Hammer Energy Research Articles

Evaluation of Becker penetration test interpretation methods for liquefaction assessment in gravelly soils

The Becker penetration test (BPT) is the only tool available for characterizing gravelly soils with a probe diameter that is meaningfully larger than that of the standard penetration test (SPT) and the cone penetration test (CPT). Measurements on the BPT system during operation provide information on how penetration is controlled by the driving energy and frictional resistance along the shaft. This has led to development of the instrumented Becker penetration test (iBPT), which uses measurements of force and acceleration obtained directly behind the drill string tip to compute the residual energy and displacement induced by each hammer blow. These measurements are used to produce a continuous profile of normalized blow counts that are repeatable, unaffected by varying driving energy or accumulated shaft resistance, and can be used to directly estimate equivalent SPT N60 blow count values as per DeJong et al. and Ghafghazi et al. in their 2017 studies. The measurements obtained also enabled evaluation of previously developed methods by Harder and Seed in 1986 and Sy and Campanella in 1994. This evaluation revealed that the hammer energy normalization approaches employed by Sy and Campanella and especially Harder and Seed are not robust across the broad range of conditions observed. The predicted equivalent SPT N60 values by Harder and Seed and Sy and Campanella methods are influenced by the shaft resistance magnitude as both methods are based on above-ground field measurements. Estimated N60 values produced by the two methods can be inconsistent with each other, with N60 values produced by the iBPT, and with measured N60 values obtained directly from SPT (where values are obtained in the absence of gravel).

An international standard for the measurement of underwater sound radiated from marine pile-driving

The pile-driving of marine foundations radiates substantial levels of low-frequency impulsive noise into the water column, which can propagate over large distances. Concern over the potential for impact on marine fauna often results in a regulatory requirement to measure the radiated noise level over distances which may extend to tens of kilometres. Furthermore, if the transmission loss is to be established or validated it is necessary to measure as a function of range from the pile at a number of positions and, because of the variation in acoustic output during the pile-driving, particularly if a soft-start is employed, it is desirable to perform the measurement at a fixed range for the duration of the pile-driving operation. The noise generation mechanisms are complex, and a number of factors influence the noise radiated into the water column, including the water depth (exposing a different amount of the surface area of the pile), the seabed properties, and the penetration depth into the seabed by the pile, the pile dimensions, and the hammer energy. A standard method for the measurement of underwater radiated sound from percussive pile driving has been developed and is described here. The method includes a combination of fixed-range recordings and range-dependent hydrophone deployments. The method was established by Working Group 3 of Technical Committee 43 (Sub-Committee 3) of the International Organization for Standardization (ISO), and is published in 2017 as ISO 18406.

The Effect of Stress Wave Dispersion on the Drivability Analysis of Large-Diameter Monopiles

Due to the increasing need for energy from renewable resources, a large number of offshore wind farms are planned to be constructed in the near future. Despite the plethora of available foundation concepts for offshore wind turbines, the monopile foundation is the most widely adopted concept in practice. To predict the installation process for a monopile a so-called drivability study is performed. Such a study allows one to decide on a number of key parameters for the installation process, such as, the appropriate size of the hydraulic hammer, the number of hammer blows and energy input needed to reach the final penetration depth, and the induced stresses in the system. The latter is important for the prediction of the fatigue life of the pile.Currently, drivability studies are based on one-dimensional wave equation models as first proposed by Smith in the 1950s. These models are valid as long as the diameter of the pile is small compared to the excited wavelengths in the structure due to the hammer impact. For large-diameter monopiles that are currently being used in the offshore wind industry, the latter condition is not met and the effect of stress wave dispersion can no longer be neglected.In this paper the classical wave equation model is amended by an extra term which accounts for the lateral inertia of the cross-section, resulting in the so-called Rayleigh-Love rod theory. With this new model, a parametric study is performed in which the effect of stress wave dispersion on the induced stresses and the number of hammer blows needed to reach the final penetration depth are assessed. A comparison with the results obtained from the classical model is also included in order to define the applicability range of the models. It is shown that the effect of stress wave dispersion can not be neglected for a drivability study of large-diameter monopiles.

