Relative Density Dr Research Articles

Physical property of MICP-treated calcareous sand under seawater conditions by CPTU

MICP (Microbially induced calcite precipitation), an environmentally friendly soil improvement technique, has great potential in ocean engineering due to its ability to promote the precipitation of calcium carbonate through microbial activity to enhance the engineering properties of geomaterials. In this study, piezocone penetration test (CPTU) is used to evaluate the effectiveness of MICP treatment in calcareous sand. The change of physical properties (relative density Dr and total unit weight γt) of MICP treated calcareous sand is investigated by conducting CPTU on the geomaterials prepared in a series of mini calibration chambers (25 cm × 50 cm). Results indicate that CPTU (tip stress, sleeve friction, and porewater pressure) measurements can be used to interpret the physical characteristics of calcareous sand treated with MICP under seawater conditions. Additionally, a relationship between CPTU measurements, physical parameters (relative density Dr and total unit weight γt) of MICP treated calcareous sand is proposed and calibrated. The findings of the research extend the implementation of in-situ testing techniques such as CPTU towards physical property evaluation of bio-treated geomaterials in ocean environment, and demonstrate the potential of scaling up MICP techniques for broader engineering application.

Investigation of the Effect of Relative Density on the Dynamic Modulus and Damping Ratio for Coarse Grained Soil

As the critical dynamic parameters for soil, an extensive examination of the dynamic elastic modulus Ed and damping ratio λ in coarse-grained soil is of significant theoretical and practical importance. Currently, there is a scarcity of experimental equipment and methods for measuring the dynamic elastic modulus and damping ratio of coarse-grained soils. Moreover, studies examining the influence of relative density on these parameters in coarse-grained soils are largely absent. To investigate the behavior of the dynamic elastic modulus and damping ratio in coarse-grained soil under varying relative densities, a number of dynamic triaxial tests were conducted on a specific coarse-grained soil using the DYNTTS type dynamic triaxial test apparatus. The findings reveal that, under various gradations, the Ed of coarse-grained soils exhibits a decreasing trend with increasing dynamic strain, a trend that intensifies with higher relative densities. Additionally, as relative density increases, the degradation rate of the dynamic shear modulus ratio Gd/Gdmax to dynamic shear strain γd curve escalates. The maximum dynamic shear modulus Gdmax rises with increasing relative density Dr, displaying a linear relationship between Gdmax and Dr. Furthermore, both the increasing rate of λ to γd curve and the maximum damping ratio λmax progressively diminish with the escalation of relative density Dr. Notably, the maximum damping ratio has a power function relationship with the relative density.

Interface frictional anisotropy of dilative sand.

Understanding direction-dependent friction anisotropy is necessary to optimize interface shear resistance across soil-structure. Previous studies estimated interface frictional anisotropy quantitatively using contractive sands. However, no studies have explored how sand with a high dilative tendency around the structural surface affects the interface shear response. In this study, a series of interface direct shear tests are conducted with selected French standard sand and snakeskin-inspired surfaces under three vertical stresses (50, 100, and 200kPa) and two shearing directions (cranial → caudal or caudal → cranial). First, the sand-sand test observes a higher dilative response, and a significant difference between the peak and residual friction angles (ϕpeak - ϕres = 8°) is obtained at even a lower initial relative density Dr = 40%. In addition, the interface test results show that (1) shearing against the scales (cranial shearing) mobilizes a larger shear resistance and produces a dilative response than shearing along the scales (caudal shearing), (2) a higher scale height or shorter scale length exhibits a higher dilative tendency and produces a higher interface friction angle, and (3) the interface anisotropy response is more pronounced during cranial shearing in all cases. Further analysis reveals that the interface friction angle and dilation angle are decreased with the scale geometry ratio (L/H). For L/H values between 16.67 and 60, the interface dilation angle varies between 9° and 4° for cranial first shearing and 3.9°-2.6° for caudal first shearing. However, the difference in dilation angle within the same shearing direction is less than 1°.

