Research PaperTime-dependent load transfer behavior of grouted anchors in laterite
Introduction
Laterite refers to a type of maroon clay formed by the weathering (or laterization) of carbonate rocks or rocks rich in iron and aluminum oxides in hot and humid climates (Tan and Kong, 2006, Lin, 1989), which exists widely in humid areas with abundant rainfall in Southern China (Huang and Fu, 1998, Cheng et al., 2004). In recent decades, a large number of laterite slopes supported by grouted anchors have been formed in Southern China owing to the plentiful construction of basic infrastructural facilities, such as tunnels, railways, etc. (Zhang et al., 2015, Chen et al., 2014, Zhang et al., 2018, Luo et al., 2003, Ehrlich and Silva, 2015). Laterite has the characteristics of easy softening in water, strong plasticity and easy creep because of a high content of hydrophilic minerals (Zhang et al., 2015, Chen et al., 2014, Zhu et al., 2019, Chen et al., 2019). Consequently, the time-dependent mechanical behaviors (creep and stress relaxation) of grouted anchors become the key factor in determining the long-term stability of anchored laterite slopes.
The mechanical properties of grouted anchors are decisively dependent on the grout - soil interface shear behavior. Previous studies on interface shear behavior (Hong et al., 2017, Borana et al., 2017, Kim et al., 2013, Zhu et al., 2011, Chu and Yin, 2005, Su et al., 2010, Chen et al., 2015, Gurpersaud et al., 2013, Ye et al., 2017) or load transfer behavior of grouted anchors (Farmer, 1975, Hong et al., 2017, Huang et al., 2012, Ren et al., 2010, Martín et al., 2011, Ma et al., 2016, Chen et al., 2019) mainly focused on the working condition with short-term load. However, when adopting grouted anchors as long-term supporting structures in geotechnical engineering, much attention shall be paid on the time-dependent behavior (including creep (Chen et al., 2016, [Zhang et al, 2015]) or stress relaxation (Shi et al., 2019, Chen et al., 2018)). Otherwise, rheological damage could occur during the service period (Yang et al., 2014).
The creep phenomena of grouted anchors comes down to tensile creep of the anchor bar, shear creep of the surrounding soil and shear creep on the grout - soil interface. Among them, the interface shear creep behavior between grout and soil is the most intricate point that directly determines the long-term bearing capacity of grouted anchors (Chen et al., 2016). Some researchers have studied the influence of various factors (such as physical properties of soil (Zhang et al., 2020); grouting pressure (Chen et al., 2019) and in-service environment (EI Menoufy and Soudki, 2014)on the interface shear creep behavior between grout and soil through long-term (creep) pullout tests for element specimens of grouted anchors. Furthermore, for characterizing the interface creep behavior of the grouted anchors, several rheological models (such as empirical rheological model with hyperbolic form (Chen et al., 2016), hybrid rheological model (Zhang et al., 2020); kriging method-based creep model (Chen et al., 2019) and damage creep model (Xu et al., 2002); modified Burgers model (Kränkel et al., 2015)were typically established based on corresponding testing results.
In general, the stress distributions of grouted anchors are nonlinear (Farmer, 1975). The existing theoretical studies on time-dependent load transfer behavior of grouted anchors generally assumed that the geotechnical materials or structural materials are rheological, such as tensioned bars (Zhang et al., 2015); grouting material (Yang et al., 2014) and soil (Wu, 2009). Based on these assumptions, time-dependent distributions of both tensile force and shear stress could be deduced via load transfer method. However, for grouted anchors embedded in laterite, the creep destruction was mostly occurred in the interface region, and creep deformation of the anchor is relatively small and controllable compared with the interface shear creep displacement between grout and soil. Therefore, it would be more appropriate to consider the interface shear creep behavior between grout and soil in the simulation, whereas relevant studies are not yet reported.
In order to study the time-dependent load transfer behavior of grouted anchors in laterite, a special creep pullout test apparatus was developed in present work. A creep pullout model test of full-length-bond grouted anchors was carried out using this apparatus. The creep pullout load–displacement response at anchor head and time history curves of axial strain were obtained. Red clay (one type of laterite) collected from Hengyang red beds basin, Hunan Province, China, was used in this study, whose chemical composition, mineral composition and basic mechanical properties were tested. The Merchant rheological model was utilized as constitutive model for simulating the creep interaction between grout and soil. By comparing the experimental data with the predictions, the proposed theoretical analysis method turned to be effective and practical. Additionally, the effects of bond length, axial stiffness and three rheological model parameters on the time-dependent mechanical behavior of grouted anchors were further studied parametrically.