Some new observations on the underwater sound field from impact pile driving

The underwater sound field from impact pile driving has been studied in recent years, motivated largely by the high levels and impulsive character of the sound and potential impacts on marine life. Here we report on new observations made on a vertical line array (VLA) and neutrally buoyant geophone (vector sensor) both positioned 120 m from the pile, to inform future modeling and mitigation efforts. These observations include: (1) a ground-wave precursor of amplitude 200 Pa, or 10% of peak pressure (2) delayed arrival structure in the impulsive time series due to injection of airborne sound from the hammering process, and (3) properties of the Scholte wave as a function of receiver depth. The study originates from Puget Sound, WA, and involves a 30-cm diameter steel pile installed with impact hammer energy ~200 kJ. Water depth at pile was 9 m, gradually increasing to 17 m at the VLA range. Pile depth was recorded over the sequence of 300 pile strikes, and this knowledge is essential to interpret these observations as the pile was driven 12 m into the sediment. [Research supported by Washington State Dept. of Transportation with partial support from ONR.]

Influence of resin system on the energy absorption capability and morphological properties of plain woven kenaf composites

Due to both environmental and technical advantages, natural fibers are being used as reinforcement of polymeric composite in many industries. The flexibility of the most natural fibers is one of the important technical characteristic which allows them to resist impact forces. An investigation was carried out to compare the energy absorption capability of kenaf/PVB film and kenaf/epoxy composites. The hot and cold press techniques were used to fabricate the specimens with 35% kenaf fibre weight fraction. The charpy impact test was performed on forty notched specimens using a pendulum impact tester with different hammer energy. The results showed that the kenaf/PVB film composite has the highest energy absorption, strength and toughness compared with the epoxy composite. At high energy levels, the impact strength and toughness of the kenaf/PVB film was six times of kenaf/epoxy composite. In addition, the scanning electron microscopy was assessed to demonstrate the different failure in fracture surfaces. It was found that the kenaf/PVB film composite failed by fibre fracture while kenaf/epoxy composite failed by a combination of fibre pull-out and fibre fracture as well as crack propagations through the matrix.

An application of wave equation analysis program to pile dynamic formulae

Wave equation analysis programs (WEAP) such as GRLWEAP and TNOWave were primarily developed for pre-driving analysis. They can also be used for post-driving measurement applications with some refinements. In the case of pre-driving analysis, the programs are used for the purpose of selecting the right equipment for a given ground condition and controlling stresses during pile driving processes. Recently, the program is increasingly used for the post-driving measurement application, where an assessment based on a variety of input parameters such as hammer, driving system and dynamic behaviour of soil is carried out. The process of this type of analysis is quite simple and it is performed by matching accurately known parameters, such as from CAPWAP analysis, to the parameters used in GRLWEAP analysis. The parameters that are refined in the typical analysis are pile stresses, hammer energy, capacity, damping and quakes. Matching of these known quantities by adjusting hammer, cushion and soil parameters in the wave equation program results in blow counts or sets and stresses for other hammer energies and capacities and cushion configuration. The result of this analysis is output on a Bearing Graph that establishes a relationship between ultimate capacity and net set per blow. A further application of this refinement method can be applied to the assessment of dynamic formulae, which are extensively used in pile capacity calculation during pile driving process. In this paper, WEAP analysis is carried out to establish the relationship between the ultimate capacities and sets using the various parameters and using this relationship to recalibrate the dynamic formula. The results of this analysis presented show that some of the shortcoming of the dynamic formula can be overcome and the results can be improved by the introduction of a correction factor.

