Excess Pore Water Pressure Research Articles

Suction penetration characteristics and resistance calculation of bucket foundation in sand

• Based on the suction penetration test of bucket foundation, the distribution regularity of the excess porewater pressure of soil and soil pressure on both sides of bucket wall and bucket end are revealed. • Based on finite element method, the seepage characteristics of the bucket foundation during the penetration process are analyzed, and the change regularity of the effective stress and resistance of soil during the penetration process of bucket foundation is obtained. • Considering the effect of effective stress on seepage, a calculation method for required suction of bucket foundation with few easy-obtained parameters is established. The accurate estimation of penetration resistance of the bucket foundation is the key step for its installation, and the core part of the estimation of the penetration resistance is the exact prediction of the drag reduction effect due to suction. Therefore, in the present paper, the change regularity of the excess porewater pressure along the bucket wall and at the tip is analyzed by combining the model test and finite element analysis method, along with the soil pressure of the bucket foundation during the suction penetration process in sand. The results showed that, during the suction penetration process of the bucket foundation, the soil pressure and excess porewater pressure change approximately linearly with the depth of the bucket wall, and the reduction degree of lateral resistance due to seepage increases in a power function growth trend. Based on the effective stress principle of soil and basic theory of seepage and considering the effect of seepage on penetration resistance, the change regularity of the effective stress of soil along the bucket wall during the penetration process is obtained. Besides, the calculation method for penetration resistance and required suction of bucket foundation in sand soil is established, and the effectiveness of the present method is verified by comparing with the model test and engineering case, which can provide theoretical basis for engineering design and construction of bucket foundation.

Theoretical Analysis on Reduction of Load-Induced Excess Pore-Water Pressures in Roads with Geogrids

Theoretical Analysis on Reduction of Load-Induced Excess Pore-Water Pressures in Roads with Geogrids

Analytical solution for consolidation of sand‐filled nodular pile (SFNP) foundation and its engineering application

AbstractThe sand‐filled nodular pile (SFNP) foundation is newly proposed to improve the bearing capacity and accelerate consolidation settlement of foundations installed in soft clay soil. By filling sand while driving the nodular pile into the soft clay soil, the SFNP foundation provides an extra drainage path with the aid of the nodular segment, while maintaining the high modulus reinforcement body at the core of the composite foundation. The performance of the SFNP foundation is greatly influenced by its consolidation behaviour. This study develops a generalized model for the SFNP foundation, and a closed‐form solution is then established considering the smear and well resistance effects. The developed model and the associated analytical solution are employed to investigate the consolidation rate and load distribution of the SFNP foundation. Finally, the analytical solution is utilized to evaluate the performance of SFNP foundation for an expressway project located in Zhejiang, China. The predicted dissipation of the excess pore water pressure employing the developed analytical solution agreed well with measured response from the field test, which further confirmed the advantages of the SFNP foundation and the reliability of the developed solution.

Macro-and meso-scale study on dynamic mechanical properties of shaft lining concrete exposed to high water pressure

This study presents the impact dynamic properties and pore structure characteristics of shaft lining concrete after exposure to various water pressure levels and durations, which provides guidance for design and utilization of supporting materials at ingate. The maximum impact pressure was 0.55 MPa, the highest water pressure was 10 MPa and the longest duration was 14 days. Research found that impact pressure remained constant, and water pressure lasted for 1 day, impact strength increased with increasing water pressure, whereas impact strength exhibited a decreasing trend with increasing water pressure when water pressure lasted for a longer time. Water pressure remained unchanged, impact strength exhibited an increasing trend as the impact pressure increased, which was due to strength enhancement of the Stefan effect, inertia effect, and excess pore water pressure formed by water in the specimens under impact load. However, impact strength decreased significantly under the same impact pressure as the water pressure lasted longer. After exposure to water pressure, internal pores of specimens were dominated by micropores and small pores, accounting for more than 88.39%. With the increase in water pressure and its duration, the proportion of macropores gradually increased, and the total number of pores increased rapidly, because pressure water applied splitting load to microcracks and micropores in the specimens to promote their further expansion, accompanied by the generation of new flaws. Results show that impact strength increases when the damage effect induced by microcracks and micropores expansion under water pressure is less than the enhancement benefit under impact dynamic load, and vice versa.