Prediction model for small-strain shear modulus of non-plastic fine–coarse-grained soil mixtures based on extreme void ratios

The small-strain shear modulus G0 is a fundamental parameter for characterizing the dynamic behavior of soils. In this study, bender element tests were performed to investigate how the effective confining stress σ'c, relative density Dr, void ratio e, and a wide range of fines content FC (0%–100%) influence the G0 of soil mixtures containing both fine and coarse grains. The results show that under the same e and σ'c, G0 first decreases and then increases with increasing FC. Furthermore, as characteristic state parameters, the extreme void ratios (i.e., the maximum void ratio emax and the minimum void ratio emin) reflect comprehensively the particle size distribution and shape of fine–coarse-grained soil mixtures. Under the same σ'c, the lower limit of G0 (G0min) decreases with increasing emax and the upper limit (G0max) decreases with increasing emin, and the extrapolated upper and lower limits of the normalized G0/(σ'c/Pa) show a negative power-law relationship with emin and emax, respectively. Empirical formulas are established for the G0max and G0min of fine–coarse-grained soil mixtures, and G0 under various Dr can be interpolated according to G0min (for Dr = 0) and G0max (for Dr = 1). Finally, a G0 prediction model that offers reasonable characterization of fine–coarse-grained soil mixtures with different FC is established based on emin and emax.

Influences of particle size distribution and fines content on the excess pore water pressure generation of sand-silt mixtures under cyclic loading

The mechanical behaviors of binary mixtures are different from that of uniform soils. However, experimental studies on the dynamic responses of sand-silt mixtures considering the combined effects of fines content (FC) and host sand gradation are limited in the literature. In this paper, an experimental program was designed concerning five binary mixtures with three grain size ratios (Rd) and three sand uniformity coefficients (Cus) for investigating the effects of fines content and host sand gradation on both the liquefaction resistance and the excess pore water pressure (EPWP) generation of sand-silt mixtures. Results show that the effect of FC on the liquefaction resistance of sand-silt mixtures depends on relative density (Dr), grain size ratio, and sand uniformity coefficient. The liquefaction resistance of sand-silt mixture can be uniquely characterized by the equivalent relative density Dr* regardless of FC, Dr, and host sand gradation. Relationship between the EPWP ratio Ru and the cycle ratio N/NL for the sand-silt mixtures can be well expressed by the Seed model, which is significantly affected by cyclic stress ratio (CSR), FC, and Dr but insensitive to the change of host sand gradation. A trained artificial neural networks (ANN) model is conducted to predict the fitting parameter β of the Seed model with a maximum difference of 25% between the predicted and measured values. Moreover, there is an arctangent relationship between Ru and shear strain amplitude γa of each specimen, and the fitting parameter A for the relationship is sensitive to the particle size distribution and stress amplitude. A unique relationship between a density-corrected parameter A/Dr* and CSR is proposed regardless of FC and host sand gradation.

Experimental study on liquefaction characteristics of saturated Yellow River silt under cycles loading

The Yellow River silt can be effectively used as highway subgrade filler, which cannot only relieve the flood control pressure in the lower reaches of the Yellow River, but also meet the economic development needs of the areas along the Yellow River, with significant economic and social benefits. It cannot be ignored that the highway subgrade may be produced liquefaction under the action of earthquake and traffic loads. The problem of the dynamic characteristics of the Yellow River silt is a fundamental scientific problem that needs to be solved urgently. In this paper, a series of undrained tests were carried out on saturated Yellow River silt. Effects of relative density Dr, effective confining pressure σ3c, loading frequency f and cycles stress ratio CSR on pore pressure, axial strain development characteristics and dynamic strength characteristics of saturated Yellow River silt were studied. The test results show that: The number of cycles vibration required for liquefaction failure of the Yellow River silt was affected by relative density, loading frequency, effective confining pressure and cycles stress ratio. There are significant differences in the stress-strain development patterns of the Yellow River silt under different frequencies. Under the action of low frequency load, the Yellow River silt presents “hardening” liquefaction characteristics. Under the action of high frequency load, the Yellow River silt presents the characteristics of “softening” liquefaction. The Yellow River silt doesn't liquefy under the effect of weak earthquakes, while it is highly susceptible to liquefaction under the effect of strong earthquakes. Compared with the high-frequency load, when the low-frequency load is applied, more energy is required for the Yellow River silt to reach the initial liquefaction state. The cycles stress ratio CSR and the relative density Dr have significant effects on the pore pressure development of the Yellow River silt. Finally, a modified Seed model was proposed to characterize the pore pressure development of the Yellow River silt.

