Canadian Geotechnical Journal Research Articles

Simulation of subway tunnel construction process based on fi-nite element analysis

Simulation of subway tunnel construction process based on fi-nite element analysis

Application of constitutive model in simulation analysis of tunnel construction

Application of constitutive model in simulation analysis of tunnel construction

Assessment of earthquake-induced liquefaction hazard in urban areas of Hanoi city using LPI-based method

Assessment of earthquake-induced liquefaction hazard in urban areas of Hanoi city using LPI-based method

The Uselessness of Elephants in Compacting Fill

This article is based on an article that was originally published in the August 1967 Canadian Geotechnical Journal (Vol. IV, Number 3).

Special Editorial for the 50th Anniversary Year of the Canadian Geotechnical Journal

Special Editorial for the 50th Anniversary Year of the Canadian Geotechnical Journal

Reply to the discussion by Wang and Dallo on “Hydraulic conductivity of saturated granular soils determined using a constriction-based technique” 1Appears in the Canadian Geotechnical Journal, 49(10): 1221–1222 [doi:10.1139/t2012-078

1. Equation [6] has been typed incorrectly and the correct equation is indeed the one given by the Discussers. The correct equation and its derivation have been given in the Ph.D. thesis of co-Author Nguyen (2012), and the computer program uses the correct equation. A corrigendum has already been submitted to the Canadian Geotechnical Journal giving the correct equation, which has subsequently been published (Indraratna et al. 2012). 2. The papers by Silveira (1965), Silveira et al. (1975), and Locke et al. (2001) discuss various aspects of the constriction-size distribution (CSD) corresponding to a given particle-size distribution (PSD). Locke’s (2001) Ph.D. thesis at the University of Wollongong extended the classical work of Silveira (1965) and Silveira et al. (1975) considerably. However, papers published later by Indraratna and Raut (2006), Indraratna et al. (2007), and Raut and Indraratna (2008) further extended the work of Locke et al. (2001) by introducing the novel concept of critical constriction size, Dc35. The Discussers have clearly overlooked the most important aspect that these recent papers have proposed in terms of critical constriction size for the accurate assessment of filtration effectiveness. 3. The Authors agree with the Discussers that the Kozeny– Carmen (KC) equation cannot be applied unless the void ratio is known or assumed. As the void ratios were not provided in past studies, the Authors employed the approach proposed by Aberg (1992) for the determination of the void ratios based on the PSD and associated relative densities. Given that this technique takes into account the compacted density in addition to PSD, indirectly, it can be considered equivalent to the CSD approach. 4. In this study, the Authors used the KC equation (eq. [2] in the paper) that is mathematically arranged to obtain another form (Carrier 2003) in which the shape factor, SF, captures the angularity ranging from 6.0 to 8.4. As the materials used for testing were mainly sand of high angularity, and having calibrated the experimental data for a range of SF values, the Authors determined SF 8.4 to be the most appropriate value for the KC equation for these angular sand particles. Any value of SF less than 8.4 within the range presented above will induce significant discrepancies (overprediction) when using the KC equation. Therefore, the data presented in Table 3 are related to SF 8.4. SF 1.36 cited by the Discussers is not appropriate for any realistic sandy material that contains predominantly angular grains. 5. The Authors agree that if the specific surface area is determined accurately, the predictions using the KC equation are proper. However, in this manner, using the KC equation requires more dependence and calibration using laboratory data, and this in itself shows the disadvantage of the KC equation. Empirically, SF needs to be estimated, presenting the inaccuracies of this approach. Therefore, the Discussers are correct in pointing out that poor predictions can be encountered if the surface areas of silty sands and similar particle gradations are not properly evaluated. Besides, for highly anisotropic materials, the KC equation hardly gives an accurate estimation of the hydraulic conductivity, and for materials such as uniform fine sand that are closer to being isotropic in pore distribution, Chapuis and Aubertin’s (2003) statement “. . . the KC equation provides good predictions for vertical hydraulic conductivity . . .” makes little sense. For very small particles, the Melvern particle-size analyser and other electronic and laser techniques are now being used for better estimation of the surface areas of particles.