Study on Reinforcement Mechanism and Reinforcement Effect of Saturated Soil with a Weak Layer by DC

This paper presents a numerical investigation on the improvement mechanism of dynamic compaction (DC) in saturated soil of a weak layer with high levels of groundwater, using an improved fluid–solid coupling method with a Drucker–Prager–Cap soil model. The numerical model is verified by comparing with published test data at first, which show that the dual-phase coupling method can approximately reflect the development law of excess pore water pressure and the improvement effect of layered saturated soil foundation under DC. Then, based on the numerical model, the influences of the thickness and depth of the weak layer as well as tamping energy on the development and dissipation of excess pore water pressure, effective stress, and the relative degree of reinforcement during DC were investigated. The results showed that the embedment depth and thickness of the weak interlayer may greatly affect the effective reinforcement depth of DC. Meanwhile, the tamping energy and the groundwater table also play a great role in the improvement of the layered saturated soil under DC. The groundwater table should be lowered by dewatering or adding a drainage layer to achieve a better compaction effect during DC.

Experimental study on the cyclic behavior of silty sands reinforced by disposal of shredded facemask

Due to the COVID-19 pandemic, personal protective waste generation has increased worldwide. Given this problem,urgent waste management methods are required to reduce waste surcharge to the environment. The present study tries to clarify the question using particle-level modeling combined with 36 undrained cyclic triaxial shear tests. The physical properties of the base materials and the face mask (FM) are first investigated and scanning electron microscopy is used to image the soil particles.This study used two kinds of sand with different median grain (D50) sizes.In doing so, shredded face mask (FM) contenthas been modifiedfrom 0 % to 1 %. In a Small silt system (fine content ≤ 40 %), liquefaction resistance decreased with silt content addition and had an opposite behavior in a Large silt system (fine content ≥ 40 %) for both sands. FM addition to silty samples leads to sustainable improvements such as more dilatative behavior and dissipation of excess pore water pressure, and enhanced liquefaction resistance. The effectiveness of FM reinforcement diminished with increasing the median grain size (D50). Also, the shear modulus of clean and silty sands improved with FM addition.

Liquefaction analysis of Izumio sands under variation of ground motions during strong earthquake in Osaka, Japan

This paper presents a study of liquefaction analysis at sand layers of the Izumio site, under ground motion variation during a strong earthquake in Osaka, Japan. Site investigation using standard penetration test and shear wave velocity measurement is conducted. Finite element liquefaction site response analysis integrated with a strain space multiple mechanism model is conducted. Ground motions variation is considered based on the seismic record at surrounding seismic stations. Attenuation analysis is conducted to determine the scaling factor for ground motions. Several results, such as acceleration profiles and cyclic behaviours are presented. The empirical analysis is also conducted to verify the results of the numerical analysis. The results explained that cyclic behaviours of sandy layers in the Izumio site show the liquefaction tendency. The results also showed that sandy layers are indicated as critical layers during the strong earthquake due to the excess pore water pressure reaching the liquefaction threshold. The results of the empirical analysis also present liquefaction indication at sand layers under the variation of ground motion, since the factor of safety against liquefaction is less than 1. The results are generally well-agree with liquefaction evidence and prediction presented in the previous study. The results could bring practical importance in understanding liquefaction potential in the study area.