Deformation characteristics of natural river sand under compression loading incorporating extreme particle diameters impacts

The particle size is one of the most important factors influencing the behavior of soils. To study the impact of extreme particle diameters (Dmax and Dmin) and mean grain diameter (D50), a series of undrained triaxial compression tests were carried out with eighteen loose natural river sandy samples; considering a maximum particle diameter range (1.60 mm ≤ Dmax ≤ 4.00 mm), mean particle size ranges (0.25 mm ≤ D50 ≤ 1.00 mm) and the same minimum diameter Dmin = 0.0016 mm for the group1. For the group 2 consists of sandy samples having maximum diameter Dmax = 4.00 mm, minimum particle diameter ranges (0.0016 mm ≤ Dmin ≤ 0.63 mm), and mean diameter range (1.00 mm ≤ D50 ≤ 2.50 mm). The sandy samples were prepared with initial relative density Dr = 25% and subjected under a constant confining pressure (P’c = 50 kPa). The obtained test results indicate that the extreme particle diameters have significant effects on mechanical response of sandy soils and appear as important parameters for the prediction of the undrained shear strength of the tested soils. The maximum shear resistance can be correlated to the maximum relative diameter (Dmax/D50) and minimum relative diameter (Dmin/D50) of the tested samples.

Model Test of the Pullout Bearing Capacity of End-Bearing Torpedo Anchors

Torpedo anchors (TAs) are regarded as one of the most efficient mooring solutions for taut mooring systems, and end-bearing TAs are a new type of TA that primarily relies on end-bearing plates at the tail to generate a pile-end resistance to improve their pulloutbearing capacity (P). Therefore, the estimation of the pullout capacity of the end-bearing TA is vital for the design of offshore floating facilities. In this study, pullout model tests were conducted to investigate the P of conventional and end-bearing TAs and examine the effects of factors such as the embedment depth (h), the relative density (Dr), the pullout angle (α), and the area (A) of the bearing plates on P. The test results show that, under oblique pullout loading, the P on the conventional TA increased slowly as displacement increased, while there was a peak on the load–displacement curve of each end-bearing TA with a relatively large A. The end-bearing TAs considerably outperformed the conventional TAs in terms of the P. In addition, increasing h, Dr, and A significantly increased the P of the end-bearing TAs. However, increasing h and Dr slightly decreased the ability of the bearing plates to increase the P of the end-bearing TAs. These research results can provide a guideline for TA installation in deep-sea engineering.

