Soft Soil Foundation Research Articles

Economic benefit analysis of low-level high vacuum compaction method from the perspective of low carbon

In order to discuss the superiorities of High Vacuum Drubbing Means (HVDM) in soft foundation treatment of roads, this paper takes the soft foundation treatment project of Wucheng Road in Wuwei County of Wanjiang City Belt in China as an example. By comparing and analyzing the economic benefit differences between HVDM method and traditional powder injection pile method in soft soil foundation treatment, the following conclusions are drawn: Low-level high-vacuum compaction method soft base processing method is better than traditional powder-jet pile method in soft foundation treatment. The method can better reduce the consumption of raw materials such as cement and stone, avoid the pollution of the social environment caused by cement production, shorten the construction period by about 50 % and save the direct labor cost. Compared with the traditional powder-sprayed pile method, total cost of the project can be saved by more than 30 % and the construction quality is controllable. The construction process is green and its social and economic benefits are remarkable.

Centrifuge tests to investigate global performance of geosynthetic-reinforced pile-supported embankments with side slopes

Three centrifuge model tests were conducted to investigate the influence of the number of geosynthetic layers and the pile clear spacing on the global performance of Geosynthetic-Reinforced Pile-Supported (GRPS) embankments with side slopes constructed on soft soil foundations. This study found that the change of the geogrid number from one to two did not significantly affect the foundation settlement, the geogrid deflection, and the vertical stress at the embankment base. For the GRPS embankment with a single geogrid layer, the geogrid strain distribution at the embankment base showed an “M” shape along the transverse direction with the maximum strain near the embankment shoulder. When two geogrid layers with sand in between were used, the upper and lower layers showed different strain distributions with the maximum strains happening near the embankment shoulder and at the center of the embankment for the upper and lower layers respectively. The strains of the upper geogrid were smaller than those of the lower geogrid. Smaller pile clear spacing reduced the geogrid deflection and the foundation settlement. Despite the change of the pile clear spacing, the progressive development of soil arching with the normalized displacement at the embankment base followed a similar trend without an obvious stress recovery stage.

Large‐scale shaking table test on pile‐soil‐structure interaction on soft soils

SUMMARYThe two large‐scale shaking table tests of tall buildings on soft soils in pile group foundations are performed to capture the effect of the seismic pile‐soil‐structure interaction (PSSI) on the dynamic responses of the pile, soil, and structure. The two different model conditions are observed, including a fixed‐base structure and a structure supported by 3‐by‐3 pile group foundation in soft soil, representing the situations excluding the soil‐structure interaction (SSI) and considering the SSI, respectively. In the tests, the superstructure is a tall building with 12‐story reinforced concrete frame. The pile‐soil‐structure system rests in a shear laminar soil container, which is designed to minimize the boundary effects during shaking table tests. The two models are subjected to various intensity seismic excitations of Shanghai bedrock waves, 1995 Kobe earthquake, and 1999 Chi‐Chi earthquake events. According to the experimental and analytical results, SSI systems have longer natural periods than the fixed‐base structure. In addition, soft soil has amplification effect under smaller seismic excitations and isolation effects under larger earthquake intensities. The strain amplitude at the top of pile is large, and the strain at the middle and tip is relatively small. Whereas the contact pressure is small at the top of pile and large at the middle and tip. From the dynamic responses of the superstructure, it is found that the PSSI amplifies the peak displacements and interstory drifts of the structures supported by pile group foundations by comparing with the fixed‐base structure. Whereas the peak acceleration and interstory shear force of the structure are reduced considering seismic PSSI. The results show that the seismic SSI is not always favorable, however, it may increase certain dynamic responses of the structure. Consequently, the seismic SSI should be considered reasonably, providing insight towards the rational seismic design of buildings rested on soft soils.

