Journal of Geotechnical and Geoenvironmental Engineering

This study focused on quantifying relative contributions of abiotic and biotic compression of municipal solid waste (MSW). Abiotic mechanisms include immediate compression, mechanical creep, and moisture-induced waste softening. The biotic mechanism is decomposition of the MSW organic fraction, which when coupled with mechanical creep, yields biocompression. Three 610-mm-diameter laboratory compression experiments were conducted for 1,150 days under the following conditions: (1) waste with no liquid addition (dry), (2) liquid addition spiked with biocide (abiotic), and (3) leachate recirculation (biotic). Immediate compression strain was similar in all three tests (24–27%). Mechanical creep, moisture-induced softening, and biocompression were compared via time-dependent compression ratios ($C_{\alpha }^{\prime }$). Moisture-induced softening occurred in both the abiotic and biotic cells in response to liquid addition and leachate recirculation. Moisture-induced softening accelerated the accumulation of mechanical creep (i.e., approximately doubled $C_{\alpha }^{\prime }$ due to mechanical creep relative to the dry cell), but did not increase the overall magnitude. $C_{\alpha }^{\prime }$, in the biotic cell, correlated with the methane flow rate when methanogenesis was controlled by the rate of solids hydrolysis. $C_{\alpha }^{\prime }$, due to mechanical creep in the dry cell and biocompression in the biotic cell, increased exponentially with temperature, and can be represented with an exponential model. $C_{\alpha }^{\prime }$, due to biocompression, was approximately one order of magnitude larger than $C_{\alpha }^{\prime }$ due to mechanical creep.

To evaluate the differences in the hydrological performance of actual earthen cap overlying municipal solid waste (MSW) versus a lysimeter, which is commonly used to measure the hydrologic water balance, a field-scale test section ($30\times 20\times 2\mathrm{m}$) of an earthen cap made up of compacted native glacial clay was constructed and instrumented at a landfill near Detroit. A lysimeter pan was installed within the middle of the test section, and the instrumented area of the test section was expanded upslope and downslope of the lysimeter to monitor water balance parameters within and beyond the lysimeter footprint, in order to evaluate the effect of artificial drainage boundary introduced by the lysimeter. About 50 sensors were installed to monitor meteorological parameters, water content, water potentials, soil temperatures, water levels, gas pressures, percolation, and subsurface lateral flow. The water balance model called Unsaturated Soil Water and Heat Flow Model (UNSAT-H) was used to simulate the water balance of the test section. The UNSAT-H was able to predict the percolation relatively accurately. Relative changes or trends in the soil water storage were generally accurately captured by the numerical model. The numerical model that was validated for the lysimeter was used to simulate the water balance of the actual cap, where the cap was placed on MSW. The net percolation over the monitoring period estimated by the UNSAT-H across the interface between the cap and the underlying landfilled waste was negative (upward), as well as positive (downward into the waste). However, net percolation from the actual cap estimated by the UNSAT-H was relatively close to that measured by the lysimeter. Thus, the field data and modeling results indicate that the soil cap is able to pull moisture from the underlying waste under evapotranspirative gradients.

A standard penetration test (SPT)-based liquefaction case history database for liquefaction triggering criteria is reexamined and reevaluated. The updated database incorporates a number of additional case histories, replaces prior estimates of earthquake magnitudes with current estimates of their moment magnitudes, uses improved estimates of peak ground accelerations when available, and includes a reexamination of the selection and computation of representative SPT $(N_1{)}_{60}$ values for most case histories. The approach used to select and compute representative SPT $(N_1{)}_{60cs}$ values is illustrated using select case histories. The distribution of the case history data relative to the Idriss-Boulanger triggering correlation is examined for any bias with respect to various parameters and to identify the conditions that are, and are not, well covered by available case history data.

