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We used three-dimensional finite element analysis to simulate an X-shaped cast-in-situ concrete (XCC) pile-supported embankment with asphalt pavement under the load of moving vehicles. We investigated the dynamic stress transfer mechanism, the trapping effect of the embankment and XCC piles, and the asymmetric distribution of dynamic stress around an XCC pile. The results show that the embankment and XCC piles play an important role in spreading the radiated energy as a waveguide. The ground in the center is subjected to the majority of dynamic stress owing to the trapping effect of the embankment and XCC piles. There is also a significant difference between the dynamic stress in the flat and concave areas within up to two times the outsourcing diameter of the XCC pile.

Energy piles have dual function of supporting a superstructure and acting as a shallow geothermal heat exchanger. Field tests on the thermal response characteristics of micro-steel-pipe piles under five operating temperature conditions (summer intermittent: 12 h for heating and 12 h for stopping as a cycle, winter intermittent: 12 h for cooling and 12 h for stopping as a cycle, summer continuous, recovery and winter continuous) were conducted. The heat transfer efficiency, the coefficient of performance (COP), the temperature and thermal induced stress of micro-steel-pipe piles were measured and analyzed. The results indicated that values of the heat transfer efficiency and COP were decreased with the process of cycles. The average COP and the average heat exchange rate per unit length under summer intermittent condition were relative higher than those in the corresponding period under summer continuous condition (the same trend in winter). The heat transfer efficiency in winter conditions was relative lower than that in summer conditions. In this field test condition, the additional compressive stress in micro-steel-pipe piles was increased by 200 kPa/°C, and the average heat exchange rate per metre was −49 W/m under Condition 5, 95 W/m under Condition 3.

This paper introduces a simplified method to investigate the influence of thermal loads on the shaft friction and tip resistance of energy piles. The method is based on the influence factors (λ and η) which are back-calculated drawing on a large number of field and model tests. Values for λ and η during heating and cooling are suggested. Moreover, a new equation is proposed to calculate total shaft friction. The equations concerning the relationship between η and temperature difference are recommended to investigate the impacts of the thermal load on the pile tip resistance. The slope of the linear equation of an end-bearing pile is 2.14 times that of a floating pile indicating that the pile tip resistance of an end-bearing pile is much more affected by the same thermal load.

In this paper, a predictive model for simulating temporal behaviors of clayey sand during seepage-induced erosion has been developed by coupling discrete element method (DEM) with computational fluid dynamics (CFD). In this model, the particle–fluid coupling simulation is solved by a “fixed coarse-grid” scheme in 3D particle flow code (PFC3D), and the suffusion of clay matrix in the initiation of erosion is converted to a degradation process of bonding strength between particles according to a degradation law. The law is derived from the well-known shear stress threshold law dealing with soil internal erosion, which is based on two erosion parameters—the critical shear stress and the erosion coefficient. Then the degradation law is implemented in the CFD–DEM model via developing customized code using the Python language. The ability of the model to predict the interfacial erosion of soils is confirmed by two numerical tests. The results are seen to match the empirical criteria, such as revealing a clearly defined critical tangential shear stress, beyond which erosion occurs, and a positive correlation between the rate of erosion and the pressure gradient. It is believed that the numerical model is able to reproduce the time-dependent evolution process of seepage-induced erosion in clayey sand.

This paper presents the experimental results of small-scale model tests of an instrumented floating energy pile group in which the piles were embedded in dry medium-dense sand and subjected to the seasonal temperature pattern of the city of Nanjing in China. The study also included a model test to assess the effect of including nonthermal piles on the thermo-mechanical behaviour of the floating energy pile group. For comparison, a model test of a single floating energy pile embedded in the same soil and subjected to a similar temperature pattern was also conducted. The results show that the thermo-mechanical behaviour of an energy pile group is different from that of a single energy pile in terms of the thermally induced change in axial pile stress and the displacement of the pile top and tip. This difference in behaviour could be explained by the higher lateral confining pressure expected on a single pile than on a pile in a group due to pile interaction effects, which could lead to different end restraint boundary conditions. We conclude that the thermo-mechanical behaviour of an energy pile is controlled mainly by the end restraint boundary conditions.

