Shape Acceleration Array Research Articles

Case Study on Instrumenting and Monitoring Geosynthetic-Reinforced Pile-Supported Mechanically Stabilized Earth Wall Built over Soft Soil

This paper presents a case study on instrumenting, monitoring, and finite element modeling (FEM) of geosynthetic-reinforced pile-supported (GRPS) mechanically stabilized earth (MSE) walls. The GRPS-MSE wall was monitored using various instruments such as piezometers, earth pressure cells, shape-acceleration arrays (SAAs), and strain gauges. The performance criteria included efficacy, stress concentration ratio (SCR), differential settlement, and reinforcement tension. Collected data, such as excess pore-water pressures, contact pressures on pile and soft soil, differential settlements, and lateral displacement of MSE wall, were analyzed thoroughly. A 3D FEM was also developed to simulate the GRPS MSE wall, and the results are in good agreement with field data. The results demonstrated significant load transfer from soil to piles as a result of soil arching, yielding 30–32 SCR. The field efficacy was measured at 37.69 %, while the FEM efficacy was estimated as 42.4. Strains in geogrids within the geosynthetic-reinforced load transfer platform (GLTP) system were under 1%, less than the 5% maximum recommended by FHWA. The maximum differential settlement measured between pile cap and soft soil from SAAs is 7.1 mm, while it is estimated to be 8.3 mm from FEM. The MSE wall exhibited low lateral displacement (<25 mm), indicating enhanced stability because of GLTP. The comparison between five analytical GLTP design methods showed that the CUR226 methods gave the closest results to field measurements and FEM results. This study offers crucial insights into leveraging GLTP and MSE walls in highway construction.

Investigations of seismic response to an irregular-section subway station structure located in a soft clay site

In this study, shaking table tests were performed to investigate the dynamic interaction of a silty-clay soil with an irregular-section subway station. During the tests, a shape acceleration array (SAA) was used to measure the lateral deformation of the model soil, and a non-contact dynamic displacement testing method was applied to visualize and digitalize the seismic damage process of the station structure. Typical test results, including the dynamic earth pressure, seismic settlement, deformation, and acceleration of different levels of the structure, were interpreted. The results indicated that the movement of the subway station was more controlled by the surrounding silty-clay soil in terms of phase and amplitude. SAA can effectively measure the soil deformation, and the relationship between the relative lateral displacement and soil depth can be well fitted in a cosine function, especially when subjected to strong earthquakes. Seismic settlement is significantly linked to Arias intensity, and the subway station experienced significant uneven settlement, resulting in soil-structure separation in the vertical direction. The multi-story irregular-section subway station deforms in a shear mode. The maximum inter-story drift ratio was approximately 1/171. The components in the lower layers of the shallow-buried subway station structure, particularly in the central columns, underwent cumulative damage. Hence, more robust forms of structural members and the ductility of central columns should be carefully considered in the seismic design of subway station structures.

Deformation Activity Analysis of a Ground Fissure Based on Instantaneous Total Energy.

This study proposes a novel instantaneous total energy method to perform an activity analysis of ground fissures deformation, which is calculated by integrating the extreme-point symmetric mode decomposition (ESMD) method and kinetic energy based on the time-series displacement acquired by shape acceleration array (SAA) sensors. The proposed method is tested on the Xiwang Road fissure in Beijing, China. First, to fully monitor the hanging wall and footwall of the monitored ground fissure, a 4 m-long SAA in the vertical direction and an 8 m-long SAA in the horizontal direction were embedded in a ground fissure to obtain an accurate time-series displacement with an accuracy of ±1.5 mm/32 m and a displacement acquisition frequency of once an hour. Second, to improve the accuracy of the activity analysis, the ESMD method and Spearman’s rho are applied to perform signal denoising of the original time-series displacement obtained by the SAA sensors. Finally, the instantaneous total energy is obtained to analyze the activity of the monitored ground fissure. The results demonstrate that the proposed method is more reliable to reflect the activity of a monitored ground fissure compared to the time-series displacement.

