2021

Permanent URI for this collectionhttps://hdl.handle.net/1807/104118

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Fusion of geotechnical and geophysical data for 2D subsurface site characterization using multi-sources Bayesian compressive sampling
(Canadian Science Publishing, 2021-12-13) Xu, Jiabao; Wang, Yu; Zhang, Lulu
Subsurface site characterization is essential for geotechnical engineering applications (e.g., slope stability analysis, deep excavation design), which is usually achieved through geotechnical site investigation and might be supplemented by geophysical survey. Geotechnical and geophysical investigations are complementary in many aspects. Geotechnical investigation provides direct measurement data with high accuracy but only at limited locations. On the other hand, geophysical survey provides abundant two-dimensional (2D) or three-dimensional (3D) measurements, but the data is often indirect. In addition, geotechnical and geophysical data are usually correlated. It is, therefore, beneficial for fusion of geotechnical and geophysical data during site characterization. This paper proposed a novel data fusion method, called multi-sources Bayesian compressive sampling (MS-BCS), for fusion of geotechnical and geophysical data and statistical characterization of 2D subsurface profiles. The proposed method is data-driven and non-parametric, without a need of an empirical parametric function between geotechnical and geophysical data. The proposed method was illustrated and validated using both numerical and real-life examples. The results show that the proposed method not only properly characterizes 2D subsurface profiles but also explicitly quantifies statistical uncertainty associated with the site characterization.
Model for predicting evolution of microstructural void ratio in compacted clayey soils
(Canadian Science Publishing, 2021-12-20) Yin, Penghai; Vanapalli, Sai
The hydromechanical behavior of compacted clayey soils is significantly influenced by its microstructure. The microstructural void ratio is a key parameter that is strongly associated with the microstructural state. The objective of this study is to provide a practical and reliable estimation approach for predicting the evolution of the microstructural void ratio of compacted clays soils subjected to wetting and drying paths. In this paper, the microstructural evolution of 12 clayey soils were investigated quantitatively using the mercury intrusion porosimetry (MIP) results. Based on this study, a comprehensive criterion has been developed for identifying different pore populations of compacted clayey soils for interpreting the MIP results. The “as-compacted state line” (ACSL) was proposed to estimate the initial microstructural void ratio of clayey soils at the as-compacted state. A incremental linear constitutive model was proposed for correlating the microstructural void ratio to the “microstructural average skeleton stress” in compacted clayey soils following monotonic wetting and drying paths. The developed approach is validated by providing comparisons between the predicted and interpreted microstructural void ratios for all the examined soils. The proposed approach can be extended in constitutive modelling of the hydromechanical behavior of compacted clayey soils by incorporating explicitly the microstructural information.
Consequences of drying on the hydro-mechanical response of fibrous peats upon compression
(Canadian Science Publishing, 2021-01-05) Zhao, Hongfen; Jommi, Cristina
Peats are encountered in waterlogged deltaic areas, where degradation is delayed by favourable environmental conditions. The recent increase in frequency and severity of droughts is expected to accelerate peats degradation, in turn increasing subsidence and flood risk, urging better understanding of the response of peats to drying events. To this aim, compression tests on natural and reconstituted peat samples were performed, supported by X-ray Micro Computer Tomography. The peat fabric is found to be the key factor in the response to drying, with fibres playing the most significant role. Drying in peats starts affecting the macro-fabric, with an irreversible reduction in volume and disruption of the fibrous network occurring under saturated conditions until a threshold void ratio is reached, below which desaturation occurs of the intra-fibres and intra-peds pores. The first drying stage decreases dramatically the compressibility, while the hydraulic conductivity is hardly affected due to enlargement of macropores. Secondary compressibility is affected by the peat fabric besides the organic content. The total organic content does not change substantially over drying, hence, it is not the best proxy to describe the consequences of drying on the response of fibrous peats. The fibre content can be better used to the aim.