Three-dimensional numerical analyses were conducted to study the effects of the ratio of the breadth of an existing horseshoe-shaped tunnel to the diameter of new circular tunnels (B/D) on the interaction of perpendicularly crossing tunnels in sand. Hypoplasticity constitutive soil model with small strain stiffness was adopted in the study. For different cover depths, the computed results revealed that the induced maximum settlement at the centre of an existing tunnel invert is unaffected by its size. The sagging settlement profile along the existing tunnel crown gradually changes into a hogging shape with increasing B/D ratios for smaller cover depth. The mid-plane deformations of the existing tunnel are vertically elongated and horizontally compressed.

Foundation settlement under long-term train loads is a realistic engineering issue. Train loads can cause a different stress path and non-coaxial strain compared to other loads. The non-coaxial str...

The Micropile-Mechanically Stabilized Earth (MSE) wall, specially designed for mountain roads, is proposed to improve the MSE wall local stability, global stability and impact resistance of roadside barriers. Model tests and the corresponding numerical modeling were conducted to validate the serviceability of the Micropile-MSE wall and the reliability of the numerical method. Then, a parametric study of the stress and deformation of Micropile-MSE wall based on the backfill strength and interfacial friction angle between backfill and backslope is conducted to evaluate its performance. The test results indicate that the surcharge-induced horizontal earth pressure, base pressure and lateral displacement of the wall panel of Micropile-MSE wall decrease. The corresponding numerical results are nearly equal to the measured values. The basic failure mode of MSE wall in steep terrain is the sliding of backfill along the backslope, while A-frame style micropiles are capable of preventing the sliding trend. The maximum resultant displacement can be decreased by 6.25% to 46.9% based on different interfacial friction angles, and the displacement can be reduced by 6% ~ 56.1% based on different backfill strengths. Furthermore, the reduction increases when the interfacial friction angle and internal friction angle of backfill decrease. In addition, the lateral displacement of wall panel, the deformation of backfill decrease and the tension strain of geogrid obviously, which guarantees the MSE wall functions and provides good conditions for mountain roads.

In order to obtain the temperature variation of super long cast-in-place pile, the monitoring test of pile temperature is carried out based on Brillouin Optical Time Domain Reflectometer (BOTDR) technology. The results show that the temperature decreases with the depth gradually, it decreases under the ground and the temperature variation is little between 18 m and 111 m in depth. The temperature variation of pile top monitored by optical fiber sensor and air temperature variation are compared, it shows that the temperature variation of pile top is basically in accordance with air temperature variation. The numerical model is built to study the temperature variation of super long cast-in-place pile, the monitoring and numerical results are analyzed together according to the site situation, and it proves that the trend of numerical simulation and optical fiber monitoring results are consistent.

Soil behavior can reflect the characteristics of principal stress rotation under dynamic wave and traffic loads. Unequal amplitudes of tensile and compressive stresses applied to soils have complex effects on foundation soils in comparison with the pure principal stress rotation path. A series of undrained cyclic hollow torsional shear tests were performed on typical remolded soft clay from the Ilexi area of Nanjing, China. The main control parameters were the tensile and compressive stress amplitude ratio (α) and the cyclic dynamic stress ratio (η). It was found that the critical η tended to remain constant at 0.13, when the value of the compressive stress amplitude was higher than the tensile stress amplitude. However, the influence of the tensile stress was limited by the dynamic stress level when α= 1. For obvious structural change in the soil, the corresponding numbers of cyclic vibration cycles were found to be independent of α at low stress levels and were only related to η. Finally, a new method for evaluating the failure of remolded soft clay was presented. It considers the influence of the tensile and compressive stresses which caused by complex paths of the principal stress rotation. This criterion can distinguish stable, critical, and destructive states based on the pore-water-pressure-strain coupling curve while also providing a range of failure strain and vibration cycles. These results provide the theoretical support for systematic studies of principal stress rotation using constitu tive models.

Energy piles are now considered as an efficient energy solution for heating and cooling buildings. However, once the energy pile has a breakdown especially of the heat exchange elements, it is diff...