Shear Behaviour of Aeolian Sand with Different Density and Confining Pressure

Different from the other roadbed material, the unique mechanical properties of aeolian sand bring great difficulties to the construction and maintenance of desert highways. However, the main attention was usually paid to the engineering properties of aeolian sand, such as collapsibility, strong permeability, and poor gradation. To investigate the shear behaviour of aeolian sand under different engineering conditions, the drained and undrained tests were performed on aeolian sand with relatively large range of density and confining pressure. Under this condition, both the drained and undrained tests tend to the same critical state line, and the shear behaviour of aeolian sand is directly dependent on its density. Under the undrained condition, the q-ε1 curves and the effective stress paths in triaxial stress space exhibit four types of undrained shear behaviour, such as flow, limited flow, strain hardening, and strain softening. Meanwhile all the specimens exhibit three types of failure, such as flow slip, bulging failure, and shear bands. In the q-p’ plane, the analogous drained and undrained stress paths can be followed by aeolian sand with same initial relative density but different confining pressures, and there are two critical state lines due to the generation of shear bands for dense sand. In addition, the critical state lines in e-lnp’ plane decrease with increasing initial relative density Dr, that is, the material constant eᴦ decreases with increasing Dr, and the λ is also not constant but decreases with the increase in Dr. The results suggest that the strength behaviours of aeolian sand can be fitted by a straight line considering relative density and confining pressure and that two empirical formulas are established to describe this feature.

Fabrication of ZrC/ZrB<sub>2</sub>/C Composites Having High Mechanical Properties at Elevated Temperatures

Ultra-high temperature ceramics (UHTCs) are most recently getting much attention for structural parts of hypersonic missiles with their cruising speed of more than Mach 5. Most of the UHTCs are poor sinterability carbides, nitrides, and borides. Therefore, they have been studied and developed for a long time. However, there are still many problems to solve. In this paper, based on the solid-state reaction presented as an equation of (x + y)·ZrC + 2·y·B → x·ZrC + y·ZrB2 + y·C, three-phase ZrC/ZrB2/C composites have been fabricated from ZrC and amorphous B powders using pulsed electric-current pressure sintering at 1373 to 2173 K for 6.0 × 102 s under 50 MPa in a vacuum. ZrC/ZrB2/C = 30/70/C~70/30/C vol% composites with the relative densities Dr of 96.6 to 98.7% were obtained at 2073 K. The 60/40/C vol% composite revealed high bending strength σb (554 MPa), Vickers hardness Hv (19.2 GPa) and moderate fracture toughness KIC (5.25 MPa·m1/2) at room temperature. Furthermore, all composites showed elastic deformation up to 1873 K and revealed σb more than 600 MPa at this temperature, in addition, some composites showed higher σb than 900 MPa at the same temperature. These high mechanical behaviors are discussed with those of the simple binary ZrC/ZrB2 composites which were fabricated under the same conditions except for their starting materials. The best mechanical properties of binary composites were σb (474 MPa), Hv (18.5 GPa), and KIC (4.45 MPa·m1/2) at room temperature, and σb of 400 - 700 MPa at 1873 K. Overall, three-phase composites, nevertheless including soft carbon, have higher mechanical properties than the binary composites.

Determination of Relative Density and Degree of Saturation in Mineral Soils Based on In Situ Tests.

Based on the results of dynamic probing (DP), time-domain reflectometry (TDR/MUX/MPTS), resistivity cone penetration tests (RCPT), Marchetti dilatometer tests (DMT), and seismic dilatometer tests (SDMT), it is possible to develop a relationship to calculate the relative density (Dr) and degree of saturation (Sr) of selected sandy soils. Compiled databases from documented research points for selected sandy soils were used to construct and develop direct correlations between the measured pressures p0 and p1 from DMT and shear wave velocity (Vs) from SDMT, along with pore water pressures (u0) and atmospheric pressure (Pa). The results allowed us to make a preliminary prediction when evaluating the parameters. Further, they allowed limiting the use of an additional device, especially in the case of multilayer heavy preconsolidated subsoils. Moreover, soil physical and mechanical characteristics (temperature, humidity, pressure, swelling, salinity) measured from TDR/MUX/MPTS (laboratory/field-operated meter for simultaneous measurements of soil moisture, matric potential, temperature, and salinity—bulk electrical conductivity) were assessed. The main achievement of this paper is the original proposal of using a new nomogram chart to determine the relative density and degree of saturation based on DMT and SDMT tests.