Factors Influencing Post-Construction Responses of Underlying Tunnel below Excavation Base in Gravelly Clay

This paper investigates the response mechanism behind an existing tunnel subjected to a long and deep collinear excavation in Shenzhen granite residual strata. The maximum excavation depth was 18.0 m and the minimum residual soil depth above the tunnel crown was only 6.3 m, causing appreciable tunnel heave and transverse deformation. Two-dimensional parametric numerical study is adopted to examine the impacts of influential factors (excavation dimensions, ground permeability coefficient, and exposure time of the excavation base) on the tunnel responses. The hardening soil model with small strain (HS-Small) is used to model the soil stress–strain behavior. It is found that the long-term deformation of the tunnel after excavation and unloading cannot be ignored. The soil will continue to consolidate and deform, and the tunnel will continue to heave with soil due to the dissipation of the negative excess pore water pressure. The long-term deformation of the tunnel after excavation and unloading is significantly affected by the excavation geometry. With the increase in excavation width B, the final tunnel heave after excavation and unloading increases first and then tends to be stable. Furthermore, the relative position of the tunnel and the excavation base is also one of the major contributors to the long-term deformation of the tunnel. The growth of tunnel deformation Δf and the exposure time T are exponentially negatively correlated with Ly. The change in the permeability coefficient k has no effect on the final stable tunnel heave and the growth of tunnel deformation Δf, which is exponentially negatively correlated with the exposure time T.

Evaluation of Liquefaction Properties of East Coast Sand of New Zealand Mixed with Varied Kaolinite Contents Using the Dynamically Induced Porewater Pressure Characteristics

In earthquake geotechnical engineering, physical model experiments have proven to be significant and valuable in understanding the complex physics and engineering behaviors of prototype undrained soils in fields. An executed literature review indicated that large-scale physical model testing, such as shaking table (ST) and centrifuge devices, have associated advantages and limitations. The current paper presents the design, fabrication, and calibration of a 600N-capacity, small-scale, one-directional (1-D) laboratory ST device that enables quick and valuable assessment of soil liquefaction mechanisms. The dynamically induced porewater pressure (PWP) generation characteristics of sand soil mixed with different percentage weights of clay were evaluated and illustrated as a case study for testing the ST device’s performance. The east coast sand (ECS) of New Zealand’s North Island was mixed with different percentages of kaolinite clay to produce five variants of ECS (00, 05, 10, 20, 25, and 30). Three input sine wave ground motions of a constant frequency of 10 Hz and amplitudes of 2, 3, and 4 were applied and classified in the current study as low, intermediate, and moderate ground motions, respectively, to evaluate the evolution of the dynamic excess pore pressures in the soil samples. The results indicated that the clean ECS and mixed samples with lower clay content (ECS00, ECS05, ECS10, and ECS15) produced the highest excess PWP throughout the three shaking cycles, with higher tendencies of contraction and liquefaction properties. On the other hand, soil samples with a higher percentage of clay (ECS20 and ECS20) yielded the lowest PWP, with softening and dilative properties.

General analytical solutions for one-dimensional large strain consolidation of soft soils under electro-osmosis–surcharge preloading

In this study, the governing equation for one-dimensional large strain consolidation of soft soils under electro-osmosis–surcharge preloading is derived with some assumptions, and the general analytical solution is proposed for the first time by using the methods of algebraic transformation and separation variable. The expressions for the specific analytical solutions under several common cases in foundation treatment are developed. Besides, the correctness of the proposed analytical solutions is verified by comparing them with the existing analytical solutions and finite difference solution. Finally, based on the proposed analytical solutions, the effects of effective voltage Vm, the ratio of electro-osmosis (EO) conductivity to hydraulic conductivity ke/kv and volume compressibility coefficient mv1 on the consolidation behaviors are analyzed. It is found that the increase of Vm increases the absolute values of excess pore water pressure (EPWP) and hence the settlement increases. Furthermore, the increasing ratio of ke/kv leads to larger absolute values of EPWP generated in the soil, resulting in an increase of settlement. The consolidation degree Us defined by settlement based on small strain and large strain models decreases with the increase of mv1, and both the differences of Us and settlement between the two consolidation theories increase with the increase of mv1. In conclusion, the proposed analytical solution is simple in form and practical, which can be adopted to analyze the one-dimensional large strain consolidation behaviors under electro-osmosis–surcharge preloading.