Effects of the skew angle of new tunneling on an existing tunnel: Three-dimensional centrifuge and numerical modeling
(Canadian Science Publishing, 2021-12-06) Ng, C.W.W.; Wong, Yan Yan Annie; Shakeel, Muhammad
Tunneling results in stress relief and arching in the ground. New tunnel excavation beneath an existing tunnel but at different angles can lead to different patterns of stress redistribution. Studies on multi-tunnel interaction have mainly focused on perpendicular tunnels, and the effects of tunneling skew angle remain poorly understood. Three-dimensional centrifuge modeling and numerical back-analyses were conducted to investigate the effects of twin-tunnel interaction at three skew angles (30°, 60° and 90°). The effects of new tunnel excavation on an existing tunnel were simulated by controlling tunnel volume and weight losses in-flight. A hypoplastic soil model capable of simulating path-dependent and strain-dependent soil stiffness was adopted for the numerical back-analyses. Distinct load redistribution patterns were identified to explain deformations of the existing tunnel at different skew angles due to the advancement of the new tunnel. For 90° tunneling, hoop force increased at the crown and decreased at the left springline of the existing tunnel. The opposite responses were identified at 30° tunneling. A critical skew angle of 30° tunneling led to the maximum invert settlement and tunnel deformation of the existing tunnel. At 30° tunneling, the induced strain in the tunnel lining was 2.3 times larger than that of tunneling at 90°, exceeding the cracking limit suggested by the American Concrete Institute.
Theoretical and experimental investigations of anchoring force loss behavior for prestressed ground anchors
(Canadian Science Publishing, 2021-11-29) Zhu, Shimin; Chen, Changfu; Zhang, Genbao; Du, Cheng
Anchoring force loss is critically concerned for in-service performance of prestressed ground anchors. This time-dependent loss of pretension exerted at the anchor head is caused primarily by stress relaxation, which integrally manifests the rheological properties of the anchor and the geomaterial in which the anchor is embedded. A load-transfer modeling framework was established to derive the time-dependent anchoring force response. The modeling parameters were directly calibrated via element-scale pullout stress relaxation test using a specially developed setup. The applicability and effectiveness of this analytical modeling framework were verified via large-scale laboratory model tests and in-situ tests of prestressed anchors. The predictions derived using the presented modeling framework were in good agreement with measurements in both laboratory model tests and in-situ tests, particularly for evolutions of anchoring force over time. The sensitivity evaluation of the model parameters was performed to study their respective impact on the anchoring force loss response. This work can provide insights into the understanding of anchoring force loss behavior of prestressed ground anchors and facilitate their design practice for in-service performance.
Common characteristics between cyclic behaviour at different frequencies and monotonic behaviours of clay
(Canadian Science Publishing, 2021-09-13) Wu, Tingyu; Tong, Junhao; Sun, Honglei; Yuan, Zonghao; Guo, Lin
The loading frequencies in cyclic tests and the rate of strain or stress in monotonic tests have a significant effect on the soil behaviour, particularly of clayey soil. This study aims to determine the common characteristics of the behaviour of clay under cyclic loading at different frequencies and the relationship between cyclic and monotonic behaviours. Monotonic triaxial tests and cyclic triaxial tests at frequencies of 0.1 Hz and 0.001 Hz were conducted on undrained saturated reconstituted soft clay. The results show that the frequency of 0.001 Hz is sufficiently low to make the soil response comparable to that in monotonic tests. Second, there exists a unique ‘feature line’ for cyclic tests in the plot of allowable stress versus strain, independent of the frequency. Third, the feature lines for the cyclic and monotonic tests are close and parallel to each other. Therefore, although the cyclic and monotonic loadings are quite different from each other, there are connections between these different loadings in terms of the relationship between the allowable stress and strain.
Stability and load-displacement behaviour of axially cyclic loaded displacement piles in sands
(Canadian Science Publishing, 2021-11-17) Rimoy, Siya; Silva, Matias; Jardine, Richard J.