Comparison of sand liquefaction in cyclic triaxial and simple shear tests

The liquefaction resistance and correction factors Kσ and Kα of Nakdong River sand obtained from cyclic triaxial (CTX) tests were compared with those determined by cyclic simple shear (CSS) tests to ascertain the importance of the reduction factor Cr and correction factors Kσ and Kα in liquefaction evaluations, especially in view of the lack of comparative liquefaction assessments based on different laboratory test apparatuses. All samples used for the comparisons were obtained from the same type of sand by using similar preparation methods and they were subjected to similar stress states to minimize the number of factors influencing the comparison results; moreover, the apparatuses used in the two tests were manufactured by the same company and all tests were conducted by a single operator. It was found that the liquefaction resistance in CTX tests was always greater than that in CSS tests. Furthermore, Cr varied from 0.63 to 0.36, and it depended on the relative density Dr and initial static shear ratio α. Kσ, which increased with the normal effective stress σ′nc in CTX tests, was identical to Kσ observed in CSS tests when α was increased up to 0.1. By contrast, Kα in the CSS tests was 58%–97% of Kα measured in the CTX tests, and it depended on the combined effect of Dr, σ′nc, and α. The relationship between Kα and α in both CTX and CSS tests was well represented by a parabolic function. Moreover, the differences in Kα values between the CTX and CSS tests were also found to be a parabolic function of α. This information can be used for converting CTX (or CSS) values into equivalent CSS (or CTX) values.

Subgrade assessment using automated dynamic cone penetrometer to manage geo-infrastructures

For the efficient management of geo-infrastructures in the field, engineering properties of the subgrade should be reliably and rapidly investigated. The objective of this study is to estimate and compare the strength and stiffness parameters of subgrades using portable in-situ devices. An automated dynamic cone penetrometer (ACP), dynamic cone penetrometer (DCP), and light falling weight deflectometer (LFWD) are adopted and applied at nine points of soft ground in South Korea. The Nvalue from the ACP (NACP), which efficiently assesses the relatively deep subgrade, is correlated with the dynamic cone penetration index (DCPI) and dynamic deflection modulus (Evd). Test results show that the DCPI and Evd can be estimated in terms of NACP. In particular, the relationship between Evd and NACP is improved when the strain influence factor of the target ground is considered. For the assessment of strength and stiffness parameters, the California bearing ratio (CBR), relative density (Dr), internal friction angle (φ), and elastic moduli determined by the plate loading test (PLT), soil stiffness gauge (SSG), falling weight deflectometer (FWD) are estimated using NACP. The ACP test with the relationships between engineering parameters and NACP may be an effectively method to assess the overall characteristics of the subgrade.

An insight into the liquefaction resistance of sand using cyclic undrained triaxial tests: Effect of the relative density and the loading amplitude

Abstract A stability analysis of soils prone to liquefaction based on their undrained shear-strength characteristics is an indispensable challenge in earthquake geotechnical engineering. This paper presents a laboratory study of the influence of relative density on the cyclic behavior of Chlef sand. The experimental program includes undrained, triaxial cyclic tests that were carried out for three different relative densities (Dr = 15, 50 and to 65 %) with various cyclic stress ratios (CSR = 0.15, 0.25 and 0.35). All the samples were consolidated under one initial effective confining pressure σ'c = 100 kPa. The main results show that the increases in the relative density led to significant increases in the shear strength established by an increase in the number of cycles and with an exponential rise. In contrast, it was demonstrated that the number of cycles was decreased when increasing the cyclic stress ratio due to the shearing frequency. The two main effects of the studied parameters did not have the same influence on the cyclic undrained response of the sandy soil submitted to seismic loading: an increase of the deviatoric stress due to the high relative density that participates in the increase of the loading capacity of the compacted soils by minimizing the void ratios, and an increase of the pore-water pressure that has a negative effect on the liquefaction of the soil. From the results obtained, it can be concluded that these two mechanisms led to a global increase of the maximum shearing stress.

