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Tunneling in karstic geology confronts numerous challenges due to unpredictable occurrence of voids. The current approach of karstic void risk assessment is qualitative or semi-quantitative and lacks consideration of the spatial variability and distribution of voids. This often influences the pricing strategies, and design and construction activities on tunnel projects. This paper presents a geostatistical modeling-based methodology to develop a quantitative assessment of karstic void risk for a tunnel project in a karstic geological setting. The methodology is applied on an actual mixed-ground tunnel project situated in a karstic geological environment in Malaysia. The geology at the tunnel project site consists of sedimentary rock formations with limestone as the predominant rock type overlain by weak sedimentary residual soils. Pluri-Gaussian simulation (PGS) technique, a stochastic geostatistical-modeling algorithm, is applied to characterize the spatial distribution of voids in 3D along tunnel alignment. Simulations from PGS take into consideration the anisotropic distribution of voids on the tunnel project site. PGS utilizes void data from borehole investigations to model different void sizes (Vs) as categorical variables. The variability in multiple realizations from PGS technique is used to quantify the uncertainty in occurrence probabilities, number, and frequency of karstic voids. The proposed methodology demonstrates the ability to develop probabilistic estimates of occurrence frequency of different void sizes. Probabilistic assessments indicating 95% confidence interval (CI) on number of voids and respective occurrence probabilities are presented. The probabilistic assessment results are applied to estimate the grout quantity required for void treatment, while considering uncertainty in void occurrence. A minimum, mean, and maximum cumulative grout volume of about 2000 m3, 4000 m3, and 8000 m3 (for 95% CI), respectively, is estimated along the alignment.

The application of geostatistical analyses of site investigation data for tunneling projects has gained significant attention in the literature. While the proposed techniques are useful for...

Urban soft-ground tunneling projects involve significant risks related to the spatial variability and uncertainty in geotechnical parameters. However, standard practice typically does not i...

A novel application for outlier detection is in ground deformation monitoring. During any type of underground construction in urban settings, sensors are placed on the ground surface to monitor the vertical displacement with the goal of ensuring that there is no substantial heaving or settling of the ground. As a result, a large spatial-temporal data set is produced, but the sensors are often very sensitive, and spurious readings are commonly observed, resulting in both random and systematic outliers. In this work, we present a novel, fast spatial-temporal quality control procedure that is designed to remove these spurious readings prior to subsequent ground deformation monitoring. First, a robust kriging model is applied to the spatial ground deformations at each time point to remove systematic errors; next, an exponential moving average model is applied to the time series of ground deformations at each station to remove random outliers. A case study using ground deformation data when four subway tunnels are bored under a railyard in Queens, New York is used to illustrate the methodology. Methods used to construct outlier bounds are described, and the accuracy of our outlier detection approach is evaluated by calculating the percentages of outliers detected in an introduced artificial outlier set.

Ground volume loss induced by shield tunnel construction is the major factor leading to ground settlement and deformation. The general equations predicting surface settlement based on ground volume loss involve a settlement trough width coefficient (parameter i) which in previous models was set as a constant in both the transverse and longitudinal directions. In this work, the equations predicting surface settlement during the construction were modified by introducing the parameter j – the width coefficient in the longitudinal direction, assumed to be different from that in the transverse direction. A model shield machine was adopted to carry a laboratory test under 1 g to investigate surface settlement induced by earth-pressure-balance shield tunnel construction in unsaturated sandy soil. The surface settlement during the excavating observed in the test was compared with that predicted by general equations from previous studies and the modified. The results showed that surface settlement above shield machine obtained by the modified equation proposed here fits the test data better than those obtained by the general equations because of the introduced longitudinal width coefficient.

Recent extreme weather with heavy rainfall has brought new challenges to the operation of a karst tunnel as a large amount of groundwater flowing toward the tunnel in a short time exceeded the drainage capacity and caused high external water pressure. By evacuating the air in the inner space of the tunnel structure, an apparatus was developed to simulate the external water pressure on the tunnel structure. It was also employed to study the behavior of a highway tunnel structure with a large cross section considering cavities behind the liner. The results showed that the bending moment of the liner increased with the external water pressure, which helps to decrease the nonuniform distribution of the thrust force, and the maximum bending moment and eccentricity were generally located at the knees or side walls. Lower external water pressure contributed to reducing the eccentricity of the liner while higher external water pressure does not further reduce the eccentricity. Under external water pressure, fractures appeared first at the knee, then at the invert and finally at the vault. The air tightness tests under external water pressure also showed that the cavity decreased the bearing capacity of the liner and significantly aggravated the fractures in the liner nearby. The results help to estimate the bearing capacity of the liner under external water pressure, and the method of simulating external water pressure can also be used to study tunnels with different cross section geometries.

This paper examines the role of slurry TBM operational parameters, namely face, annulus and grout pressures, on ground deformation. The analysis includes both field data and computational modelling. Field data from the very successful Queens bored metro tunnels (6.9 m diameter) project in New York City is employed to illustrate phenomenologically how ground deformation was controlled via slurry TBM parameters. Computational modelling is then employed to support the experimental findings and to further investigate the relative influence of TBM parameters through parametric analysis. The results quantify the importance of the various pressures on controlling ground deformation.

