Low-strain Testing Research Articles

Defects Discrimination and Error Analysis of Wharf Bored Piles Detected by Low Strain Reflection Wave Method

Based on the field test of bored piles at wharf detected by low strain reflection wave method, time-history curve features and defect position of intact piles and defective piles contrastively analyzed, with verification of on-site drilled core testing. The reason for discrimination error between specific defect position and actual data when processing low strain reflection wave method are derived, based on the analysis of effect of defective piles strengthened by pressure grouting method retested by low strain testing, practical measures of on-site low strain reflection wave testing are purposed to improve detection accuracy.

Numerical Assessment of Factors Affecting Waveform Based on Low Strain Testing of Piles

In this paper dynamic testing of piles using the low strain method is performed by means of numerical analyses based on solid finite element model. To this end, velocity-time curves are presented investigating the influence of various parameters such as mesh density, impulse width, receiving point, and soil modulus on the waveform characteristics. Then, find regularity of waveform affected by different parameters to provide reference of the real project detection.

Testing and Analysis of Bearing Capacity on Pile Foundation

The application of pile foundation is promoted by the rapid development of the high speed railway, highway, high-rise buildings and big volume weight of building. However, the static load test and low strain test play a very important role in pile foundation inspection and ensurement of the quality of pile foundation engineering. In this paper, combined with the engineering of the basis of a hospital in lanhou, the author analyzed the results of 7 test piles static load test and a large number of low strain test and summarised pile testing contents and methods. At the same time,the bearing capacity of anchor pile in static load test is discussed.

Damage identification of piles based on vibration characteristics.

A method of damage identification of piles was established by using vibration characteristics. The approach focused on the application of the element strain energy and sensitive modals. A damage identification equation of piles was deduced using the structural vibration equation. The equation contained three major factors: change rate of element modal strain energy, damage factor of pile, and sensitivity factor of modal damage. The sensitive modals of damage identification were selected by using sensitivity factor of modal damage firstly. Subsequently, the indexes for early-warning of pile damage were established by applying the change rate of strain energy. Then the technology of computational analysis of wavelet transform was used to damage identification for pile. The identification of small damage of pile was completely achieved, including the location of damage and the extent of damage. In the process of identifying the extent of damage of pile, the equation of damage identification was used in many times. Finally, a stadium project was used as an example to demonstrate the effectiveness of the proposed method of damage identification for piles. The correctness and practicability of the proposed method were verified by comparing the results of damage identification with that of low strain test. The research provided a new way for damage identification of piles.

The impact of structure on elasticity, switchability, stability and functionality of an all-in-one carboxybetaine elastomer

In this work, we designed and synthesized an all-in-one zwitterionic material (poly2-((2-hydroxyethyl)(2-methacrylamidoethyl)(methyl)ammonio)acetate (pCBMAA-1)) bearing elasticity, switchable antimicrobial/antifouling properties, and stability. Zwitterionic materials have drawn special attention due to their outstanding antifouling properties; however, conventional zwitterionic materials lack tunable elasticity, stability and antimicrobial properties. We addressed these challenges by integrating all desired properties into a single zwitterionic molecule through rational design. pCBMAA-1 hydrogel showed typical elastomeric stress–strain curves with low Young's modulus and high yield strain, in both tensile and compression tests. About 65% tensile strain and 85% compressive strain were achieved. pCBMAA-1 hydrogel can switch between cationic antimicrobial form and zwitterionic antifouling form. In its cationic ring form, pCBMAA-1 hydrogel killed 99.5% of attached bacterial cells and then released 95% of killed cells. pCBMAA-1 surfaces highly resisted the protein adsorption from 100% blood plasma and serum. The amount of adsorbed protein was below the detection limit (0.3 ng cm−2) of the SPR sensor. Compared to existing zwitterionic materials, this material showed the dramatically improved stability in both basic and acidic conditions. We believe that this all-in-one material will broaden the application spectrum of zwitterionic materials to a great extent.

Incorporating Set-up Effects into Pile Design

The increase in pile bearing capacity with time after installation is known as soil/pile set-up. A mechanism of pile set-up is discussed in detail and a three-phase model is suggested. A serious of low-strain dynamic tests on full scale pile was carried out in mixed soil for monitoring the increase of wave velocity and stiffness. Wave velocity and stiffness have similar increase trend, but the stiffness shows a larger increase rate. An optimized design procedure to incorporate the pile set-up effects is proposed.

Application of Genetic BP Algorithm in Low Strain Test of Pile Integrity

This paper puts forward a neural network algorithm in pile integrity test on the basis of field data and the strengths of genetic algorithm and neural network algorithm. The result proves that it has faster convergence speed than simple BP algorithm, which can avert the artificial intervention during the data handling procedure and improve the reliability of the test result.