Experimental Study on Glass Sand Well

Aiming at the disposal of waste glass, our paper proposes a method of filling sand wells with glass sand formed by mixing waste glass and sand as a backfill material. In this paper, the basic properties of glass sand are studied by penetration test, consolidation test and consolidation bearing capacity test. The results show that the permeability of mixture is better than that of common sand well when glass particles are incorporated into sand. When bearing the same bearing capacity, the average bearing capacity of common sand well is smaller than sand well, and the bearing capacity of the soil in the upper part of the model box is greater than the bearing capacity of the lower soil. The sedimentation of clay with sand well is higher than that of common clay. Glass sand well can accelerate the consolidation of soil in soft soil foundation by utilizing the good permeability of glass and sand.

Numerical Study of Seismic Vibrations of Closely Located Buried Large Structures

The paper presents an efficient numerical technique for 3D-modeling of seismic stability of large buried structures. This technique allows considering the subsoil-structure contact interaction, gravity field effects, the inhomogeneous structure of soil and the varieties location of the earthquake hypocenter. As part of this technique is substantiated sizing of the soil-structure computational domain and continuum model for hard and soft soil foundations describing. The numerical technique for determining the kinematic conditions at the lower boundary of the computational domain from the experimental accelerations at the soil surface is given, offered special non-reflecting waves boundary conditions. The methods described above and algorithms for seismic resistance solving have been implemented in certified software package “Dynamica-3”, parallelization of the algorithm has been held according to the spatial domain decomposition principle. The developed numerical technique allows correctly posing the problem of seismic vibrations of buried structure, reducing computing costs and increasing the efficiency of numerical studies of Earthquake Engineering. Through this, the multiple recalculation of the task with different action scenarios generated from experimental seismograms by probabilistic methods became technically possible. The results of these calculations allow reflecting the experience of many earthquakes, which increases reliability of the estimates. The paper presents the model calculations results of seismic stability of large-sized buried structure—the mutual vertical and horizontal displacement of soil and building walls—which can then be used to assess strength of adjacent underground pipelines. A number of numerical experiments on seismic vibrations of nearby large-sized structures have been carried out to assess the mutual influence of structures on their behavior in an earthquake. It is established that the influence of nearby large-sized objects on seismic vibrations of structures differs for different buildings.

Consolidation Analysis of Ideal Sand-Drained Ground with Fractional-Derivative Merchant Model and Non-Darcian Flow Described by Non-Newtonian Index

To further investigate the rheological consolidation mechanism of soft soil ground with vertical drains, the fractional-derivative Merchant model (FDMM) is introduced to describe the viscoelastic behavior of saturated clay around the vertical drains, and the flow model with the non-Newtonian index is employed to describe the non-Darcian flow in the process of rheological consolidation. Accordingly, the governing partial differential equation of the ideal sand-drained ground with coupled radial-vertical flow is obtained under the assumption that the vertical strains develop freely. Then, the numerical solution to the consolidation system is conducted using the implicit finite difference method. The validity of this method is verified by comparing the results of Barron’s consolidation theory. Furthermore, the effects of the parameters of non-Darcian flow and FDMM on the rheological consolidation of ground with vertical drains are illustrated and discussed.

Study on Performance of Cement Mixing Pile in Marine and Continental Deposition Soft Soil Area

Soft soil was widely distributed in the coastal area, and the key characters were high water content and low capacity. Cement Mixing Pile (CMP) is an effective method to treat soft soil foundation. While CMP construction quality was difficult to control and it was of different reinforce effect for different geology origin. In this paper, five geology origins have been divided for the littoral area, lagoon area, alluvial area (Yangtse River), alluvial area (Ancient Yellow River) and lacustrine area. CMP, used in 26 expressways which were constructed during the period of 2008 - 2016, has been divided two-part (Upper & Lower part) to test the construction quality of CMP through Standard Penetration Test (SPT), Unconfined Compaction Strength (UCS) and Cement Mixing Pile Quality Designation (CMPQD). Results show that geology origins have great influence on the construction quality of CMP at the same construction maintenance condition. Depth has a significant effect on UCS of the lower part of CMP while the little effect on UCS of the upper part. Construction quality of long CMP was more difficult to control than short CMP. The high quality of the upper part may cause the unqualified lower part evaluated as qualified or good, which may lead to some engineering accidents.

