Parallel Seismic Research Articles

Available methods for the identification of the foundation system and depth in case of existing bridges

The new Italian “Guidelines for classifying and managing the risk, assessing the safety and monitoring existing bridges” (LLG) are based on a multi-level and multi-risk approach. The Level 0 of this approach is focused on collecting the basic information about both the bridge under consideration and the environment in which it is located (for the assessment of seismic, hydraulic and landslide hazards). These can be retrieved in the project documentation, via available seismic/hydraulic/landslide hazard maps, accelerometric and hydraulic monitoring stations and interferometric data. The Level 1, instead, consists of carrying out visual inspections and compiling some inspection forms for each risk (structure-foundation, seismic, hydraulic and landslide). Then, in the Level 2 all the collected data are organized and used for defining the so-called Class of Attention (5 classes: low, low-medium, medium, medium-high, high) for each risk and the overall Class of Attention. Based on the experiences gained in the last three years by the geotechnical staff of the University of Pisa (member of the FABRE Consortium) one of the main issues encountered in the Levels 0 and 1 (and therefore in the Level 2) was the difficulty to properly identifying the type, geometry, layout, material, and depth of the foundation system of existing bridges. This contribution is focused on describing Non-Destructive Tests, such as Low-Strain Surface tests, Low-Strain Down-hole tests, Parallel Seismic testing (PS) and Electrical Resistivity Tomography (ERT) with the aim of showing main capabilities, limitations, and field of application. These techniques can be useful to improve the classification of existing bridges according to the new Italian Guidelines.

Dynamic Soil Reactions around a Beam-on-Multiple-Piles Structure and their Application in the Parallel Seismic Integrity Test

In this paper, an analytical solution to the dynamic reaction of half-space soil around a beam-on-multiple-piles structure is proposed. This can be used to evaluate the effect of an adjacent vibrating pile of unequal length or pile defects on parallel seismic (PS) integrity test results. The structure–soil interaction (SSI) problem was decomposed into a beam–multiple-pile coupled vibrating model and an extended half-space soil model. The surrounding soil reactions were calculated employing the half-space soil excited by known vibration (HEKV) solution scheme. The HEKV solution scheme and the accuracy of the analytical results were validated through comparisons with finite-element analysis (FEA). The validated model was then used to study the influence of an adjacent vibrating pile on the pile response, and to optimize the selection of technical parameters for the PS test. The obtained results were used to discuss the uncertainties of the PS test in terms of multiple-pile foundations and adjacent vibrating piles, and to develop the theoretical basis for testing multiple-pile foundations. Finally, practical guidance is provided for the application of the PS test to multiple-pile foundations in practice.

Dry Parallel Seismic: A Novel Method for Determining Thickness of Buried Concrete Pad Foundations

The structural capacity of concrete foundations supporting, for example, telecommunications and electrical transmission towers depends, among other things, upon the thickness of the concrete foundation. Current methodology for investigating the thickness of concrete foundations nondestructively has largely been focused upon deep foundations, such as caissons, and in situations where the top of the foundation is exposed. For example, the parallel seismic (PS) method is a borehole method that uses the arrival times of waves imparted in a foundation at a sensor next to a buried foundation to detect the thickness of the foundation but is typically used for deep caisson type foundations. However, in many instances, these foundations are pad and pier type footings that can be buried deep below ground and can be relatively thin, for example, less than 45 cm in thickness. The objective of the present work is to present a nondestructive method for determining the thickness of concrete pads with no direct access. The dry PS method was developed to determine the thickness of thin, buried concrete foundations. The method was first used to verify the as-built thickness, as mentioned in the engineering drawings of a guyed tower dead-man block. Second, it was used to determine the thickness of the pad foundations of five telecommunication towers with pad and pier concrete foundations in South Asia. These towers had foundation thicknesses ranging from 16 to 36 cm, as verified through excavation. Analysis of the data collected during dry PS testing resulted in a mean absolute error (MAE) of 18 mm, which equates to approximately 6% error. Thus, this paper demonstrates that the dry PS method overcomes the limitations of the current methodology and is capable of accurately determining the thickness of buried concrete foundations.

