In Situ Pore-Pressure Generation Behavior of Liquefiable Sand

To overcome current limitations in predicting in situ pore-pressure generation, a new field testing technique is used to measure directly the coupled, local response between the induced shear strains and the generated excess pore pressure. The pore-pressure generation characteristics from two in situ liquefaction tests performed on field reconstituted specimens are presented, including the pore- pressure generation patterns at various strain levels, the observed stages of pore-pressure generation, and pore-pressure generation curves. Comparisons of the in situ pore-pressure generation curves with data in the literature and from laboratory strain-controlled, cyclic direct simple shear tests support the in situ testing results. In addition, the effects of effective confining stress on threshold shear strain and pore- pressure generation curves are discussed. Comparisons of the rate of pore-pressure generation among the in situ tests, laboratory strain-controlled tests, and a model based on stress-controlled tests reveal that in situ pore pressures generated in reconstituted soil specimens during dynamic loading develop more similarly to those from cyclic strain-controlled laboratory testing. This observation implies that the evaluation of induced strains rather than induced shear stresses may be more appropriate for the simulation of pore-pressure generation.     

Undrained Anisotropic Monotonic Behavior of Sand from In Situ Tests

A procedure for estimating the undrained stress-strain behavior of sand from drained self-boring pressuremeter and seismic piezocone penetration tests is proposed in this paper. The procedure offers an inexpensive alternative to laboratory testing and avoids the uncertainty of the empirical methods based on index measurements such as the Standard Penetration Test blow count and the tip resistance in a Piezocone Penetration Test (CPTU). To check its validity, the proposed procedure was used to infer the undrained triaxial stress-strain curves and the results were compared with laboratory triaxial tests on undisturbed samples. The undrained limit equilibrium stability of a dike was also assessed using the inferred stress-strain behavior to illustrate the usefulness of the procedure. The result of the stability analysis was found to be in qualitative agreement with the observed performance of the dike during a recent field experiment attempting to trigger static liquefaction.     

In Situ Performance Testing of Deteriorating Water Tanks for Durability Assessment

Reports of failure of existing concrete structures due to a lack of durability, rather than a deficiency in structural strength, has made concrete technologists, engineers, and researchers focus research on the parameters influencing durability performance with respect to time. Systematic performance monitoring, with respect to chosen durability parameters of existing concrete structures, will decide the direction of future research in this area. Inferences based on laboratory simulations and testing need to be confirmed by in situ field measurements and studies. In situ condition rating and performance monitoring surveys have been conducted by many researchers, scientists, and professional associations, and reported in literature. Inferences of few such studies are summarized and discussed. Deterioration of concrete structures constructed in recent times is observed at relatively faster rates, and has been mainly attributed to cracking. Cracking is associated with the use of faster-hydrating portland cements with increased fineness and the tricalcium silicate (C3S) content to support the high speed of modern construction. In the present research, a case study of deteriorated water tank structures situated in the semitropical region of India is presented. Some selected parameters—such as concrete cover, carbonation depth, chloride concentration, compressive strength, etc. which influence long term durability of structures—have been measured.     

Stream Bank Erosion: In Situ Flume Tests

A new technique for testing the erodibility of cohesive stream banks using an in situ flume is presented. The erosion rate is estimated from direct measurements of bed surface elevations by acoustic sensors. The sediment resuspension rate is obtained using data on sediment concentrations measured by optical backscatter sensors and from water samples. The bed-load contribution to the total erosion rate is evaluated from the conservation equation for sediments. Temporal patterns of erosion and resuspension rates are studied employing stepwise increments of bed-shear stress. The data show that bed load plays a significant role in cohesive bank erosion. The data analysis suggests that erosion and resuspension thresholds observed in experiments were very low or equal to zero. The data support the power type equation for the erosion and resuspension rates with bed-shear stress as the key factor. The data also highlights the potential importance of mud content and water content on erosion.     