Uncertainties regarding the axial cyclic behaviour of piles driven in sands led to an extended programme of calibration chamber instrumented pile experiments. Broad trends are identified and interpreted with reference to normalised cyclic loading parameters Qcyclic/QT, Qmean/QT and N. Cyclic damage is shown to be related to changes in the radial effective stress regime close to the shaft. While stable loading leads to little or no change as cycling continues in the sand masses’ effective stress regime, high-level cyclic loading can affect stresses far out into the sand mass. The test systems’ chamber-to-pile diameter ratio has a significant impact on outcomes. Piles installed in loose, fine, sand are far more susceptible to cyclic loading than in denser, coarser sand. Little or no change in pile stiffness was seen in tests that remained within the stable cyclic region, even over 10,000 or more cycles. Unstable tests lost their stiffness rapidly and metastable cases showed intermediate behaviours. The permanent deflections developed under cycling depend on the combined influence of Qcyclic/QT, Qmean/QT and N. While model tests provide many valuable insights into the behaviour of piles driven in sand, they are unable to capture some key features observed in the field.
Compressibility and Permeability of Sand-Silt Tailings Mixtures
(Canadian Science Publishing, 2021-10-31) Fan, Jiying; Rowe, R. Kerry; Brachman, Richard W.I.
Microstructure showing the involvement of the fine and coarse grains in the soil skeleton is evaluated. Incremental loading tests using a stress-dependent permeameter are conducted on the mixtures of poorly graded sand and nonplastic fines originating from tailings. The results are compared with the published data of various tailings. It is shown that increasing the fines content from 0 to 100%, the involvement of the fine and coarse components of soil skeleton can be classified into four categories: no fines involvement (
A Coupled Bio-Chemo-Hydro-Mechanical Model for Bio-cementation in Porous Media
(Canadian Science Publishing, 2021-12-07) Mehrabi, Ronak; Atefi-Monfared, Kamelia
A key challenge involving microbial induced carbonate precipitation (MICP) is lack of rigorous yet practical theoretical models to predict the intricate biological-chemical-hydraulic-mechanical (BCHM) processes and the resulting bio-cement production. This paper presents a novel BCHM model based on multiphase, multispecies reactive transport approach in the framework of poroelasticity, aimed at achieving reasonable prediction of the produced bio-cement, and the enhanced geomechanical characteristics. The proposed model incorporates four key components: (i) coupling of hydro-mechanical stress/strain alterations with bio-chemical processes; (ii) stress/strain changes induced due to precipitation and growth of bio-cement within the porous matrix; (iii) spatiotemporal variability in hydraulic and stiffness characteristics of the treated medium; (iv) and velocity dependency of the attachment rate of bacteria. The fully-coupled BCHM model predicts key unknown parameters during treatment including: concentration of bacteria and chemical solutions, precipitated calcium carbonate, hydraulic properties of the solid skeleton, and in-situ pore pressures and strains. The model was able to reasonably predict bio-cementation from two different laboratory column experiments. The Kozeny–Carman permeability equation is found to underestimate permeability reductions due to bio-cementation, while the Verma–Pruess relation could be more accurate. A sensitivity analysis revealed bio-cement distribution to be particularly sensitive to the attachment rate of bacteria.
Using Synthetic Climate Datasets for Geotechnical and Geoenvironmental Design Problems
(Canadian Science Publishing, 2021-12-13) Bashir, Rashid; Sahi, Muhammad Abid Nawaz; Sharma, Jitendra
Location-specific climate datasets are required for the design and evaluation of a number of civil engineering projects. It requires huge effort to compile a multi-year quality-controlled climate dataset. In this paper, a method of generating simulated daily climate variables of interest from readily-available climate normal using a general purpose weather generator SIMETAW is presented. The accuracy of this method is assessed by comparing the climate datasets generated using SIMETAW with the recorded historical climate datasets for nine different sites across Canada with climates ranging from semi-arid to pre-humid. This comparison was done using visual presentations as well as statistical analyses of the two datasets. It was found that the multi-year daily climate datasets generated by SIMETAW using just 12 monthly climate normal values are fairly similar to the recorded historical climate datasets. The usefulness of SIMETAW-generated climate datasets was demonstrated by using them in numerical simulations of three different design problems, namely, infiltration into soils, swelling potential of an expansive soil, and soil cover design. From the results of these numerical simulations, it is concluded that the SIMETAW-generated multi-year daily climate datasets are satisfactory for use in the geotechnical and geoenvironmental problems of the kind simulated herein.
