Soft Soil Foundation Research Articles

Construction and Reinforcement Technology Practice of Soft Soil Foundation in Road Construction

Construction and Reinforcement Technology Practice of Soft Soil Foundation in Road Construction

Analysis and Application of Soft Soil Foundation Treatment Technology in Construction Engineering

Analysis and Application of Soft Soil Foundation Treatment Technology in Construction Engineering

A Review on the Behaviour of Combined Stone Columns and Pile Foundations in Soft Soils when Placed under Rigid Raft Foundation

In the last few decades, it has been observed that raft foundations are very commonly used as a foundation solution for moderate to high rise structures either by resting on stone columns or on piles in soft soils. It is believed that, combining stone columns and piles in one foundation system is the more suitable foundation for medium rise structures. The combined foundation system provides a superior and more economical alternative to pile, and a more attractive alternative to stone columns in respect to ground improvement. This paper presents the review of existing studies reported in the literature in the last two decades about the behaviour of stone columns under raft foundations and piled raft foundation in soft soil, notably the failure mechanism and the bearing capacity. Also, a limited work from the literature concerning the performance of combined (pile/stone columns) foundation system in soft soil is comprised. Furthermore, very extensive ongoing research work regarding the investigation and study on the performance of combined (pile/stone columns) foundation system in soft soils is discussed. The main goals and methodology to study the performance of the combined (pile/stone columns) foundation systems in soft soil are also addressed.

The Rheological Analytical Solution and Parameter Inversion of Soft Soil Foundation

In soft soil engineering projects, the building loads are always required to be symmetrically distributed on the surface of the foundation to prevent uneven settlement. Even if the buildings and soft clay are controlled by engineers, it can still lead to the rheology of the foundation. The analytical solution based on the Laplace integral transformation method has positive significance for providing a simple and highly efficient way to solve engineering problems, especially in the long-term uneven settlement deformation prediction of buildings on soft soil foundations. This paper proposes an analytical solution to analyze the deformation of soft soil foundations. The methodology is based on calculus theory, Laplace integral transformation, and viscoelastic theory. It combines an analytical solution with finite theory to solve the construction sequences and loading processes. In addition, an improved quantum genetic algorithm is put forward to inverse the parameters of soft soil foundations. The analytical solution based on Laplace integral transformation is validated through an engineering case. The results clearly illustrate the accuracy of the method.

A new simplified method for calculating short-term and long-term consolidation settlements of multi-layered soils considering creep limit

The long-term consolidation settlement of soft soils under infrastructures is seriously concerned in coastal areas. In practice, soft soil ground is usually composed of multiple layers with different properties, and the effect of soil creep is nonnegligible. However, in conventional consolidation analysis, creep is seldom included during the “primary” consolidation. With conventional creep model, creep strain will reach infinity with time, which is unreasonable in the long-term view. In this study, a new simplified method based on Hypothesis B is presented to calculate both short-term and long-term consolidation settlements of multi-layered soils exhibiting non-linear creep. There are three main characteristics for this new simplified method: (a) the consolidation analysis for multi-layered soil is conducted using spectral method; (b) a nonlinear creep function with creep limit is incorporated to calculate both short-term and long-term creep settlements; (c) the “primary” consolidation and creep are calculated independently and combined with an empirical parameter α together with the consolidation degree U for correcting the creep settlement. Finite element analysis with a self-developed Elastic Visco-Plastic (EVP) constitutive model considering creep limit was also carried out. Verifications by field cases and finite element simulation demonstrate the efficiency and accuracy of the new simplified method in calculating the long-term settlements of soft soil ground under varied engineering conditions. Influences of major parameters selection in the calculation of the new simplified method are also discussed.