A Deformation Prediction Approach for Supertall Building Using Sensor Monitoring System

Using high-precision sensors to monitor and predict the deformation trend of supertall buildings is a hot research topic for a long time. And in terms of deformation trend prediction, the main way to realized deformation trend prediction is the deep learning algorithm, but the accuracy of prediction result needs to be improved. To solve the problem described above, firstly, based on the conditional deep belief network (CDBN) model, the levenberg-marquardt (LM) was used to optimize the CDBN model; the LM-CDBN model has been constructed. Then taking CITIC tower, the tallest building in Beijing as the research object, the real-time monitoring data of the shape acceleration array (SAA) as an example, we used LM-CDBN model to analyse and predict the building deformation. Finally, to verify the accuracy and robustness of LM-CDBN model, the prediction results of the LM-CDBN model are compared with the prediction results of the CDBN model, the extreme learning machine (ELM) model, and the unscented Kalman filter-support vector regression (UKF-SVR) model, and we evaluated the result from three aspects: training error, fitness, and stability of prediction results. The results show that the LM-CDBN model has higher precision and fitting degree in the prediction of deformation trend of supertall buildings. And the MRE, MAE, and RMSE of the LM-CDBN model prediction results are only 0.0060, 0.0023mm, and 0.0031mm, and the prediction result was more in line with the actual deformation trend.

Assessment of ground-based monitoring techniques applied to landslide investigations

A landslide complex in the Whitby Mudstone Formation at Hollin Hill, North Yorkshire, UK is periodically re-activated in response to rainfall-induced pore-water pressure fluctuations. This paper compares long-term measurements (i.e., 2009–2014) obtained from a combination of monitoring techniques that have been employed together for the first time on an active landslide. The results highlight the relative performance of the different techniques, and can provide guidance for researchers and practitioners for selecting and installing appropriate monitoring techniques to assess unstable slopes. Particular attention is given to the spatial and temporal resolutions offered by the different approaches that include: Real Time Kinematic-GPS (RTK-GPS) monitoring of a ground surface marker array, conventional inclinometers, Shape Acceleration Arrays (SAA), tilt meters, active waveguides with Acoustic Emission (AE) monitoring, and piezometers. High spatial resolution information has allowed locating areas of stability and instability across a large slope. This has enabled identification of areas where further monitoring efforts should be focused. High temporal resolution information allowed the capture of ‘S’-shaped slope displacement-time behaviour (i.e. phases of slope acceleration, deceleration and stability) in response to elevations in pore-water pressures. This study shows that a well-balanced suite of monitoring techniques that provides high temporal and spatial resolutions on both measurement and slope scale is necessary to fully understand failure and movement mechanisms of slopes. In the case of the Hollin Hill landslide it enabled detailed interpretation of the geomorphological processes governing landslide activity. It highlights the benefit of regularly surveying a network of GPS markers to determine areas for installation of movement monitoring techniques that offer higher resolution both temporally and spatially. The small sensitivity of tilt meter measurements to translational movements limited the ability to record characteristic ‘S’-shaped landslide movements at Hollin Hill, which were identified using SAA and AE measurements. This high sensitivity to landslide movements indicates the applicability of SAA and AE monitoring to be used in early warning systems, through detecting and quantifying accelerations of slope movement.

Installation Effects of Controlled Modulus Column Ground Improvement Piles on Surrounding Soil

AbstractThe installation of foundations and ground improvement systems alters soil stresses affecting their soil-structure interaction and behavior under vertical loading. The installation effects have been investigated for several foundation types, especially for driven piles; however, experimental full-scale investigations of drilled displacement piles are very limited. This paper focuses on investigating the short-term installation effects of controlled modulus columns (CMCs) using an instrumented full-scale field test unit. The soil was instrumented using push-in pressure sensors (PS) and shape acceleration arrays (SAAs) to monitor the evolution of soil horizontal stresses, pore water pressures, and lateral displacements during installation and vertical load test. These sensors were installed at approximately 1D, 2D, 3D, and 4D from the outside surface of the CMC shaft, where D is the diameter of the CMC. The measurements presented in this paper clearly show that the soil experienced an increase of ho...

Interaction between Laterally Loaded Pile and Surrounding Soil

AbstractA fully instrumented experiment was conducted to investigate the soil-structure interaction of single short, stiff laterally loaded piles. A hollow steel pipe pile with a diameter of 102 mm, a thickness of 6.4 mm, and a length of 1.524 m was installed in well-graded sand and subjected to increasing lateral load. The pile and surrounding soil were fully instrumented using advanced sensors, including flexible shape acceleration arrays, thin tactile pressure sheets, and in-soil null pressure sensors. The sensors attached to the pile were used to develop the compressive soil-pile interaction pressures and the lateral displacement along the pile length. The tactile pressure sheet sensors provided the soil-pile interaction compressive pressures on the circumference of the pile at a specific depth and along the length of the pile. The measured soil-pile interaction compressive pressures combined with the measured lateral displacement along the pile length were used to develop the soil-pile interaction fo...