Calibration of resistance factors for bearing resistance design of shallow foundations under seismic and wind loading
(Canadian Science Publishing, 2021-12-08) He, Pengpeng; Fenton, Gordon A.; Griffiths, D.V.
Although the geotechnical resistance 19 factors at ultimate limit state used for dynamic loading conditions should be different from those for static loading conditions, most current structural and geotechnical design codes do not specifically provide dynamic resistance factors. In this paper, the ultimate limit state reliability analysis of individual shallow foundations for drained and undrained soil conditions under seismic (pseudo-dynamic) and wind loads using the Random Finite Element Method is carried out using the provisions of the National Building Code of Canada. The geotechnical resistance factors required to achieve target maximum lifetime failure probabilities are estimated for a few major Canadian cities. The results indicate that the failure probability for drained soil conditions is slightly greater than that for undrained soil conditions. In addition, the results suggest that the dynamic resistance factors for foundation bearing capacity design at ULS are lower than those for static foundation design specified by the code. The current analysis can be used to guide the calibration of these geotechnical resistance factors.
Field performance of four vibrating-wire piezometer installation methods
(Canadian Science Publishing, 2021-11-03) Young, Nathan Lee; Lemieux, Jean-Michel; Mony, Laura; Germain, Alexandra; Locat, Pascal; Demers, Denis; Locat, A.; Locat, Jacques
Vibrating wire piezometers provide a number of advantages over the traditional hydraulic piezometer design. There are currently many methods and configurations for installing vibrating-wire piezometers, the most common being: single piezometers in sand packs (SP), multilevel piezometers in sand packs (MLSP), and fully-grouted multilevel piezometers using either bentonite (FGB) or cement-bentonite grout (FGCB). This study assesses the performance of these four different installation methods at a field site possessing complex stratigraphy, including glacial and marine sediments. To accomplish this objective, pore pressure data recorded between December 2017 and July 2019 were analyzed. Data indicate that SP, MLSP, and FGB piezometers performed most reliably, based on the fact that piezometers installed at the same depth with these methods recorded similar pressure variations that were coherent with the hydrogeological setting. Of the two fully-grouted installations using cement-bentonite grout, one installation failed completely due to a hydraulic short circuit, likely caused by preferential flow occurring along the wires of the embedded instruments. The lack of a standard method for mixing cement-bentonite grout at the time of construction likely contributed to the failure of the FGCB installations, as the grout mixture used in this study was likely too viscous to provide a suitable seal.
Stratigraphic profiling, slip surface detection, and assessment of remolding in sensitive clay landslides using the CPT
(Canadian Science Publishing, 2021-01-01) Potvin, Joshua; Woeller, David; Sharp, James; Take, W. Andy
A multi-year cone penetration testing program was initiated at a landslide subject to episodic retrogression in Mud Creek, Ottawa, to assess whether a hand-operated mobile CPT could yield new insights into the current degree of remoulding under progressive failure in metastable areas of a landslide where conventional tracked rigs are unable to gain access. The mobile CPT rig permitted tests to be performed through the entire thickness of the Champlain Sea deposit at a penetration rate of 0.5 cm/s, with similar results to tests performed at the standard 2 cm/s. Measurements of pore pressure varied considerably with cone size, with the magnitude of pore pressure response decreasing with cone size. The elevation of the slip surface was identified in the tip resistance as the point of transition between the remolded soil above the slip surface and the intact soil below the slip surface, whereas a further 0.5 m of penetration was required to elevate pore pressures to values indicative of the intact soil behaviour. In-situ measurements of shear strength of corresponding layers between the intact and remolded profiles to be compared indicating that the soil above the slip surface had remolded to 50% of its fully remolded strength.
