Soft Ground Research Articles

Evaluating vehicle trafficability on soft ground using wheel force information

In the areas of aerospace and military industry, wheeled vehicles are expected to have the ability of passing various ground surfaces, including lunar soil, sand, marsh, mud flat, etc. This makes vehicle trafficability on soft ground become a very hot research topic. There are very a few difficulties in the present research of vehicle trafficability on soft ground, such as obtaining wheel-ground interaction information, inaccurate identification of soil mechanical characteristics parameters, and single evaluation index. In this paper, a novel approach of evaluating the vehicle trafficability on soft ground using wheel force information is proposed. As parts of the proposed approach, the methods of obtaining wheel force information, identification of soil mechanical characteristics parameters and integated method of trafficability evaluation, are discussed in detail. The proposed approach was validated through a practical test.

A study on settlements of road embankments on soft ground using vertical drains

In civil engineering, the study of embankment settlement on soft ground is a vital geotechnical task in order to maintain serviceability of the road embankment, pavement, and facilities. This paper presents a study on settlements of road embankment on soft ground using vertical drains, including prefabricated-vertical drain (PVD), sand drain (SD), and sand compaction pile (SCP) on a number of packages of Hanoi – Haiphong Expressway Construction Project. The effectiveness of settlement prediction of vertical drain solutions is evaluated considering the ratios between the observed consolidation settlements and settlements predicted in the Detailed Design, in relation to the thickness of soft soil and the depth of treatment. Regression analysis is used to establish the correlation between the observed settlement and the height of embankment. The results show that (i) the design generally overestimated settlements; (ii) the ratios between observed and predicted settlements tend to positively correlate with the thickness of soft soil and the depth of treatment, and (iii) there are positive correlations between the height of embankment and the observed settlement. These correlations can be a valuable source of reference for anticipating settlements in basic design of highway projects with soft ground treated by vertical drains, in the regions that have geological stratum similar to Thabinh and Haihung formations of Bacbo Plain

Assessing sand sedimentation in drilling slurry using particle methods for ground excavation management

In the construction of cast-in-place concrete piles, residual sand portions in the drilling slurry that are not completely removed can significantly influence the strength and characteristics of the concrete piles. Understanding the sedimentation behavior of these sand portions during concrete placement is crucial to ensure pile quality. However, directly observing this process in real-time at construction sites is challenging, making it difficult to accurately assess the impact of the sand portions. When predicting the sedimentation of sand particles in drilling slurry, the conventionally used Stokes' equation can only express one-dimensional motion of a single particle size, but to accurately capture the real phenomenon, three-dimensional behavior must be considered. In this study, a numerical simulation method based on the particle method (MPS method) was used to visually evaluate the sedimentation process of sand in the drilling slurry. By modeling the drilling slurry and sand particles using the MPS method, the complex three-dimensional settling behavior of sand particles in the drilling slurry at both laboratory and full scales was successfully represented, demonstrating the effectiveness of this modeling approach. The MPS method allows for the analytical visualization of the three-dimensional sedimentation behavior, enabling real-time observation and quantitative evaluation of the sand sedimentation process. Using this method, the temporal evolution of the settling process of sand components in the drilling slurry can be tracked, providing valuable insights into factors that influence the quality of concrete piles. The results of this study demonstrate the potential of the MPS method for visually evaluating the settling behavior of sand components in drilling slurry. This approach offers a more accurate and reliable method for assessing the impact of residual sand on the strength and characteristics of cast-in-place concrete piles. By enhancing the understanding of this process, more effective foundation techniques can be developed to improve the safety and stability of structures built on soft ground, particularly in earthquake-prone regions where fine particles such as clay and silt pose additional challenges to construction practices.

Hydraulic conductivity of cement and fly ash stabilised clay mixes – Application to soil mixing techniques for seepage barrier construction

