Journal of Geotechnical and Geoenvironmental Engineering

Jet grouting is a ground improvement technique that involves the injection of binder (with or without air) in soil at high pressure. One aspect of this technique that has not been investigated until now is the risk of failure due to the shadow effect, defined as the interruption of continuity during jetting produced by obstructions, such as boulders. This can represent a very serious problem because boulders do not allow the jet to reach and erode the soil, thus reducing the diameter or preventing the complete formation of the columns. This paper presents a mathematical theoretical discussion considering boulders as spheres. Three conditions possibly causing a failure of the jet-grouted continuous system are identified. A statistical risk analysis related to the probability of an unidentified spherical boulder causing a failure of the watertightness requirement of a jet-grouting wall is assessed. The goal of this research is to provide a tool by which engineers can estimate the risk related to the shadow effect.

The use of industrial by-products in highway embankments is becoming popular due to their large-volume use in such systems. Steel slag is one of these by-products. Previous research shows that steel slag has mechanical properties comparable to those of traditional embankment fill material; however, the environmental impacts of using steel slag need to be carefully evaluated. In this study, a series of sequential water leach and column leach tests are performed in order to assess the trace metal leaching characteristics from pure or treated steel slag highway embankments into surface waters. In addition, a numerical model is used to determine the metal concentrations within the surface waters with respect to distance from the embankment. The results show that placing a clayey embankment soil around pure or treated steel slag significantly decreases the metal concentrations of the leachate. In addition, the numerical model results indicate that, after the slag leachate meets the surface waters, the concentrations decrease to levels significantly lower than the regulatory limits.

Nanoscale iron particles (NIP) have been found effective for remediation of contaminated groundwater, but their transport in subsurface after injection is limited due to aggregation and sedimentation. Lactate-modified NIP (LMNIP) are found to be effective for remediation as well as possess adequate transport characteristics in subsurface after injection. Advection-dispersion transport with adsorption and decay equation is used to simulate NIP and LMNIP transport in saturated sand (groundwater). However, significant uncertainty exists in selecting values of important input parameters such as dispersion coefficient, retardation coefficient, and first-order decay constant. The objective of this study is to assess the variability of these transport parameters and perform a reliable assessment of NIP and LMNIP transport behavior through groundwater. Probabilistic modeling is performed using reliability-based analysis with first-order reliability method (FORM) to account for the uncertainty in the parameters for NIP and LMNIP transport. The mean and standard deviation values of transport parameters were chosen based on the statistical analysis of the results of previous column experiments. Results indicated that the effect of dependency among the random transport parameters on reliability index for LMNIP and NIP transport should be given due consideration when designing contaminant remediation strategies. The reliability analysis also indicated that the coefficient of variation (COV) associated with the dispersion coefficient is relatively the most influential parameter compared with retardation coefficient and decay constant. The breakthrough time curves presented in the form of design charts are useful to determine extent and time required for NIP/LMNIP transport through soils.

Self-drilled hollow bar micropiles are more popular for soil improvement projects than the use of the traditional solid bar system because they decrease construction costs and time. Little research has been published about the load-deformation behavior of hollow bar micropiles; thus, the effect of installation techniques and the nature of the surrounding ground on their bond strength remains unverified. The current study proposes three grouting methods to test the load-displacement behavior of hollow-bar micropiles in both clay and gravel. A field study was performed by installing 21 full-scale tests on hollow bar micropiles at two sites. Time-dependent grouting methods were used to evaluate the grout–ground bond strength. The observed load-displacement behavior indicated that the induced bond diameter of the hollow-bar micropiles was greater than the results of theoretical calculations and that their estimated bond strength was greater than the values recommended in existing codes. Moreover, elastic behavior was greater in micropiles which were grouted at higher drilling and injection durations and sequences.

The time-dependent increase in axial resistance (setup) of jacked or driven piles in sand is still not well understood, and its quantification remains a challenge. In this paper, a series of tests is performed on model piles jacked in sand in a half-cylindrical calibration chamber with image analysis capabilities to study setup. Load cell measurements, which are used to determine changes in pile resistance with time, are considered in combination with digital images taken with CMOS cameras and a handheld microscope positioned in front of the transparent observation windows of the chamber. Using the digital image correlation (DIC) technique, images taken during pile installation and throughout a waiting period of up to 10 days are analyzed to detect any change in the displacement and strain field in the sand domain that would indicate stress redistribution leading to changes in axial resistance. In addition, images of a set of 50 particles are analyzed to investigate any possible enhancement of particle interlocking or any other change in particle position or orientation during the waiting periods. The results of the analyses show negligible relative displacements and strains in the sand domain and negligible displacement or rotation of individual sand particles. These results are consistent with the measured axial capacities of the model piles, which are largely the same regardless of the time after installation at which the load tests were performed.