Numerical Simulation of the Effect of High Confining Pressure on Drainage Behavior of Liquefiable Clean Sand

This article presents numerical simulations investigating pore pressure buildup of a sand layer with a free drainage boundary at the top under both low and high overburden pressures and subjected to earthquake base excitation. The numerical runs simulate two centrifuge experiments previously conducted and reported. In these tests, a 5-m layer of clean Ottawa sand with relative density Dr=45% was tested under overburden pressures of ∼100 and ∼600 kPa (1 and 6 atm). The simulations were performed using Dmod2000, a nonlinear effective stress numerical one-dimensional (1D) site response analysis code. The tests revealed that the response was partially drained rather than undrained, with much more partial drainage at ∼600 kPa (6 atm) compared to ∼100 kPa (1 atm). The simulations correctly modeled this behavior, with very good agreement between simulated and measured centrifuge excess pore pressures. A key aspect of this good accord in the simulations was the correct selection in the simulations of the 1D drained volumetric stiffness of the sand, M′=1/mv, because the coefficient of consolidation, cv, is proportional to M′. Both cv and M′ were 2.5–3 times greater at ∼600 kPa (6 atm) than at ∼100 kPa (1 atm) in both centrifuge tests and simulations. Any future simulation of pore pressure response of sand under field drainage conditions needs to consider this large increase in volumetric stiffness at high overburden pressure. Good agreement was found between values of M′ back-calculated from the centrifuge tests and from a consolidometer test on a different sand reported in the literature. The value of M′ seems to increase approximately with the root square of the overburden pressure, and future simulations for high overburden and realistic field drainage conditions should account for this increase. The proper high-pressure correction factor, Kσ, to be used in conjunction with liquefaction charts may be higher than 1 for some realistic field drainage conditions due to this substantial decrease of sand compressibility under high overburden pressure.

Soil Densification Effect on the Behaviour of Chlef Sand (Algeria) under Static and Cyclic Loading: A Laboratory Investigation

This paper presents a laboratory investigation on soil densification effect on the behaviour of Chlef sand (Algeria). The study is carried out via a series of monotonic and cyclic tests in drained and undrained conditions using the triaxial apparatus. It’s conducted in three stages: the first consists on the study of the sand behaviour under monotonic loading in drained conditions. Effects of the confining pressure and of the relative density Dr on the sand’s shear strength are observed. In the second step, the undrained behaviour of the studied sand under monotonic loading is studied, and finally the last step deals with the sand undrained behaviour under cyclic loading. In each step, sand samples with different values of relative density that are ranging from loose, medium and dense state are tested (Dr = 10%, 15, 18%, 50%, 65% and 80%). The obtained results show a significant upgrading of the mechanical properties of the sand samples proportionally to the densification rise. The aim of the study is to highlight the improvement that can bring soil densification process on the behaviour of Chlef sand, and therefore its use as a soil reinforcement technique to solve soil deformations in the study area, which is a prone zone to seismic risk.

Unique determination of cyclic instability state in flow liquefaction of sand

Flow liquefaction is a catastrophic failure phenomenon of loose sand when subjected to wave or seismic load, and an instability state can be regarded as the onset of flow liquefaction. Most of the previous studies focused mainly on the static instability state, while the investigations on cyclic instability state (CIS) are very limited and unsystematic. The characteristics of CIS are complex and there is no clear consensus about the determination of CIS. Therefore, this study aims to investigate the characteristics of CIS in flow liquefaction via a series of undrained triaxial tests performed on saturated loose sand. The testing program covers a broad range of initial deviatoric stresses qs , cyclic stress amplitudes qcyc , and relative densities Dr . The test results indicate that CIS will occur at either compressive side or extensive side, depending uniquely on the ratio of qs /qcyc . The slopes of CIS lines increase with an increase in the relative density. Under the same qcyc , the mean effective stress at CIS first decreases and then increases as qs increases. Finally, CIS is predicted by a useful method, which is able to monitor CIS both in situ and in laboratory tests.