Experimental and Numerical Investigation on the Effects of Foundation Pit Excavation on Adjacent Tunnels in Soft Soil

Excavations near an existing tunnel are often encountered in underground construction. The influence of the excavation on the adjacent tunnels is not yet fully understood. This study presented a centrifugal model test about excavation next to existing tunnels in soft soil foundation. The bending moment of diaphragm wall, surface settlement, tunnel deformation, and earth pressure around the tunnel were mainly studied. The influence of tunnel location is further studied by numerical simulation. During the stabilization stage of foundation pit, the diaphragm walls present convex deformation towards foundation pit, and the surface settlement outside the diaphragm wall appears to be the concave groove type. During the overexcavation stage, the diaphragm walls are almost damaged, and the shear bands are nearly tangent to the tunnels. The displacement of the tunnels and the surface settlement rapidly increase. The deformation of the diaphragm wall and the surface settlement are limited by the existing tunnel. The numerical results indicate that the change of tunnel location has little effect on the retaining wall but an obvious effect on the tunnel itself.

Experimental Investigation of Influence of Air-Boost Pressure and Duration on Air-Boost Vacuum Preloading Consolidation

Abstract The air-boost vacuum preloading method has become popular in soft soil foundation reinforcement, especially in land reclamation projects. However, there are still some consolidation mechan...

Performance Evaluation of Recycled-Plastic-Pin-Supported Embankment over Soft Soil

AbstractThis paper investigates the efficacy of recycled-plastic pins (RPPs) for controlling the ground settlement of soft foundation soil. Two field test sections (6×7.5 m) were constructed over ...

Creep modelling of soft soil based on the fractional flow rule: Simulation and parameter study

The creep deformation of soft soil is a critical factor in geotechnical design of engineering facilities built on soft soil foundations. In this study, a novel fractional creep model for soft soil is developed by introducing the Almeida fractional derivative into the classic elastic-viscoplastic model. A series of numerical analyses are conducted to determine the kernel function of the proposed model with the best performance, and the good agreement between the model predictions and test results is observed. With the advantage of introducing the fractional flow rule, the fractional creep model exhibits higher accuracy and convenience than conventional models as fewer material parameters and state variables are required. Furthermore, a parameter study reveals that the fractional order directly relates to the stress level, and the different deformation patterns of soft soil under low and high stresses could be reflected by the tendency of the order.

Application Analysis of Urban Road Soft Soil Foundation Treatment Engineering

Application Analysis of Urban Road Soft Soil Foundation Treatment Engineering

Effect of Geological Conditions on Vibration Characteristics of Ground Due to Subway Tunnel: Field Investigation

Field measurements of the ground vibrations due to subway moving load are carried out in two distinct geological conditions (soft soil ground, granite ground) in China. Vibration measurements are performed on the tunnel ground after the vibration generated by another running subway transmitting in the medium. Vibration accelerations, frequency spectrum and 1/3 octave curves are obtained and the effects of geological conditions of the measured ground vibrations are well considered. It is found that vibration acceleration of the granite ground is approximately 5 times higher than soft soil ground under the subway trains moving load. In addition, much higher frequency vibrations is observed in the granite ground, which is absent in the soft soil ground. Furthermore, the maximum vibration level in granite ground is nearly 90 dB that seriously affects adjacent structures, sensitive machineries, and even passengers.

Laboratory Investigation on Performance of Soil–Cement Columns Under Axisymmetric Condition

The inclusion of soil–cement columns in soft soil is a ground improvement technique that is used to reduce the settlement and improve the bearing capacity of the soft soil ground. In the present study, model tests have been carried out on soft soil improved with groups of end-bearing and floating columns under the axisymmetric condition to evaluate the relative improvement in the stiffness and failure stress of the soft ground due to the installation of soil–cement columns. The effect of various group foundation parameters, such as area ratio, length and diameter of columns and binder content are investigated. The failure mode of end-bearing and floating columns after exhumation are presented. For the same area ratio, of the improved soil–cement columns to the present soft clay deposit, the usage of the smaller sized soil–cement columns rather than large size soil–cement columns is found to be relatively more beneficial in case of both end-bearing and floating columns. The stiffness and failure stress of the composite ground increase with an increase in the length of the columns. However, the increase in strength is only marginal for the increase in column length beyond 10 times the column diameter. In the case of end-bearing columns, area ratio has a significant effect on failure pattern. At an area ratio of 25%, the column failed by outward displacement and bending. On the other hand, at an area ratio of 32%, the columns failed due to bending at approximately one-half to two-third of the column length from the base of the footing. In the case of floating column, the relative strength of columns to the soil $$( {c_{\text{uc}}}/{c_{\text{us}}})$$ appears to be the major governing factor. For the high value of $$( {c_{\text{uc}}}/{c_{\text{us}}})$$ used in the present study, punching failure was observed with slight outward displacement and some horizontal cracks for area ratios of 25% and 32%. For validation, the failure stresses of model ground were compared with the results obtained using numerical analysis. The results show a good agreement between the bearing capacity value obtained from the experiment and the numerical software.