Recording and Analyzing Underwater Noise During Pile Driving for Bridge Construction

Underwater sound generated by pile driving was recorded during the Hong Kong–Zhuhai–Macau Bridge (China) construction in 2014.The important parameters on the source level, the transmission loss, the time-frequency characteristics, and the method of the noise measurement were introduced in this paper. Signal analysis showed that the waveform of pile driving resembles a series of short pulses, composed of many different frequencies with main frequency energy distribution from 100 Hz to 2 kHz; the maximum value occurs at about 200 Hz. The best-fit shallow water sound propagation model gave a root-mean-square source level of 208.2 dB re $$1~\upmu \hbox {Pa}$$ at 1 m, a transmission spreading coefficient of 17.76, and an absorption coefficient of 0.015 dB/m. The value of transmission loss is in good agreement with the results calculated by the Marsh and Schulkin (M&S) semi-empirical expressions above 1 kHz, but is higher than the M&S results under 1 kHz, which may be due to the muddy seabed and turbid sea water in our study area. Although it is difficult to compare our research results with other studies as there is a lack of details on monitoring conditions (including pile size, hammer energy, environmental background, etc.), this paper provides a new method for underwater noise monitoring and analysis for pile driving in shallow water.

Energy, Torque, and Dynamics in Impact Wrench Tightening

Dynamic measurements were made on an impact wrench tightening several bolted joints. Using hammer energy and bolted joint characteristics, energy absorbed by the joint and other parts of the system was calculated. The impact process is found to be consistent with an energy model in which kinetic energy of the tool hammer is primarily absorbed by the bolted joint. Hammer energy was also absorbed by elastic deformation of the tool output shaft and by friction-type losses in the components being assembled. Bolt torque is closely correlated with hammer energy delivered by the tool as was hammer rebound angle.

Prediction of Ground Vibrations Produced in DMC Type of Piling Through Soft and Hard Strata

Pile foundations are used when surface soil is unsuitable for shallow foundations and the load that transfers to the ground is very high. Conventional bored cast in situ piles with bentonite were accepted as the most reliable piling system for most of the projects. Chiselling hammers with varying weights are used for advancing boreholes having different diameter of piles. The chiselling action produces low energy compared to precast pile driving. But this low energy, even causes problems because of proximity of structures to the construction site. Energy is directly imparted to the soil during the chiselling operations by dropping the chisel into the borehole, creating stress waves. In the present study, ground vibration measurements are conducted in a model study of boring operation for direct mud circulation (DMC) type of piling. Ground vibration analyses were carried out for two different soil profiles with hard and soft stratum. The intensity of vibrations produced during impact loading at different distances and depths from the source of vibration were measured on layered soft clay and lateritic soil mediums with accelerometers connected to data acquisition system. Variation of the vertical acceleration was found to comply with the previous studies. From the pattern of the horizontal acceleration, and also the material damping coefficients calculated at different depths, gave an idea about the material through which the wave propagates. With the scaled energy used in the present study the rate of attenuation and peak particle velocity for unit distance is calculated. From this the peak particle velocity can be calculated for higher hammer energies which are used in real DMC method of piling. Finally a method is suggested to predict the probable ground vibrations that produced during piling by using accelerometers and auxiliary boreholes at the time of site investigation using a modified SPT setup for any type of soil profiles.

Drivability Analyses for Pipe-Ramming Installations

AbstractThe evaluation of the drivability of a proposed pipe is a critical task in the planning and execution of pipe-ramming installations, because it results in increased efficiency, safe installations, and significant cost savings. The analysis of drivability provides a means for optimizing the hammer energy required for a given pipe-ramming installation, and it minimizes potential damage to the pipe due to overstressing the pipe material. Four full-scale pipes with diameters ranging from 610 to 3,660 mm installed using pipe-ramming hammers were instrumented to observe the measurement of hammer-pipe energy transfer, driving stresses, and total (static and dynamic) soil resistance to penetration and formed the basis for evaluating drivability. First, the hammer-pipe energy transfer calculated from the observed force and velocity time histories was characterized, indicating the quantity of energy that actually results in the penetration of the pipe through soil. Then, the dynamic model parameters known a...