Spectral Analysis of Parallel Seismic Method Data for Surveying Underground Structures

Spectral Analysis of Parallel Seismic Method Data for Surveying Underground Structures

Analytical Model for Laterally Loaded Soil-Extended Pile Shaft Applied to Verifying the Applicability of Lateral PS Method

This paper investigates the dynamic response of soil around a laterally vibrating extended pile shaft and its application to the lateral parallel seismic (PS) integrity testing method. Considering the high pile to soil relative stiffness ratio, a new analytical model is proposed incorporating an extended half-space soil model excited by the laterally vibrating pile. The developed equations of the analytical model are solved by employing the Fourier-Hankel integral transform. This scheme avoids the complicated pile–soil coupling analysis while maintaining high accuracy. The developed model and its analytical solution are then utilized to verify the applicability of the lateral PS method to predict the unknown pile length. The effects of pile and soil properties on the soil dynamic response and technical aspects of the PS test are investigated through a comprehensive parametric study. The obtained results demonstrate that the lateral PS test could be successfully used in practice to overcome the limitations of the low-strain pile integrity test (PIT).

Hydrostatic Dehydration Fabrics of Antigorite at High Pressure and High Temperature: Implications for Trench Parallel Seismic Anisotropy at Convergent Plate Boundaries

AbstractAntigorite dehydration is well known as a key process at convergent boundaries for the genesis of mantle wedge partial melting and intermediate‐depth earthquakes. However, the crystallographic preferred orientations (CPOs) of prograde minerals from antigorite dehydration and their effects on the seismic anisotropy of subducting slabs remain ambiguous and controversial. Here we report antigorite dehydration experiments on a foliated serpentinized peridotite at pressures of 0.3–6 GPa and temperatures of 700–900°C. Our results show that olivine CPO evolves from a fiber‐[100] type in fine grains to a type‐C like in coarse grains. We propose that the fiber‐[100] olivine CPO is developed by topotactic growth during incipient hydrostatic dehydration, while the orthorhombic type‐C like olivine CPO is developed by anisotropic growth resulting from an anisotropic fluid flow during later dehydration. The type‐C like olivine CPO in the antigorite‐rich layers after antigorite dehydration could contribute to the trench parallel fast shear wave seismic anisotropy at convergent plate boundaries.

Systematic field test of non-destructive techniques for driven cast in situ pile lengths

The need for reliable non-destructive techniques (NDTs) to determine pile toe depths is highly relevant to the reuse of piles; this is particularly relevant in congested brownfield urban sites. A systematic full-scale ‘blind’ site trial of four geophysical techniques by five independent specialist contractors was conducted to assess the most appropriate sensing tool/s for the detection of driven cast in situ (DCIS) pile toe depths. There is dearth of published studies detailing direct comparative pile length test programmes. This investigation provided a unique opportunity to evaluate widely used NDTs in a controlled and methodical manner. Magnetometry, ground penetrating radar, parallel seismic (PS) testing and transient dynamic response (TDR) were carried out on four specifically constructed end-bearing 380 mm dia. DCIS piles up to 8.5 m long, with a range of embedment lengths in the founding sand stratum. Boreholes at 500, 800 and 1300 mm offsets from each pile were installed to examine the influence of sensor lateral distance from the pile. These trials yielded variable results, with typical accuracy within ±500 mm. It was considered that TDR (frequency domain) when used in tandem with PS test was the most successful geophysical NDT. However, the results were not comparably repeatable between individual contractors thereby illustrating the influence of test methodology and data interpretation.

