Canadian Geotechnical Journal
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Published By Canadian Science Publishing

1208-6010, 0008-3674
Updated Friday, 03 December 2021

Author(s):  
Rodrigo Carreira Weber ◽  
Enrique E. Romero Morales ◽  
Antonio Lloret

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.


Author(s):  
Chengcan Wang ◽  
Jin-Tae Han ◽  
Seokjung Kim

A waveform microiple(WMP) uses jet grouting method to generate shear keys along the pile shaft for improving the shaft resistance and cost efficiency. In this study,field loading tests were performed in this study to characterize the load sharing behavior upon inclusion of a waveform micropile (WMP) in a group of four micropiled-raft. First, single-pile compressive loading tests were conducted on three WMPs and five Type A micropiles (MP). Subsequently, a group-pile loading test was performed on a piled raft comprising 2 × 2 MPs and a central WMP. The load–settlements, axial stiffnesses, and load transfer mechanisms of individual MPs were analyzed during the tests, including the short- and long-term effects of the axial stiffnesses of the MPs on the load sharing ratio of the micropiled-raft. The single-pile loading test results revealed that the shear keys along the WMPs caused its bearing capacities and axial stiffnesses to be 1.5 times and 2–5 times higher than those of MPs, respectively. In the micropiled-raft loading test, the load sharing ratios of the MPs increased with their axial stiffnesses, and the highest load sharing capacity was exhibited by the WMP, which constituted 30% of the total load and 2–3 times that of MPs. Moreover, the influence of raft on the load-sharing capacity should be considered as well.


Author(s):  
C.W.W. Ng ◽  
Haiming Liu ◽  
Clarence E. Choi ◽  
Aastha Bhatta ◽  
Min Zheng

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.


Author(s):  
Joshua Potvin ◽  
David Woeller ◽  
James Sharp ◽  
W. Andy Take

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.


Author(s):  
Wenqi Ding ◽  
Dong Zhou ◽  
Xiaoqing Chen ◽  
Chao Duan ◽  
Qingzhao Zhang

Grouting reinforcement was used to improve rock strength and avoid seepage in rock engineering. A self-developed visualised test platform was developed and the influences of different fracture openness on grouting diffusion modes were revealed; the Bingham rheological model was imported to simulate the grouting diffusion process in a single plate fracture, the spatio-temporal distribution of the velocity field under different obstructions was determined using the finite element method. The results indicate that: 1) The grout diffuses faster with the increase of fracture openness, while a stagnation effect of the grouting diffusion velocity behind the obstruction occurs. 2) Due to obstructions, the grouting diffusion process can be divided into four stages: circular diffusion, flat diffusion, vortex diffusion, and butterfly diffusion. 3) The grouting diffusion area is divided into a fully-reinforced zone and a semi-reinforced zone, and the area of the latter increases with the fracture openness, while being little affected by the size of any obstruction. 4) Furthermore, some new grouting diffusion laws were revealed considering the asymmetrical arrangement of obstructions. The results presented in this work will be helpful for describing and predicting the grouting process in fracture networks.


Author(s):  
Noor M. Mohamed Nihaaj ◽  
Takashi Kiyota ◽  
Matthew Gapuz Chua

When disintegrated mudstone due to the slaking, subjected to hydraulic pressure, could lead to internal erosion. To examine the combined effects of slaking and internal erosion of gravelly mudstone in 1D deformation under a constant vertical load, a series of modified oedometer tests and laboratory penetration tests were conducted with drying/wetting and hydraulic pressure cycles. Some loading conditions showed the sever erosion in progressing of the cycle, susceptibility of the internal erosion was evaluated in terms of non-filter and fitter factors coefficient Keywords: Vertical strain, Slaking, Internal-erosion, Particle-breakage.