A Constitutive Model for Saturated Gravelly Sand Based on Higher‐Order Dilatancy Equation

A standard stress path triaxial test system was applied to carry out conventional triaxial shearing tests for gravelly sands under confining pressures ranging from 50 kPa to 400 kPa at the initial relative densities of 0.15, 0.35, 0.55, and 0.75, respectively. The test results show that all the samples of gravelly sand present strain hardening and shear contraction during the process of shearing test. Additionally, gravelly sands are significantly affected by the initial relative density. The hardening degree of gravelly sand samples rises in line with increasing initial relative densities during shearing tests. When initial relative densities Dr are at 0.15 and 0.35, the volume shrinkage of samples decreases with the increasing confining pressures. Instead, when initial relative densities Dr are at 0.55 and 0.75, the volume shrinkage of samples increases with the growth of confining pressures. To describe these triaxial shearing mechanical properties of gravelly sands, a higher‐order dilatancy equation was proposed based on the concept of a super yield surface. A constitutive model which can describe the mechanical properties of gravelly sand was established when the associated flow laws were applied to compare with the results of the triaxial shearing test under the consolidated drained condition. The comparison results showed that the proposed model can reflect the strain hardening and shear contraction characteristics of gravelly sands from low to high confining pressures under different initial relative densities.

Behavior of zeolite-cement grouted sand under triaxial compression test

Abstract Permeation grouting with cement agent is one of the most widely used methods in various geotechnical projects, such as increasing bearing capacity, controlling deformation, and reducing permeability of soils. Due to air pollution induced during cement production as well as its high energy consumption, the use of supplementary materials to replace in part cement can be attractive. Natural zeolite (NZ), as an environmentally friendly material, is an alternative to reduce cement consumption. In the present study, a series of consolidated undrained (CU) triaxial tests on loose sandy soil (with relative density Dr = 30%) grouted with cementitious materials (zeolite and cement) having cement replacement with zeolite content (Z) of 0%, 10%, 30%, 50%, 70% and 90%, and water to cementitious material ratios (W/CM) of 3, 5 and 7 has been conducted. The results indicated that the peak deviatoric stress (qmax) of the grouted specimens increased with Z up to 50% (Z50) and then decreased. The strength of the grouted specimens reduced with increasing W/CM of the grouts from 3 to 7. In addition, by increasing the stress applied on the grouted specimens from yield stress (qy) to the maximum stress (qmax), due to the bond breakage, the effect of cohesion (c′) on the shear strength reduced gradually, while the effect of friction angle (φ′) increased. Furthermore, in some grouted specimens, high confining pressure caused breakage of the cemented bonds and reduced their expected strength.

Experimental Study on the Shear Behaviors of PolypropyleneFiber-Reinforced Sand

With excellent water permeability and high shear strength S, fiber-reinforced sand (FRS) is an ideal material for subgrades and has promising application prospects. In this study, the FRS were formed by adding the randomly distributed fibers to the sand specimens. Based on the triaxial consolidated drained tests, the effects of factors such as fiber content ζ, fiber length lf, relative density Dr and confining pressure σ3 on the S of FRS were systematically investigated. The test results showed that the S of the FRS increased as ζ, lf, Dr and σ3 increased. Under axial loads, the stress-strain curve of the FRS exhibited a hardening trend. Under specific Dr and σ3, the S increment of the FRS had a strong linear relationship with ζ and lf. The Mohr's stress circle results showed that the FRS possessed not only frictional strength but also high cohesive strength. Based on the triaxial consolidated drained test results, the S of the FRS was calculated using the Zornberg model and Michalowski model. The calculation results showed that the S predicated by the Zornberg model differed significantly from the measured values. However, the S predicted by the Michalowski model were in good agreement with the measured values.