In-situ ground improvement techniques, namely, deep soil mixing, jet grouting, cutter soil mixing, and mass stabilisation are often utilized to improve the strength of soft grounds, and construct seepage barriers. Due to economic and environmental concerns, there is a global shift towards using industrial wastes such as fly ash (FA) from conventional binders such as ordinary Portland cement and lime. There is a plethora of literature on unconfined compressive strength (UCS) of cement-treated clays, and clays treated with fly ash-cement mixes with alkali activator (FCAA) binders. However, much remains unclear about the hydraulic conductivity of the FCAA-treated clays as low permeable hydraulic barrier systems. In this paper, the hydraulic conductivities of cement-treated and FCAA-treated clays are studied both quantitatively and qualitatively for different binder-content, FA:cement ratios, curing periods, and effective confining stress. The hydraulic conductivity of treated clay is measured by performing a series of accelerated permeability tests using a custom-fabricated triaxial system. The trends obtained from the measured hydraulic conductivity values are explained from the observations of X-ray diffraction analysis and scanning electron microscopy analysis. Results showed that the values of hydraulic conductivity for cement-treated clay were mostly higher than those of untreated clay. On the contrary, the hydraulic conductivities for the FCAA clay mixes were comparable to, or even lower than those for the untreated clay. The hydraulic conductivity reduced with the increase in effective confining stress; the influence of effective confining stress, however, became less substantial for 28 days curing period and higher cement-content (40 and 50 %). The relationships between the hydraulic conductivity, UCS, and water-binder (w/b) ratios were also determined for both cement-treated and FCAA-treated clays. The exponential function was found suitable to express the relationship between hydraulic conductivity and UCS of treated clays. In contrast, a strong logarithmic relationship was obtained for measured values of hydraulic conductivity and adopted w/b ratios. The results shall serve as a guide to adopting suitable binder-content or target UCS for achieving design hydraulic conductivity in ground improvement projects that involve cement and/or FCAA-treatment of clays.

Integrated Time-Dependent Analysis of a Hydraulic Structure on Soft Foundations during Construction

An integrated model that considers multiphysics is necessary to accurately analyze the time-dependent response of hydraulic structures on soft foundations. This study develops an integrated superstructure–foundation–backfills model and investigates the time-dependent displacement and stress of a lock head project on a soft foundation during the construction period. Finite element analyses are conducted, incorporating a transient thermal creep model for concrete and an elasto-plastic consolidation model for the soil. The modified Cam-clay model is employed to describe the elasto-plastic behavior of the soil. Subsequently, global sensitivity analyses are conducted to determine the relative importance of the model parameters on the system’s response, using Garson’s and partial derivative algorithms based on the backpropagation (BP) neural network. The results indicate that the integrated system exhibits pronounced time-dependent displacement and stress, with dangerous values appearing during specific periods. These values are easily neglected, highlighting the importance of integrated time-dependent analysis. Construction activities, particularly the backfilling process, could cause a sudden change in stress and significantly impact the stress redistribution of the superstructure. Additionally, the mechanical properties of concrete have a significant impact on the stress on the superstructure, while the mechanical properties of the soil control the settlement of the integrated system.

Behavior of group of geosynthetic encased granular piles with tire chips- aggregates mixture under static and cyclic loading – A model study

The current study addresses the dual challenges of improving the performance of soft soil beds subjected to static and cyclic stresses and managing the environmental impact of waste tire disposal. This research contributes valuable insights into the sustainable use of recycled tire chips in granular pile construction, coupled with the efficacy of combi-grid encasement for improved soft ground under static and cyclic loading conditions. A series of laboratory model tests were carried out on a group of granular piles to examine the principal parameters, such as the selection of geosynthetic materials and cyclic loading characteristics, including cyclic loading amplitude (qca) and cyclic loading frequency (f). The granular pile composition consists of (25% tire chips + 75% aggregates). The performance of granular piles on improved ground is assessed based on the settlement reduction ratio (Sc,r), accumulation of excess pore water pressure (Pexc), and stress concentration ratio (n). The key findings from static model tests are that the load-bearing capacity is significantly increased with installing a group of ordinary granular piles (= 58%) and substantially increased with combi-grid encasement (= 335%). The effectiveness of ordinary granular piles (OGP) in enhancing the performance of a soft soil bed becomes greater when subjected to lower cyclic loading frequencies (f) and smaller cyclic loading amplitudes (qca). The incorporation of combi-grid encasement greatly enhanced the cyclic performance of a group of granular piles by substantially minimizing cyclic-induced settlement (Sc) across both principle parameters f and qca. This study also examines the increased cyclic stresses on the improved soft bed, resulting in the accumulation of excess pore water pressure (Pexc) development, which is reduced to a greater extent with the help of combi-grid encasement across both principle parameters.

Seismic performance of soft soil foundation with a new type of assembled wall tuned mass damper.