Assessment of Reclamation-induced Consolidation Settlement Considering Stratigraphic Uncertainty and Spatial Variability of Soil Properties
(Canadian Science Publishing, 2021-12-08) Shi, Chao; Wang, Yu
Consolidation analysis is a key task for reclamation design. Although consolidation is a long-term process, acceleration of consolidation is often preferred for speeding up the reclamations. Before proposing measures to accelerate consolidation and reclamation process, it is imperative to have an accurate prediction of consolidation settlement for fine-grained materials, which is greatly affected by spatial distribution of subsurface zones with different soil types (i.e., stratigraphic heterogeneities and uncertainty) and spatial variability of soil properties. In current practice, calculation of consolidation settlement often uses simplified stratigraphic boundaries and deterministic consolidation parameters without considering stratigraphic uncertainty or soil property spatial variability. The oversimplified practice might result in unconservative estimations of consolidation settlement and pose threats to safety and serviceability of constructed facilities on reclaimed lands. In this study, a stochastic framework is proposed for consolidation settlement assessment with explicit modeling of stratigraphic uncertainty and spatial variability of soil properties by machine learning and random field simulation from limited site investigation data. The proposed method effectively generates multiple realizations of geological cross-section and random field samples of geotechnical properties from limited measurements and offers valuable insights into spatial distribution of the estimated total primary consolidation settlement curves and angular distortion.
Strain Rate Effect on Static and Dynamic Behaviors of Eastern Canada Fine Grained Soils
(Canadian Science Publishing, 2021-08-27) Abdellaziz, Mustapha; Karray, Mourad; Betegard, Jeudy; Locat, Pascal; Ledoux, Catherine; Mompin, Rmi; Chekired, Mohamed
The assessment of the strain rate effect on the geotechnical properties of soils constitutes an important step toward a more accurate analysis of their response. This study presents the experimental results of monotonic and cyclic simple shear tests performed to examine the strain rate effect on the behavior of eastern Canada soils. Eight natural soils sampled from different locations in eastern Canada were used in this study. The tests were performed on a simple shear device using a strain-controlled mode. In addition to the obtained experimental results, published data in the literature were used to draw the conclusions of this study. Analysis of the data indicates that the undrained shear strength increases proportionally with the strain rate by approximately 10–17% per log cycle of . The results also show that the secant shear modulus G increases with the strain rate, especially at large strain amplitude. Moreover, the analysis of the data revealed that the magnitude of the strain rate effect seems to be correlated with the shear strain amplitude and plasticity index (Ip). A practical application of the outcomes on the backbone curves is given in which illustrates the influence of and on the strain rate effect.
Shear strength and yield surface of a partially saturated sandy silt under generalized stress states
(Canadian Science Publishing, 2021-11-24) Weber, Rodrigo Carreira; Romero Morales, Enrique E.; Lloret, Antonio
This paper studies the hydromechanical behavior of a slightly compacted mixture of sand and clayey silt (30%/70%) under a generalized stress state. The experimental study focused on analyzing the yielding response and shear strength behavior at different stress states (characterized by the intermediate principal stress parameter b, or Lode angle) and at different initial total suctions (as-compacted state). For the investigation, a hollow cylinder apparatus was used. The shear strength results allowed defining the variation of the critical state line with the Lode angle and the suction. Different models were proposed for isotropic and anisotropic yield surfaces, and their shape and rotation were calibrated with experimental results. The modeled yield surfaces fitted reasonably well the experimental results, considering their inclination and dependence on the suction, mean and deviatoric stresses and Lode angle. In addition, some relationships between the stresses and the model parameters were proposed to normalize the yield surface equation.