Seismic Performance Levels of a Large Underground Subway Station in Different Soil Foundations

ABSTRACT With the soil constitutive model developed for the dynamic large deformation of soft soil, a finite element model was constructed to simulate the soil–underground structure static and dynamic coupling interaction system, in which the dynamic contact between soil and underground structure and the dynamic damage of reinforced concrete were considered. The seismic performance and damage mechanism of the large underground subway station in different soil foundations were investigated and evaluated in detail. It was proven that the interaction mechanism between the soil and underground structure would change with the type of soil foundation and the peak acceleration of input ground motion, which can be evaluated by the interaction coefficient between the soils and underground structure. At the same time, some regulations on the seismic performance of underground structure in China code are already unsuitable for evaluating the seismic performance of a large underground subway station in the soft soil foundation or subjected to a strong earthquake, which should be investigate by the specialized time–history analysis method instead. In this study, five seismic performance levels were firstly defined by the inter-storey drift angle of underground structure and corresponding earthquake damage states.

Study on the Reasonable Spacing of Post-pouring Zone for 50m Long Inverted-T Type Concrete Structure on Soft Foundation

There are a large number of inverted-T type concrete structures on soft soil foundation in the Yangtze River Delta area of China. Setting post-pouring belt is one of the effective methods to reduce the cracking of such structures during construction. However, there is still a lack of reference standard on how to quantify the interval between the post-pouring belts under different conditions. For this kind of structure, natural silo positions in three pouring seasons are considered, and the post-pouring belts with different spacing are set up in the base plate and pier wall. The stress development during the construction period of the concrete under different combination conditions are simulated by finite element method (FEM). The results show that under the condition of load during the construction period, the pouring blocks of the base plate on the soft foundation do not need to be provided with a post-pouring belt. While the pier wall is constrained by the base plate, the maximum tensile stress of the pier wall has a positive correlation with the maximum temperature of concrete.

Study on Earth Pressure Behind Separated Barrel Structural Wall

With the development of port shipping industry in China, barrel foundation structure is gradually applied in port engineering, especially in the case of large water depth and soft soil foundation under the sea. With the less scene workload, simple construction and short construction period, the structure has broad application prospects. The earth pressure distribution of barrel wall surface of double barrel structure is complex, so reasonably determining the barrel structure wall earth pressure calculation has a great significance for the stability of the structure. Through the numerical analysis of finite element method, establish the upper and lower barrel separation type barrel foundation finite element model, and conduct the finite element analysis of the model of barrel structure. Considering the influence of different backfill earth parameters on the earth pressure behind the wall, the corresponding earth pressure distribution curve is obtained, which is compared with the theoretical value and the reference used in Lianyungang project. The analysis results show that the barrel foundation with rubble machine tool connecting upper and lower barrels can be used in engineering, and the method of multiplying the theoretical value of earth pressure by the correction coefficient can be used to simplify the calculation. The correction coefficients of earth pressure under different soil conditions are given, which can be used as a reference for the design of barrel structures.

Development of an Artificial Intelligence Approach for Prediction of Consolidation Coefficient of Soft Soil: A Sensitivity Analysis

Background:Consolidation coefficient (Cv) is a key parameter to forecast consolidation settlement of soft soil foundation as well as in treatment design of soft soil foundation, especially when drainage consolidation is used in foundation treatment of soft soil.Objective:In this study, the main objective is to predict accurately the consolidation coefficient (Cv) of soft soil using an artificial intelligence approach named Random Forest (RF) method. In addition, we have analyzed the sensitivity of different combinations of factors for prediction of the Cv.Method:A total of 163 soil samples were collected from the construction site in Vietnam. These samples at various depth (m) were analyzed in the laboratory for the determination of clay content (%), moisture content (%), liquid limit (%), plastic limit (%), plasticity index (%), liquidity index (%), and the Cv for generating datasets for modeling. Performance of the models was validated using Mean Absolute Error (MAE), Root Mean Square Error (RMSE) and Correlation Coefficient (R) methods. In the present study, various combinations of soil parameters were applied and eight models were developed using RF algorithm for predicting the Cv of soft soil.Results:Results of model’s study show that performance of the models using different combinations of input factors is much different where R value varies from 0.715 to 0.822.Conclusion:Present study suggested that RF model with appropriate combination of soil properties input factors can help in better and accurate prediction of the Cv of soft soil.