The design of tuned mass damper (TMD) parameters is influenced by the soil-structure-TMD coupling system; thus, it is important to consider the soil-structure interaction (SSI) for the vibration control effect of the TMD. Recently, the acquisition of TMD parameters considering soil-structure interactions has only remained at the theoretical stage, lacking relevant experimental verification. Traditional TMD face the problems of occupying a large building space, increasing construction costs, and non-replaceable components. In this study, an assembled wall-type damping TMD was designed. By comparing the dynamic response of the uncontrolled and controlled structures equipped with the newly assembled wall-type damping TMD in the shaking table test on a soft soil foundation, we analyzed whether the SSI effect was considered in the TMD design parameters on the damping effect of the newly assembled wall-type tuned mass damper. The TMD parameters optimized using the artificial intelligence algorithm were verified experimentally. The results indicated that the traditional TMD design parameters were discordant because the SSI effect was not considered. The SSI effect in the soil effectively reduces the dynamic response of the superstructure. By considering the SSI effect and improving the multi-population genetic algorithm, a wall-type damping TMD with optimized parameters can achieve a good damping effect.

Settlement Forecast of Marine Soft Soil Ground Improved with Prefabricated Vertical Drain-Assisted Staged Riprap Filling

By comparing different settlement forecast methods, eight methods were selected considering the creep of marine soft soils in this case study, including the Hyperbolic Method (HM), Exponential Curve Method (ECM), Pearl Growth Curve Modeling (PGCM), Gompertz Growth Curve Modeling (GGCM), Grey (1, 1) Model (GM), Grey Verhulst Model (GVM), Back Propagation of Artificial Neural Network (BPANN) with Levenberg–Marquardt Algorithm (BPLM), and BPANN with Gradient Descent of Momentum and Adaptive Learning Rate (BPGD). Taking Lingni Seawall soil ground improved with prefabricated vertical drain-assisted staged riprap filling as an example, forecasts of the short-term, medium-term, long-term, and final settlements at different locations of the soft ground were performed with the eight selected methods. The forecasting values were compared with each other and with the monitored data. When relative errors were between 0 and −1%, both the forecasting accuracy and engineering safety were appropriate and reliable. It was concluded that the appropriate forecast methods were different not only due to the time periods during the settlement process, but also the locations of soft ground. Among these methods, only BPGD was appropriate for all the time periods and locations, such as at the edge of the berm, and at the center of the berm and embankment.

Ichnology and Main Types of Trace Fossils

Ichnology studies the traces of activities left by modern and ancient animals. The advantage of trace fossils of biological activity and solid fossils is that the trace fossils are not modified by late diagenesis. They are the original deposits of organisms on the sedimentary environment and can directly reflect the living habits of animals and their living environment. According to the sedimentary substrate in which animals live, trace fossils can be divided into tracks, traceways, trails, crawling traces, resting traces, burrows on the soft ground, and erosion traces made by animals on the hard ground.

Ground Tire Rubber as a Sustainable Additive: Transforming Desert Sand Behavior

Managing waste tires presents a significant challenge globally, particularly in regions experiencing high temperatures and shortage of landfill sites. This issue is affecting countries like Kuwait, where the abundance of waste tires is a major source of environmental and safety risks, particularly during the intensely hot summer months. This extreme heat has sparked numerous fires, leading to substantial air pollution due to thick black smoke. Given the limited disposal options, recycling waste tires and finding practical applications for ground tire rubber (GTR) is essential. To address the challenge, a comprehensive laboratory testing program was conducted, using locally produced rubber aggregates as an additive to Kuwait's local surface sands. Two new variables were examined namely the size and gradation of the GTR, and the density of the compacted mixes. For this purpose, two different sizes of rubber aggregates, fine and coarse produced locally, were utilized, and the impact of relative compaction on the strength and compressibility of the mixtures was investigated by testing samples compacted to the maximum density and to 95% of the maximum density. The results suggest that combining local surface sands with rubber tire additives results in a lighter, more permeable, and compressible material, contributing significantly to sustainable waste management. With 20% rubber additive the maximum dry density decreased by nearly 20%, and the permeability increased by 1.74–3.11 times and the compression index increased by 6.15 and 3.8 times with fine and coarse rubber respectively. The angle of friction remained unchanged at 36° with the addition of coarse rubber and decreased by 3°–4° with fine rubber. The change in behavior although not an increase in the strength and stiffness, offers a range of suitable practical applications in civil engineering and environmental management, including use as a drainage layer, embankment construction on soft ground, earth fill around retaining walls, an additive in asphalt mixes, and in manufacturing compressible tiles for sports facilities.

