Sandy Pebble Soil Research Articles

Soil Displacement of Slurry Shield Tunnelling in Sandy Pebble Soil Based on Field Monitoring and Numerical Simulation

Due to its inherent advantages, shield tunnelling has become the primary construction method for urban tunnels, such as high-speed railway and metro tunnels. However, there are numerous technical challenges to shield tunnelling in complex geological conditions. Under the disturbance induced by shield tunnelling, sandy pebble soil is highly susceptible to ground loss and disturbance, which may subsequently lead to the risk of surface collapse. In this paper, large-diameter slurry shield tunnelling in sandy pebble soil is the engineering background. A combination of field monitoring and numerical simulation is employed to analyze tunnelling parameters, surface settlement, and deep soil horizontal displacement. The patterns of ground disturbance induced by shield tunnelling in sandy pebble soil are explored. The findings reveal that slurry pressure, shield thrust, and cutterhead torque exhibit a strong correlation during shield tunnelling. In silty clay sections, surface settlement values fluctuate significantly, while in sandy pebble soil, the settlement remains relatively stable. The longitudinal horizontal displacement of deep soil is significantly greater than the transverse horizontal displacement. In order to improve the surface settlement troughs obtained by numerical simulation, a cross-anisotropic constitutive model is used to account for the anisotropy of the soil. A sensitivity analysis of the cross-anisotropy parameter α was performed, revealing that as α increases, the maximum vertical displacement of the ground surface gradually decreases, but the rate of decrease slows down and tends to level off. Conversely, as the cross-anisotropy parameter α decreases, the width of the settlement trough narrows, improving the settlement trough profile.

DEM simulation of sandy pebble soil based on polyhedral particles

DEM simulation of sandy pebble soil based on polyhedral particles

Study on the correlation of macro-fine parameters of surrounding rock in sand and cobble tunnel based on discrete element

As a mixture of soil and rock, the deformation of surrounding rock caused by tunnel excavation in the sandy cobble stratum is affected by the meso-structure of the stratum. In this paper, the mechanical and engineering characteristics of sandy cobble soil are studied in depth using a laboratory large-scale triaxial test and discrete element numerical simulation test, and the effects of main microscopic parameters on the characteristics of sandy cobble soil are analyzed, including the same specimen size, moisture content, compactness, confining pressure as well as loading method. The microscopic parameters such as contact modulus E c , friction coefficient f r , and stiffness bond ratio n of sandy pebble soil can be obtained. Meanwhile, the accuracy and uniqueness of microscopic parameters are determined using the response surface method. Moreover, the influence of different contact modulus and friction coefficient on the macroscopic mechanical properties of sandy pebble soil is quantitatively analyzed. The obtained conclusions are drawn as follows: the elastic modulus of sandy pebble soil decreases with the increase of water content. The peak value point of the stress-strain curve of sandy pebble soil increases with the increase of contact modulus and friction coefficient, respectively. The relationship between peak stress and the two types of fine-scale parameters can both be described by logarithmic functions. Compared to fine-grained soils, sandy pebble soils start to break down at about 3.5% of the axial strain, and the sandy cobble soil can still bear a certain load after reaching the peak strength. The results can provide a reference for the calculation and discrete element simulation of tunnels in sand and pebble strata.

Modified constitutive model of sandy pebble soil based on disturbed state concept

Modified constitutive model of sandy pebble soil based on disturbed state concept

Experimental study on the strength and deformation characteristics of sandy pebble soil foundation based on the equivalent density method

With the rapid development of urban construction, many bridges and subways are built on sandy pebble soil foundation. As a special kind of soil, sandy pebble soil has the characteristics of large particle size, low compressibility, low cohesion, poor self-stability, large permeability coefficient, large friction coefficient, etc. The strength and deformation characteristics of the sandy pebble soil are one of the key concerns in engineering field. Due to the size limitation of the laboratory test equipment, scaling is necessary for sandy pebble soil. The equivalent density of coarse-grained material could be obtained by equivalent density method; large-scale triaxial and interface shear tests were performed to study the comprehensive mechanical characteristics. Furthermore, appropriate models were investigated to describe the stress-strain relationships of sandy pebble soil, and the corresponding model parameters were summarized. The tests results reveal that the saturated sand pebble soil show shear shrinkage characteristics under low confining pressure, conversely unsaturated samples show shear dilatancy characteristics under low confining pressure. Under high confining pressure, obvious shear shrinkage characteristics could be observed. The shear strength parameters of unsaturated samples are obviously larger than those of saturated samples. It shows a good hyperbolic relationship between shear stress and displacement on the interface of sandy pebble soil and concrete slab, and the shear strength and normal stress are in a good linear relationship. The research could provide strong support for engineering design in sandy pebble soil.

