The vacuum preloading combined with prefabricated horizontal drain (PHD) is an effective foundation treatment method for high-water-content dredged slurry. As the key design parameter of PHD vacuum preloading technology, the vertical spacing of PHD directly affects dredged slurry consolidation efficiency. However, its optimal value has not been clearly determined yet, so it is necessary to systematically identify the optimal vertical spacing for this technology. In this study, indoor model tests were conducted to assess the impacts of two primary variables: variable PHDs vertical spacing and differing distances of the upper/lower PHD layers from the slurry surface and bottom. The variation of mass of drained water, dissipation of pore water pressure, and surface settlement were monitored. Meanwhile, the water content and vane shear strength of the consolidated dredged slurry were measured. The results show that the optimal spacing for the PHDs arrangement is 450 mm, with the upper layer 200 mm away from the slurry surface and the lower layer 100 mm away from the slurry bottom. Compared with the worst group, the optimal group showed a 22.51% increase in mass of drained water and a 14.02% increase in surface settlement. Additionally, it had a 6.15% decrease in water content and a 6.99% improvement in vane shear strength. This study confirms that optimizing the vertical spacing and layer arrangement of PHDs can improve the vacuum pressure transmission efficiency and enhance the overall consolidation effect of dredged slurry. It provides key technical parameters and a scientific basis for the design of vacuum preloading combined with PHD in practical engineering.

Coastal silty soft soils feature high water content and low bearing capacity, which readily induce large pile-soil differential settlement, amplify negative skin friction (NSF), and compromise foundation safety. To clarify NSF evolution in silty soft soil foundations, four centrifugal single-pile model tests with initial water content of 40%, 50%, 60%, and 70% were conducted to investigate the long-term behaviors of settlement of pile and soil, axial force of pile, NSF and neutral point (NP) under surcharge consolidation. The test results show that the higher the initial water content of the soil, the greater the compressibility. During the 5-year loading consolidation process, the soil settlement and the pile-soil differential settlement increase significantly with the increase of initial water content and consolidation time, which leads to the nonlinear growth trend of the peak value of axial force and the peak value of the absolute value of NSF. In addition, the NP migrates upward over time and essentially stabilizes after 2 years, while the NP shifts downward with increasing initial water content. An empirical equation correlating the initial water content with the NP depth ratio was established in this study, providing reliable data support for the design and construction of coastal pile foundations.

As an underground concealed project, pile foundations are often unable to effectively resist groundwater buoyancy, necessitating consideration of anti-floating measures. Given the limitations of current monitoring technologies in achieving real-time, full life-cycle monitoring of uplift piles, the development of distributed, high-precision, and cost-effective monitoring methods remains a key focus in the field. In this study, a sensorenabled piezoelectric geocable (SPGC) based on flexible piezoelectric sensing is used to monitor the bearing capacity characteristics of uplift piles in a distributed manner. Strain gauges are installed for comparative analysis, and the influences of pile diameter in equal diameter uplift piles and the diameter of the enlarged bottom in enlarged-base uplift piles on their ultimate bearing capacity are investigated. The test results indicate that the variation trend of pile strain obtained from SPGC normalized impedance is generally consistent with that measured by strain gauges, and a linear calculation formula for impedance-strain correlation is established. Significant differences are observed in the axial force and side friction resistance between equal diameter uplift piles and enlarged-base uplift piles. Additionally, the ultimate bearing capacity of uplift piles increases markedly with larger pile diameters and diameter of enlarged bottom. Under the same pile diameter, the ultimate bearing capacity of equal diameter uplift piles is substantially lower than that of enlarged-base uplift piles, with the latter exhibiting a 16.7%-66.7% increase. These findings demonstrate that flexible piezoelectric sensing technology holds promise as a novel solution for the long-term operation and maintenance monitoring of pile foundation anti-floating systems.

To address the negative skin friction in pile foundations caused by soil settlement under large-area surcharge loading, this study investigated two foundation treatment methods used in coastal reclamation areas: shallow vacuum preloading (≤ 5 m) and subsequent deep (secondary) vacuum preloading (15–20 m). Field tests on the negative skin friction of a single pile were conducted using two groups of PHC pipe piles in the New Campus Project of Zhejiang Oriental Vocational and Technical College. By monitoring pile and surrounding soil settlement, pore water pressure, pile shaft axial force, and shaft skin friction, the evolution of negative skin friction and the dynamic characteristics of the neutral point were analyzed. The test results show that deep vacuum preloading can significantly reduce pile settlement, surrounding soil settlement, the peak pile shaft axial force, the peak negative skin friction along the pile shaft, and the neutral point depth ratio. Over time, pile settlement, soil settlement, pile shaft axial force, and negative skin friction all increased, whereas the neutral point moved upward and gradually stabilized. Compared with shallow vacuum preloading, deep vacuum preloading reduced the average negative skin friction coefficient along the pile shaft by 30.00