Data Interpretation for In Situ Measurements of Cohesive Sediment Erosion

Methods for interpreting data from in situ flume measurements of cohesive sediment dynamics are evaluated and a technique for estimating various erosion parameters using in situ measurements is proposed. There is currently a lack of uniformity in analysis techniques for cohesive erosion data collected in flumes and with in situ instruments and the proposed technique resolves some of these inconsistencies. The data set used in this study was derived from field experiments conducted with a straight benthic in situ flume in different aquatic environments in New Zealand. The experiments with stepwise increases in flow velocity revealed that peaks in the erosion rate at the beginning of each velocity step are most likely associated with heterogeneous bed structure, as transient hydrodynamic effects due to the experimental procedure were found to be insignificant. The field data showed an exponential decay of the erosion rate with time that is indicative of depth-limited erosion. These data are used to illustrate methods for the parameterization of the proposed semiempirical erosion equation, taking into account the time dependency of the erosion process.     

Fiber Optic Sensors for Bridge Monitoring

Advances in the production of optical fibers made possible the recent development of innovative sensing systems for the health monitoring of civil structures. The main reasons for this development are the reduced weight and dimensions of fiber optic sensors, the strong immunity to electromagnetic interference, the improved environmental resistance and the scale flexibility for small-gauge and long-gauge measurements. These systems can provide high-resolution and measurement capabilities that are not feasible with conventional technologies. In addition, they can be manufactured at a low cost and they offer a number of key advantages, including the ability to multiplex an appreciable number of sensors along a single fiber and interrogate such systems over large distances. For these reasons, it is evident that fiber optic sensors will change the instrumentation industry in the same way fiber optics has revolutionized communications. This paper provides an overview of the intensity modulated and spectrometric fiber optic sensors and techniques to assess the condition of existing structures in order to enhance the durability of the new bridges, increasing lifetime and reliability and decreasing maintenance activities. Application of these sensors to monitoring strain, temperature, inclination, acceleration, load measurements, ice detection, vehicles speeds and weights, and corrosion and cracking of reinforced and prestressed concrete structures will be described.     

Cu-Fe系原位复合线材

本文研究了Cu-14.7 vol％Fe和Cu-20 vol％Fe原位复合材料的性能和显微结构。经真应变为6.4的形变后,强度分别为860MN/m~2和1090MN/m~2,远远超过混合法则的预测值。随形变量的增加,Fe相沿拉拔方向纤维化,Fe纤维尺寸(t)和间距(λ)减小,复合材料强度和Fe纤维间矩,遵循Hall-Patch关系。     

CPT-Based Probabilistic and Deterministic Assessment of In Situ Seismic Soil Liquefaction Potential

This paper presents a complete methodology for both probabilistic and deterministic assessment of seismic soil liquefaction triggering potential based on the cone penetration test (CPT). A comprehensive worldwide set of CPT-based liquefaction field case histories were compiled and back analyzed, and the data then used to develop probabilistic triggering correlations. Issues investigated in this study include improved normalization of CPT resistance measurements for the influence of effective overburden stress, and adjustment to CPT tip resistance for the potential influence of “thin” liquefiable layers. The effects of soil type and soil character (i.e., “fines” adjustment) for the new correlations are based on a combination of CPT tip and sleeve resistance. To quantify probability for performance-based engineering applications, Bayesian “regression” methods were used, and the uncertainties of all variables comprising both the seismic demand and the liquefaction resistance were estimated and included in the analysis. The resulting correlations were developed using a Bayesian framework and are presented in both probabilistic and deterministic formats. The results are compared to previous probabilistic and deterministic correlations.     

Mass Transfer of Ozone in a Novel In Situ Ozone Generator and Reactor

A porous tubular reactor that also served as an electrode for ozone generation was studied in this research to determine the effects of in situ ozone generation on mass transfer and reaction rates. Experimental data over a range of gas flow rates and ozone generation rates gave KLa values in the range 0.77–1.14?min?1. These values are more than double the values typically reported for bubble columns, and about 30% higher than that for packed beds. The specific power requirement for the laboratory-scale in situ reactor is an order of magnitude lower than that for bubble columns and stirred tank reactors that are used for ozone dissolution. A compartments-in-series fluid flow model was developed to describe the reactor system, and this model provides a good comparison to the experimental data for dissolved ozone and off-gas concentrations in the reactor. Sensitivity analyses indicate that the dissolved and off-gas ozone profiles are most sensitive to the gas–liquid partition coefficient and the overall mass transfer coefficient.     