This paper focuses on the development of load and resistance factor design (LRFD) for checks of the internal stability of mechanically stabilized earth (MSE) walls reinforced with steel strips. The internal stability of MSE walls relies on protection against two ultimate limit states (ULSs): pullout and structural failure of reinforcements. This study proposes equations for the resistances and loads that reflect the physical processes involved in the pullout and structural failure ULSs and quantify the uncertainties in these equations. These equations are then used to perform reliability analyses using the first-order reliability method (FORM) for different values of target reliability index to obtain load factors and resistance factors for use together with the equations in design. For a given target reliability index and vehicular load on top of an MSE wall, the resistance factor for pullout was highly dependent on reinforcement depth while that for structural failure was insensitive to changes in the design variables in its ULS equation.

The paper reports the results of load and resistance factor design (LRFD) calibration for pullout and yield limit states for steel strip reinforced soil walls under self-weight loading. An important feature of the calibration method is the use of bias statistics to account for prediction accuracy of the underlying deterministic models for reinforcement load, pullout capacity and yield strength of the steel strips, and random variability in input parameters. To improve the accuracy of reinforcement load predictions, small adjustments to current semiempirical American Association of State Highway and Transportation Officials (AASHTO) load design charts are proposed. Similarly, current empirical-based design charts found in AASHTO and Federal Highway Administration (FHWA) guidance documents for the estimation of the pullout resistance factor for smooth and ribbed steel strips are adjusted to improve the accuracy of pullout capacity predictions. The results of calibration lead to a load factor of 1.35 that is consistent with current practice and resistance factors that together give a consistent probability of failure of 1% for all three limit states considered. Furthermore, comparison with allowable stress design (ASD) past practice (AASHTO simplified method) shows that the operational factors of safety using a rigorous LRFD approach give the same or higher factors of safety and lower probabilities of failure. In this study, data for steel strip reinforced soil walls are used as an example to illustrate rigorous reliability theory-based LRFD calibration concepts. However, the general approach is applicable to other reinforced soil wall technologies and calibration outcomes can be updated as more data become available.

This paper reports on the seismic performance of three geosynthetic-reinforced segmental retaining wall systems backfilled with a silty sand mixture, using a shaking table excited by 1995 Kobe earthquake loadings. The preparation of the backfill mixture and its properties, the tested wall configurations, the reinforcement layouts and instrumentations, and the observed wall performance are described. Visual observations and test results indicate that walls having 0.4-m vertical reinforcement spacing, backfilled with soil containing a large percentage of fines, performed better than those having good-quality sandy soil under otherwise identical conditions. Vertical spacing of 0.8 m with removal of interlocking facing blocks in one of the walls did not lead to global collapse under repeated applications of the Kobe earthquake loadings. Only localized shear failure behind the top block layer was observed as the top facing blocks tended to topple. The good performance was attributable to apparent cohesion in the soil mixture stemming from soil matrix suction and true cohesion. Because this apparent cohesion is affected by the moisture content, its existence must be ensured by providing proper drainage to prevent seepage into the backfill. Considering the risk associated with the use of apparent cohesion, its exclusion from design is recommended.

The design of pier foundations in expansive soils is an important and challenging aspect of geotechnical engineering. Established methods for pier analysis include rigid and elastic methods. These methods have certain limitations that restrict their applicability to evaluate certain complex aspects of pier heave, including variable soil profiles, complex wetting profiles, large length-to-diameter ratios, and complex pier configurations and materials. To address those limitations, a method of analysis was developed providing a versatile and robust tool to predict both pier heave and axial forces developed by expansive soils. This method utilizes a standard finite-element code to solve for pier heave and force in the pier for the given boundary conditions. This paper contains both a discussion of the general design procedure and the finite-element formulation. This design procedure, including the finite-element code, accurately determines pier heave and force in a pier compared with field-measured data. The design procedure and the finite-element code in particular, address the limitations of the established rigid and elastic pier analysis methods with the flexibility to evaluate complex design situations. A comparison with field-measured pier heave and tensile force in the pier demonstrates that the design procedure accurately models both the magnitude of pier heave and force in the pier. The results obtained using this design procedure have been compared with those obtained using the established pier analysis methods for simplified drilled pier examples. The comparison of the various methods of analysis demonstrates that the finite-element design procedure predicts pier heave values that are generally less than the existing elastic and rigid pier analysis methods. It is believed that the proposed design method is more realistic and provides a design tool with improved accuracy compared with existing methods.