A closed-form solution for the limit pressure of undrained cylindrical cavity expansion in anisotropic clay is provided. The solution considers the effect of anisotropic strength and initial in-situ stress. The cavity-wall limit pressure under an isotropic initial stress (K = 1) was larger than the anisotropic initial stress (K ≠ 1) and holds true for all anisotropic strength ratios. The cavity-wall limit pressure increased linearly with increasing anisotropic strength ratio. The cavity-wall limit pressure was a minimum for a polar angle θ = π/2.

To study the horizontal bearing behavior of cast-in-place concrete (PCC) pipes, a horizontal static load model test is conducted based on the optical frequency domain reflectometry (OFDR) technology. The deformation distribution in the pile is studied. Results show that the pile moment increases with the horizontal load, whereas the position of the maximum point of moment is roughly unchanged. Moreover, the calculated and measured values of horizontal displacement at the pile top are compared; results show that the values are in agreement, which demonstrates that the deformation of a PCC pile can be successfully measured using the OFDR technology.

A three-dimensional dynamic finite element model of track-ballast-embankment and piled raft foundation system is established. Dynamic response of a railway embankment to a high-speed train is simulated for two cases: soft ground improved by piled raft foundation, and untreated soft ground. The obtained results are compared both in time domain and frequency domain to evaluate the effectiveness of the ground improvement in mitigating the embankment vibrations induced by high-speed trains. The results show that ground improving methods can significantly reduce the embankment vibrations at all considered train speeds (36- 432 km/h). The ground response to a moving load is dictated largely by the relationship between load speed and characteristic value of wave velocities of the ground medium. At low speeds, the ground response from a moving load is essentially quasi-static. That is, the displacements fields are essential the static fields under the load simply moving with it. For the soft ground, the displacement on the ballast surface is large at all observed train speeds. For the model case where the ground is improved by piled raft foundation, the peak displacement is reduced at all considered train speeds compared with the case without ground improvement. Based on the effect of energy-dissipating of ballast-embankment-ground system with damping, the train-induced vibration waves moving in ballast and embankment are trapped and dissipated, and thus the vibration amplitudes of dynamic displacement outside the embankment are significantly reduced. But for the vibration amplitude of dynamic velocity, the vibration waves in embankment are absorbed or reflected back, and the velocity amplitudes at the ballast and embankment surface are enhanced. For the change of the vibration character of embankment and ballast, the bearing capacity and dynamic character are improved. Therefore, both of the static and dynamic displacements are reduced by ground improvement; the dynamic velocity of ballast and embankment increases with the increase of train speed and its vibration noise is another issue of concern that should be carefully evaluated because it is associated with the running safety and comfort of high-speed trains.

Although semi-open H piles have been widely used, geometric effects (GEs) on H-shaped piles in consolidating ground subjected to negative skin friction (NSF) and downdrag are still not well...

It is an economic way to use the piled embankment for the construction of embankment over soft soil. The combination of piles and reinforcement can effectively reduce the differential settlement at the surface of embankment. The paper presents a simplified model for analysis of an embankment of granular fill on soft ground supported by reinforcement and piles. This model is based on consideration of the arching effect in granular material proposed by Hewlett & Randolph. The vertical equilibrium of the unit body at the center of pile caps immediately below the reinforcement is established. The refinements of the model are that the failure mechanisms of the arch both at the crown and at the pile cap were considered, three-dimensional situation was taken into account for reinforced piled embankment, calculation of the vertical stress carried by the subsoil due to arching effect and reinforcement for multi-layered soil was proposed. Using the simplified model, the influence of embankment height, one-dimensional compression modulus of subsoil, tensile stiffness of reinforcement on stress reduction ratio (SRR) and tensile force of reinforcement is investigated. It is found that the model can be used to assess the relative contribution of the reinforcement and subsoil. The results show that subsoil gives a major contribution to overall vertical equilibrium, while the reinforcement gives obvious contribution at relatively large settlement. The inclusion of the reinforcement can reduce the vertical stress acting on the subsoil. The simplified model is then evaluated by three case studies. The results of this model show good consistence with these cases.