Analysis on the Control Effect of Enhanced Cushion on the Difference Settlement of New and Old Subgrade in Soft Foundation Area

In order to reduce the differential settlement of the extended urban highway splicing segment, we monitored the junction of the new and old subgrade in the practical engineering, analyzed the value of pavement deformation. It found that the smaller the modulus ratio of the new and old subgrade, the greater the non-uniform settlement value. At the same time, the uneven settlement and lateral displacement of the road can be effectively reduced by using the pile-reinforced cushion structure. So the results show that the pile-reinforced cushion structure can effectively reduce the uneven settlement and lateral displacement of the old and new roads, strengthen the links between old and new roads; To enhance the stability of subgrade, it can be used for widening the old road in soft soil foundation.

Stability analysis and improvement of coastal soft soil foundation

In the construction process of coastal buildings, how to improve the stability of the soft soil foundation of coastal buildings so as to increase its service life is always a problem that needs to be paid attention to and solved in the construction process. In Qingdao sea beach, for example, according to the force of the foundation, the foundation of the wave force and tidal forces modeling analysis, and puts it into the fluid - sand erosion simulation model, the soft foundation in the best shape of certain external environment, slow down the erosion of various kinds of flow strength of foundation. Finally, we conduct sensitivity analysis and conclude that our model has good stability.

Simulation Analysis on Drainage Consolidation Characteristics of Hydraulic Fill Soft Soil

Based on the treatment of dredger fill soft soil foundation in Eastern Shantou, Guangdong Province, consolidation theory and numerical simulation based on composite consolidation coefficient are used to study the consolidation characteristics of dredger fill soft soil, and the results are compared with the field monitoring results. The calculation results show that the theoretical consolidation degree of the site is 93.4%, which is basically consistent with the final consolidation degree of field monitoring. In the first two stages of surcharge loading, field monitoring is faster than theoretical calculation. The field monitoring value of the final settlement is 1342 mm, which is about 10% less than the theoretical value. The final average consolidation degree of the two models is 97.9%, which is 4.7% more than the field monitoring value. The results show that the pore water pressure law is obvious, the dissipation rate is about 16% higher than the field monitoring value, and the consolidation effect is more obvious. The numerical simulation of the composite coefficient model has certain applicability and can be used to guide the design and construction of similar projects.

Research on ride comfort of vibratory rollers: Part-2 Cab’s semi-active HPM with fuzzy control

In order to further enhance the ride quality of vibratory roller’s cab used by the hydro-pneumatic mounts (HPM), based on a nonlinear dynamics model of the vibratory rollers under interaction of the deformable terrain and drum established based on Matlab/Simulink software, a semi-active cab’s HPM of vibratory rollers are then controlled by using the Fuzzy controller. The root-mean-square (RMS) of the accelerations of the vertical driver’s seat and the cab’s pitch angle have been used as objective studies. The research results indicate that the ride comfort of the driver's seat and the shaking of the cab are greatly affected under the deformable soil grounds, especially under a soft soil ground. However, with the HPM using the Fuzzy control, the RMS accelerations of the driver’s seat and cab pitch angle have been remarkably decreased by 40.1 % and 22.2 % under a hard soil ground. Therefore, the ride quality of the vibratory roller has been enhanced by the semi-active HPM.

