Journal of Geotechnical and Geoenvironmental Engineering

Field sampling was performed at a number of residential structures in the Denver metropolitan area for the purpose of assessing the extent of wetting below residential structures after construction and commencement of landscape irrigation. Total suction measurements using filter paper methods were undertaken on undisturbed samples. A similar data set from sites without previous development or irrigation was used to estimate the suction profile before the imposition of residential construction and landscape irrigation. Comparison of the postdevelopment profile measured at the residential structures to the predevelopment profile estimated using a site-specific procedure was used to assess the depth of wetting at each structure. Cumulative probability curves are presented for the depth of wetting arising from common residential landscape schemes and site drainage for the Denver area. The Denver-area data set was used to develop a method for assessment of depth of wetting. This method can be used to assess depth of wetting from residential development for other regions having different climatic conditions and landscape practices.

The paper investigates the accuracy of the AASHTO simplified method by using load measurements reported in a large database of full-scale instrumented walls for bar mat, welded wire, and steel strip soil reinforced walls. The accuracy of the AASHTO simplified method is quantified by computing the mean and coefficient of variation of the ratio (bias) of measured loads under operational conditions to predicted loads. The paper shows that for steel strip walls, the AASHTO simplified method is reasonably accurate for granular backfill soils with friction angles less than 45°. For bar mat walls, the method is demonstrated to be slightly conservative. The simplified method underpredicts reinforcement loads at shallow overburden depths for steel strip walls with backfill friction angles greater than 45° due to compaction-related effects. It is concluded that these compaction-induced loads near the wall top do not contribute to internal instability due to pullout.

It is well accepted that the quality of soft clay samples obtained using standard fixed piston samplers can be relatively poor and that block samples are necessary to yield very high quality samples. However, for many practical projects it is not economically viable or physically practical to obtain block samples. In this project, the quality of standard $54\mathrm{mm}$ composite piston samples of soft clay is examined by comparing six separate sets of $54\mathrm{mm}$ samples to parallel block sampling. Sampling and laboratory testing was carried out by three different organizations at a well characterized highly uniform soft clay site in Norway. As expected, the work showed that the block samples behaved significantly differently from those obtained using the $54\mathrm{mm}$ sampler and were of higher quality. Block sample-derived parameters were considerably different from those obtained from the $54\mathrm{mm}$ sample tests. However, significant differences were also found between the different sets of $54\mathrm{mm}$ samples. Although the differences are less than when compared with block samples, the consequences of poor quality $54\mathrm{mm}$ sampling will be significant in engineering design. It is concluded that the differences are due to small details in the sampling operation such as the need to keep the piston effectively stationary at all times, to avoid overcoring and to handle the recovered sample carefully. If a well trained driller follows good quality practice, then relatively good samples can be obtained by the fixed piston sampler, which are suitable for analysis and design of routine engineering works.

The lightweight deflectometer (LWD) is gaining acceptance and popularity as an in situ spot-testing device for quality control/quality assurance of earthwork compaction. Little research has been conducted to investigate the stress–strain response within the soil during LWD testing. Similarly, little research has been performed to examine the appropriateness of using homogeneous, isotropic, linear elastic half-space theory to estimate soil modulus $\left(E_{\mathrm{LWD}}\right)$ from LWD results. With this aim, an array of vertical stress and strain sensors was placed within the soil to measure the stress–strain response during LWD loading. Measured in situ stress values matched well with stresses predicted using homogeneous, isotropic, linear elastic half-space theory. In situ stress data revealed that the contact stress distribution between the soil surface and loading plate is a function of the soil type. Measured in situ strain values did not correspond well with strains predicted using homogeneous, isotropic, linear elastic elasticity. An exponentially increasing modulus function was required to match experimental with theoretical elastic strains. The results indicate that the commonly used form to predict $E_{\mathrm{LWD}}$ is inappropriate if the goal is to extract constitutive soil properties. Analysis of strain data suggests the LWD depth of influence (measurement depth) is 0.9–1.1 times the plate diameter.