Geostress-associated settlements of a raft-foundation building due to shield tunnelling in soft ground

The stress state of soil may affect the building settlements induced by tunnelling, which, however, has not been well understood. In this study, 3D numerical analyses combined with in-situ measurements were performed to investigate the geostress-associated settlements of a raft-foundation building due to tunnelling in soft ground. Basically, two types of geostress fields were investigated: the first type considered the effect of additional stress generated in the foundation soil (FAS) due to building weight; while in the second type, a sequential twin tunnelling was presumed, and the effect of additional soil stress induced by the first tunnel (TAS) on the building response to the second tunnel was considered. The results indicated that FAS may aggravate the stress release of the foundation soil, and thus gave rise to a larger building settlement or inclination. In the sequential tunnelling process, the effect of TAS can be more complex: when the first tunnel lowered the stress of foundation soil, TAS effect of the first tunnel may help reduce the building settlements induced by the second tunnel; otherwise, it may aggravate building settlements. In addition to TAS effect, the sheltering effect was also found to play an important part in twin tunnelling.

Field testing performance of prebored precast piles with enlarged base in soft ground

Prebored precast piles with an enlarged base (PPEB piles) are constructed using an innovative and environmentally sustainable method, which notably reduces noise, soil squeezing, and mud discharge. Although PPEB piles have been widely applied in many cities in China, their bearing performance, including side friction and end resistances, on soft ground remains relatively unelucidated. This paper focuses on case studies of vertical-bearing PPEB piles based on a group of vertical static load field tests in Shanghai. The following conclusions are drawn: (1) Compared with traditional hammered-driven piles, PPEB piles exhibit better construction quality and load-bearing performance, as well as a relatively slow increment of settlement even under ultimate loading. (2) The resistance of the enlarged base section of the PPEB pile was approximately 16.3% of the total resistance under ultimate loading. (3) Compared with the values proposed in the Shanghai Foundation Design Code, the side friction resistance of the PPEB pile in deep silty sand (34.5–39 m) exhibited a considerable increase of approximately 156%. Additionally, the side friction in the soft ground was close to the values proposed in code. The case studies provide practical guidelines for the application of PPEB piles in soft ground.

FAGSO-BP neural network model for settlement prediction of soft soil foundation

To address the problem of difficulty in theoretical formulas and numerical analysis methods to consider the prediction of foundation settlement in the case of multiparameter coupling, the fireworks algorithm (FWA) with a gravity search operator (FAGSO) is introduced into the back propagation (BP) neural network model, and the weight and threshold processes in the neural network are improved by the FAGSO algorithm. A soft soil foundation settlement prediction model based on a FWA optimized BP neural network (FAGSO-BP) with a gravity search operator is proposed. Based on the second phase of the soft foundation treatment project of the Shatian Port Area, Humen City, and Dongguan City, the parameters of pile load height, pore water pressure, and groundwater level were collected and tested. The results indicate that the average relative error of the predicted cumulative settlement value of the soft soil foundation was 0.06%, root mean square error was 7.68, mean absolute error was 4.30, mean absolute percentage error was 1.40%, and mean square error was 59.98. Compared with the BP neural network, GA-BP neural network, and FWA-BP neural network, the error was smaller and the model stability was higher.

Load-bearing response of deep content mixing soft soil composite foundation based on the geotechnical centrifugal model test

Deep cement mixing (DCM) is an effective method of treating soft underwater soil foundations. Currently, the real-time failure development of a composite foundation cannot be obtained by most model tests of DCM pile foundation reinforcement. In this study, a circuit device for identifying pile failure and that can reflect the real-time working state of piles arranged at different positions in a soft soil composite foundation was developed. By applying this device to a geotechnical centrifugal model test, the load-bearing response process of a bank slope reinforced with a soft-soil composite foundation and DCM piles was studied. The failure development law of the DCM piles, ultimate surcharge of the bank slope, failure mode of the foundation, and the pile-soil stress ratio were determined from the test results. The law obtained in this study provides a reference for the application of DCM piles in underwater soft soil foundation engineering.

Centrifuge model test study on consolidation characteristics of soft soil base with drainage pile in highway widening

In recent years, the widening of existing highways has emerged as a prominent focal point in highway construction. However, uneven settlement often occurs when highways are widened, which sometimes leads to the cracking of pavements, particularly, on a soft soil foundation. Drainage piles have been used to strengthen soft soils by reducing settlement and accelerating drainage consolidation. However, the drainage effect on the consolidation characteristics of drainage piles is still unclear. In this paper, a series of centrifuge model tests were conducted to study the consolidation characteristics of soft soil fixed with drainage piles in highway widening. The test results show that an obvious settlement exists in the old embankment shoulder, whereas a smaller settlement occur near the embankment axis and below the toe of the new embankment. In comparison with the ordinary pile and drainage board, the drainage piles hasten the settlement process of the soil foundation, indicating that drainage piles can significantly accelerate the consolidation of the soft soil foundation.