Discussion of “A new theoretical method to evaluate the internal stability of granular soils” 1Appears in the Canadian Geotechnical Journal, 49(1): 45–58 [doi: 10.1139/t11-083

The authors mention that the constriction size distribution curve (CSD) was obtained according to Silveira (1965), and this method takes into account only the loose or dense soil relative density. Actually the method of Silveira (1965) takes into consideration only the densest soil state (maximum relative density). In that method, groups of only three particles are considered. The relations presented by the authors belong to the Silveira et al. (1975) method, in which Silveira et al. consider groups of four particles to represent the loosest soil state (minimum relative density). Equation [3] (in the paper under discussion) is basically applicable for the loosest soil state. To check its applicability for determining the CSD of the densest state, analyses were carried out through a computer program written by the discussers originally to determine the CSD for the densest and loosest soil states according to Silveira (1965) and Silveira et al. (1975), respectively. The program results were verified with some published data (e.g., Silveira 1965; Soria et al. 1993; Indraratna et al. 2007) and exact solutions were obtained. Small modifications were made to that program to determine the CSD for the densest state using the procedure described in the paper under discussion, i.e., determination of the angle a, which gives the minimum void area, instead of determination of the maximum void area as suggested by Silveira et al. (1975). The results of the analysis are shown in Fig. D1, in which the CSD curves for the densest state of the method (in the paper under discussion) and the method of Silveira (1965) are compared — it is obvious that there is a considerable difference between the two methods. The results of laboratory tests performed by Soria et al. (1993) show good agreement with the theoretical procedure of Silveira (1965), so the discussers believe that eq. [3] (in the paper under discussion) can not be applied to the determination of the CSD in the densest state. It is worth mentioning that, for the sake of comparison, the CSD curves shown in Fig. D1 are based on the finer percentage by weight, in accordance with the analyses carried out by Silveira (1965). Analyses (not included here) based on the finer percentage by number of particles using eq. [1] (in the paper under discussion) showed the same trend. The authors suggest that the percentages of finer are computed using eq. [1] (in the paper under discussion); actually, that equation represents the percentage of finer based on the number of particles, which over-represents the finer constrictions. Humes (1996) suggested that the percentage of finer based on surface area can represent the filtration analysis more accurately, with the percentage of finer based on surface area, PSA, computed using 1⁄2D1 PSAi 1⁄4 Pmi=Di XN i1⁄41ðPmi=DiÞ

Reply to the discussion by Dallo and Wang on “A new theoretical method to evaluate the internal stability of granular soils” 1Appears in the Canadian Geotechnical Journal, 49(7): 866–868 [doi: 10.1139/t2012-036

In the original paper the authors proposed a new method to evaluate the internal stability of a granular soil. The method determines the critical diameter of suffusion, Dc, defined as the diameter of the largest particle passing across the constrictions of the soil solid skeleton. In particular, the method evaluates the constriction soil distribution (CSD) by the soil numerical percentage grain-size distribution. The discussers show instead their results in terms of the soil weight percentage grain-size distribution. They maintain that the CSDs in terms of the soil numerical percentage grain-size distribution have the same trend of the CSDs in terms of soil weight percentage grain-size distribution. Actually, the CSDs using the soil numerical percentage grain-size distribution are completely different from the CSDs using soil weight percentage grain-size distribution because the mass and number grain-size distributions are very different as demonstrated by several authors (Musso and Federico 1983; Moraci 1992). Equation [3] of the original paper has been applied to a values changing from amin to amax (eqs. [4] to [7] in the original paper) obtaining, for instance, the Sv(a) versus a curve shown in Fig. R1, for the case of four spheres shown in Fig. R2. For the case of the densest state, the minimum value Sv min is considered, while in the case of the loosest state, the maximum value Sv max is considered. For intermediate states of density, Sv values were determined by the a value using eq. [8] in the original paper. The CSD curves obtained by Simulfiltr for the dense and loose states show diameters of constrictions smaller than those obtained by the Silveira (1965) and Silveira et al. (1975) methods in terms of the soil numerical percentage grain-size distribution. This result is due to the different method used to evaluate the diameter of the equivalent circle of the constriction inside the groups of three or four particles. In the method proposed by the authors (Simulfiltr), the diameter of constrictions has been evaluated as the diameter of the equivalent circle in terms of the ratio of area to perimeter of void inside the group of contact spheres, following the ASTM (2002) D6767 standard, as follows:

Discussion of “One-dimensional consolidation behavior of cement-treated organic soil” 1Appears in the Canadian Geotechnical Journal, 48(7): 1100–1115 [doi: 10.1139/t11-020

This discussion is an application of theoretical equations of compressibility given by the principle of natural proportionality to the interpretation of experimental oedometer test data of cement-treated organic soil.

Reply to the discussion by Jefferies, Been, and Olivera on “Evaluation of static liquefaction potential of silty sand slopes”1Appears in the Canadian Geotechnical Journal,49(6): 746–750 [doi: 10.1139/t2012-039

In regular beach sand, the direct sand grain to sand grain structure creates a strong framework that will tend to dilate, unless the sand structure is made unreasonably loose by moist tamping in which the sand grains are lightly wetted before deposition and tamping, a condition that rarely occurs in nature (Wood et al. 2008). The structure of silty sand may be stronger or weaker than clean sand depending on the location of the silt particles. If the silt particles are located in the voids between the larger sand grains, the effect of the silt is to increase the strength and decrease the liquefaction potential of the structure. But if the silt particles are located between the sand grains so as to separate the sand grains, then the structure is much weaker because forces act to crush the silt particles or to make them roll or slide out into the voids. Either way, the sand structure will contract and this will result in increasing pore pressures under undrained conditions. Thus, the mechanism of contraction observed in silty sand during plastic straining is based on the initial location of the silt particles between the sand grains so that the silt particles separate the larger sand grains. How much of the silt is located in the voids and how much is separating the sand grains is an important question for silt contents below approximately 30%. Above 30%, the silt particles are located both in the voids and between the sand grains and they all act to separate the sand grains, as discussed by Lade et al. (1998) and as shown in Fig. R1. Thus, above approximately 30% silt, the sand grains are floating in a matrix of silt particles and the larger sand grains are not in contact, which would form a stronger soil. As the silt content increases the compressibility increases (Lade et al. 2009), while the permeability decreases. Thus, the mechanism of soil structure collapse is likely different from that occurring at lower silt contents. The amount of silt that participates in producing a weaker structure has been addressed by Rahman et al. (2008) and Yamamuro et al. (2008). In addition, the type of silt, in terms of gradation, grain size, and shape, also influences the liquefaction potential of silty sands (Monkul and Yamamuro 2011). When drained tests are performed on loose silty sand and the stress ratio and volume change are plotted versus the axial strain, the resulting curves appear to show no influence of confining pressure, as indicated in Fig. 14 of the paper under discussion. Very similar behavior is obtained from drained tests on normally consolidated clays, as indicated by the SHANSEP concept (Ladd and Foot 1974). These results for normally consolidated (NC) clays, as well as results for any granular material (see e.g., Lee and Seed 1967), are plotted with reference to their initial void ratio at low confining pressures. Only if further analyses are made may the void ratio after consolidation be considered (see e.g., Lee and Seed 1967; Seed and Lee 1967). Thus, the plot in Fig. 14 is not unusual, and only for special purposes is the void ratio after consolidation employed in presentation of experimental results. In fact, preparing specimens at low confining pressures with the intent of reaching a certain void ratio at a given higher confining pressure is difficult. To circumvent this difficulty, Lee and Seed (1967) performed their analyses to predict the strengths under undrained conditions from the drained test results in terms of void ratio after consolidation as interpolated or extrapolated from tests performed on specimens prepared at four different initial void ratios.