Engineering Characteristics and Reinforcement Program of Inclined Pre-stressed Concrete Pipe Piles

When it comes to the deep soft soil foundation, improper construction, preloading, and excavation may result in the inclination of the pre-stressed concrete pipe (PCP) piles. Lack of understanding on deformation characteristics may lead to inaccurate reinforcement plan, thereby causing new engineering accidents. This study analyzes an engineering accident induced by the pile inclination, based on which the finite element method model is built. Deformation characteristics of the foundation incorporating inclined PCP piles are investigated, and the reinforcement program involving placement of the pile with opposite inclination is proposed and compared with the conventional reinforcement program using vertical piles. Findings of this study are two-folds: 1) A critical inclination angle affecting the vertical settlement exists, below which the pile inclination has limited effects upon the vertical load bearing capacity of the foundation. 2) The vertical subsidence, the lateral displacement and the bending moment of the reinforcement program based on the reversely inclined pile are all decreased, which helps bear the overburden load and improve stability. In the process of engineering accident treatment, the bearing capacity of PCP piles with small inclination angles can be first reduced according to their inclination angles, followed by judgement that whether these PCP piles meet the requirements on bearing capacity. The PCP piles with large inclination angles must be strengthened, and the reverse inclined PCP piles are recommended.

Settlement and Vertical Load Transfer in Column-Supported Embankments

Column-supported embankments (CSEs) with or without a load-transfer platform (LTP) can reduce settlements, improve stability, and prevent damage to adjacent facilities when embankments are constructed on ground that would otherwise be too weak or compressible to support the new load. CSEs function by transferring the embankment load to the columns through stress redistribution above and below the foundation subgrade level. Mobilization of load-transfer mechanisms to the columns requires differential settlement at the base of the embankment between the stiff columns and foundation soils. This paper presents the load-displacement compatibility (LDC) analysis method, which estimates the transfer of vertical loads by (1) arching within the embankment fill, (2) the vertical component of tension developed in the geosynthetic reinforcement within the LTP, and (3) negative skin friction acting along the column. The LDC method incorporates the vertical displacements that accompany load transfer by considering nonlinear consolidation of the soft foundation soil, elastic compression of the columns, out-of-plane deformation of geosynthetic layers, and settlement of the embankment surface in compliance with the differential settlement at the embankment base. This paper also presents recommendations for estimating the critical height of the embankment, which is the minimum embankment height above the columns to avoid poor ride quality resulting from differential settlement at the surface of the embankment produced by differential settlements at the base of the embankment. Estimates of load transfer and reinforcement strain using the LDC method are compared to measurements from 15 full-scale embankments.

Comparative Analysis and Research of Different Ways to Deal with the Soft Soil Foundation

Taking an engineering example as background, the deformation and settlement of CFG pile and artificial bored pile composite foundation under the same geological condition are analyzed by using finite difference method. The simulation results show: the same formation and pile material and compaction process, the large diameter and deep manual bored pile foundation can significantly restrain the foundation drop, the analysis results have certain reference value for similar projects.

Application of Vacuum Preloading in Foundation Treatment of River

Vacuum preloading method is a commonly used dewatering and drying method for soft foundation soil in China, which has the characteristics of low cost and high treatment efficiency. Vacuum preloading method has been widely used throughout the country as a simple, fast and economical foundation treatment method. It is necessary to treat foundation before river construction revetment and upper landscape structure in order to meet the requirement of slope stability by taking a river course in a reclamation area as an example. In this paper, vacuum preloading method is used to treat soft foundation after comparison and selection of various foundation treatment methods. It is feasible to apply vacuum preloading technology to soft foundation treatment engineering of river course.