Soil-Pile Interaction for a Small Diameter Pile Embedded in Granular Soil Subjected to Passive Loading

AbstractThe soil-structure interaction of piles used to stabilize failing slopes (i.e., subjected to lateral soil movement known as passive piles) was experimentally investigated using a state-of-the-art soil-structure interaction facility. A 102-mm diameter, 1.58-m-long precast concrete pile was installed in well-graded sand. The pile was instrumented with displacement and tilt gauges at the pile head and strain gauges, a flexible shape acceleration array, and thin tactile pressure sheets along the pile length. Furthermore, the three-dimensional (3D) movements of the soil surface and the top of the pile were monitored using two stereo digital image correlation (DIC) systems. By monitoring the relative movement of the soil surface and pile top, the DIC systems track the progression of the soil-pile interaction that occurs as the lateral displacement of the soil increases. The use of advanced sensors allows simultaneous measurement of the pile lateral movement and the soil-pile interaction pressures along ...

Measuring Soil-structure Interaction on Laterally Loaded Piles with Digital Image Correlation

A testing system to investigate soil-structure interaction on laterally loaded piles has been developed at Lafayette College. The two-piece soil box developed for this work allows the direct or indirect loading of single or multiple pile systems. Direct loading is accomplished by attaching hydraulic rams directly to the exposed area of the piles above the soil surface. Indirect loading is accomplished by loading the top section of the two-piece soil box, transferring the load from the ram to the side of the top section of the box and then to the pile through the surrounding soil.The interaction between the piles and the soil is monitored by a variety of sensors that range from common load cells, strain gages and displacement sensors to shape acceleration arrays, sheet pressure sensors and digital image correlation. The shape acceleration array measures the displacement of the pile along its length. Sheet pressure sensors are used to record the pressure distribution of the soil/soil box interaction in front of the directly loaded piles and behind indirectly loaded piles. Digital image correlation is used to measure surface soil movement. By combining the results from the various sensors the interaction of the soil and pile can be better understood.

Real-Time Monitoring System and Advanced Characterization Technique for Civil Infrastructure Health Monitoring

Real-time monitoring of civil infrastructure provides valuable information to assess the health and condition of the associated systems. This paper presents the recently developed shape acceleration array (SAA) and local system identification (SI) technique, which constitute a major step toward long-term effective health monitoring and analysis of soil and soil-structure systems. The SAA is based on triaxial micro-electro-mechanical system (MEMS) sensors to measure in situ deformation (angles relative to gravity) and dynamic accelerations up to a depth of one hundred meters. This paper provides an assessment of this array's performance for geotechnical instrumentation applications by reviewing the recorded field data from a bridge replacement site and a full-scale levee test facility. The SI technique capitalizes on the abundance of static and dynamic measurements from the SAA. The geotechnical properties and constitutive response of soil contained within a locally instrumented zone are analyzed and identified independently of adjacent soil strata.

Wireless Shape-Acceleration Array System for Local Identification of Soil and Soil Structure Systems

Soil and soil structure systems are massive multiphase particulate systems characterized by the development of localized response mechanisms under extreme loading conditions. Identification and analysis of such systems on the basis of inverse boundary value problem formulations and sparse measurements are generally indeterminate. An alternative local inverse problem technique using measurements from the newly developed wireless shape-acceleration array (WSAA) system is presented. Local identification analyses of the constitutive behavior of water-saturated soil and soil structure systems are performed with acceleration and pore pressure records provided by a cluster of closely spaced sensors. The developed novel technique does not require the availability of boundary condition measurements or the solution of an associated boundary value problem. The constitutive behavior at a specific location of a soil or soil structure system is analyzed independently of adjacent response mechanisms or material properties. Numerical simulations and centrifuge tests of a soil-retaining wall system were used to demonstrate the capabilities of this local system identification technique. The combination of the developed WSAA and local identification technique constitute a major step toward autonomous monitoring technology and analysis tools capable of providing a realistic picture of large deformation and acceleration response or failure of soil and soil structure systems.