A dynamic finite element (FE) model of lightweight deflectometer (LWD) loading on a two-layer soil system, validated with an analytical solution and experimental data, is presented. Peak dynamic FE vertical deflections can be substantially different (almost always smaller) than FE static deflections. The numerically simulated measurement depth of the LWD center sensor is found to be 2–2.5 times the plate diameter, deeper than other experimental studies. Using the FE model, we conduct a sensitivity analysis of peak vertical deflections to the top layer Young’s modulus and underlying Young’s modulus of two-layer systems. Peak deflections from the center sensor are found to be more sensitive to the top layer Young’s modulus while peak deflections at radial offsets are found to be more sensitive to the underlying layer Young’s modulus. Sensitivities of layer moduli to FE deflections offer guidance in selecting weighting factors for the inverse solver in an LWD back-calculation procedure.

Ground-based interferometric radar (GBIR) monitoring was conducted on a slow-moving, translational failure landslide in Granby, Grand County, Colorado, USA. Radar monitoring was completed over two separate surveys in 2011 using a tripod mounted real aperture sensor. The purpose of this work is to evaluate GBIR as a temporally dense monitoring technique for monitoring landslide displacement and compare the monitoring results to ongoing GPS based surveying methods to verify measured displacements. We discuss the strengths and limitations of GBIR displacement monitoring with a variety of available sensors, and place this monitoring platform, sensor, and workflow into context of previous slope stability monitoring with GBIR. For both surveys, displacement time series were created through a small temporal baseline stacking to reduce noise and maintain high temporal resolution. The results of the displacement time series were compared to average displacement rates derived from GPS based surveying. An overall verification of radar and GPS derived displacement rates was achieved, and identifies important differences relating to the precision and uncertainty of the two techniques. This work demonstrates GBIR monitoring capability of establishing high temporal resolution on tracking variable rates of landslide movements. Spatial modeling of total observed displacements was completed for both surveys verifying a conceptual model of uniform translational landslide movement, providing greater confidence for mitigation planning.

The lightweight deflectometer (LWD) is a portable device that measures surface deflections and applied force, from which dynamic stiffness and elastic modulus can be estimated. The inclusion of radial offset sensors with LWD testing, referred to here as multiple sensor LWD testing, stemmed from the well-established falling weight deflectometer (FWD) testing method. However, little research exists in the literature addressing LWD use on stabilized or lightly bound layers with multiple sensors, or exploring the applicability of backcalculating/isolating layer moduli from multiple sensor LWD tests. To this end, over 200 multiple sensor LWD tests on stabilized base materials were performed at five sites and rigorously analyzed to determine if the test could capture growth in stabilized base stiffness while the underlying subgrade layer remained unchanged. Deflection results demonstrate that the LWD test is capable of detecting changes in the stiffness of the stabilized base material during curing as i...

This study examined the relationship between soil physico-chemical parameters and unconfined strength in various fine-grained soils when mixed with chemical additives. To be considered effective, the soil-additive mixture must exhibit a strength increase of at least 345 kPa (50 psi). The research focused on AASHTO Soil Group Classifications falling under the fine-grained soil category (A-4 to A-7). Additive amounts are given for Fly Ash (FA), Cement Kiln Dust (CKD), and Lime (hydrated and quick lime). The results of this study suggest that the surface area is perhaps the most important factor in determining if a chemical additive will be effective for stabilization. Out of the eight tested soils, the seven soils with surface areas lower than 150 m 2 /g reached the 345 kPa strength gain with the different additives. However, the one soil with a surface area higher than 150 m 2 /g never reached the strength gain with any of the additives used at any of the tested percentages.

The lightweight deflectometer (LWD) and falling weight deflectometer (FWD) are in situ dynamic plate load tests used to estimate the stiffness and elastic moduli of bound and unbound materials. The inclusion of radial offset sensors with LWD testing stemmed from the well-established FWD testing method of using deflections at the load plate center and at radial offsets to generate a deflection bowl to estimate the moduli of individual layers in a multi-layer system. Due to the similarities between the LWD and FWD tests, several studies have explored the relationship between center deflection results of the two tests. However, little research exists in the literature addressing LWD testing with multiple sensors and how well those deflections correlate with FWD deflections at the same radial offsets. To this end, 114 multiple sensor LWD and FWD tests were performed on stabilized base materials at three sites and rigorously analyzed to determine if there is a consistent relationship between LWD and FWD center and radial offset deflections across all sites and if the estimated moduli from the same backcalculation approach produce similar or correlated results. The results demonstrated that while relationships are site specific for deflections and moduli estimated from the load plate center, a consistent relationship across all sites is demonstrated from the radial offset measurements. Finite element analysis was conducted to understand the difference in induced strains from the two tests to support and better understand the observed differences in FWD and LWD deflections and backcalculated layer moduli.