Liquefaction characteristics of gap-graded gravelly soils in K0 condition

doi:10.1016/j.soildyn.2013.10.005

Soil Dynamics and Earthquake Engineering

Volume 56, January 2014, Pages 74-85

https://doi.org/10.1016/j.soildyn.2013.10.005 Get rights and content

Highlights

•
A stack-ring-reinforced membrane is used to perform K₀-CDSS tests.
•
The skeleton void ratio is a better packing index than the void ratio for gap-graded gravelly soils.
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The gravel content has only slight effect on CRRs of gravelly sands under a given e_sk.
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Gravel content correction should be used to evaluate CRRs of gravelly sands.
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A different CRR–V_s1 curve should be used to evaluate the CRRs of sandy gravels.

Abstract

A series of undrained cyclic direct simple shear tests, which used a soil container with a membrane reinforced with stack rings to maintain the K₀ condition and integrated bender elements for shear wave velocity measurement, were performed to study the liquefaction characteristics of gap-graded gravelly soils with no fines content. The intergrain state concept was employed to categorize gap-graded sand–gravel mixtures as sand-like, gravel-like, and in-transition soils, which show different liquefaction characteristics. The testing results reveal that a linear relationship exists between the shear wave velocity and the minor fraction content for sand–gravel mixtures at a given skeleton void ratio of the major fraction particles. For gap-graded gravelly sand, the gravel content has a small effect on the liquefaction resistance, and the cyclic resistance ratio (CRR) of gap-graded gravelly sands can be evaluated using current techniques for sands with gravel content corrections. In addition, the results indicate that the current shear wave velocity (V_s) based correlation underestimates the liquefaction resistance for V_s values less than 160 m/s, and different correlations should be proposed for sand-like and gravel-like gravelly soils. Preliminary modifications to the correlations used in current evaluations of liquefaction resistance have thus been proposed.

Introduction

Gravelly soils may be encountered in natural soil strata, such as residual, fluvial, alluvial, and glacial deposits, as well as man-made fills such as embankments and reclaimed gravelly fills. Despite the high hydraulic conductivity and high small strain modulus of such soils, liquefactions of loose to medium dense gravels and gravelly sands have been observed in major earthquakes (e.g., [1], [2], [3]). Previous studies on liquefied case histories reveal that most liquefiable gravelly soils are sand–gravel mixtures ([4], [5]), and natural gravelly soils are mostly well-graded with smooth grain size curves [5]. Kazama et al. [6] studied liquefied gravelly sites and concluded that the gravel content could be up to 80%. The liquefied case histories of gravelly soils used by Andrus and Stokoe [7] to establish the correlation between the normalized shear wave velocity (V_s1) and cyclic resistance ratio (CRR) show that the fines content (FC) for liquefied natural gravelly soils is less than 5%, and that the highest FC for liquefied man-made fills is 18%. In general, the majority of liquefiable gravelly soils are thus well-graded sand–gravel mixtures with a small fraction of fines.

Previous studies on the liquefaction characteristics of gravelly soils can be divided into post-earthquake field investigations and laboratory tests on undisturbed and remolded specimens. Based on the results of post-earthquake site investigations, empirical correlations have been proposed that relate the blow count of the Becker penetration test (BPT) to the CRR ([8], [9]) and normalized shear wave velocity (V_s1) to the CRR [7]. In the CRR-BPT correlation, the BPT blow count is converted to an equivalent blow count of the standard penetration test (SPT-N), and CRR-(SPT-N) correlations for sand are used to evaluate the CRR of gravelly soils. In the shear wave velocity based liquefaction evaluation procedure, gravelly soils and sand use the same correlation. The current practice for liquefaction evaluation of gravelly soils thus implies that gravelly soils behave as sandy ones.

Laboratory liquefaction tests on remolded samples and undisturbed frozen specimens have provided insights into the liquefaction characteristics of gravelly soils. Kokusho and Tanaka [10] performed large triaxial tests on both undisturbed frozen specimens recovered from liquefied gravelly soil sites as well as reconstituted specimens, and found that the undrained cyclic strength of the former is significantly higher than that of the latter. Evans and Zhou [4] performed triaxial tests on reconstituted specimens to study the effects of gravel content on the liquefaction characteristics of gap-graded sand–gravel composites, and concluded that the liquefaction resistance increases with increasing gravel content. However, laboratory data reported by Siddiqi [11], and field and laboratory investigations of liquefied gravelly decomposed granite soil in Japan after the 1995 Hyogoken-Nambu earthquake, indicated that the gravel content did not significantly influence the liquefaction resistance of gravelly soils [6]. These conflicting conclusions indicate that the current understanding of the effects of gravel content on the liquefaction characteristics of gravelly soils is incomplete.