Large-scale model test for detecting pile defects using the parallel seismic method

Although the parallel seismic (PS) method has been successfully applied to determine the unknown foundation depth of buildings and bridges, the ability to detect defects in pile foundations has not been verified. In this paper, three large-scale model piles with artificial defects are designed and constructed in multilayered ground. The capability of cross-hole sonic logging, low-strain pile integrity testing and PS method to detect the defects of pile foundation is compared. The effects of the pile-to-borehole distance and the excitation position on the stress wave transmission are analyzed in detail. Finally, the abnormal characteristics of stress waves corresponding to different types of defects are summarized. The results show that pile defects affect the difference in the stress wave impedance by the PS test, and the features of the first arrival waves can reflect the type of defect. When the distance between the borehole and pile is within 0.5 m, the wave form and amplitude of the first arrival waves can be used to distinguish the defects of necking, breaking and sedimentation. Increasing the pile-to-borehole distance by more than 1 m is not conducive to identifying defects. When the pile defect position is close to the side of the shortest path of stress wave transmission, the abnormal characteristics of the first arrival waves are much clearer than when the defect position is far from the side; otherwise, the feature of the defects will be greatly weakened.

Accuracy of Parallel Seismic Test Performance on Steel H-Piles in Layered Soils

AbstractParallel Seismic (PS) method is a straightforward Nondestructive Testing (NDT) method capable of providing valuable information of unknown bridge foundations made of various common construc...

Exploratory Study of Nondestructive Parallel Seismic Testing Challenges in Estimating the Depth of Unknown Wood Bridge Foundations

AbstractNondestructive methods have been extensively used to characterize unknown bridge foundations. Among various nondestructive methods, conventional and reverse parallel seismic (PS) methods ar...

Dynamic response of a defect pile in layered soil subjected to longitudinal vibration in parallel seismic integrity testing

The parallel seismic (PS) method is a nondestructive test technique for detection of reinforced concrete pile defects. The method can be employed to detect severe defects of piles and for existing piles supporting a superstructure. In this paper, a defect pile-fictitious soil pile coupled model is established considering three-dimensional effect of surrounding layered soil. An analytical solution is developed for the dynamic response of soil around and beneath the pile. The developed solution is then employed to investigate the effects of pile defect and layered soil condition on the dynamic response of surrounding soil. A parametric study is conducted and the results are utilized to establish practical guidance for the application of the parallel seismic method in pile integrity testing.

Dynamic soil reactions around pile-fictitious soil pile coupled model and its application in parallel seismic method

The parallel seismic (PS) method is a nondestructive test technique for evaluating pile integrity, which has a wide range of applications for detection of reinforced concrete pile length and defects. In recent years, this method has been increasingly applied in practice; however, its theoretical model still requires further refinement. In this paper, a pile-fictitious soil pile coupled model considering three-dimensional effect of surrounding soil is established, and the analytical solution for the dynamic reaction of soil around and beneath the pile is solved. The developed solution is then employed to investigate the effects of pile-soil properties and technical aspects of PS method on the dynamic response of surrounding soil. The results are used to derive some conclusions in order to provide practical guidance for application of PS test in engineering practice.

Development of a Wireless Dynamic Test Device for Low Strain Integrity Testing and Parallel Seismic Testing of Foundation Piles

The low strain integrity testing and the parallel seismic testing of foundation piles usually need dedicated instruments, respectively. The development of a wireless dynamic testing device based on Wi-Fi for foundation piles is introduced, which consists of a microcontroller with ADCs, a static RAM, a Wi-Fi transceiver module and other peripheral circuitries. The developed device features 16-bit dual-channel simultaneous sampling, variable trigger threshold and variable number of pretrigger samples, and it satisfies the requirements of both the low strain integrity testing and the parallel seismic testing of piles. A controlling computer should be present with the dynamic test device to conduct tests. Field tests were carried out on concrete bored piles with both test methods, and the test results have shown the functionality and reliability of the wireless dynamic test device.