In Situ Soil Response to Vibratory Loading and Its Relationship to Roller-Measured Soil Stiffness

An investigation was conducted to characterize and relate in situ soil stress-strain behavior to roller-measured soil stiffness. Continuous assessment of soil stiffness via roller vibration monitoring has the potential to significantly advance performance based quality assurance of earthwork. One vertically homogeneous and two layered test beds were carefully constructed with embedded sensors for the field testing program. Total normal stress and strain measurements at multiple depths reveal complex triaxial soil behavior during vibratory roller loading. Measured cyclic strain amplitudes were 15–25% of those measured during static roller passes due to viscoelasticity and curved drum/soil interaction. Low amplitude vibratory roller loading induces nonlinear in situ modulus behavior. Roller-measured stiffness and its dependence on excitation force is influenced by the stress-dependent modulus function of each soil, the varying drum/soil contact area, and by layer characteristics (modulus ratio, thickness) when layering is present. On vertically homogeneous clayey sand, roller-measured stiffness decreased with increasing excitation force, a behavior attributed to stress-dependent modulus reduction observed in situ. On the crushed rock over silt test bed, roller-measured stiffness increased with increasing excitation force despite the mild stress-dependent modulus reduction observed in the crushed rock. In this case, the stiffer crushed rock takes on a greater portion of the load, resulting in the increase in roller-measured stiffness.     

Laboratory and In Situ Tests for Long-Term Hydraulic Conductivity of a Cement-Bentonite Cutoff Wall

Slurry trench cutoff walls, constructed using self-hardening slag-cement-bentonite (Slag-CB), are the most common form of in-ground vertical contaminant barrier in the U.K., Europe, and Japan, and are increasingly being used in the United States. This paper presents a case study of the hydraulic conductivity evaluation of an 11-year-old Slag-CB wall material at a sulfate-contaminated site, using different in situ techniques and laboratory tests. The laboratory results suggest that the hydraulic conductivity of the samples, which vary in age from 4 weeks to 11 years, decreases with time for the first 3 years but then remains constant. The results indicate that the long-term performance of these containment walls is influenced by various parameters such as aging, the type/duration of contaminant exposure, mixing of surrounding soil during construction, and wall depth. Piezocone tests, packer tests, and self-boring permeameter tests were carried out in the field to determine the suitability of different in situ techniques and compare with the laboratory results. The hydraulic conductivity is affected by the type of in situ technique used and the geometric scale of the test section.     

In Situ Estimate of Shear Wave Velocity Using Borehole Spectral Analysis of Surface Waves Tool

In situ field testing has been performed over the past several years at a silty sand site in Austin, Tex. using the borehole spectral analysis of surface waves (SASW) tool to develop the technique and assess the validity of the method. The borehole SASW tool is an inflatable pressuremeterlike device that allows surface wave measurements to be performed along the wall of an uncased borehole while varying the in situ states of stress. Field results demonstrate the applicability of borehole SASW testing as a method to characterize soil sites and provide information about in situ shear wave velocity and the relationship between shear wave velocity and state of stress. Results from a borehole SASW test conducted at the Austin site are presented herein to demonstrate the applicability and validity of the method.     

In Situ Test on Cooling Effectiveness of Air Convection Embankment with Crushed Rock Slope Protection in Permafrost Regions