According to a survey by Lo Presti et al. [12], cyclic tests on gravelly soils are often conducted using triaxial and torsional shear devices with cylindrical specimens of up to 820 mm in height. In triaxial tests, a ratio of 6–8 between the specimen diameter and maximum particle size is considered necessary for meaningful results [13]. For triaxial testing on gravelly soils, membrane compliance has been shown to significantly affect the undrained cyclic loading behavior of the soils [14]. Additionally, the CRR obtained from triaxial testing must be multiplied by a correction factor that takes into account the differences in shearing modes and stress conditions in cyclic triaxial testing conditions from those of the in situ soil stratum subjected to upward propagating shear waves [15]. Furthermore, Chang [16] studied the effects of soil subjected to multi-directional horizontal shaking, and concluded that a simple shear system capable of inducing radial shear strain on the vertical plane is the best representative shear mode to mimic the in situ cyclic shearing conditions. Therefore, a cyclic simple shear system without membrane compliance effects is preferred to represent the field conditions and study the liquefaction characteristics of gravelly soils.

Gravel deposits are normally well-graded, with a smooth grain size distribution curve. Due to the limitations of testing devices, scalping of oversize particles is generally adopted in laboratory testing, which may underestimate the prototype undrained cyclic strength. Wong et al. [13] stated that the undrained cyclic resistance of well-graded gravelly soils is smaller than that of uniformly-graded soils for reconstituted specimens, and that the undrained cyclic strength will increase 10% as the specimen diameter increases from 2.8 in. to 12 in.. However, Kokusho et al. [5] performed cyclic triaxial tests on reconstituted gravelly soil specimens and concluded that the undrained cyclic strength of such soils is mainly dependent on the relative density rather than particle gradation. To reduce the complexity of describing the soil packing condition and address the quantitative effects of gravel on the liquefaction characteristics of gravelly soils, the intergrain state concept that considers the microstructure of particle packing is adopted here to categorize the soil types and interpret the behaviors of gap-graded sand–gravel mixtures subjected to undrained cyclic loadings.

A cyclic simple shear system using a stack-ring-reinforced membrane was used to perform liquefaction tests under K₀ conditions on sand–gravel mixtures. Using the intergrain state framework, sand–gravel mixtures are classified as sand- or gravel-like soils depending on the amount of gravel content. The effects of gravel content on sand-like soils and sand content on gravel-like soils are discussed in this work. In addition, bender elements are integrated in the simple shear system to study the CRR–V_s1 correlation. Preliminary modifications are proposed to the CRR evaluation of gravelly soils with V_s1.

Section snippets

Void parameters in intergrain state

The intergrain state concept has been used to describe the engineering properties of mixed soils, such as the strength of sandy gravels [17], the liquefaction resistance of silty sands [18], and the liquefaction resistance of sandy-gravel composites [4]. In natural soil deposits, packing conditions and void distribution are complicated, due to the large variations in particle size and deposition conditions. Binary packing models have thus been proposed to rationally characterize the packing

Testing apparatus

The stress condition of an in situ soil element prior to cyclic loading is under K₀ conditions, at which lateral deformation is prohibited and the coefficient of lateral earth pressure is equal to K₀. When a soil element is subjected to upward propagating shear waves, horizontal shear stress is superimposed on the K₀ condition. The stress state and shearing mode can be modeled by a K₀-CDSS system. To maintain the K₀ condition throughout the entire testing process, a soil container capable of

Summary of testing results

A summary of the K₀-CDSS liquefaction test results for sand–gravel mixtures is presented in Table 2, Table 3 for sand- and gravel-like soils, respectively. Pure sand (SC=100%) at a sand skeleton void ratio of 0.70 and pure gravel (SC=0%) at a gravel skeleton void ratio of 0.58 were used as the batch tests. The typical testing results, including time histories of shear stress, shear strain, excess pore pressure ratio ( $r_{u} = Δ u / σ_{v o}^{'}$ , where Δu is the excess pore water pressure), and hysteretic loops