Study on the ground settlement during reclamation of Xiamen airport

The settlement of soft soil foundation is a critical problem for the airport construction in coastal area. In order to study the long-term settlement characteristics of soft soil foundation of a Chinese reclamation airport (Xiamen Airport), this paper analyzed the monitoring settlement development of different regions in two runways to be built. The relationship between the total settlement from January 11, 2019 to May 22, 2020 and the thickness of soft soil was studied for guiding the settlement prediction of subsequent construction. The results showed that the development law of foundation settlement with different preloading durations under the same thickness of soft soil is different. As the preloading duration increases, the total settlement in the same period becomes smaller. Besides, the total settlement of Runway 2 increases approximately linearly with the thickness of soft soil (silt soil). However, the total settlement of Runway 1 under different thickness of soft soil is similar, which probably indicates primary consolidation has basically completed in this region. The research results in this paper is useful to understanding the settlement characteristics of Xiamen Airport, and can be used to analyse the settlement characteristics of other similar reclamation airports.

Equivalent plane strain model of stone column reinforced foundation

Stone column replacement of soft soil foundation construction method is more and more used in water conservancy projects. On the one hand, the stone column has high permeability, which enhances the dissipation capacity of excess pore water pressure; on the other hand, it has a high stiffness, which reduces the additional stress in the soil, and therefore reduces the excess pore water pressure. These two mechanisms work together to improve the bearing capacity of soil. In the previous plane strain transformation model of column-soil, only the high permeability of stone column is simply considered, while the stiffness of stone column is ignored. According to the previous research results, and based on the principle of genetic algorithm, this paper puts forward two conversion models which only consider the permeability of stone column and one conversion model which considers two kinds of action mechanism of gravel pile at the same time. The results of finite element calculation show that the transformation method considering the two mechanisms of stone columns are more consistent with the axisymmetric model.

Research and Engineering Application of Soft Soil Unloading and Deformation Model

Soft soil is a multiphase medium composed of solid soil particles, pore water, pore gas and combined water film adsorbed on the surface of particle group and colloid between particles. It is widely distributed in coastal, middle and lower reaches of rivers and delta of lakes. Its physical and mechanical properties and engineering characteristics are complex and regional differences are obvious. With the rapid development of social economy and urbanization, it will inevitably lead to serious problems such as urban land tension, traffic congestion and environmental pollution. These coastal cities are the leaders of China’s economic development. After more than 30 years of rapid economic development, the construction scale of these cities in China is also expanding, and the supply and demand of construction land is becoming increasingly tight. The contradiction between supply and demand is more prominent. With the scarcity of land resources and the rapid development of economy, a large number of construction projects in Qianhai area have been started, among which the construction of subway is also on a large scale. The shortage of land resources and the increase of land development make the high density and high strength building development along the subway line. The development of these building properties is bound to appear a large number of complex deep foundation pit projects, and the excavation of deep and complex foundation pit near the side of subway tunnel is a common form of excavation. In practical construction projects, due to the influence of external factors such as complex construction site conditions and urgent time requirements, people often pursue the progress of foundation pit excavation too much in actual construction, ignoring the research and application of mechanical properties of soft soil foundation, which leads to the safety accidents of subway tunnel structure from time to time. This is closely related to the mechanical properties of soft soil with high moisture content, high compressibility and low bearing capacity. Therefore, deep and large foundation pit engineering in soft soil area is prone to heavy engineering safety problems such as underground continuous wall and other retaining structures. Therefore, the further study of the unloading deformation model of soft soil, the physical and mechanical properties and engineering characteristics of soft soil has a positive and important economic value and social role in engineering in the future.

In-situ test on impact loads of a five-module 100% low-floor tram and the prediction of damage characteristics of a pile-plank-supported tram track

To mitigate the differential settlement of the soft soil foundation and to reduce the maintenance work of the embedded tram track, an innovative pile-plank-supported tram track configuration is proposed and utilized in Shanghai Tram Line T1/T2. Since this is the first application of this new structure in tram track projects, the dynamic properties and service performance of this structure are still not clear. In this work, an in-situ test on the dynamic performance of the pile-plank-supported ballastless tram track is carried out. The contact forces between the independently rotating wheelset of a five-module 100% low-floor tram and the channel rail of tram track are measured and investigated as well as the vertical acceleration of the plank. The measured wheel-rail contact forces are employed as a loading condition for a track-subgrade coupling model. The influence of multi-factors (i.e. dynamic loading, thermal conditions and subgrade settlement) on the tram track damage is investigated. The results indicate that the long-term service performance of the pile-plank-supported tram track is stable under the dynamic tram loads.