Filter mudcakes are produced by filtering and dewatering waste slurries from engineering construction and river dredging. The poor mechanical properties of filter mudcakes make them unsuitable for subgrade filling, but converting them into subgrade filling that meets road engineering requirements solves disposal problems. In this work, the performance of modified filter mudcakes (MFMs) was assessed through the optimisation of curing agents, assessment of engineering characteristics and centrifuge modelling. The solidification effect was found to be greatest when 8% ground granulated blast-furnace slag, 4% quicklime and 1% gypsum were added to the filter mudcake. For this mix, the compressive strength was 2730 kPa after 7 days and the water stability coefficient was 85%. The California bearing ratio of these filter mudcakes was 33.7% at 7 days, and the compression coefficient (<0.1 MPa-1) and the permeability coefficient (5.39 x 10(-8 )cm/s) both met the specification requirements at a dosage of 4%. As the degree of compaction was increased from 88% to 97%, the final settlement of the new MFM subgrade at the centre decreased from 50.9 mm to 35.4 mm, and that of the shoulder decreased from 42.3 mm to 29.6 mm, meeting specification requirements (<100 mm). The results support the excellent long-term stability and application potential of MFMs as subgrade materials.

High-density polyethylene (HDPE) pipes, valued for their flexibility and corrosion resistance, are increasingly used in infrastructure, yet their behavior under uneven settlement in soft soil remains underexplored.Uneven settlement directly threatens the safety of buried pipelines. This study investigated the mechanical response of HDPE pipelines in soft soil foundations through a combined approach of model tests and numerical simulation (FLAC3D). The results indicate that, under single-factor conditions, increasing the pipe diameter significantly reduces the peak stress in the pipeline (by up to 44.78% in tests), while its effect on suppressing vertical displacement remains limited. Conversely, increases in burial depth and settlement range exacerbate the bending moment, stress, and displacement responses, leading to more pronounced structural deformation. Unlike single-factor studies, this study conducted a systematic multi-factor coupling analysis, which reveals that under shallow burial conditions(≤1.4 m), using a large diameter (≥480 mm) can effectively control both stress and displacement. For a small settlement range (<2.7 m), pipe diameter plays a dominant role in displacement control, whereas stress rebound may occur for a large settlement range (>5.4 m). The influence of burial depth is more significant within a small settlement range (<3.6 m) but diminishes for a large settlement range (>4.5 m). Based on the numerical results, a multi-factor coupled prediction model for stress and displacement was established using nonlinear surface regression, with a verified prediction error within ±10%. However, its applicability is strictly limited to the geological conditions and parameter ranges studied herein. In practical applications, it must be validated against site-specific conditions and should not be extrapolated to scenarios significantly different from those considered in this study.The findings of this study provide theoretical foundations and practical tools for the preliminary design and selection, monitoring point placement at critical sections, maintenance strategy optimization, safety assessment, and design refinement of HDPE pipes in soft soil regions.

Buried bending deformation and failure are the most critical threats to pipeline structural integrity, making realtime deformation monitoring essential. This study presents a novel monitoring approach using a sensor-enabled piezoelectric geocable (SPGC) to assess buried pipeline bending deformation. Overhead and buried pipeline experiments were conducted under dynamic loading conditions using a dynamic-static test system. Monitoring performance was evaluated using voltage and impedance signals generated by the SPGC. The overhead pipeline tests demonstrated that impedance signals accurately characterize deformation states, with the bending degree exhibiting a proportional relationship with normalized impedance variation. The tensile side provided the most reliable deformation data. For buried pipelines subjected to simulated vehicle loads, fully-loaded vehicles generated voltage signals 2.5 times higher and normalized impedance variations 1.8 times greater than those from empty vehicles at identical speeds. Furthermore, generalized voltage-speed and impedance-strain calculation models were derived through laboratory testing. Unlike conventional strain gauges limited by spatial resolution and power dependence, the SPGC system enables real-time, distributed, and energy-autonomous monitoring of buried pipeline deformation. These findings demonstrate the potential of the SPGC-based monitoring technique for long-term buried pipeline integrity assessment, providing critical deformation data for structural health assessment.