An experimental air convection embankment (ACE) was constructed in Beiluhe on the Qinghai-Tibet Plateau during 2001–2003, using coarse (5–8 and 40–50 cm), poorly graded crushed rock fill material on the slope of embankment with thick ground ice permafrost foundation, which should be called the air convection embankment with crushed rock slope protection (ACE–CRSP). The highly permeable ACE–CRSP installation was designed to test the cooling effectiveness of ACE–CRSP concept in an actual railway project. Ground temperature data were collected from test sections on the railway with thermistor sensor strings. The results showed that the mean ground temperature under the layer of the crushed rock with coarse particle diameter of 40–50 cm was lower than that under one with finer particle diameter of 5–8 cm, and the fluctuating range of temperature under the former was bigger than that under the latter. It was obvious that the maximum thaw depth was raised under the layer of crushed rock with coarse particle diameter of 40–50 cm, which resulted from the stronger cooling effectiveness of air convection during the winter. The amount of heat exchange also showed that the absorbed cooling energy of the foundation, under the layer of the crushed rock with coarse diameter, was larger than that with finer diameter.So, we believe that the cooling effectiveness of the crushed rock layer with coarse diameter was stronger than that one with finer diameter.     

In Situ Pore Pressure Responses of Native Peat and Soil under Train Load: A Case Study

Settlement and formation of piping holes on surfaces were observed along a rail embankment subject to normal traffic load. Piezometers were installed in the native peat and soil underneath the embankment inside and outside problematic area to measure the pore pressure responses during train traffic. Peculiar pore pressure responses were observed. Cyclic pore pressures were only measured during the first 60–80?s of the 6-min train passage, and thereafter the pressures decayed rapidly to the initial values. The pore pressure changes in the shallow peat layer were lower than those in the deep soil layer. Possible mechanisms causing such peculiar pore pressure responses, surface settlement, and piping holes were explored and identified. It was found that the stiffness contrast between the stiff, upper granular fill and the soft, native peat material could lead to a redistribution of tensile stress in the granular fill layer to the peat layer due to the moving train load. This stress redistribution promotes the propensity of vertical piping in the peat layer.     

Behavior of Plate Load Tests on Soil Layers Improved with Cement and Fiber

The load-settlement response from three plate load tests (300 mm diameter, 25.4 mm thick) carried out directly on a homogeneous residual soil stratum, as well as on a layered system formed by two different top layers (300 mm thick)—sand-cement and sand-cement fiber—overlaying the residual soil stratum, is discussed in this technical note. The utilization of a cemented top layer increased bearing capacity, reduced displacement at failure, and changed soil behavior to a noticeable brittle behavior. After maximum load, the bearing capacity dropped towards approximately the same value found for the plate test carried out directly on the residual soil. The addition of fiber to the cemented top layer maintained roughly the same bearing capacity but changed the postfailure behavior to a ductile behavior. A punching failure mechanism was observed in the field for the load test bearing on the sand-cement top layer, with tension cracks being formed from the bottom to the top of the layer. A completely distinct mechanism was observed in the case of the sand-cement-fiber top layer, the failure occurring through the formation of a thick shear band around the border of the plate, which allowed the stresses to spread through a larger area over the residual soil stratum.     

In Situ Investigation of the Allotropic Transformation in Iron

Previous studies on the allotropic transformation in iron suggested a high transformation temperature and a controversial transformation mechanism. At present, however, our understanding of the transformation characteristics in iron seems insufficient, especially as there is a general lack of in situ data on morphological evolution and lattice parameter changes during the transformation. In this study, the characteristics of the morphology, the crystallographic relationships, and short‐range diffusion in the allotropic transformation are investigated systematically on the basis of in situ and ex situ observations using time resolved X‐ray diffraction, laser scanning confocal microscopy, and electron backscattering diffraction. In contrast to the martensitic transformation, the characteristics of the allotropic transformation will be highlighted. Finally, the results are compared with previous reports in order to provide further insight into the nature of the phase transformation based on the in situ observations.     