CRR for gap-graded gravelly sands

The variations of CRR_M=7.5 of sand-like soils with various gravel contents at the two sand skeleton void ratios are plotted in Fig. 10. For sand-like soils, the CRR_M=7.5 increases as the sand skeleton void ratio decreases, which is similar to the trend seen for clean sand or sand with a small fraction of fines content (FC<10% in Chang and Hong [20]). Due to the metastable packing condition, the soil with GC=60% has the lowest CRR_M=7.5 at a given sand skeleton void ratio.

For gap-graded gravelly

Conclusion

A stack-ring-reinforced membrane was developed in this work for performing CDSS tests under K₀ conditions. A series of undrained K₀-CDSS tests on reconstituted sand–gravel mixtures with shear wave velocity measurements using integrated bender elements were performed to study the liquefaction characteristics of gap-graded gravelly soils with no fines content. The intergrain state concept was used to categorize the sand–gravel mixtures. The testing results and findings are summarized below.

(1)
Based

Acknowledgments

This study was supported by the National Science Council, Taiwan, under Grant NSC96–2211-E-260-019, which is gratefully acknowledged. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors, and do not necessarily reflect the views of the National Science Council, Taiwan.

References (30)

M. Kazama et al.
Liquefaction and settlement of reclaimed ground with gravelly decomposed granite soil
Soils Found
(2003)
W.J. Chang
Evaluation of undrained shear strains in multi-directional horizontal shaking
Soil Dyn Earthquake Eng
(2011)
S. Thevanayagam et al.
Liquefaction in silty soils screening and remediation issues
Soil Dyn Earthq Eng
(2002)
T. Kokusho
Correlation of pore-pressure B-value with P-wave velocity and Poisson's ratio for imperfectly saturated sand or gravel
Soils Found
(2000)
J.P. Koester et al.
In situ investigation of liquefiable gravels
Transportation Res Rec TRB
(2000)
P.S. Lin et al.
Damage investigation and liquefaction potential analysis of gravelly soil
J Chin Inst Eng
(2002)
Z. Cao et al.
Distribution and characteristics of gravelly soil liquefaction in the Wenchuan Ms 8.0 earthquake
Earthq Eng Eng Vib
(2010)
M.D. Evans et al.
Liquefaction behavior of sand–gravel composites
J Geotech Eng, ASCE
(1995)
T. Kokusho et al.
Undrained shear strength of granular soils with different particle gradations
J Geotech Geoenviron Eng ASCE
(2004)
R.D. Andrus
Stokoe, KHII. Liquefaction resistance of soils from shear-wave velocity
J Geotech Geoenviron Eng ASCE
(2000)

L.F. Harder et al.

Determination of penetration resistance for coarse-grained soils using the Becker hammer drill

(1986)

A. Sy et al.

Becker and standard penetration tests (BPT–SPT) correlations with consideration of casing friction

Can Geotech J

(1994)

T. Kokusho et al.

Dynamic properties of gravel layers investigated by in-situ freezing sampling

F.H. Siddiqi

Strength evaluation of cohesionless soils with oversized particles

(1984)

D.C.F. Lo Presti et al.

Stress–strain–strength behaviour of undisturbed and reconstituted gravelly soil samples

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Liquefaction characteristics of gap-graded gravelly soils in K0 condition

Highlights

Abstract

Introduction

Section snippets

Void parameters in intergrain state

Testing apparatus

Summary of testing results

CRR for gap-graded gravelly sands

Conclusion

Acknowledgments

Soils Found

Soil Dyn Earthquake Eng

Soil Dyn Earthq Eng

Soils Found

In situ investigation of liquefiable gravels

Transportation Res Rec TRB

Damage investigation and liquefaction potential analysis of gravelly soil

J Chin Inst Eng

Distribution and characteristics of gravelly soil liquefaction in the Wenchuan Ms 8.0 earthquake

Earthq Eng Eng Vib

Liquefaction behavior of sand–gravel composites

J Geotech Eng, ASCE

Undrained shear strength of granular soils with different particle gradations

J Geotech Geoenviron Eng ASCE

Stokoe, KHII. Liquefaction resistance of soils from shear-wave velocity