Reply to the discussion by Fellenius on “Critical assessment of pile modulus determination methods”1Appears in the Canadian Geotechnical Journal, 49(5): 614–621 [doi: 10.1139/t2012-027

Reply to the discussion by Fellenius on “Critical assessment of pile modulus determination methods”¹Appears in the Canadian Geotechnical Journal, <b>49</b>(5): 614–621 [doi: 10.1139/t2012-027

Corrigendum: Strength mobilization in clays and silts

The range of settlements implied by the range of M = 2 in the database (shown in Fig. 10) is calculated as 2.2 to 65.1 mm. At the upper end of this range there would be serviceability concerns for most structures. Increasing M to 3.5 reduces this range to 0.9–25.5 mm. The upper end of this range roughly corresponds to an upper limit on tolerable settlements. This further underlines the finding of the paper that a large mobilization factor is needed for settlement control if no knowledge of soil stress–strain behaviour is considered. The authors apologise to the readers of Canadian Geotechnical Journal for these mistakes in the original paper.

Reply to the discussion by Lam and Jefferis on “Distribution of residual load and true shaft resistance for a driven instrumented test pile”1Appears in the Canadian Geotechnical Journal, 49(2): 244–245 [doi: 10.1139/t11-108

Reply to the discussion by Lam and Jefferis on “Distribution of residual load and true shaft resistance for a driven instrumented test pile”1Appears in the Canadian Geotechnical Journal, 49(2): 244–245 [doi: 10.1139/t11-108

Discussion of “Distribution of residual load and true shaft resistance for a driven instrumented test pile”1Appears in the Canadian Geotechnical Journal,48(4): 583–598 [doi: 10.1139/t10-084

The authors have presented a well-documented case study of the load test interpretation of prestressed high-strength concrete (PHC) piles, which are very popular in the Far East and are often favoured over steel piles on the basis of cost. Despite their popularity, well-analyzed load test case histories are rare and hence the authors’ paper is a valuable contribution to the technical knowledge base. Although the authors’ have considered the geotechnical aspects in detail, the discussers believe that this case study also would benefit from a fuller analysis of the structural conditions of the piles. This is because the authors have identified that the key design aspects for this site are actually the maximum load in the pile and the pile structural strength, but not the pile capacity. Based on the load test results, the authors concluded that the long-term maximum load in the pile will approach the pile structural strength and hence grouting the central void should be considered. The discussers have carried out an assessment of the pile strength using a different approach and compared the results with the current design guidelines. It was found that even with the central void grouted, the PHC piles are still not sufficiently robust and a different pile size or type may need to be considered. The discussers’ assessment and, where appropriate, comparisons with the authors’ results are described as follows.

Discussion of “Influence of particle size on the correlation between shear wave velocity and cone tip resistance”1Appears in the Canadian Geotechnical Journal, 48(4): 599–615 [doi: 10.1139/t10-092

Discussion of “Influence of particle size on the correlation between shear wave velocity and cone tip resistance”¹Appears in the Canadian Geotechnical Journal, <b>48</b>(4): 599–615 [doi: 10.1139/t10-092

Reply to the discussion by P.K. Robertson on “Influence of particle size on the correlation between shear wave velocity and cone tip resistance”1Appears in the Canadian Geotechnical Journal, 49(1): 121–123 [doi: 10.1139/t11-100

The authors would first like to thank the discusser for his interest and comments. The paper discussed here (Karray and al. 2011) shows, based on data from the Peribonka and CANLEX projects, that the ratio between shear wave velocity, Vs, and the cone tip resistance, qc, cone penetration test (qc– CPT), increases with increasing mean grain size, D50, in the case of granular material (D50 > 0.2 mm). The discusser indicates, however, that the tendency with D50 is reversed when compared with the relationships proposed by Robertson (2009) and Andrus et al. (2007). Responses to these concerns are discussed in the following.