To investigate the effect of PVD installation depth on the efficiency of surcharge preloading for soft ground improvement, centrifuge model tests were conducted based on a typical airport runway project. Four test groups were designed with PVD installation depths of 18, 22, 26, and 30 m. Key indicators, including settlement, porewater pressure, water content, and undrained shear strength, were monitored to systematically analyze the influence of PVD depth variation on soil consolidation behavior. The results showed that with each 4 m increase in PVD depth, the settlement increment was 10.39 %, 4.44 %, and 0.81 %, respectively. When the installation depth exceeded 22 m, the improvement effect tended to plateau. Therefore, under the conditions of this project, the reasonable installation depth of PVDs lies within the range of 18-22 m, while the precise optimal depth still requires further investigation. Based on one-dimensional and multidimensional consolidation theories, this study proposed a settlement prediction method that converts multi-stage surcharge into an equivalent single-stage load through stress-time integration correction. The predicted results agreed well with the experimental data, with errors in shallow and deep settlement controlled within 5.3 % and 11.6 %, respectively, both within the acceptable range for engineering applications.

For the convenience of designing reinforced concrete (RC) box culverts in road/railway transportation systems, a practical graphic method for evaluating the vertical stress increments under an RC box culvert has been developed. Firstly, like Osterberg's method, influence values for the vertical stress increments under the shoulder, the middle of the slope, and the toe of an embankment have been newly produced in graphic forms. Secondly, a graphic form correction factor (alpha 1) has been created to consider the vertical load difference between an RC box culvert location and the both side embankments. Then multiplying the vertical stress increments from an embankment load by alpha 1, the desired vertical stress increments under an RC box culvert can be obtained. The method was applied to a road RC box culvert in Saga, Japan, to demonstrate its usefulness. With the evaluated vertical stress increments, settlements under the RC box culvert were calculated and they are comparable with the field measurements. Further investigation about this case history regarding to the effects of soil-cement columns under the box culvert was carried out by finite element analysis.

To study the dynamic seismic responses of buried socketed high-density polyethylene (HDPE) pipes in sandy soil foundations during seismic excitations, pipe acceleration, pipe strain and displacement response data were obtained via indoor scaling tests and FLAC3D numerical simulations to establish a socketed HDPE pipe model. The numerical simulation results were compared with the experimental data to validate the effectiveness of the model. A large-diameter HDPE pipe model was established to simulate actual engineering situations. The difference in the seismic liquefaction response between socketed pipes and nonsocketed pipes was systematically analysed. The mechanical responses of socketed pipes were determined via numerical simulations. Compared with those of straight pipes, the acceleration response and strain of socketed HDPE pipes undergo greater changes, whereas the displacement of straight pipes is greater. The peak strain of the socketed pipe decreases axially from the centre to the ends, with the maximum strain occurring at the pipe centre and the minimum strain occurring at the pipe ends, and the peak strain in the middle of the pipe is more than 4 times greater than that at the ends of the pipe. The peak acceleration of the socketed pipes and its range both increase with increases in the input acceleration peak. The displacement of the socketed pipes increases with increases in the input acceleration peak and the depth of the pipeline, and it decreases with increases in the relative density of the soil body and the diameter of the pipe. In the numerical analysis, different diameters were simulated many times, and an equation for the axial strain and displacement of a pipeline with changes in the pipeline diameter is proposed. At a given burial depth, the socketed pipe strain decreases with increasing pipe diameter, whereas the pipeline displacement increases. For a given pipe diameter, both the strain and displacement of a socketed pipe increase with increasing burial depth.

The explosion replacement method is an effective treatment for weak soil layers exceeding 15 m in thickness. To investigate the effect of explosive deposition depth on treatment efficacy,model tests involving silt blasting were conducted,and vane shear tests were performed using an automatic cross shear apparatus. The effects of explosive deposition depth on the undrained shear strength and water content of silt were examined. Additionally,the soil microstructure before and after blasting at various depths was observed using a scanning electron microscope. The results indicated that blasting disrupted the soil structure around the explosion point,increasing the void ratio and causing a sudden drop in undrained shear strength,thereby forming a blasting disturbance zone. The soil outside the disturbed zone was compacted,resulting in increased undrained shear strength and forming a blast-compacted zone. After blasting,soil water content decreased;the farther from the explosion center,the more significant the decrease. When the explosive deposition depth was 0.3 times the soil layer thickness,the reduction in undrained shear strength was most significant at about 27％,and the disturbed zone was largest at approximately 19.2d (where d is the explosive diameter),making the explosion most effective. Therefore,there exists an optimal deposition depth of the explosive,which makes the best explosion treatment effect and the largest range of disturbed soil. And,the range of blasting disturbance can be determined by undrained shear strength. The results of the study can provide technical support and reference for the design of explosive deposition depth in related projects.