The Calibration of High Energy-Rate Impact Forging Hammers by the Copper-Column Upsetting Method and High Speed Camera Measurements

The hammer forging is a well-known technology to incrementally produce geometrically complex forgings by compressing the material against the dies using several forming blows. When forging aeronautical components with this technology, it is crucial to control the final grain size of the part since this variable highly influences the high temperature low cycle fatigue properties. Nowadays, it is common practice to use the finite element models coupled with recrystallization models to optimize the process parameters and strategy. However, a very important variable to conduct these simulations is the real available hammer energy, which must be calibrated, not being an easy task since very high forces are generated in the impact of the anvils. In the present paper, the copper-column upsetting method is compared with a novel method where a high speed camera has been used to compute the anvils’ velocity and corresponding energies. The compressive behavior of the copper samples has been characterized using Rastegaev compression tests. The experimental and calculated results using the high speed camera are compared to the ones obtained using high purity copper samples. These measurements have enable to quantify the influence the friction and the elastic rebound have during the energy transfer from the anvils to the billet. This makes possible a precise future characterization of hammers using the conventional copper-column upsetting method if high speed cameras are not available in workshop.

SPT 에너지효율 측정 롯드를 이용한 매입말뚝의 선단지지력 예측

국내외에서 널리 사용 중인 표준관입시험(Standard Penetration Test, SPT)은 작업의 용이성, 다양한 지반정수와 강도정수를 결정방법 등의 장점을 지니고 있다. 이러한 SPT 수행시에 발생하는 해머 에너지는 N치의 산정 및 보정에 매우 중요한 영향인자가 된다. SPT시험시 해머 타격에 의하여 롯드로 응력파가 전달되는 현상이 말뚝 항타 시에 발생하는 현상과 동일하다하여 SPT에 PDA장비를 적용하여 관입에너지를 측정하는 방법이 개발되어 사용 중에 있다. 본 연구에서는 SPT 롯드를 말뚝으로 가정하여 SPT 에너지 효율 측정롯드를 SPT시험과 동적콘관입시험에 적용하여 얻어진 힘과 속도의 파형을 매칭기법(CAPWAP, CAse Pile Wave Analysis Program) 분석을 수행하여 매입말뚝에 대한 극한선단지지력을 예측하는 기법을 제안하였다. 또한, SPT 에너지 효율 측정롯드에서 예측된 선단지지력과 실물 말뚝정재하시험을 통하여 산정된 선단지지력을 비교분석하였다. 연구결과를 토대로 SPT나 동적콘관입시험을 통하여 매입말뚝의 지지력을 간편하게 예측할 수 있는 경험식을 제시하였다. The standard penetration test (SPT) has been widely used because of its usability, economy, and many correlations with soil properties among other factors. In SPT, hammer energy is an important factor to evaluate and calibrate N values. To measure hammer energy, an instrumented SPT rod was developed considering that stress waves transferring on rods during SPT driving are the same as stress waves transferring on piles due to pile driving. Using this idea, an instrumented SPT rod with a pile driving analyzer was applied as a pile capacity prediction tool in this study. In order to evaluate this method, SPT and dynamic cone tests with the instrumented SPT rod were conducted and also 2 pile load tests were performed on pre-bored steel pipe piles at the same test site. End bearings were predicted by CAPWAP analysis on force and velocity waves from dynamic cone penetration tests and SPT. Comparing these predicted end bearings with static pile load tests, a new prediction method of the end bearing capacity using the instrumented SPT rod was proposed.