High-frequency interference in low strain integrity testing of large-diameter pipe piles

The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transient point load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing is deduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domain velocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various points suffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence of vibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point mainly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors affecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that the larger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The least high-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increase of pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modulus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width and larger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geometrical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditions such as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on the external conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some external measures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adopting suitable receiving point.

Propagation characteristics of transient waves in low-strain integrity testing on cast-in-situ concrete thin-wall pipe piles

The three-dimensional effects of pile head and the applicability of plane-section assumption are main problems in low-strain dynamic tests on cast-in-situ concrete thin-wall pipe piles. The velocity and displacement responses were calculated by a theoretical formula deduced by the authors. The frequency and influencing factor of high-frequency interference were analyzed. A numerical method was established to calculate the peak value and arrival time of incoming waves on top of the piles. The regularity along circumferential and the influence of radius or impulse width were studied. The applicability of plane-section assumption was investigated by comparison of velocity responses at different points in the sections at different depths. The waveform of velocity response at different points forked after the first peak, indicating that the propagation of stress waves did not well meet the plane- section assumption.

Application of PCC pile in soil improvement of highway

The construction process and load-bearing behaviors of Cast-in-place concrete thin-wall pipe piles are analyzed based on its application on Yantong Expressway Project. The low strain test, static load test and field excavation were also carried out, and the bearing capacity of the new pile can meet the requirements of design. With the increase of pile diameter, the bearing capacity is increased. The settlement of composite foundation is decreased, when the replacement ratio of pile is increased. The test results also show that the load carried by inner soils is neglectable. According to the tests and application, it can be concluded that the new type of pile is convenient to construction with high bearing capacity and reliable quality, which has great potential in practical engineering.

Pile response and free field vibrations due to low strain dynamic loading

This paper presents the results of in situ measurements during dynamic pile testing at a construction site in Louvain-la-Neuve. Main objectives are the investigation of the pile response and the free field vibrations due to low strain dynamic loading on a single cast in situ pile with a 5.5 kg hammer impact on the pile head. Whereas low strain testing is usually performed to assess the integrity of the pile as a structural member, this study focuses on both pile and ground vibrations. The pile head response and ground motions are measured with accelerometers during different blows with the impact hammer. The dynamic characteristics of the soil are determined with a SASW test. Experimental results are compared with predictions obtained with a coupled finite element–boundary element model. The computed pile head and free field response show a good correspondence with the measured response. In addition, the static stiffness of the pile estimated by means of the mobility function shows a very good agreement with the value calculated by an analytical formulation.

Study of RHQT-processed Nb3Al wires for high-field accelerator magnet applications

We have developed Nb3Al wires with a low Nb matrix ratio in order to attain a high critical current density. Test wires were prepared with different fabrication parameters, mainly the Nb matrix ratio, RHQ current, and the area reduction ratio of the wire after an RHQ heat treatment. The critical current and n-values of these wires were measured. Our newly developed wire with a Nb matrix ratio of 0.6 was almost the same RHQ heat-treatment effect and area reduction effect as those of samples with different Nb matrix ratios. However, the critical current density of our wire was lower than that of these samples. In order to determine the reason for this low critical current density, Tc measurements and tensile strain tests were also performed. In this paper, we report the characteristics of the sample with a Nb matrix ratio of 0.6 and compare them with those of the other samples.

NDT of Piled Foundations: Data Processing with Artificial Neural Networks

The low strain test method is the prevalent method for integrity testing of cast in situ foundation piles. The automated interpretation of sonic echo traces from this test may prove beneficial to industry through standardisation of the test method and a reduction in the time spent analysing data. In this research the generalisation and feature extraction strengths of artificial neural networks have been exploited for test data interpretation. This study involved the use of a multilayer perceptron network considered most suitable for this heteroassociative function approximation task. The network was trained using numerically generated data. Field data from two sites confirmed that the network identified, located and quantified changes in pile diameter as well as detecting pile lengths to within 5% of their design values.