Responses of metro shield tunnels to an adjacent deep excavation in Shanghai soft ground

Deformation in metro shield tunnels is a consequence of conducting adjacent deep excavations. Accordingly, this research examines the response of existing metro shield tunnels in Shanghai’s soft ground to nearby deep excavations, focusing on how tunnel deformation correlates with the distance to the excavation. Utilizing actual measurement data from metro shield tunnels located 12-45 m from an 11.5-24.1-m-deep excavation, the study initiates with a project overview before analyzing the deformation data of the metro tunnels. This analysis includes the settlement and transverse convergence of both upward and downward lines. Furthermore, by integrating the settlement history curve and settlement increment ratio statistics, the study explores the deformation of the metro tunnels across different construction stages of the adjacent excavation. Additionally, the effect of the distance to the excavation on metro tunnel deformation is discussed, considering identical excavation depths, supporting stiffness, construction levels, and soil conditions. This investigation aims to provide insights applicable to similar cases and inform future research.

Behavior of Cofferdam Using Non-uniform Geotextile Mats on Soft-overlying-stiff Foundation

Non-uniform geotextile mats are employed as soft foundations in cofferdams. However, investigations on the influence of complicated geological conditions on the mechanical behavior of cofferdams are limited. We investigated the behavior of a cofferdam using non-uniform geotextile mats to explore the failure mechanism of non-uniform geotextile mats over a soft overlying stiff foundation and quantify its stability. The two typical failure modes, global and local failure modes, differed distinctly in the velocity field and sliding surface shape. Geometric factors may partially affect the failure mode, whereas a higher soil strength can enhance the stability of the cofferdam, especially when stiff soil is involved. The failure mechanisms of cofferdams using non-uniform geotextile mats on soft overlying stiff clay and a corresponding stability prediction method are proposed to guide the design of cofferdams using non-uniform geotextile mats.

Deformation and reinforcement effects of soft soil deep foundation pits for shield tunnel launching

Deformation and reinforcement effects of soft soil deep foundation pits for shield tunnel launching

Numerical analysis of failure mechanism and stability of reinforced embankment with DCM soft soil composite foundation

The deep cement mixing (DCM) method has been widely used in offshore geotechnical engineering. At present, the reinforcement form of pile has been researched widely, but there is a lack of understanding of the failure mode of DCM pile composite foundation reinforcement for bank slopes. In this paper, a series of unconfined compression tests was conducted to obtain necessary numerical analysis parameters. A series of study on the failure mechanism and stability control of DCM pile composite foundation reinforcement bank slope has been conducted through numerical analysis. The results of numerical analysis indicate that under different reinforcement conditions, there exists an optimal reinforcement depth, and the safety coefficient will gradually stabilize at 1.45; The bending moment of the piles under the bank slope the bending moment of the pile body under the road surface Under different overloads. The maximum bending moment of the pile body is located near one-third of the pile body, and the maximum bending moment of the pile body is located between the shoulder and foot of the slope.

Mechanical mechanism of soft soil foundation improved by geosynthetic-reinforced pile-supported technology based on field experiment

Geosynthetic-reinforced pile-supported (GRPS) technology is an effective method for improving soft soil foundations. Conducting field tests is crucial for accurately assessing the mechanical behavior of GRPS technology. Based on the fourth expansion project at Pudong Airport, field tests were conducted to investigate the effects of GRPS technology on soft-foundation treatment. Specifically, the tests examined the changes in the pile and soil settlement, pore water pressure, and pile and soil stress. The results showed that the settlement of the GRPS foundation mainly occurred during the loading period, accounting for approximately 65% of the total foundation settlement. Increasing the pile modulus and reducing the pile spacing decreased the total foundation settlement. The filling load was mainly transferred to the piles through the soil arching effect, resulting in a large excess pore water pressure in the soil layer near the pile tip. In addition, when the filling height was low, the load transfer relied predominantly on the tensile membrane effect of the geogrid, which was more pronounced near the piles. However, as the filling height increased, the soil arching effect surpassed the tensile membrane effect and played a key role in load transfer.