Large-strain rheological consolidation analysis of multi-layered marine soft clays exhibiting natural structural characteristics

The destruction of marine soft clays’ macropore structure results in large-strain deformation during consolidation, as well as the potential to alter rheological deformation characteristics. A sectionalised regimes rheological model was adopted to describe the structural characteristics under the isotache framework, which led to a nonlinear variation of geometrical boundaries and material properties during consolidation. A semi-analytical theory combining numerical and analytical methods was developed, and the solutions for excess pore water pressure, degree of consolidation, and settlement were derived and computationally programmed. Using parametric analysis, the effects of rheological and structural characteristics on the consolidation behaviour of soft clay were discussed compared to the solutions of other theories. The coefficient of secondary consolidation in the transitional regime has an impact beginning in the middle of primary consolidation. The proposed solutions for degree of consolidation are smaller than the small-strain solutions during the early period of primary consolidation but change larger as consolidation progresses.

Accumulative responses of soft clayey seabed: A case study from the Eastern Coast of China

Existing seawalls along the eastern coast of China are increasingly becoming the focus of upgrade operations. Concerns arise regarding the settling and stability of seawalls built on soft clayey seabed during upgrade operations. Pore water pressure (PWP) and horizontal displacement accumulations induced by combined tide and wave loadings are observed in in-situ measurements of the clayey seabed underneath the seawall. The measurement results show clear correlations between the oscillations of excess PWP and variations in the tidal height. To reproduce the quasi-static interaction behaviors of the gravity-type seawall and clayey seabed under combined cyclic loadings from waves and currents, a finite element model has been built after incorporating a stiffness degradation law that is evaluated from laboratory triaxial tests on the seabed soil. Demonstrably, with a suitable stiffness degradation law for the seabed soil, the accumulative behaviors can be reasonably reproduced using finite-element modeling.

Impacts of Excess Pore-Water Pressure on Dynamic Properties of Saturated Clay

Impacts of Excess Pore-Water Pressure on Dynamic Properties of Saturated Clay

Field Research on the Treatment of Coastal Phase Liquefaction Foundation with Clay Interlayer Using Resonance Probe Compaction Method

The resonance probe compaction (RPC) method is an effective technique for particular soils, which mainly includes sandy and loess. However, the application of RPC on contaioning clay interlayer area has never been seen. In this study, a successful case of using the RPB method to treat the clay interlayer foundation is presented in detail. The test results of Huaiyan high-speed railway construction project are introduced. The test is divided into the laboratory test and the field test, mainly including standard penetration test (SPT), cone penetration test (CPT) and seismic wave cone penetration test (SCPT). The test results indicated that the cone resistance of silt and silty sand layers increased to an average of 2.13 times compared with an average of 4.39 MPa before treatment, and the sleeve friction whose initial average is 54.17 kPa increased to an average of 1.74 times. The existence of the clay interlayer does not affect the consolidation and drainage of the silt layer and the silt sand layer, and after the construction, the excess pore water pressure around the vibration point can be dissipated by more than 90% within 15 minutes. After reinforcement, the standard penetration number of subsoil, increased by about 15%–95% compared with an average of 19 blows before treatment and the clay particle content of some clay interlayers are reduced to less than 10%. The shear wave velocity of the subsoil in the treatment depth increased by about 15%–48% compared with 140 m/s before treatment. The RPC method was successful for the coastal phase liquefaction foundations.