Experimental Study on Shearing Strength of Sand Pebble in Southeast Tibet

In order to study the shearing strength characteristics of sandy pebble soil in southeast Tibet, this paper takes the sandy pebble packing of high road embankment of lalin high grade highway as the research object, and conducts particle analysis test on sandy pebble soil. On the basis of natural gradation, sand pebble soil was gradated and improved. In this paper, the undisturbed sand pebble soil and sand pebble soil with improved gradation were tested by direct shear tests under different vertical pressures.The results show that the stress-strain relationship of sandy pebble soil is mostly strain softening. The sandy pebble soil shears first,dilatancy occurs after,and the whole presents obvious dilatancy.The natural sandy pebble soil all has the phenomenon of grain deficiency,the shear strength of natural sandy pebble soil was improved by gradation. With the increase of the percentage of soil particle mass with a particle size of 20mm-60mm, the shear strength of sandy pebble soil increases accordingly. The physical and mechanical properties of sandy pebble soil was analyzed in this paper, which provides technical reference for the high embankment filling project in southeast Tibet.

Design of Groundwater Extraction in Open Cut Foundation Pit and Simplified Calculation of Ground Subsidence due to Dewatering in Sandy Pebble Soil Strata

In order to study the design of incomplete well point for groundwater extraction in open cut foundation pit in which the inner and outer aquifers are not completely isolated and the change mechanism of ground subsidence due to dewatering in the foundation pit, an open cut foundation pit for a subway station on Chengdu Metro Line 6 is taken as an example; meanwhile, the typical sandy pebble soil strata are also considered as a research object in this paper. Firstly, a new method for designing groundwater extraction in the open cut foundation pit is presented and applied to the practical project. The dewatering funnel curve is derived based on Dupuit’s assumption, and the ground subsidence around the foundation pit due to groundwater extraction is calculated using the stratification summation method as well as considering the effect of seepage force. The finite difference software FLAC3D is employed to simulate the groundwater extraction process in the foundation pit, and the simulation of groundwater extraction by single well point and group well points is also carried out and the unapparent effect of group well points is obtained. The comparison among on‐site monitoring, theoretical calculation, and numerical simulation shows that these values have the same trend in indicating ground subsidence, and the conventional stratification summation method is conservative, and the algorithm considering the effect of seepage force is more accurate. Therefore, the ground subsidence curve caused by groundwater extraction in the foundation pit is presented. The above research methods and results can be applicable for practical engineering and be used to guide the design and construction of groundwater extraction in the foundation pit by using the open cut method in sandy pebble soil strata.

Research on Portland Cement Grouting Material in Sandy Pebble Soil

Research on Portland Cement Grouting Material in Sandy Pebble Soil

Equivalent deformation modulus of sandy pebble soil-Mathematical derivation and numerical simulation.

This study aims to investigate the mechanical properties of sandy pebble soil through theoretical deduction and finite element analysis. Based on the assumption of stress uniformity or strain uniformity, the analytical formulas for calculating the equivalent deformation modulus of pebble soil are derived through RVEs. To verify the accuracy of the formulas, a series of numerical experiments are conducted through ABAQUS. Results show that theoretical calculation values match numerical simulation results well and the analytical formulas are effective when the pebble content is 0-60%. For pebble content lower than 20%, the equivalent deformation modulus could be described by "Stress Uniformity Model". When content is 20%-60%, pebble soil is a transition state from "Stress Uniformity" to "Strain Uniformity", for which the constitutive model could be expressed as a modified transition formula. This research is helpful for further investigation of mechanical properties of pebble soil. The theories developed in this study can be used in determining shield excavation parameters, and predicting the ground settlement caused by shield excavation.