The horizontal deformation monitoring of rock and soil masses is of great significance in soft soil foundations, foundation pits, seawalls, and slope engineering fields. Although existing technology has been widely used in the horizontal displacement monitoring of rock and soil masses, no single technology can fully meet the long-term, distributed, automated, and low-cost requirements. Therefore, a novel piezoelectric inclinometer tube is proposed, which, for the first time, is combined with a sensor-enabled piezoelectric geocable (SPGC) as well as installed with a strain gauge (SG) and distributed strain-sensing optical cable (DSSOC). The results show that, compared with polyvinyl chloride (PVC) piezoelectric inclinometer tubes, acrylonitrile-butadiene-styrene (ABS) piezoelectric inclinometer tubes are more suitable for monitoring large deformations of rock and soil masses because of their high toughness and elastic modulus. In addition, the establishment of a normalized impedance change value–strain calibration formula for the piezoelectric clinometer tube revealed that there is a significant linear correlation between the normalized impedance change value and strain at different measuring points. Moreover, a theoretical formula for the normalized impedance change value and deflection of the cantilever beam was obtained by combining the beam bending theory and difference method. The experimental results show that the accuracy values of the strain and deflection are 10 με and 1 mm, respectively. This study provides a solid theoretical basis and practical guidance for the application of distributed piezoelectric sensors based on SPGCs in the horizontal displacement monitoring of rock and soil masses and thus has significant engineering application potential.

The soil extrusion effect induced by pile driving poses a significant risk to the safe operation of buried pipelines in soft soil foundations. It is therefore essential to investigate the mechanical response of pipelines under such conditions. In this study, field tests were first carried out to explore the propagation law of soil pressure in soft soil foundations subjected to pile driving-induced extrusion and to reveal the dynamic response characteristics of adjacent High-Density Polyethylene (HDPE) pipelines. Second, an integrated finite element model of the HDPE pipe-soft soil-pile system was established using the Arbitrary Lagrangian-Eulerian (ALE) large-deformation meshing method in Abaqus. Comparison between the numerical results and field measurements confirmed the accuracy of the model and the reliability of the tests, achieving an accurate simulation of the dynamic response of the buried pipeline under soil extrusion. Finally, further numerical analyses were conducted to evaluate the influence of pipe diameter, pipeline burial depth, pile–pipe distance, and pile driving depth. The main findings are as follows: (1) The deformation of the pipeline near the pile side is significantly greater than that at the far end, while the top and bottom parts of the pipeline experience the least deformation.(2) The horizontal displacement of the pipeline increases with pile driving depth until approximately 15 m; beyond this depth, the variation in pipeline stress and displacement diminishes.(3) When the pile–pipe distance exceeds 7.1 times the pile diameter, the effect of soil extrusion on the pipeline becomes negligible.(4) Safe operation of the pipeline can be ensured by controlling the burial depth between 2 and 3.5 m, using a pipe diameter in the range of 500–600 mm, and maintaining a pile-pipe distance greater than 7.1 times the pile diameter.

In recent years, numerous offshore marine structures, such as offshore wind turbines, oil and gas drilling platforms, have been continuously constructed in reclaimed areas. Due to the clays of foundation formed by hydraulic fill techniques, a portion of the clay may remain in an under-consolidated state. As a result, in such engineering projects, the under-consolidated marine soft clay around pile foundations is typically affected by cyclic shear stress induced by cyclic loadings such as waves, wind, and earthquake. In this study, a suite of cyclic simple shear tests were performed on marine soft clay with various cyclic stress ratios (CSRs) and consolidation degrees (Us). Several useful conclusions are obtained. First, the cyclic shear strength increases with the U, while specimens with higher U require greater CSR to reach their critical state. Second, at the same CSR, the higher U specimen showed predominantly elastic deformation with smaller strain, while the lower U specimen exhibited a combination of elastic and plastic deformation, along with more significant softening. Finally, a softening model for marine soft clay considering Us was then established based on the proposed threshold CSR and verified against the experimental results.