Three-dimensional fully coupled hydro-mechanical-chemical model for solute transport under mechanical and osmotic loading conditions

Mechanical deformation and chemico-osmotic consolidation of clay liners can change its intrinsic transport properties in all direction and can alter fluid and solute transport processes in the entire model domain. These phenomena are described inadequately by lower-dimensional models. Based on the Biot’s consolidation theory, fluid and solute mass conservation equations, a three-dimensional (3D) fully-coupled hydro-mechanical-chemical (HMC) model has been proposed in this study. The impacts of mechanical consolidation and chemico-osmotic consolidation on permeability, hydrodynamic dispersion, solute sorption, membrane efficiency, and chemical osmosis are considered in the model. The model is applied to evaluate performances of a single compacted clay liner (CCL) and a damaged geomembrane-compacted clay composite liner (GMB/CCL) to contain a generic landfill contaminant. Effect of model dimensionality on solute spread for CCL is found to be marginal, but for GMB/CCL the effect is significantly large. After 50-year simulation period, solute concentration at the half-length of the GMB/CCL liner is predicted to be 40% of the source concentration during 1D simulation, which is only 6% during the 3D simulation. The results revealed approximately 74% over-estimation of liner settlement in 1D simulation than that of the 3D for GMB/CL system. Solute spread accelerates (over-estimates) vertically than horizontally since overburden load and consequent mechanical loading-induced solute convection occurs in the same direction. However, in homogeneous and isotropic soils, horizontal spread retards the overall migration of contaminants, and it highlights the importance of 3D models to study solute transports under mechanical and chemico-osmotic loading conditions in semi-permeable clays, especially, for damaged geomembrane-clay liners. The results show the utility of geomembranes to reduce soil settlement, undulation, and restriction of solute migration. Furthermore, application of geomembrane can inhibit development of elevated negative excess pore water pressure at deeper portion of a clay liner.

The undrained behaviour of over-consolidated clay subjected to pure rotation of principal stress directions

Foundation soil of offshore structures may be subjected to various non-proportional cyclic loadings, such as wave loading, tide loading and earthquake loading. The consolidation state may affect the undrained behaviour of clay under pure rotation of principal stress directions. A series of cyclic undrained torsional tests were performed on normally and over consolidated clay subjected to pure rotation of principal stress directions at constant deviatoric stress conditions. The effects of over consolidation ratio (OCR) on the excess pore water pressure, stress-strain loop, stiffness and non-coaxial behaviour of the clay were analyzed under different deviatoric stresses and intermediate principal stress coefficients (b values). The results indicate that owing to the pure principal stress rotation alone, strain and excess pore water pressure accumulated in samples and the accumulation is affected by OCRs, deviatoric stress amplitudes and b values. Negative excess pore water pressure and stress dilatancy can be observed in over consolidated clay. Compared with shear stiffness, the normal differential stiffness experiences greater degradation under the pure rotation of principal stress. The shear stiffness of over consolidated clay may show an increase with loading cycles, while the normal differential stiffness degrades at low deviatoric stress value. Over consolidated clay shows non-coaxial behaviour and the greater the OCR values or the smaller the deviatoric stress, the larger the non-coaxial angle. The effects of b values on the non-coaxial behaviour of over consolidated clay are also observed. HIGHLIGHTS Over-consolidated clay subjected to pure rotation of principal stress. The effects of OCR, deviatoric stress and b value were analyzed. Negative EPWP and stress dilatancy were observed in over consolidated clay. The greater the OCR, the larger the non-coaxial angle.

A Deep Learning Approach for Predicting Two-Dimensional Soil Consolidation Using Physics-Informed Neural Networks (PINN)

The unidirectional consolidation theory of soils is widely used in certain conditions and approximate calculations. The multidirectional theory of soil consolidation is more reasonable than the unidirectional theory in practical applications but is much more complicated in terms of index determination and solution. To address the above problem, in this paper, we propose a deep learning method using physics-informed neural networks (PINN) to predict the excess pore water pressure of two-dimensional soil consolidation. In the proposed method, (1) a fully connected neural network is constructed; (2) the computational domain, partial differential equation (PDE), and constraints are defined to generate data for model training; and (3) the PDE of two-dimensional soil consolidation and the model of the neural network are connected to reduce the loss of the model. The effectiveness of the proposed method is verified by comparison with the numerical solution of PDE for two-dimensional consolidation. Moreover, the FEM and the proposed PINN-based method are applied to predict the consolidation of foundation soils in a real case of Sichuan Railway in China, and the results are quite consistent. The proposed deep learning approach can be used to investigate large and complex multidirectional soil consolidation.