Numerical modeling of parallel seismic method for detecting existing piles in layered soil

For piles connected to superstructures, whose pile tops are inaccessible, a lateral horizontal impact on the side of the piles through the generation of a flexural wave of the pile shaft is a more feasible approach. This paper presents a parallel seismic (PS) method based on the flexural wave of the pile shaft that combines down-hole tests for the length and an integrity evaluation of existing piles in layered soil. It is suggested that two PS tests be conducted by horizontal striking on the side surface of the pile along and perpendicular to the pile-to-borehole direction, respectively. The first arrivals of the transmitted P-wave and S-wave at the pile-soil interface obtained in these two PS tests and the results of down-hole tests are combined to analyze the pile length and to distinguish the embedded defects for the pile integrity evaluation. A simplified theoretical model for PS tests in layered soil is established, and a correction formula is proposed to correct the initial estimated pile length accordingly. A three-dimensional finite element model is then established to verify the effectiveness and reliability of the proposed PS method in layered soil and the correction formula.

Use of Parallel-Seismic and Induction-Logging Tests for Foundation Depth Evaluation Under Difficult Conditions, a Root-Pile Foundation Embedded in Rock

A case study on the application of the parallel-seismic (PS) and induction-logging (IL) tests combined to evaluate the depth of a 25-cm diameter root-pile belonging to the foundations of a telecommunication tower located in Santana de Parnaíba, São Paulo, Brazil, is presented. The foundation element is embedded in a friable and altered meta-sandstone rock. The relatively small diameter of the pile and the presence of rock as surrounding material tend to limit the interpretation of the PS test. Nevertheless, the technique applied in this study showed satisfactory results. On the other hand, the existence of electromagnetic interference from the antenna itself limited the interpretation of the IL test in this case. The estimated depth of the foundation element was evaluated from the PS test as ranging from 6.5 to 7.5 m, which was later verified to be in agreement with the pile as-built documentation. When the possibility to drill boreholes at a site under investigation exists, the methods presented in this paper may become good options for the determination of the unknown depth of foundation elements in altered rock

PSIN: A scalable, Parallel algorithm for Seismic INterferometry of large-N ambient-noise data

Seismic interferometry is a technique for extracting deterministic signals (i.e., ambient-noise Green's functions) from recordings of ambient-noise wavefields through cross-correlation and other related signal processing techniques. The extracted ambient-noise Green's functions can be used in ambient-noise tomography for constructing seismic structure models of the Earth's interior. The amount of calculations involved in the seismic interferometry procedure can be significant, especially for ambient-noise datasets collected by large seismic sensor arrays (i.e., “large-N” data). We present an efficient parallel algorithm, named pSIN (Parallel Seismic INterferometry), for solving seismic interferometry problems on conventional distributed-memory computer clusters. The design of the algorithm is based on a two-dimensional partition of the ambient-noise data recorded by a seismic sensor array. We pay special attention to the balance of the computational load, inter-process communication overhead and memory usage across all MPI processes and we minimize the total number of I/O operations. We have tested the algorithm using a real ambient-noise dataset and obtained a significant amount of savings in processing time. Scaling tests have shown excellent strong scalability from 80 cores to over 2000 cores.

Theoretical basis and numerical simulation of parallel seismic test for existing piles using flexural wave

This paper presents theoretical analysis of the parallel seismic (PS) method for evaluating existing piles using the flexural mode wave exited by a horizontal impact on the lateral surface of a pile. A simplified theoretical model of the flexural wave for PS method was established to elaborate the theoretical basis. A correction factor was then obtained and proposed to correct the pile depth obtained from the PS method, thus providing a more accurate estimation. A three dimension (3-D) finite element (FE) model was developed and the existence of the flexural waves on branch F(1, 1) in the pile shaft has been verified. Two time domain methods were used to calculate the flexural wave velocity in the pile. One was based on the pile tip reflection signal using a model where pile head reflection was minimized, and another method used the slope of the upper fitted line in the PS test. The flexural wave velocities from both methods match well with the predicted flexural wave group velocity determined from the dispersion curve of a 1-D rod embedded in the soil. The accuracy in estimation of pile tip depth is improved by applying the correction factor. A series of parametric studies were carried out to demonstrate the effectiveness of using flexural wave for PS test and the correction factor proposed in this study.