Section snippets
Material properties
The soil used in this test was taken from a weathered eluvium located in the Hengyang red beds basin of Hunan province, China (Fig. 1), which appears to be maroon. Chemical composition of the collected soil was obtained by X-Ray Fluorescence Spectrometer (XRF), which was: silica (SiO2) (46.5%), alumina (Al2O3) (25.5%), ferric oxide (Fe2O3) (13.3%), potassium oxide (K2O) (2.3%), titanium dioxide (TiO2) (1.4%), magnesium oxide (MgO) (0.6%) and ignition loss (10.4%). Mineral composition of the
Time-dependent load transfer modelling of grouted anchors
The creep problem could occur in both the anchor and the grout–soil interface under long-term load. For grouted anchors in laterite, it was observed in the above physical model test results that the interface shear creep displacement is dominant compared with the tensile creep deformation of the anchor. For instance, under the load of 5.15 kN, the grout–soil interface displacement reached 3.74 mm, while the tensile deformation of the anchor was only about 0.03 mm. The reason for this phenomenon
Theoretical prediction for model test response
Based on the model test results, theoretical analyses using the above proposed method are conducted for simulating the creep behavior of grouted anchors in laterite. Model parameters have a significant influence on the theoretical prediction results. In this work, Merchant rheological model was adopted for considering the creep interaction between grout and soil. Its three parameters are not only related to material properties, but also stress level (Chen et al., 2016, Sun, 1999). To obtain
Parametric studies
The soil properties, bond length and axial stiffness of the anchors can influence the time-dependent behavior of grouted anchors under a coupled mechanism. The impact of soil properties on the grout-soil interface creep behavior can be reflected in the magnitude of Merchant model parameters. Exemplarily, the higher soil viscosity leads to a greater magnitude of the parameter η but a smaller magnitude of the parameter G1; while the higher soil strength corresponds to a greater magnitude of
Conclusions
Creep pullout model test for full-length-bond grouted anchors embedded in laterite was carried out using a specially designed pullout setup. Time-dependent pullout response, i.e. tensile force and shear stress distributions over bond length, and pullout displacement creep curves of anchor head were measured in the physical model test. The time-dependent load transfer analysis method on the grouted anchor embedded in laterite was developed by modelling the anchor-laterite interface shear creep
CRediT authorship contribution statement
Changfu Chen: Supervision, Methodology, Funding acquisition. Shimin Zhu: Investigation, Data curation, Writing - original draft, Writing - review & editing. Genbao Zhang: Writing - review & editing. Fengshan Mao: Investigation, Writing - original draft. Huan Cai: Writing - original draft.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was sponsored by the National Natural Science Foundation of China (grant numbers 41572298, 51978254, 51908201). The authors appreciate their financial support.
References (41)
- et al.
A new method of predicting the prestress variations in anchored cables with excavation unloading destruction
Eng. Geol.
(2018) - et al.
Properties and microstructure of a natural slip zone in loose deposits of red beds, southwestern China
Eng. Geol.
(2014) - et al.
Behavior of a 31 m high excavation supported by anchoring and nailing in residual soil of gneiss
Eng. Geol.
(2015) Stress distribution along a resin grouted rock anchor
Int. J. Rock. Mech. Min. Sci. Geomech. Abstr.
(1975)- et al.
The effect of pressure-grouted soil nails on the stability of weathered soil slopes
Comput. Geotech.
(2013) - et al.
Prediction of the creep behaviour of bonded anchors until failure–A rheological approach
Constr. Build. Mater.
(2015) - et al.
A numerical model of fully grouted anchors considering the tri-linear shear bond–slip model
Tunn. Undergr. Space Technol.
(2016) - et al.
An analytical analysis of the full-range behaviour of grouted rockanchors based on a tri-linear bond-slip model
Constr. Build. Mater.
(2010) - et al.
Coupled calculation model for anchoring force loss in a slope reinforced by a frame beam and anchor cables
Eng. Geol.
(2019) - et al.
Influences of overburden pressure and soil dilation on soil nail pull-out resistance
Comput. Geotech.
(2010)
Creep behavior of epoxy-bonded anchor system
Int. J. Rock Mech. Min. Sci.
Numerical and experimental studies of the mechanical behaviour for compaction grouted soil nails in sandy soil
Comput. Geotech.
Dynamics characteristic of red clay in a deep-seated landslide, Northwest China: An experiment study
Eng. Geol.
Influences of initial water content and roughness on skin friction of piles using FBG technique
Int. J. Geomech.
Anchoring solid-soil interface behavior using a novel laboratory testing technique
Chin. J. Geotech. Eng.
Tests on shearing creep of anchor-soil interface and its empirical model
Chin. J. Geotech. Eng.
Kriging method-based creep model for anchor-soil interface considering grouting pressure
Chin. J. Geotech. Eng.
Characterization and modelling of coupled consolidation-creep behavior of red clay
J. Eng. Geol.
Element nail pullout tests for prediction of soil nail pullout resistance in expansive clays
Geotech. Test. J.
The distributes and geologic environment characteristics of red beds in china
J. Eng. Geol.
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2021, Computers and GeotechnicsCitation Excerpt :Soil moisture content and soil dry density were 28% and 1.4 g.cm−3, respectively, and the other material parameters were shown in Table A1. The detailed specimen preparing programs can refer to Zhang et al. (2020), Chen et al. (2021). Specimen B represented the cemented soil-steel tube element-scale pullout specimen, whose diameter was 200 mm and bond length was 80 mm.