The effect of the subsoil is generally ignored, as this support may be unreliable in the long-term as consolidation proceeds. In this paper, the idealised long-term behaviour of the subsoil was investigated, in conjunction with the reinforcement. The numerical analyses showed that the subsoil could make a major contribution to overall vertical equilibrium. Moreover, the reinforcement can make obvious contribution at relatively large settlement. The subsoil response was found to be somewhat underestimated by the consideration of one-dimensional stiffness. The contribution of the subsoil to the vertical equilibrium is generally more significant than that of the reinforcement. Finally, a simple equation was achieved to predict the maximum settlement at the surface of the subsoil.

A new pile type with tapered pile body and an enlarged pile tip, referred herein as belled wedge pile, has been developed to improve both side resistance and tip resistance of pile when compared to the conventional tapered or belled cross-section piles. The new pile shape, due to wedge shape, can also reduce the development of negative skin friction when the surrounding soils are deforming under the applied surcharge loads. The construction method, quality assurance and quality control of the belled wedge piles are described. A numerical modelling technique using FLAC3D is used to perform numerical simulations to gain insight on the load carrying capacity and the load transfer behaviour of the belled wedge piles, in comparison to other pile shapes including the conventional belled piles, the tapered piles and uniform cross-section circular piles. The comparison study of the performance of these four pile shapes under compression loads, uplift loads and surcharge loads indicates that the belled wedge pile ...

A development of 2 and 3 storey town houses and 4 storey apartment blocks were constructed on a site bordering the River Erne in Enniskillen, Northern Ireland. Within two years of completion, the ground deformations around the buildings constructed on the ‘load transfer platform’ (LTP) were becoming noticeable. Sometime later, the pile caps ‘punched’ into the material above, causing significant deformation. According to detailed investigation and assessment of the cause of failure (Milligan, 2006) [1], the problems were caused by excessive and continuing deformation of the load transfer platform. The analytical analyses have been used to investigate the performance of reinforced piled embankment over very soft soil to understand the reason for failure. Results showed that subsoil could give a major contribution to overall vertical equilibrium, and reinforcement can only give contribution at relatively large settlement. The performance of actual structures has on occasions been problematic when relying on multiple layers of relatively low strength geogrid.

Based on Mohr-Coulomb (M-C) criterion, the parameters of Druker-Prager (D-P) criterion for geomaterial were determined under non-associated flow rule, and thus a new D-P type criterion was presented. Two assumptions were employed during the derivation: 1) principal strains by M-C model and D-P model are equal, and 2) the material is under plane strain condition. Based on the analysis of the surface on π plane, it is found that the proposed D-P type criterion is better than the D-P criterion with M-C circumscribed circle or M-C inscribed circle, and is applicable for stress Lode angle less than zero. By comparing the predicted results with the test data of sand under plane strain condition and other D-P criteria, the proposed criterion is verified and agrees well with the test data, which is further proved to be better than other D-P type criteria in certain range of Lode angle. The criterion was compiled into a finite difference package FLAC3D by user-subroutine, and was used to analyze the stability of a slope by strength reduction method. The predicted slope safety factor from the proposed criterion agrees well with that by Spencer method, and it is more accurate than that from classic D-P criteria.

Combined with practical engineering application, the test researches were carried out to analyze the soil compacting effects of Cast-in-situ concrete pipe pile while the pile was driven by vibration hammer. This article is focused on the characteristics of soil uplift and lateral deformation around pile, included surface soil and deep soil. In addition, the change characteristic of pore water pressure of soil around pile is also analyzed, and some useful rules were concluded. All researches are helpful to optimize the construction parameters, such as distance between piles, pile diameter etc., to improve the quality of pile foundation, also to reduce the construction impact on environment.

Stress state of soft soil foundation under vacuum preloading is completely different from its counterpart under surcharge preloading, and the method of calculating the final settlement of soil mass by means of surcharge preloading (positive pressure) is unreasonable in present design. According to a case of soft foundation stabilized with vacuum preloading and through consolidated-undrained triaxial (CU) test on the specimens sampled in situ, the stress paths under different confining pressure are obtained. The settlement of soft foundation treated with vacuum preloading is calculated by strain isoline method. Compared with the practically measured field data, the errors are analyzed and discussed.