Traffic load is one of the main factors affecting problems such as cracking, warping deformation, and subsidence of buried pipelines in soft soil. Therefore, the study of the dynamic responses of buried pipelines in soft soil under traffic loading is important. Through field experiments, the propagation of soil pressure in soft soil under traffic loading and the dynamic responses of pipelines were studied. Combined with Abaqus software, a traffic load DLOAD subroutine was developed, and a 3D finite element model of the integrated rigid pipe-soft soil system under traffic loading was established to accurately simulate the dynamic response characteristics. Based on the numerical model, the influences of various factors were explored. The research results revealed that (1) under the combined effect of axial stress at the bottom of the pipe and the Poisson effect of the internal pressure, the maximum axial stress at the bottom centre of the pipe was the highest. (2) Under the long-term action of a vehicle load, the impact on the dynamic response of the pipeline increased. (3) When the burial depth of the pipeline was between 2 and 3 m, the pipe diameter was between 200 and 700 mm under shallow burial conditions, and the speed and load had to be controlled to avoid driving under overload conditions, ensuring safe operation of the pipelines in the research area.

The causes of geological fissures are complex, and the disaster situation is very serious, and it is very difficult to carry out early warning and monitoring. To this end, a new type of Sensor-enabled piezoelectric geocables (SPGC) is used for geological fissure monitoring, which has piezoelectric effect and impedance-strain effect. Model tests were carried out to study the accuracy of fixed-point SPGC to determine the location of geological cracks, and the characteristics of soil internal deformation were analyzed based on SPGC monitoring data, so as to achieve early warning effect. The test results show that SPGC can accurately locate the crack location compared with the traditional point sensor, and the shorter the segmentation, the more accurate the identification of the crack location. The faster the soil collapse rate, the smaller the crack volume, the smaller the normalized impedance of SPGC, and the smaller the soil strain change. The voltage generated by the vibration of SPGC can react significantly to the internal collapse of the soil. The results show that SPGC can realize the catastrophic location and precursor identification of ground fissures.

Geosynthetic materials are widely used as reinforcement materials, and strain monitoring is becoming increasingly important to ensure the safety of reinforced soil structures. A sensor-enabled piezoelectric geobelt (SPGB) is composed of piezoelectric ceramics, conductive carbon black, and a base material. Owing to the impedance strain and piezoelectric effects, the SPGB can sense its own strain and ambient vibration through impedance and voltage, while providing enhancement. To determine the performance of SPGB at various service temperatures, the strain signal response of SPGB at various service temperatures was investigated experimentally. The results showed that the fracture strength and elongation at break of the SPGB were affected by the coupling of temperature and tensile strain rate. Experimental regression analysis established functional equations to predict the strength and sensing characteristics of the SPGB under different temperature and deformation conditions. Based on the application of SPGB at different ambient temperatures, a linear normalized impedance correction model considering the temperature effect was proposed in this study. The measurement accuracy of SPGB is up to millimeter, with an average error of 3.75

In the combined method of horizontal drainage board vacuum preloading and sealed geomembrane bags, the horizontal drainage board serves as the sole drainage channel, making its diameter coefficient critical in determining the appropriate filling height. Based on the theoretical model for vertical drainage boards, this study analyzes the influence range of a horizontal drainage board using the sealed geomembrane bag method. Model tests show that the maximum influence diameter coefficient of the horizontal drainage board lies between 24.6 and 25.3. By referencing the minimum influence diameter coefficient typically used for vertical drains, the applicable range for horizontal drainage boards in sealed geomembrane bags is suggested to be 15.0 to 25.3. Results also reveal that the upper slurry layer drains more efficiently than the lower layer due to gravity-assisted downward flow. In contrast, upward drainage in the lower zone is less effective. Adding a drainage board at the bottom creates a direct flow path and improves consolidation in the lower zone. To mitigate clogging during testing, the drainage board was embedded in geotextile, which reduced clogging to some extent. However, as clogging is difficult to avoid in practice, the proposed coefficient does not account for its effects.

Grouting-vacuum preloading is a recently developed efficient soft soil improvement technique that enhances soil consolidation efficiency by promoting soil particle flocculation. However, as the grouting pipe lifting rate governs soil flocculation, its optimal value remains undetermined in engineering practice, making it necessary to identify the optimal rate. To address this gap, grouting-vacuum preloading tests under different lifting rates were conducted in this study. Pore water pressure dissipation, settlement, and drainage volume were monitored during the test, while the vane shear strength and water content of the consolidated soil were systematically measured. The results showed that excessively high or low lifting rates reduce the soil consolidation efficiency by inhibiting pore water pressure dissipation and decreasing drainage capacity. When the lifting rate was 35 cm·min−1, pore water pressure dissipation was significantly accelerated, drainage volume markedly increased, and settlement substantially enhanced, with the consolidation time shortened by 69.21