Use of Recombinant Bioluminescent Bacteria for On-Site Monitoring of Toluene Analogs at Petroleum Contaminated Sites

This paper describes the application of a genetically engineered microorganism, Pseudomonas putida mt-2 KG1206, to monitor toluene analogs in groundwater collected from petroleum hydrocarbon contaminated sites. KG1206 contains the intact TOL plasmid and a second plasmid with the Pm-lux gene allowing it to produce bioluminescence in the presence of toluene analogs and their derivatives such as toluene, xylenes, and m-toluate. The simple bioluminescence assay consisted of mixing one volume of groundwater sample with four volumes of broth culture followed by bioluminescence measurement after 30?min. The maximum bioluminescent response with pure chemicals followed the order: m-methyl benzyl alchohol>m-toluate>toluene>m-xylene>benzoate>p-xylene>o-xylene. The bioluminescence production was well correlated to the m-toluate concentrations (R2>0.97) in field samples, with concentrations predicted from the bioassay falling within 75–158% of true concentration. However, no strong correlation was observed between the bioluminescence intensity and the total inducer concentration in the groundwater. Results from this study demonstrate the potential of using recombinant bioluminescent bacteria as a rapid and simple tool for monitoring specific pollutants at contaminated sites.     

Theoretical Modeling of Signal Loss versus Crack Opening for a Novel Crack Sensor

The degradation of concrete structures is always accompanied by the formation of cracks. Crack monitoring is hence useful in assessing the “health condition” of the structure. In our previous investigation on an optical-fiber crack sensor, we have successfully demonstrated the possibility of crack detection and monitoring without requiring prior knowledge of crack locations. Also, a single fiber can be employed to monitor a number of cracks. In practical applications, the signal loss versus crack opening relationship of the sensor needs to be properly “designed” to satisfy performance requirements on sensitivity to small cracks and/or the total number of detectable cracks (which is limited by the maximum loss at each crack). In this paper, a theoretical model for the signal loss versus crack opening relationship is developed through a combination of mechanical and optical analyses. Using concrete beams with embedded sensors, crack monitoring experiments are conducted. Test results are found to be in reasonably good agreement with predictions from the model. With the verified model, simulations are carried out to study the effect of various parameters on sensor performance. The potential application of the theoretical model to generate sensor design guidelines is hence demonstrated.     

Load Performance of In Situ Corrugated Steel Highway Culverts

This paper presents the results of field performance tests of 39 in-service corrugated steel highway culverts in Ohio. The culverts had span lengths varying from 3.23?m (10.6?ft)?to?7.04?m (23.1?ft) and backfill soil heights over the crown varying from 0.27?m (0.9?ft)?to?7.47?m (24.5?ft). Static and dynamic load tests were conducted by driving heavy trucks across the culverts. Static loads were applied at ten different locations above each culvert. Dynamic load tests were conducted at six truck speeds varying from 8?km/h (5?mi/h)?to?64?km/h (40?mi/h). A portable instrumentation frame was installed inside each test culvert to monitor deflections. Strains on the culvert walls were also measured at 14 locations using strain gauges. Effects of backfill height and loading conditions are investigated. According to the experimental results, a plot of maximum culvert deflection versus backfill height shows a nonlinear relationship. Maximum static load deflections were found to be consistently larger than the maximum dynamic deflections obtained using the same test truck. Deflections were nearly zero for deep culverts with backfill heights exceeding 4?m (13?ft). Maximum deflections correlate more closely to equivalent line loads than to total truck weight. The data also indicate that culvert behavior is more difficult to predict when backfill heights are shallow because other factors, such as culvert age and condition and soil type, likely play a significant role.     

Assessing Probability-based Methods for Liquefaction Potential Evaluation

This paper presents an assessment of existing and new probabilistic methods for liquefaction potential evaluation. Emphasis is placed on comparison of probabilities of liquefaction calculated with two different approaches, logistic regression and Bayesian mapping. Logistic regression is a well-established statistical procedure, whereas Bayesian mapping is a relatively new application of the Bayes’ theorem to the evaluation of soil liquefaction. In the present study, simplified procedures for soil liquefaction evaluation, including the Seed–Idriss, Robertson–Wride, and Andrus–Stokoe methods, based on the standard penetration test, cone penetration test, and shear wave velocity measurement, respectively, are used as the basis for developing Bayesian mapping functions. The present study shows that the Bayesian mapping approach is preferred over the logistic regression approach for estimating the site-specific probability of liquefaction, although both methods yield comparable probabilities. The paper also compares the three simplified methods in the context of probability of liquefaction, and argues for the use of probability-based procedures for evaluating liquefaction potential.