Mud pumping in high-speed railway: in-situ soil core test and full-scale model testing

Mud pumping induced by moving train loads on rainwater-intruded roadbed causes intensive track vibrations and threatens safety of high-speed trains. In this paper, a vehicle–track–subgrade finite element model was established to analyze the dynamic responses of a ballastless track, and results showed that the concrete base and roadbed were detached because of the whipping effect arising from the rainwater intrusion channel. An in-situ soil core test showed that the intruded rainwater accumulated in roadbed to form standing water and saturated the roadbed. The flapping action of the concrete base caused by the whipping effect led to mud formation mixed with fine particles and rainwater, which migrated upward under the pore-water pressure (PWP) gradient. Mud pumping resulted from continuous particle migration in the saturated roadbed under moving train loads: under normal roadbed condition, coarse and fine particles were uniformly distributed in the roadbed; in early period of mud pumping, fine particles migrated downward to bottom of the roadbed because of the rainwater infiltration flow; in middle stage of mud pumping, fine particles migrated upward and gathered at the roadbed surface under PWP gradient; in later period of mud pumping, fine particles were entrained and removed with the dissipation of excess PWP. Moreover, a full-scale physical model was established to reproduce mud pumping, and polyurethane injection remediation against mud pumping was validated on this physical model. The remediation method was applied to an in-situ mud pumping. The deviation of the vertical track profile reduced remarkably and remained at a low level within half a year, showing a good long-term service performance of the polyurethane remediated roadbed.

Seismic responses of rectangular tunnels in liquefiable soil considering spatial variability of soil properties

The objective of this paper was to investigate the dynamic response of a tunnel-soil system in the soil with spatial variability of shear modulus with various coefficients of variation and scales of fluctuation. The soil shear modulus was highlighted and modeled as an isotropic random field using the spectral representation method, then mapped into the finite difference model. The dynamic stochastic responses of the excess pore water pressure ratio, the liquefied zone, the ground displacement, and the uplift displacement of the tunnel were discussed. It was observed that the effect of coefficient of variation was pronounced in which an increase of the coefficient of variation brought out a reduction in the corresponding dynamic stochastic responses. However, the scale of fluctuation was found to be insignificant in the tunnel soil system.

Field investigation of steel pipe pile under lateral loading in extensively soft soil

The construction of railway and highway embankments has a significant influence on the behavior of existing pile foundations, especially in the situation of high embankments and extensively soft soils, which are commonly encountered in coastal areas. A high embankment might produce large lateral movement and bending moment to the existing adjacent piles, which would cause the failure of the pile if the surcharge loading is not properly considered. A field test was designed and performed to investigate the effect of lateral surcharge loading on the existing adjacent pile in extensively soft soils. A 4 m high embankment was constructed in five lifts and was close to the existing adjacent steel pipe pile with a length of 35 m. The deformation of the pile and the soft soils, the excess pore water pressure, and lateral earth pressures were measured during the surcharge loading test. The test results showed that the lateral displacement of the steel pipe pile at the ground surface exceeded 229.9 mm and could not maintain constant due to the surcharge loading. The lateral displacement decreased along with the pile depth and was relatively small when the pile depth exceeded 10 m. Large lateral displacements were observed in the soft soils at different locations. The surcharge loading zone showed obvious downward displacements, while the soft soils close to the loading zone showed upward displacements. The excess pore water pressure changed regularly with the construction of the embankment, and its maximum value reached 53.6 kPa. The lateral earth pressures that acted on the pile continuously increased with the increase in the embankment height, which caused large deformation of the pile.