Landfills consisting of waste natural lumpy soils from open-pit mining are being deposited. The shear strength of excavated lumpy soils is important for designing the landfills. To this end, a series of oedometer and triaxial tests (including conventional, constant $p^{\prime }$, and undrained triaxial tests) were performed on a natural lumpy soil taken from an open-pit mine in Germany. In addition, reconstituted and natural intact counterparts were investigated as a reference. The test data reveal that interlump porosity is substantially reduced because of the rearrangement of the lumps at a stress level of 100 kPa, which is significantly lower than the yield stress of the natural lumps (4,380 kPa). The critical state line of the natural lumpy soil can be defined in terms of the $p^{\prime }\text{-}q$ relationship; however, it is not unique in the $v\text{-}{p}^{\prime }$ compression plane, which depends on the loading stress path. The critical state points of the natural lumpy soil ($p^{\prime }\text{-}q$ plane) are located above the critical state line of the reconstituted soil. The diagenetic soil structure of the natural lumps may be responsible for the difference in critical state between the natural lumpy soil and the reconstituted soil. After being normalized by the Hvorslev equivalent pressure, the fitting line of the critical state points of the natural lumpy soil crossed that of the reconstituted soil. The difference between the critical state of the lumpy soil and the reconstituted soil diminished with the increase of the consolidation stress.

Reductions in geosynthetic clay liner (GCL) panel overlap are reported for two needle-punched and thermally treated GCLs (GCL1 and GCL2) and compared with values for two other needle-punched but not thermally treated GCLs (GCL3 and GCL4) at the same field-scale test site. The GCLs were covered only by a black geomembrane and otherwise left exposed to study the implications of leaving the composite liner exposed for nearly 5 years on reductions in the overlapped seams between adjacent GCL panels. It was found that all but GCL2 experienced a significant reduction in overlap. After 4.8 years, GCL2 experienced the smallest overlap reductions of only 30 mm (i.e., 90% of the initial 300 mm panel overlap remained), GCL3 overlaps were reduced by 75 mm, whereas GCL1 and GCL4 had the largest reductions with values greater than 600 and 400 mm, respectively, after 4.8 years. Overlap reductions appear to correlate with reference water content and overlap adhesion, which are two laboratory indices affected by confinement and texture of the four GCLs resulting from subtle, but, distinct differences in the method of manufacture.

Gravel–structure interfaces exist widely in civil engineering practices, and their mechanical behaviors are crucial items in soil–structure interaction analysis. The interfaces are always characterized by three-dimensional (3D) features, which seldom have been explored. This paper presents the 3D behaviors of a gravel–structure interface from large-scale two-way beeline, cross, circular, and arc shear tests. The normal displacement can be divided into irreversible and reversible components. The shear stress–displacement hysteretic relationship exhibits an elliptical response in circular shear paths, other than the hyperbolic trend observed in linear shear paths. The shear strength is isotropic, and behaves in accordance with the Mohr–Coulomb failure criterion. The shear path plays a significant role in the 3D interface behaviors. Good consistency is found to exist in the irreversible normal displacement versus shear work density relationship, the reversible normal displacement versus resultant tangential displacement relationship, and the resultant shear stress versus resultant tangential displacement hysteretic relationship, regardless of the shear paths.

Determination of interface shear strength is crucial in the design of many geotechnical structures. To study the effect of interface roughness, particle geometry (size and shape), and sand gradation on the interface friction angle, direct interface shear tests were performed for 10 sands with varying particle sizes, shapes, and gradations and four steel surfaces with different levels of rusting. When sheared along the same interface, the interface friction angle was greater for sands with smaller particle sizes and more angular or elongated particle shapes. For a given sand, the interface friction angle increases with increasing surface roughness. For sands with uniform particle size, a unique relationship was found between the normalized surface roughness and the ratio of the sand–steel critical-state interface friction angle to the internal critical-state friction angle of the sand. Given the same surface roughness and mean particle size, smaller critical-state interface friction angles were mobilized for graded sands than for sands with uniform particle sizes.

Shallow underground structures are commonly built in close proximity to tall buildings in dense urban environments. Although it is well known that such buildings have the potential to affect ground motions in their vicinity and transmit significant forces and moments into their foundations and surrounding soil during earthquakes, their impacts on adjacent underground structures are not well understood. This study evaluates the impact of an adjacent midrise or high-rise building on the seismic response of a cut-and-cover tunnel structure and a braced excavation in centrifuge experiments and corresponding numerical simulations. The underground structures are first studied without buildings present, and then with an adjacent 13-story midrise or 42-story high-rise structure. Results indicate that adjacent buildings transmit large lateral loads to the underground structures during ground shaking and that the distribution of loading is nonlinear with depth. The loading is proportional to building base shear and is dependent upon the geometric details of both the underground structure and the building foundation. Numerical analyses are shown to reasonably reproduce the experimentally measured response of the structure–soil–underground structure system. For design purposes, these interactions must be accounted for, and the assumptions of free-field or isolated conditions are not appropriate for underground structures in urban settings.

At present, there is no well-accepted method for the design of tunnels built in cement-admixed soils. Moreover, spatial variability and heterogeneity in strength have been reported for such treated soils. This paper presents a two-dimensional plane-strain study of tunnel stability in cement-admixed soft soil surrounds considering spatial variability. The influence of spatial variability was studied by varying the coefficient of variation and scale of fluctuation in the mean strength and stiffness of improved soil surround using random finite-element analysis. The critical tunnel support pressures from the random analyses were compared with results of deterministic analyses to compute appropriate design strengths and strength reduction factors for varying spatial variability in treated soils. By using appropriate values of design strength or the strength reduction factor, equivalent strength and stiffness can be prescribed for homogeneous improved soil surrounds in deterministic finite-element analyses. The worst scale of fluctuation was also investigated and found to be approximately two-thirds of the thickness of improved soil surround.