Author(s):  
Rajith Sudilan Dayarathne ◽  
Bipul C. Hawlader ◽  
Ryan Phillips ◽  
Dilan Robert

Coupled thermo-hydro-mechanical finite element (FE) modelling of thaw consolidation is presented. One-dimensional FE analyses are performed for thaw consolidation of a soil column due to self-weight and with a combination of self-weight and surcharge, with the linear and nonlinear void ratio–effective stress–hydraulic conductivity relationships of thawed soil. The nonlinear behaviour of thawed soil is modelled using a modified Drucker–Prager Cap model, while the hydraulic conductivity is varied with the void ratio. Finally, two-dimensional FE modelling of thaw consolidation around a warm pipeline buried in permafrost is performed. The rapid reduction of the void ratio with consolidation, especially at the low-stress level, results in a wide variation of hydraulic conductivity within the thawed zone. The significantly large hydraulic conductivity of soil elements along the curved thaw front, as compared to that of thaw consolidated soil, causes the flow of water along the thaw front, instead of a vertical flow, as assumed in previous 1-D thaw consolidation modelling of buried pipelines.


Author(s):  
Chandra Bhanu Gupt ◽  
Sanandam Bordoloi ◽  
Metta Niranjan Bhatlu ◽  
Sreedeep Sekharan

Compacted bentonite-sand (B-S) and bentonite-fly ash (B-FA) are established combinations for the construction of landfill liners. This study determined the upper and lower bounds of equilibrium hydraulic conductivity (keq) of amended bentonite under extended duration of flow. The keq for constant volume flow condition differed from free swelling condition by more than two orders of magnitude due to the difference in geomaterial interaction, microstructural changes, and mineralization. Considering constant volume and free swelling condition, B-FA mix with class F and class C fulfilled the hydraulic conductivity criterion up to 70 % and 30 % amendment, respectively. The higher keq observed for the B mixed with class C FA was attributed to the formation of porous calcium aluminium silicate hydrate gel and ettringite needle type minerals. The time taken to achieve equilibrium was inversely related to keq by a power relationship. The data from this study were used to propose empirical relationships for estimating keq (long-term) based on k obtained at 48 hours (short-term), plasticity and geomaterial type. The study reveals that FA can be used as an alternate for S as amendment material and keq based on free swelling condition should be used for designing the liner.


Author(s):  
Honglei Sun ◽  
Zili He ◽  
Xueyu Geng ◽  
Mengfen Shen ◽  
Yuanqiang Cai ◽  
...  

Vacuum preloading combined with prefabricated vertical drains (PVDs) system has been widely used to improve the soft clay with high water content. Clogging is usually formed around the PVDs during the vacuum preloading, impeding the propagation of the vacuum pressure and slowing down the consolidation process. In order to understand the forming mechanism of the clogging, particle image velocimetry (PIV) technique and particle tracking velocimetry (PTV) technique were adopted in the model test of vacuum preloading test. Through this study, three stages can be identified from the results of water volume discharge rate and maximum displacements versus time. In the first stage, the soil around the PVD is horizontal consolidated, which leads to the rapid formation of clogging. In the second stage, the formation of clogging slows down due to the loss of vacuum pressure, which further reduces the drainage. In the third stage, the clogging tends to be stable, and the drainage consolidation rate is significantly reduced. PTV results show that there is difference in the displacement of large and small particles during improvement. Two methods were proposed to estimate the thickness of clogging zone, reflecting a growing layer of clogging zone compressed around the PVD. This study provides new insights to investigate the formation mechanism of clogging during vacuum preloading test.


Author(s):  
Jeongki Lee ◽  
Dante Fratta ◽  
Idil Deniz Akin

We developed an experimental program to monitor how interparticle forces control fine-grained soils' mechanical behavior when saturation changes from the tightly adsorbed regime to saturation. The testing program uses stiffness (i.e., S-wave velocity) and strength (i.e., Brazilian tensile strength) tests on kaolinite, silica flour, and diatomaceous earth soil samples at very low confining stresses (< 5 kPa). Three fine-grained soils yield a range of different properties, including particle size, specific surface area, negative charge density, and internal/external particle porosity. Results show that shear stiffness and tensile strength follow similar trends, emphasizing that the same interparticle forces control the mechanical responses. In particular, the interpretation of S-wave velocity measurements shows three different behavior ranges: a van der Waals attraction range, a capillary-dominated interparticle forces range, and the continuous decrease in the capillary forces from the saturation at the air-entry pressure until full saturation. We show that the interparticle forces respond to a complex function of water content, particle size, particle separations, surface charge density, and the presence of internal particle porosity.


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