A database of 534 large-scale direct shear test results was assembled in this study to evaluate the interface shear strength between geosynthetic clay liners (GCLs) and geomembranes (GMs). The tests were conducted between 1992 and 2003 by a single independent laboratory using procedures consistent with current testing standards. The number of results in the database allowed quantification of the impact of GCL type, GM type, normal stress, and procedures for specimen hydration and consolidation on the shear strength of GCL-GM interfaces, as well as identification of sources of shear strength variability. The interface shear strength was found to be sensitive to the type of GCL internal reinforcement, GM polymer, and GM texturing, but not to the GM thickness or manufacturer. On average, the GCL internal shear strength was observed to be higher than the GCL-GM interface shear strength when tested using the same procedures. GCLs sheared internally show similar stress-displacement responses and friction angles to GCL-GM interfaces that incorporate a GCL with the same reinforcement type. Hydration under normal stresses below those used during shearing (followed by a consolidation period) led to higher GCL internal shear strength, but lower GCL-GM interface shear strength, than when hydration was conducted under the shearing normal stress. Such different responses are attributed to bentonite extrusion from the GCL into the interface. Good repeatability of test results was obtained using GCL and GM specimens from the same manufacturing lot, while high variability was obtained using specimens from different lots. GCL-GM interface peak shear strength variability was found to increase linearly with normal stress.

This paper describes the application of a quasi-one-demensional (1D) network, bubble model to simulate the filtration of a microfine cement suspension injected through a column of sand. The bubble model represents the soil column as a series of homogeneous sites linked through bundles of cylindrical bonds that characterize the distribution of pores. The model captures mechanisms of particle sieving at the inlet sites and infiltration within each of the bonds under the action of hydrodynamic and gravitational forces. The behavior of each bond is based on numerical simulations of particle transport, collection, mounding, and clogging within a cylindrical model pore. Two empirical parameters are introduced to account for uncertainties in particle attachment at the pore wall and observed mechanisms of resuspension of hindered particles. In principal, these parameters can be calibrated from measurements of effluent concentrations. The bubble model provides useful physical insights to explain the transient dynamics of filtration processes. The model is able to provide consistent predictions of pore pressures measured in 1D column injection tests reported in the literature.

Bleeding is known to occur in bored piles (drilled pier). The generally accepted view is that bleeding in piles is confined to the upper part of the pile only. Under certain conditions during bleeding, channeling may happen. Practising engineers believed that the associated problems with bleeding and channeling in bored piles can be overcome by overcasting the piles. A case study of extensive integrity tests consisting of cross-hole sonic logging tests and dynamic load tests on bore piles, as well as continuous corings from top to bottom of the piles carried out, revealed that some bored piles have channeling of concrete at various depths. Most of them were larger diameter piles. The finding that bleeding and channeling are not confined to the upper part of the pile is contrary to the generally accepted view. This paper attempts to develop a theory for the bleeding and channeling of concrete to explain the mechanics of the occurrence of channeling in bored piles. The proposed theory is verified by the close correlation of the predictions of the theory with field observations of the case study. Based on the proposed theory, recommendation with regards to the quality of concrete will be made to avoid the occurrence of channeling of concrete in large-diameter bored piles. The implications on the structural performance pertaining to axial capacity, compressibility and durability of bored piles with channels will be investigated.

There has been much advancement using conceptual models and analytical methods to explain various aspects of pile performance. They are mainly based on the findings of model tests and full-scale pile tests in fine-grained and coarse-grained soils, and driven piles on land are normally less than $40\mathrm{m}$ . Design methods developed from this data bank of pile geometries and soil conditions for long piles should be treated with caution. In this paper, 13 $H$ -piles of $34–60\mathrm{m}$ and $\mathrm{7,096}\mathrm{kN}$ capacity founded on granitic saprolite are studied. Among them, two piles were restriked at different time intervals. All piles were axially load tested statically using a maintained load method. In contrast to the short rigid piles founded on weaker soil, their load-transfer mechanism varied with the magnitude of applied load and pile length. They deformed almost linearly at small loads and might have buckled when the loads were large and the creep settlements were found to be length dependent. Existing criteria might not be able to interpret failure loads sometimes, but a pile dynamic analyzer was found to give the best estimate on pile capacity.

This study investigates the aging effects on the small-strain shear modulus and damping ratio of sands and offers explanations for the measured results based on the concept of contact-force homogenization. Resonant column tests of aged sands under various aging conditions were conducted. The results show that loose sands exhibit greater aging effects than dense sands do at a confining pressure of $35\mathrm{kPa}$ and the effects are completely opposite when the aging pressure is increased to $100\mathrm{kPa}$ . The aging effects can be partially erased by unloading-reloading; the remaining effects can be restored when the applied pressure is the same as the original pressure used during aging and cannot be further erased by additional unloading-reloading cycles. The stress history is also a factor that affects aging behavior: unloading reloading and overconsolidation can reduce the aging rate in terms of the shear-modulus increase. The aging effects, however, can be wiped out by large strain shearing. An addition of fines (dry kaolinite powder) in the sand samples can increase the aging rate because of higher creep made by the kaolinite.