In this field trial, a new monitoring technique using distributed strain sensing known as Brillouin optical time-domain reflectometry (BOTDR) was introduced to monitor the behavior of bolted-concrete linings of a recently completed tunnel when a second bored tunnel was constructed side by side at a distance less than one tunnel diameter apart. This was done by measuring circumferential strains in 12 rings using optical fiber that was installed using the point-fixing method. The strain distributions around the circumference of the rings show a generally similar profile. Maximum compressive strains measured below the tunnel springline nearest to the excavated tunnel were larger than the maximum tensile strains measured at the tunnel crown, distorting the circular tunnel into an oval/ellipsoid that was about symmetrical to the horizontal axis. Several methods were introduced to compare strain measurements made by BOTDR and diameter changes recorded by tape extensometer. This involves the use of a symmetrical tunnel distortion model and the basic differential equation for a circular arch. The calculated results showed some degree of similarity between the two methods. The analysis highlighted the importance of measuring the axial strain in the tunnel ring and subtracting the axial strain component to calculate the actual deflection of the lining as a result of bending.

Leaching of four trace elements [cadmium (Cd), chromium (Cr), selenium (Se), and silver (Ag)] from soft organic soils stabilized with high carbon fly ashes (HCFAs) was assessed using water leach tests (WLTs) and column leach tests (CLTs) on soil alone, fly ash alone, and soil-fly ash mixtures. Concentrations from the WLTs on soil-fly ash mixtures were lower than concentrations from the WLTs on fly ash alone, and were controlled more by the fly ash than the soil. However, dilution calculations based on tests on soil alone and fly ash alone were unreliable. Thus, leaching assessments should be conducted directly on soil-fly ash mixtures. Leaching patterns from the CLTs followed first-flush and lagged-response patterns with comparable frequency, although first-flush patterns were more common with fly ash with higher calcium oxide content. Cd and Cr exhibited first-flush leaching more frequently, Ag a lagged-response pattern more frequently, and Se exhibited first-flush or lagged-response patterns with similar frequency. The hydrogen ion concentration (pH) had a strong effect on leaching concentrations, with lower concentrations of Ag and Cd and higher concentrations of Cr at a higher pH. Peak concentrations of Ag and Cd for flow-through conditions can conservatively be estimated as 50 times the WLT concentration, whereas a factor of 100 should be applied for Cr and Se for organic soil-HCFA mixtures.

This paper contains the results of a combined laboratory and field demonstration project exploring the use of dredged material (DM) blended with steel slag fines [SSF; 9.5 mm ($3/8\mathrm{in}.$) minus] as synthetic fill materials. The granular nature [a well graded sand (SW) soil], mineralogy, reactivity, and residual lime content of the SSF media make it well suited for blending with DM high-plasticity organic (OH) soil, so that geotechnical and environmental soil improvement occur simultaneously with one amendment. The source materials (100% DM, 100% SSF) were evaluated along with $80/20$, $60/40$, $50/50$, $40/60$, and $20/80$ DM-SSF blends (dry weight basis), where the DM content is reported first. Key findings include that the 100% DM had a ${\varphi }_{\mathrm{CI}\overline{\mathrm{U}}}^{\prime }$ of 27.3°, which increased to a peak ${\varphi }_{\mathrm{CI}\overline{\mathrm{U}}}^{\prime }$ value of 45° for the $50/50$ DM-SSF blend. The hydraulic conductivity ($k$) of the 100% DM (${10}^{-8}\mathrm{cm}/\mathrm{s}$) remained relatively constant until SSF content reached 80%, where an abrupt increase to ${10}^{-5}\mathrm{cm}/\mathrm{s}$ was observed. The field demonstration project confirmed that the DM-SSF blends could be easily blended to within $\pm 5\%$ of their target DM content. Trial highway embankments were constructed with 100% DM, 100% SSF, and the $80/20$, $50/50$, and $20/80$ DM-SSF blends to modified Proctor compaction goals ranging from 85 to 95% relative compaction on the maximum dry unit weight, depending on the blend. The average cone penetration test (CPT) tip resistance for 100% DM and 100% SSF media were approximately 1.3 and 57.3 MPa, respectively. The compacted $80/20$, $50/50$, and $20/80$ DM-SSF blend embankments were generally characterized by average CPT tip resistances on the order of 2.9, 6.2, and 11.6 MPa, respectively.