Experimental Study of Nondestructive Geophysical Methods for Evaluating the Condition of Concrete Structures

It is often necessary to evaluate the integrity and reliability of concrete structures that are exposed to extreme environmental conditions over a long period of time. This paper presents a range of nondestructive geophysical methods, including Ultraseismic, Parallel Seismic, and Impulse Response techniques that use elastic-wave properties to inspect concrete-foundation structures. These approaches depend on basic waveform properties such as wave speed, amplitude, and frequency. The goal of this research is to obtain an appropriate test procedure and identify parameters for i) verifying the wave reflected from internal concrete defects, and ii) identifying the effective depth of a pre-built test foundation. To do so, we have established an experimental laboratory to calibrate and check the reliability of the measured data and understand the wave properties for different concrete conditions (i.e., fractures). It is often necessary to evaluate the integrity and reliability of concrete structures that are exposed to extreme environmental conditions over a long period of time. This paper presents a range of nondestructive geophysical methods, including Ultraseismic, Parallel Seismic, and Impulse Response techniques that use elastic-wave properties to inspect concrete-foundation structures. These approaches depend on basic waveform properties such as wave speed, amplitude, and frequency. The goal of this research is to obtain an appropriate test procedure and identify parameters for i) verifying the wave reflected from internal concrete defects, and ii) identifying the effective depth of a pre-built test foundation. To do so, we have established an experimental laboratory to calibrate and check the reliability of the measured data and understand the wave properties for different concrete conditions (i.e., fractures). We concluded that the aforementioned geophysical approaches could provide vital information for quality control and rehabilitation purposes.

Improvement and extension of the parallel seismic method for foundation depthmeasurement

The parallel seismic (PS) method is used for determination of the unknown or undocumented depth of foundations, mostly piles. It was developed several decades ago and has not much changed since. PS is based on impulse generation on the pile head and registration of travel times in a borehole parallel to the foundation. The method is applicable to many foundation types, including single piles, pile walls, or sheet piles. While the accuracy is known to be high if the distance between foundation and borehole is small, the foundation length is overestimated with increasing distance.This paper presents the results of a systematic study on the influence of geometric and material parameters on the measurement results and explains the effects by studying the underlying wave phenomena based on numerical studies. It can be shown that several parameters (e.g. borehole inclination) have a strong influence. Foundation flaws and soil layers have also to be taken into account, while the possibilities in the other direction (derivation of soil parameters or detection of flaws from the results) are limited.Based on the simulation results, a new mathematical algorithm for data interpretation has been developed which takes into account the soil layers and the borehole inclination. This novel data interpretation scheme was used in combination with different data inversion methods. The new interpretation method was successfully validated using several sets of simulated data. Not only was it shown to be more accurate than all other available methods, but it also extended the maximum allowable pile–borehole distance to 2–3m.Today, parallel seismics is the only method applicable on both metallic and non-metallic foundations which can be used without calibration. It has the largest range of all borehole methods. To enhance its efficiency it can be combined with downhole seismic measurements in the very same borehole to retrieve soil parameters.

Experimental study for the evaluation of stress wave approaches on a group pile foundation

This paper investigates the relative performance of the sonic echo (SE), impulse response (IR), and parallel seismic (PS) tests using a field constructed pile foundation incorporating simulated defects. Tests were performed before and after the construction of a pile cap. According to the experimental results, the SE method has the best performance with regard to defect detection in an isolated pile. The results of the PS test were more consistent with regard to the length determination of the piles with a cap than those obtained using the SE and IR methods. The pile length estimated from the PS method increases with increasing borehole-to-pile distance, but this over-estimation can be reduced by applying length correction factors, thus providing more conservative estimations of the pile length. The two length correction approaches for the PS test produced similar results.