Effects of basal clearance on the impact dynamics of dry granular flow against dual rigid barriers
(Canadian Science Publishing, 2021-11-16) Ng, C.W.W.; Liu, Haiming; Choi, Clarence E.; Bhatta, Aastha; Zheng, Min
A basal clearance is usually designed beneath barriers to enable sufficient discharge to minimise the maintenance work over service life. Current design guidelines for multiple barriers usually neglect the influence of basal clearance, resulting in either an over-conservative or a non-conservative design impact force acting on the subsequent barriers. In this study, physical model tests were carried out to investigate the effects of basal clearance height (Hc) beneath first barrier on the interaction between dry granular flow and dual rigid barriers. A new approach based on the hydrodynamic equation is proposed to estimate the impact force on the second barrier exerted by the basal discharge from the first barrier. This basal discharge can attenuate the impact force exerted on the second barrier by dissipating the kinetic energy of landing flow and apportioning the load contributions from discharge and overflow. For the first barrier with a barrier height HB1 that was twice of the flow depth h0, the impact force on the second barrier was governed by overflow when Hc/h0 ≤ 0.6 and was dominated by basal discharge when Hc/h0 ≥ 0.8. These two criteria provide a basis for optimising the impact forces for multiple-barrier systems with basal clearances.
The Effects of Upstream Flexible Barrier on the Debris Flow Entrainment and Impact Dynamics on a Terminal Barrier
(Canadian Science Publishing, 2021-09-22) Vicari, Herv; Ng, C.W.W.; Nordal, Steinar; Thakur, Vikas; De Silva, W.A. Roanga K.; Liu, Haiming; Choi, Clarence E.
The destructive nature of debris flows is mainly caused by flow bulking from entrainment of an erodible channel bed. To arrest these flows, multiple flexible barriers are commonly installed along the predicted flow path. Despite the importance of an erodible bed, its effects are generally ignored when designing barriers. In this study, three unique experiments were carried out in a 28 m-long flume to investigate the impact of a debris flow on both single and dual flexible barriers installed in a channel with a 6 m-long erodible soil bed. Initial debris volumes of 2.5 m
Effect of microwave treatment on the thermal properties and dynamic splitting behavior of red sandstone
(Canadian Science Publishing, 2021-12-07) Yang, Chun; Hassani, Ferri; Zhou, Keping; Xiong, Xin; Wang, Famin; Shao, Yan
Microwave energy is a promising application in future rock breakage operations in the civil, mining, processing and space industries. Rock engineering projects frequently experience mechanical vibration and blasting impacts. Thus, understanding the dynamic fracturing behavior of microwave-treated rock is essential for its future application in microwave-assisted mechanical rock breakage. A customized industrial microwave system with a multimode resonant cavity was used to heat red sandstone at different microwave power levels (up to 4 kW) for a constant exposure time (4 min). The rock surface temperature distribution after microwave treatment was measured by an infrared camera. Dynamic splitting tests were conducted using a split Hopkinson pressure bar (SHPB) system in combination with a high-speed camera. Experimental results indicate that the rock dynamic splitting strength is negatively related to the microwave power, and the maximum reduction is 47.8%. Microwave treatment induced an obvious nonuniform temperature distribution and C-shaped surface cracks on disc specimens. During the dynamic splitting test, the crack induced by dynamic loading always initiates from the crack tip induced by microwave irradiation and then propagates along the loading diameter. The distribution of the inner high-temperature zone in the disc specimen is symmetric along the horizontal centerline of the disc specimen.
A MPM framework for large deformation seismic response analysis
(Canadian Science Publishing, 2021-10-12) Kohler, Marc; Stoecklin, Andreas; Puzrin, Alexander M.
Landslides are often triggered by earthquakes and can cause immense damage due to large mass movements. To model such large-deformation events, the material point method (MPM) has become increasingly popular in recent years. A limitation of existing MPM implementations is the lack of appropriate boundary conditions to perform seismic response analysis of slopes. In this article, an extension to the basic MPM framework is proposed for simulating the seismic triggering and subsequent collapse of slopes within a single analysis step. Original implementations of a compliant base boundary and free-field boundary conditions in the MPM framework are presented, enabling the application of input ground motions while accounting for the absorption of outgoing waves and the free-ground movement at the lateral boundaries. An example slope is analysed to illustrate the proposed procedure and to benchmark it against the results obtained using an independent simulation technique, based on a three-step FE analysis. The comparison generally shows a good agreement of the results obtained from the two independent procedures and highlights advantages of the presented “all-in-one” MPM approach, in particular for long duration strong motions.

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