Microbially induced carbonate precipitation (MICP) using ureolytic bacteria shows promise in the field of geotechnical engineering for several different applications, such as ground improvement and groundwater control. This study examined optimal use and efficient control of Sporosarcina pasteurii to induce the precipitation of ${\mathrm{CaCO}}_3$ in open environments. Laboratory tests were conducted to investigate the effect of changing treatment factors, such as chemical concentrations, retention times, and effective input rates ($\mathrm{mol}/\mathrm{L}/\mathrm{h}$) on chemical efficiency. Chemical efficiency was measured based on weight measurements of ${\mathrm{CaCO}}_3$ precipitation compared with the amount of chemical reactants injected to samples. Based on the experimental results, the optimal time required for the precipitation process to take place in porous media for a specific range of bacterial optical density was determined. Results show that, below a certain urea and ${\mathrm{CaCl}}_2$ input rate ($0.042\mathrm{mol}/\mathrm{L}/\mathrm{h}$) and for a bacterial optical density (${\mathrm{OD}}_{600}$) between 0.8 and 1.2, the reaction efficiency remained high and the amount of precipitation was not affected by the liquid medium concentration (for input concentrations up to 1 M). However, the precipitation pattern at the pore scale was found to be affected by the injected concentration. Scanning electron microscopy images taken of different samples at different levels of cementation showed that, for the same amount of precipitation, the use of lower chemical concentrations in injections resulted in better distribution of calcite precipitation, especially at lower cementation levels. This variation in precipitation pattern is expected to affect the use of MICP for different applications.

The objective of this study is to investigate the relationships between the scalar particle shape descriptors and macroscopic dissipative properties of dry, clean sands. To define these relationships in a consistent and useful manner, it is important to identify and examine the relevant microscopic particulate shape characteristics and their effects upon the macroscopic strain-dependent damping ratio curves, $\xi (\gamma )$, as measured by resonant column procedures. The scalar particle shape descriptors are examined to determine the appropriate representative definitions for each of the three scales of particle shape (roughness, roundness, and sphericity). Quantitative mineralogy scanning technology and image analysis procedures are used to quantify these representative particulate descriptors and the specific surface for a significantly larger number of standardized sand samples’ constituent particles than previously examined. Particle descriptor data are projected to represent each of the standardized sands and then related to the shifts in small-strain $\xi (\gamma )$. From this study, it was found that the roundness and roughness were more influential shape scales than the sphericity, and three representative scalar particulate descriptors (specific surface, Hayakawa and Oguchi roundness, and solidity) display strong linear relationships with respect to the measures of the slopes of each sand’s $\xi (\gamma )$.

Rock instability and rockfalls are commonly preceded by the initiation and propagation of cracks. This process is accompanied by the release of microseismic energy, which can be detected by means of an appropriate monitoring system. Because an increase in rockfall events have been observed in the Matterhorn Peak area since 2003, in 2007 a microseismic monitoring system and a thermometric monitoring system were installed on the Italian side of the Matterhorn peak, close to the J. A. Carrel hut, as part of the Interreg IIIA Alcotra “PERMAdataROC” project. The objective of the installation was to determine whether this instability increase was connected to climatic fluctuations. Detailed analysis of the recorded microseismic data shows a spatial concentration of microseismic activity on the western side of the investigated slope, and a correlation of these data with thermal information shows that the temporal concentration of the microseismic activity could be traced back to the transitions from warm to cold periods. Cold periods, characterized by a continuous and rapid temperature decrease in time, incurred a higher average daily number of microseismic events.