Geostatistical interpolation for modelling SPT data in northern Izmir

In this study, it was aimed to map the corrected Standard Penetration Test (SPT) values in Karşıyaka city center by kriging approach. Six maps were prepared by this geostatistical approach at depths of 3, 6, 9, 13.5, 18 and 25.5 m. Borehole test results obtained from 388 boreholes in central Karşıyaka were used to model the spatial variation of (N1)60cs values in an area of 5.5 km2. Corrections were made for depth, hammer energy, rod length, sampler, borehole diameter and fines content, to the data in hand. At various depths, prepared variograms and the kriging method were used together to model the variation of corrected SPT data in the region, which enabled the estimation of missing data in the region. The results revealed that the estimation ability of the models were acceptable, which were validated by a number of parameters as well as the comparisons of the actual and estimated data. Outcomes of this study can be used in microzonation studies, site response analyses, calculation of bearing capacity of subsoils in the region and producing a number of parameters which are empirically related to corrected SPT number as well.

Efficient application of encapsulated bubbles and foam elements to mitigate offshore piling noise

The very high noise levels of offshore piling noise during the installation of offshore wind converters are dangerous to marine life like harbor porpoises and fishes. Encapsulated bubbles and foam elements are successfully used to reduce the very high noise levels. There are different physical effects such as impedance mismatch, resonance and scattering effects and material damping effects that are responsible to the measured noise reduction between about 10 dB (SEL) and 23 dB (SEL). The radiation of underwater noise from the pile surface, the propagation and the reflections of the radiated waves are investigated together with the influence of encapsulated bubbles and foam elements in the near field of the pile. Only a very small part of the impact energy is radiated directly from the pile into the surrounding water. Most of the hammer energy is driven into the ground. A small part from this is radiated indirectly from the ground into the water. The efficiency of encapsulated bubbles and foam elements in underwater noise mitigation is investigated by theoretical studies, laboratory measurements, and by offshore measurements with different elements and combinations.

A Monte Carlo approach to determining marine mammal exposure risk to long term marine piling operations

The expansion of offshore renewable developments, primarily offshore wind, has led to widespread use of large scale percussive piling for foundation construction. In UK waters alone, over 900 foundations installed up to 2013, mostly mono-piles with extensive up-scaling of developments planned for the next decade. Pile diameters range from a few meters to greater than 6 m and penetration depths of 20–30 m. These piles are typically percussively driven with several thousand hammer strikes over periods of several hours with individual strike hammer energies in excess of 1900 kJ occasionally used and reported per strike underwater Sound Exposure Level source levels of 215 dB re 1 μPa2s-m2. Potential exists for injury to occur from cumulative sound exposure to repetitive but lower level signals at greater range. If simple receptor behaviors are assumed (static, fleeing, etc.) exposure over time to an entire pile construction sequence can be estimated. These models have been extended using a Monte Carlo approach to model long term, entire wind farm construction scenarios with repetitive foundation construction periods of 24–36 h. The statistical distribution of exposure risk is modeled as well as analysis of the sensitivity of behavioral responses to potential impact effects such as habitat exclusion.

Underwater radiated noise and impact assessment of marine piling operations during offshore windfarm construction

In UK waters numerous large scale offshore wind farm developments have been constructed typically using large hollow steel mono-pile foundations with pile diameters varying from a few meters to greater than 6 m diameter and lengths 60-80 m. Piles may be driven 20-30 m into the seabed in water depths from a few meters to greater than 30 m. Typically percussive piling construction operations are used with many thousands of individual strikes over periods of several hours resulting in repetitive high amplitude impulsive sound within the water column that has potential for impact on marine life. Data is presented for in-situ measurements made during installation a range of mono-pile diameters used on offshore windfarms. Full piling sequences were recorded at fixed ranges using fixed autonomous data loggers and sampled range dependent boat based measurements. Simultaneous recordings at multiple ranges varying from 10’s meters to 10’s km were made. Data is analyzed in terms of received levels, spectral and temporal components. Using range dependent propagation loss modeling equivalent mono-pole source levels are estimated. Level dependence on range, hammer energy, etc. are discussed. A Monte Carlo approach is used to obtain total cumulative exposure (SEL) risk for single foundation to whole windfarm construction scenarios.