Discussion of “A review of 41 legal cases involving geotechnical practice in Canada”1Appears in the Canadian Geotechnical Journal, 47(10): 1047–1059.

Discussion of “A review of 41 legal cases involving geotechnical practice in Canada”1Appears in the Canadian Geotechnical Journal, 47(10): 1047–1059.

Reply to the discussion by J.M. Oswell on “A review of 41 legal cases involving geotechnical practice in Canada”1Appears in the Canadian Geotechnical Journal, 48(4): 676–677.

Reply to the discussion by J.M. Oswell on “A review of 41 legal cases involving geotechnical practice in Canada”¹Appears in the Canadian Geotechnical Journal, <b>48</b>(4): 676–677.

Reply to discussion by Haghighi et al. on “Measurements of suction versus water content for bentonite–sand mixtures”Appears in the Canadian Geotechnical Journal 48(2): 336–337 (2011)

The discussers presented filter paper calibration data measured using the vapour equilibrium technique using a salt solution for suctions greater than 300 kPa and through a pressure plate apparatus, in which the filter papers sandwiched between two soil samples were equilibrated to the induced suction values. The data presented agree well with those obtained by the authors for the matric suction (or the in-contact) filter paper calibration up to about 800 kPa and for the total suction greater than 8000 kPa. It should be noted that the accuracy of the total suction measurement using the noncontact technique reduces as total suction decreases. In contrast, the error of the matric suction measurement using the in-contact filter paper increases with increasing matric suction. The total suction (or the noncontact filter paper) calibration data presented by the authors were obtained for total suctions greater than 4000 kPa. It is thought that the errors associated with the measurement of total suction lower than this value are high and are not only caused by the possible temperature gradient during calibration, but also by the error in preparation of the salt solution involving a small amount of salt. No attempt was made by the authors to induce total suction less than 4000 kPa due to the above-mentioned reasons. However, the data presented in Agus (2005) suggest that an extrapolation to total suction values between 2000 and 4000 kPa is possible, but with a maximum possible error of 860 kPa. The use of this technique for measuring total suction of less than 2000 kPa is not recommended. The discussers have shown that in the suction range from 4000 to 8000 kPa the measured filter paper water contents are lower than those presented by the authors for the same total suction values. Filter papers equilibrated to total suctions within this range will normally undergo a wetting process due to the initially relatively dry filter paper used. The amount of water absorbed by the filter paper during the equilibration period is a function of the equilibration time allowed. Equilibrium is thought to be attained after a relatively long equilibration time and is affected by the temperature fluctuation in the calibration system, or more importantly by the temperature gradient between the salt solution, vapor space, and filter paper. The discussers used a 2 week equilibration time as opposed to a 5 week equilibration time adopted by the authors. It is thought that the discussers’ data would be closer to those obtained by the authors if the same equilibration time had been used. The resulting total suction calibration curve will consequently be different from that obtained for the matric suction measurement. Similarly, the equibration time at high matric suctions (i.e., close to 1500 kPa) is thought to be long as water may transfer in vapor form without good contact between the ceramic disk and the filter paper during the matric suction measurement. At high matric suctions, filter paper tends to absorb a smaller amount of absorbed water than it should had a sufficiently long equilibration time not been allowed. Hence, although theoretically the technique can be used to measure matric suction as high as 1500 kPa, the calibration data for matric suctions ranging from 1000 to 1500 kPa are difficult to obtain with sufficient accuracy. In conclusion, reasonable measurement accuracy will be obtained when the filter paper technique is used to measure matric suctions of less than 1000 kPa, or total suctions of greater than 4000 kPa.

Discussion of “Use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks”Appears in the Canadian Geotechnical Journal: 46(12): 1379–1390.

Discussion of “Use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks”Appears in the Canadian Geotechnical Journal: <b>46</b>(12): 1379–1390.