Cyclic Simple Shear Apparatus for Low-Strain Soil Tests

A testing system has been developed to study the behavior of saturated sand under low-level cyclic shearing strains. The system has been used to determine threshold shear strain levels for fabric destruction in sand aged for different time periods. The system includes a special soil chamber and a direct simple shear (DSS) machine. To impose very small shearing strains, the DSS machine was designed to apply and measure horizontal deformations as small as 0.0005 mm (2 × 10−5 inches). Data obtained to date support the results of previous investigators who performed triaxial tests on freshly deposited samples, indicating a threshold cyclic shear strain level of approximately 0.01 percent. At strains in excess of those levels, destruction of the sand fabric occurred, as evidenced by a reduction in shear modulus at low strain levels. Subsequent modest increases in shear modulus were observed after the specimens were allowed to recover for 24 hours and then tested again. During the recovery period, drainage valves were left open to allow for dissipation of excess pore pressures and for potential consolidation during the short aging period. The DSS system was found to work well for low strain measurements. Furthermore, since shear strains are measured directly under DSS conditions (as opposed to triaxial conditions), the DSS system shows much promise as a device for studying parameters that may influence threshold shear strain levels and fabric evolution and destruction in sands.

Cyclic Simple Shear Apparatus for Low-Strain Soil Tests

A testing system has been developed to study the behavior of saturated sand under low-level cyclic shearing strains. The system has been used to determine threshold shear strain levels for fabric destruction in sand aged for different time periods. The system includes a special soil chamber and a direct simple shear (DSS) machine. To impose very small shearing strains, the DSS machine was designed to apply and measure horizontal deformations as small as 0.0005 mm (2 × 10−5 inches). Data obtained to date support the results of previous investigators who performed triaxial tests on freshly deposited samples, indicating a threshold cyclic shear strain level of approximately 0.01 percent. At strains in excess of those levels, destruction of the sand fabric occurred, as evidenced by a reduction in shear modulus at low strain levels. Subsequent modest increases in shear modulus were observed after the specimens were allowed to recover for 24 hours and then tested again. During the recovery period, drainage valv...

Low and High Strain Macrobehavior of Grain Masses—The Effect of Particle Eccentricity

High, medium, and low strain tests were conducted on green peas, white navy beans, and rice. These grains were selected to assess the effect of particle eccentricity on the mechanical behavior at different strain levels. Tests included interfacial ring shear, axisymmetric and true triaxials, simple shear, and wave propagation measurements. Index properties, microfabric analysis, and mechanical parameters are documented. Differences were found between the behavior of rice and the other two grains, which were explained as the result of the mechanical and geometrical characteristics of grains. Low-strain measurements reflected contact properties and fabric; both low and high strain properties were affected by stress history; major fabric changes occurred when shear strains exceed 3 to 10%; and extensive particle alignment took place after high shear deformation in elongated particles such as rice. The shear behavior at the interface with a rough surface was very similar for the three grains.

Relationship of Water Content to Textural Characteristics, Water Activity, and Thermal Conductivity of Some Commercial Sausages

ABSTRACTMechanical properties from cyclic low strain testing, texture profile parameters and thermal conductivity were evaluated for 7 types of commercial sausage products ranging in moisture content from 27.7% to 62.4% and aw from 0.857 to 0.993. Hardness, fracturability, the apparent moduli, stress al 20% compression, mechanical hysteresis loss, and strain energy all increased with decreasing moisture level, while springiness and the degree of elasticity decreased. Moisture had no significant effect on cohesiveness. A linear relationship was observed between the aw and the effective mole fraction of water in the brine, the exact nature of which depended on the thermal process which the product had received. Thermal conductivity decreased with decreasing moisture in a linear manner.

The cyclic stress-strain response of copper at low strains—i. Constant amplitude testing

A controversy has arisen over whether or not the cyclic stress-strain (CSS) curve for polycrystalline copper can be correlated with that for monocrystals, particularly in showing a plateau and a fatigue limit at an equivalent stress and strain (equivalence being expressed via Taylor's factor). Bhat and Laird suggested this correlation but Mughrabi opposed it on the grounds that interpretetion of the mechanical data was equivocal and he did not believe persistent slip band (PSB's) would exist in the bulk of polycrystals. To help settle this controversy, low strain tests under both constant strain-control and constant stress-control (Part I) have been carried out in polycrystals as well as extensive observations of the dislocation structures by TEM. It is concluded that the strain-control curve does not show a true plateau, in agreement with the views of Mughrabi. However, a definite change of slope occurs at a stress and strain corresponding to the fatigue limit and initial formation of PSB's in monocrystals, in agreement with the views of Bhat and Laird. Furthermore, the stress-control CSS curve tends strongly to a plateau, differing from the strain-control CSS curve at low strains; also dipolar wall structures analogous to those of monocrystalline PSB's but not so regularly ladder-like, are found in the bulk of polycrystalline copper. The dislocation structures corresponding to the different CSS curves in load and strain control are documented, and reasons for history dependence in CSS response are provided. Thus a close correlation between the CSS curves and cyclic response of polycrystals and monocrystals is demonstrated. In a companion paper (Part II), similar correlation is demonstrated for tests conducted under variable amplitudes.