The effects of pH on the liquefaction susceptibility of fine-grained soils were examined by performing undrained cyclic ring-shear tests on artificial mixtures and a natural soil under different pH conditions. Solutions of diluted sulphuric acid $\left({\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4\right)$ and dissolved sodium hydroxide (NaOH) were used to create acidic and alkaline environments, respectively, while distilled water was used as a reference liquid. Low plasticity kaolin and illite-sand mixtures and a medium plasticity bentonite-sand mixture were selected to investigate the influence of plasticity and clay mineralogy on the pH-dependent response of soil to cyclic loading. The results showed that the effects of pH were more pronounced for the medium plasticity mixture, and depended greatly on the mineralogy of clay fraction. For example, in an acidic medium, the kaolin-sand mixture became slightly more resistant to liquefaction while the illite-sand mixture became more susceptible to liquefaction. The bentonite-sand mixture was observed to be the most sensitive to changes in pH environment. While resistant to liquefaction in distilled water, it rapidly liquefied in acidic and alkaline mediums. Cyclic behavior of a medium plasticity soil, which was collected from an earthquake-induced landslide, was also affected by changes in pH. Although being overall resistant to liquefaction regardless of pH, it decreased its cyclic strength in both acidic and alkaline environments. Based on the available literature and the obtained results, an attempt was made to explain the influence of pH on the undrained cyclic behavior of fine-grained soils.

Glyben is an artificial soil comprising bentonite mixed with glycerin that has been used recently in scaled model tests to study seismic soil structure interaction. In spite of recent interest in glyben, factors affecting the dynamic properties of this material have not been well established. This paper presents the results of vane shear tests, cyclic triaxial tests, resonant column tests and bender element tests undertaken to characterize the dynamic properties of glyben. The results show that the modulus ratio of glyben decreases with increasing shear strain amplitude similar to that observed for natural clays. However, there are significant thixotropic changes in the properties of glyben after mixing bentonite with glycerin. In addition, glyben exhibits time-dependent volumetric compression after the application of isotropic consolidation pressure, the damping ratio of glyben is higher than that of natural clays and the dynamic properties of glyben are strongly influenced by temperature. These factors should be considered when interpreting the results of scaled physical model tests using glyben.

The predicted performance using a geotechnical prediction model is expected to deviate from reality. A practical approach to assess the model error is through calibration with observed performances in physical model tests. In this paper, a Bayesian framework of model calibration using centrifuge modeling tests is proposed and the procedure of model calibration is illustrated. Two centrifuge tests conducted to investigate the performance of soil slopes under rainfall conditions are used to calibrate a coupled hydromechanical analysis model. It is found that for centrifuge tests with different levels of soil variability, the test with a smaller variability of soil properties is more efficient for model calibration. According to the concept of random field, a centrifuge model with a larger model size and accelerated to a lower acceleration is better for model calibration. When the discrepancy between the performance interpreted from the centrifuge model and the field performance is small, the improvement of the reliability estimation for a new slope is significant. However, when there is little information about the discrepancy, the reliability estimation cannot be significantly improved by the information from centrifuge modeling. The proposed procedure is shown to be able to quantify the calibration effects of centrifuge tests and may be used to achieve a more reliable calibration.

Mexico City soil has very high specific surface, plasticity and void ratio; its natural structure is preserved until the yield pressure ${\sigma }_y^{\prime }$ , which is typically above the in situ effective stress ${\sigma }_v^{\prime }$ , and the mechanical response changes significantly when the effective confining stress ${\sigma }_{\mathrm{o}}^{\prime }$ exceeds the yield pressure ${\sigma }_y^{\prime }$ . In this study, the effects of strain rate on the undrained response of Mexico City soil are explored using undisturbed specimens subjected to monotonic triaxial compression tests at a constant rate of deformation. Results show that strain-rate effects on undrained strength and mode of failure depend on ${\sigma }_y^{\prime }∕{\sigma }_{\mathrm{o}}^{\prime }$ , hence, on the degree of natural structure preserved in the specimen. Undrained strength increase with strain rate, particularly in the more structured specimens (i.e., higher ${\sigma }_y^{\prime }∕{\sigma }_{\mathrm{o}}^{\prime }$ ). The role of ${\sigma }_y^{\prime }∕{\sigma }_{\mathrm{o}}^{\prime }$ on strain-rate effects in this unremolded natural soil resembles the effect of overconsolidation ratio on resedimented specimens. The limitations in using standard triaxial equipment for strain-rate effect studies are discussed.