96%of background noises in displacement results can be removed.We also found that landslides on the east and west slopes are easier to detect than other slope aspects for the Sentinel-1 images.By repressing background noises,this method can serve as a convenient tool to detect landslide precursors in mountainous areas.

Structural characteristics and implication on tectonic evolution of the Daerbute strike-slip fault in West Junggar area, NW China

The Daerbute fault zone, located in the northwestern margin of the Junggar basin, in the Central Asian Orogenic Belt, is a regional strike-slip fault with a length of 400 km. The NE-SW trending Daerbute fault zone presents a distinct linear trend in plain view, cutting through both the Zair Mountain and the Hala＇alate Mountain. Because of the intense contraction and shearing, the rocks within the fault zone experienced high degree of cataclasis, schistosity, and mylonization, resulting in rocks that are easily eroded to form a valley with a width of 300- 500 m and a depth of 50-100 m after weathering and erosion. The well-exposed outcrops along the Daerbute fault zone present sub-horizontal striations and sub-vertical fault steps, indicating sub-horizontal shearing along the observed fault planes. Flower structures and horizontal drag folds are also observed in both the well-exposed outcrops and high-resolution satellite images. The distribution of accommodating strike-slip splay faults, e.g., the 973-pluton fault and the Great Jurassic Trough fault, are in accordance with the Riedel model of simple shear. The seismic and time-frequency electromagnetic （TFEM） sections also demonstrate the typical strike-slip characteristics of the Daerbute fault zone. Based on detailed field observations of well-exposed outcrops and seismic sections, the Daerbute fault can be subdivided into two segments： the western segment presents multiple fault cores and damage zones, whereas the eastern segment only presents a single fault core, in which the rocks experienced a higher degree of rock cataclasis, schistosity, and mylonization. In the central overlapping portion between the two segments, the sediments within the fault zone are primarily reddish sandstones, conglomerates, and some mudstones, of which the palynological tests suggest middle Permian as the timing of deposition. The deformation timing of the Daerbute fault was estimated by integrating the depocenters＇ basinward migration and initiation of the splay faults （e.g., the Great Jurassic Trough fault and the 973-pluton fault）. These results indicate that there were probably two periods of faulting deformation for the Daerbute fault. By integrating our study with previous studies, we speculate that the Daerbute fault experienced a two-phase strike-slip faulting deformation, commencing with the initial dextral strike-slip faulting in mid-late Permian, and then being inversed to sinistral strike-slip faulting since the Triassic. The results of this study can provide useful insights for the regional tectonics and local hydrocarbon exploration.

Gement improved highly weathered phyllite for highway subgrades:A case study in Shaanxi province

In a cost-saving move, the soft rocks composed of highly-weathered phyllites available on- site were used to fill the subgrade in the eastern Ankang section of the expressway of Shiyan to Tianshui, China. Cement admixture was used to improve the performance of the weathered phyllites. In order to determine the best mix ratio, values corresponding to compaction performance, unconfined compressive strength, and the California bearing ratio （CBR） were analyzed for variable cement content weight percentages （3%, 4%, 5%, and 6%） using test subgrade plots in the field. Field measurements of resilience modulus and deflection confirmed that the strength of the subgrade increased as the cement ratio increased. In order to further evaluate the cement/phyllite mixture, the performance of the 3% cement ratio sample was evaluated under saturated conditions （with various levels of moisture addition and soaking time） using both the wetting deformation and resilient modulus values. Results suggest that moisture added and soaking time are key factors that affect the seepage depth, water content, and resilient modulus. The recommend values for the cement addition and for the water content are given out. This study can aid in pre- vention of highway damage by improving the foundation capacity and lengthening the lifecycle of the highway in phyllite distributed region at home and abroad.