The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions, and the rotation of principal stresses can also be simulated by the model with cyclic behavior of anisotropic consolidated sands. Seismic residual deformations of typical caisson quay walls under different engineering situations are analyzed in detail by the plastic model, and then an index of liquefaction extent is applied to describe the regularity of seismic residual deformation of caisson quay wall top under different engineering situations. Some correlated prediction formulas are derived from the results of regression analysis between seismic residual deformation of quay wall top and extent of liquefaction in the relative safety backfill sand site. Finally, the rationality and the reliability of the prediction methods are validated by test results of a 120 g-centrifuge shaking table, and the comparisons show that some reliable seismic residual deformation of caisson quay can be predicted by appropriate prediction formulas and appropriate index of liquefaction extent.

Aimed at problems lying in the exiting methods for calculation of laterally loaded piles installed in layered soils, the elasto-plasticity solution of cast-in-place concrete pipe pile with large diameter (PCC pile) in layered soil under lateral load based two-parameter foundation model and unity limiting force profile, deduced the finite difference solution based unity limiting force profile(LFP), established the calculation program of the displacement and internal force of pile. It was shown that the calculated pile moment and pile displacement coincided very well by computation and comparison of model test and FEM, verified the method’s correction. Meanwhile, the method was more precise and efficient than the existing conversion methods of subgrade modulus. Therefore, it could be useful for the design and analysis of PCC pile under lateral load.

A new method of using large diameter, cast-in-situ concrete pipe piles for the construction of highway and high-speed railway embankment over soft clay is introduced in this chapter. This so-called PCC pile method offers a relative speedy and cost-effective way for soil improvement as compared with other existing soil improvement methods. The principles and construction techniques involved in this method are described. Large-scale model tests are conducted to investigate the performance of piles under vertical and horizontal loads. Case studies are presented to illustrate the application of this method for highway and high-speed railway.

X-section cast-in-place (referred to as XCC) pile, which is one of new pile types developed by Hohai University, is widely used for pile foundation and pile-supported embankment over soft ground in China. However, little research has been carried out on this new type pile, especially the surrounding soil disturbance under XCC pile installation. This paper presents an analytical solution for estimating the horizontal stress and displacement of surrounding soil of XCC pile after XCC pile installation. The reliability and accuracy of the present solution are verified by comparing them with the field test results. Then, parametric studies, such as outsourcing diameter(a), open arc distance(b), open arc angle(θ), the undrained strength(Su), the limit pile cavity pressure(Plim), and the radius of the plastic zone(Rp), are discussed for the practice engineering design. The results show that the stress and displacement distributions of surrounding soil calculated by this paper are in agreement with field test results.

A new driven cast-in-place Y pile was developed according to the innovative design concept of Y pile and the traditional construction technology of driven cast-in-place pile in China. In this paper the pile-soil stress ratio was calculated based on the hypothesis that the pile body was modeled as an equivalent constant section elastic bar. The influence factors and variation of the pile-soil stress were analyzed. Then the theoretical results were compared with the field data obtained from a ground improvement project for an expressway bridge abutment using driven cast-in-place Y piles. According to the field static loading test and theoretical analysis, the driven cast-in-place Y pile can improve the bearing capacity significantly with the same engineering quantity. It can be indicated that Y pile is either a friction-based friction pile or end-support friction pile and has a great bearing capacity. Besides the Y pile composite foundation has better bearing characteristics while the foundation settlement and post-construction settlement of embankment are substantially reduced. The results from this study can provide reference for the future design of similar composite foundation.

A multi-shear mechanism plasticity model is defined in strain space to simulate pore pressure generation and development in sand under cyclic loading and undrained conditions in the paper. The seismic horizontal deformation of typical caisson quay are analyzed in detail by the plasticity model under different engineering situations. An index of liquefaction extent is applied to describe the pattern of residual horizontal deformation of quay top under different engineering situations. Some prediction equations are derived from the F-E analysis results between residual horizontal deformation and extent of liquefaction in the relative safe soil site. Then, the reasonableness and the reliability of the derived prediction equations are validated by a 1g shaking table test results.The comparison results show when the unit weight of quay is relatively lower, the predicted value is better by the application of high liquefaction extent and even regressive equation, and when the unit weight of quay is relatively higher, the predicted value is better by the application of high liquefaction extent and broad band regressive equation of lower curve.