Review of correlations between SPT N and shear modulus: A new correlation applicable to any region

A low strain shear modulus plays a fundamental role in earthquake geotechnical engineering to estimate the ground response parameters for seismic microzonation. A large number of site response studies are being carried out using the standard penetration test (SPT) data, considering the existing correlation between SPT N values and shear modulus. The purpose of this paper is to review the available empirical correlations between shear modulus and SPT N values and to generate a new correlation by combining the new data obtained by the author and the old available data. The review shows that only few authors have used measured density and shear wave velocity to estimate shear modulus, which were related to the SPT N values. Others have assumed a constant density for all the shear wave velocities to estimate the shear modulus. Many authors used the SPT N values of less than 1 and more than 100 to generate the correlation by extrapolation or assumption, but practically these N values have limited applications, as measuring of the SPT N values of less than 1 is not possible and more than 100 is not carried out. Most of the existing correlations were developed based on the studies carried out in Japan, where N values are measured with a hammer energy of 78%, which may not be directly applicable for other regions because of the variation in SPT hammer energy. A new correlation has been generated using the measured values in Japan and in India by eliminating the assumed and extrapolated data. This correlation has higher regression coefficient and lower standard error. Finally modification factors are suggested for other regions, where the hammer energy is different from 78%.

Pit bearing capacity effect on status of soil plug during pile driving in ocean engineering

Foundation piles of the offshore oil platforms in the Bohai Bay are usually longer than 100 m with a diameter larger than 2 m. Driving such long and large-sized piles into the ground is a difficult task. It needs a comprehensive consider ation of the pile dimensions, soil properties and the hammer energy. Thoughtful drivability analysis has to be performed in the design stage. It has been shown that judging whether the soil column inside the pile is fully plugged, which makes the pile behave as close-ended, strongly influences the accuracy of drivability analysis. Engineering practice repeatedly indicates that the current methods widely used for soil plug judgment often give incorrect results, leading the designers to make a wrong decision. It has been found that this problem is caused by the ignorance of the bearing capacity provided by the soil surrounding the pile. Based on the Terzaghi’s bearing capacity calculation method for deep foundation, a new approach for judging soil plug status is put forward, in which the surcharge effect has been considered and the dynamic effect coefficient is included. This approach has been applied to some practical engineering projects successfully, which may give more reasonable results than the currently used method does.

Improving the Predictability of Hiley Pile Driving Formula in the Quality Control of the Pile Foundation

Pile Dynamic Formulas are the oldest and frequently used method to determine bearing capacity of piles. The more recent method is based on the Wave Equation analysis and different formulations such as Case Mathod, TNO, CAPWAP and TEPWAP which were developed for pre-driving analysis and post-driving measurements applications. The major factors for the common use of the dynamic formulas have been due to their simplicity, cost effectiveness and applicability in various piling situations. However, in some literature the energy approach have been given an unfair reputation as being unreliable and less accurate than the more analytical or dynamic testing methods. One of the issues due to the poor performance of the dynamic formulas is that, historically, the hammer energy and the energy trasferred to pile had to be assumed. Nevertheless, with the advent of computers, new technologies are emerging with the advancement in construction industry. This has produced gradual improvements that have resulted in the dynamic method to be used on many projects with greater reliability. In this paper, a review of the different testing methods as well as pros and cons of the pile driving formulas are discussed. Also, an approach to improving the widely used Hiley dynamic equation is presented. This approach enables evaluation of the pile capacity to be made more accurately.

Analysis of hammer movement based on a parametrically excited pendulum model

Motions of the hammer were analyzed to understand the mechanism of acceleration with a hula-hoop model using an energy pumping mechanism. The condition that makes the time derivative of the energy positive is derived as energy pumping for hammer. The condition is expressed in terms of the tugging force times velocity to pump the hammer energy. In this study, motions of the hammer were analyzed and numerical experiments were performed to examine the validity of the theory.