Macro-Micromechanical Properties of Sandy Pebble Soil of Different Coarse-Grained Content

Sandy pebble stratum is a typical discrete particle unstable stratum, mainly consisting of sand and pebble. However, the effect of coarse-grained content on the stability of stratum is not clear. This paper defined the sandy pebble soil of different coarse-grained content in Chengdu City, Sichuan Province, China as the research object. Research on macro-mesomechanical properties of sandy pebble soil of different coarse-grained content was carried out using the method combining the indoor large-scale triaxial test of coarse-grained soil with the discrete element numerical triaxial test. The research results showed that the stress-strain curve of sandy pebble soil exhibited strain softening with the increase of coarse-grained content; when the confining pressure was the same, the stress peak increased and the strain when the peak was reached decreased gradually with the increase of coarse-grained content. It revealed the functional relationship between coarse-grained content and mechanical indexes of sandy pebble soil such as internal friction angle and cohesion. The internal friction angle and cohesion of sandy pebble soil linearly increased with the rise of coarse-grained material; it proposed the particle discrete element micro parameters of sandy pebble soil of different coarse-grained content, including contact modulus, friction coefficient, particle stiffness ratio, contact bond strength. The research results provided the theoretical support for the new design and construction of sandy pebble stratum project.

An Experimental Study on the Dynamic Strength of Earth-Rock Aggregate

This paper, based on dynamic triaxial apparatus of GDS, makes a consolidated undrained dynamic triaxial test of the saturated earth-rock aggregate of different earth-rock ratio, analyzes its processes and results, and preliminary discusses the influence of confining pressure, dynamic stress and earth-rock ratio on the dynamic strength of sandy pebble soil samples. Therefore, it providess some cognition of the study of earth-rock aggregate.

The Effect of Interaction on the Dynamic Characteristics of Mega Frame Structure

In the paper, the sandy pebble soil which was most massively distributed in Sichuan was used as foundation. The finite element model of mega frame structure including the superstructure, raft foundation and the sandy pebble groundwork was built by applying the finite element analysis software ANSYS. The response of the mega frame structures under dynamic load was analyzed to study the mechanical properties, deformational properties and the interaction between mega frame structures and the sandy pebble soil. At last, in the same structural style and same foundation soil, the dynamic behaviors of such structure which take no account of the interaction between mega frame structures and the sandy pebble soil was compared with structure which took account of the interaction. The research in the paper could provide certain reference value for the future engineering.

Experimental Study on Static Characteristics of Sandy Pebble Soil

Through the consolidation drained triaxial shear test of sandy pebble soil, the stress-strain curve of sandy pebble soil is obtained, analysis manifest that in the shearing process, shear dilatancy deformation and shear contraction deformation of sandy pebble soil are intercoupling, making asymptote of the curve after peak stress nearly a horizontal line. Meanwhile, based on the Duncan-Chang model, elastic modulus and Poisson ratio features of sandy pebble soil are analyzed, and Duncan-Chang model parameters are obtained.

Experimental Study on Dynamic Characteristics of Sandy Pebble Soil

Through the laboratory dynamic triaxial test of sandy pebble soil, evolution law of influence of confining pressure and vibration frequency on dynamic strength is analyzed. Analysis indicates that dynamic stress of sandy pebble soil improves in a large degree with accretion of vibration frequency, dynamic strength of which increases significantly with confining pressure rising, and relation of dynamic stress and dynamic strain can also be symbolized with the R.L.Kondner hyperbola curve. Meanwhile, dynamic elastic modulus of sandy pebble soil decreases with growth of dynamic strain, while increases with growth of consolidation pressure.

Experimental Investigation on Dynamic Constitutive Model of Saturated Sandy Pebble Soil

The dynamic constitutive model could show the dynamic characteristics of soil, so it was essential in ground motion in earthquake safety evaluation and seismic response analysis of soil, and it had great influence on research and analysis of seismic performance of soil and the stability of the foundation. Sandy pebble soil distributed abroad in Sichuan, so it was widely used in engineering construction. Based on the test results of dynamic triaxial non-drain consolidation test，this paper studied the dynamic constitutive model of saturated sandy pebble soil to provide reference for the future use.