Offshore piles are subjected to complex loading regimes that include both rapidly applied static and cyclic loads. This paper describes an experimental investigation conducted to assess the factors influencing the response of offshore piles to these loading conditions. The tests were performed using instrumented model piles installed in soft clay. During cyclic loading, the piles demonstrated a transition from stable to unstable behavior when the applied loads reached a specific load threshold. Stable behavior was defined when increments of plastic displacement decreased as the number of load cycles increased. During stable behavior, radial effective stresses at the pile-soil interface remained constant. During unstable behavior, pore pressures at the pile-soil interface rose as the number of cycles increased. This resulted in reduced radial effective stresses and progressively increasing displacement rates. Because of the presence of these excess pore pressures, the shaft resistance recorded during static load tests, performed after unstable cyclic loading, were lower than those measured on piles where the pore pressure was fully equalized. However, the axial resistance was seen to be rate dependent. Fast loading of the pile resulted in reductions of pore water pressure at the soil-pile interface and enhanced shaft resistance, which might overcome the negative effect caused by cyclic loading.

Dispersion analysis in surface wave testing is conventionally associated with a certain method of data acquisition, such as phase angle analysis in the two-station spectral analysis of surface wave (SASW) method and two-dimensional (2D) multistation wavefield transformation in the multistation analysis of surface wave (MASW) method. A new procedure has been developed to reconstruct the SASW data as MASW-imitating data, taking advantage of the 2D multistation wavefield transformation to better analyze the SASW data. Numerical simulations and a real-world example demonstrate the feasibility of this procedure, but also reveal an unwanted side effect associated with aliasing. A common-receiver survey is proposed for future experiments to eliminate this unwanted side effect and at the same time increase the lateral resolution.

The objective of this work is to examine the dynamics of soil-structure systems supported on isolated spread footings, in contradistinction with the rigid basemat often used in soil-structure interaction (SSI) studies. By considering a column-supported single-story structure on isolated footings, an explicit formula for the fundamental natural period of the system was obtained. This allows examination of the relative importance of the various system parameters that cause the natural period of the SSI system to increase compared with that of the corresponding fixed-base system. The key parameter is the relative stiffness of an individual column to the rocking stiffness of the corresponding footing. If this parameter is small ($<0.5$), there is little interaction (change in period $<20\%$). If it is large ($>4$), the base of the column behaves essentially as a hinge, and the natural period tends to double with respect to that of the structure on a rigid base because of the effect of rocking of the individual footings. The lateral and vertical stiffness of the individual footings play a lesser role. Numerical results for a particular model illustrate this effect.

Loose sandy soil subject to undrained shearing manifests deviatoric strain softening, and such a behavior has been referred to as collapse, static liquefaction, or instability. This paper uses the term instability and characterizes its triggering by the corresponding effective stress ratio, referred to as the instability ratio, ${\eta }_{IS}$. To capture the influence of fines on ${\eta }_{IS}$, the state parameter, $\psi$, as originally proposed by Been and Jefferies, was generalized to an equivalent granular state parameter, ${\psi }^{*}$. This is achieved simply by replacing the void ratio, $e$, with the equivalent granular void ratio, $e^{*}$. The conversion from $e$ to $e^{*}$ was achieved by a predictive approach, and backanalysis is not required. It was hypothesized that, provided the fines content is less than the threshold value, ${\eta }_{IS}$ and ${\psi }^{*}$, at the start of undrained shearing, can be described by a single relationship irrespective of the fines content. Two published databases and a series of undrained triaxial tests results are used to evaluate this hypothesis. The importance of this relationship is significant, because it can be used to predict ${\eta }_{IS}$ for sand with different fines content.

Experimental results concerning the in situ pullout resistance of dynamically driven nails are presented. These results show that the actual pullout resistance is much higher than that predicted by the classical approach. A dimensional analysis approach is proposed to find a formula describing the actual performance of such nails.