The Feasibility Study on Treating Soft-Soil with Lightweight-Pile Composite Foundation

The new method of soft foundation treatment in continuous exploration, the introduction of lightweight materials to overcome the low bearing capacity of soft soil foundation is considered to have a good prospect. In this article, it is assumed that the lightweight material can be used as the vertical reinforcement in the form of short pile to form the composite foundation with the soft soil, and to bear the overlying load. Firstly, the material parameters of the lightweight pile under the working conditions were calculated by numerical analysis. According to the calculated parameters of the pile body, the feasible materials were selected, EPS (expanded polystyrene) was preferred for further study in materials that meet the parameters. Through centrifugal model test, settlement and stress state of lightweight material pile composite foundation were analyzed, its smooth settlement and ideal working condition shows a good treatment effect. The results of numerical analysis and centrifuge model test show that it is theoretically feasible to treat soft foundation with lightweight pile composite foundation.

Research on Deformation Characteristics of New Breakwater Structure

With the increasingly stringent of environmental protection requirements of the China, there is fewer and fewer land reclamation projects, so the related research on dredged soil treatment technology has become a hot spot. A new type of mud-sand interbedded structure is put forward in this paper. The dredged soil is filled in membrane bag and interbedded with sandy membrane bag, which gradually forms a stable new seawall core structure. From the finite element simulation results, it is known that the maximum displacement of mud-sand interbedded structure is 2.73 m. After the calculation, the top surface of the mud-sand interbedded structure is 1.9 m from the back surface, and the compression of the mud-sand interbedded structure is mainly occurs in the middle of the body, the bottom and top are less compressed. The design and construction of the breakwater meets the engineering requirements, and it is a feasible and fast breakwater technology on soft soil foundation.

Improved Double-Layer Soil Consolidation Theory and Its Application in Marine Soft Soil Engineering

Marine soft soil foundation is a double-layer foundation structure with a crust layer and soft substratum. Moreover, it is common that there are various forms of drainage. Accordingly, based on Terzaghi’s consolidation theory and the continuous drainage boundary conditions theory of controllable drainage conditions, an improved double-layer soil consolidation theory considering continuous drainage boundary conditions was proposed. To improve the computational efficiency and accuracy, the Laplace transform and the Stehfest algorithm was used to deduce the numerical solution of the improved double-layer soil consolidation theory considering continuous drainage boundary conditions and to compile a computer program. Subsequently, the theory was validated and analyzed by the degenerated model of the perfectly permeable boundary conditions and the semi-permeable boundary conditions, respectively, which showed that this theory has higher accuracy. Simultaneously, the analysis of double-layer consolidation settlement under continuous drainage boundary conditions for marine soft soil foundation of Guangxi Binhai Highway was carried on. The result showed that the consolidation settlement calculated by the improved double-layer consolidation theory presented is basically consistent with the field measurement results, and that the correlation coefficient between them is higher. Accordingly, the research results can provide useful basic information for marine soft foundation engineering.

Study on Settlement Deformation Characteristics of Reinforced Soil Subgrade

Based on a high fill subgrade in Indonesia, this paper uses finite element software to simulate the settlement deformation characteristics of high fill subgrade under the condition of reinforced cushion. The calculation results show that although the existence of the reinforced cushion cannot significantly reduce the foundation settlement, it has obvious effect in ensuring the stability of the shoulder. The stability safety factor of the 9m high roadbed with the reinforced cushion layer increases by about 0.2. It is suggested that the reinforced soil cushion can be used as a reinforcement measure to ensure the stability of the shoulder when high-fill roadbed construction is carried out on soft soil foundation.

Performance of a pile foundation in soft soil

This paper presents the field instrumentation on the pile foundation of the 492 m high Shanghai World Financial Centre (SWFC), which is supported on steel pipe piles of 700 mm dia. and 60 m long in the deep, soft soil of the Yangtze River delta. During the whole construction stage, the performance of the pile foundation, including pile load, contact pressure, pore-water pressure and settlement, was intensively and successfully investigated. The monitored data indicated that the force acting on the pile, in stark contrast to the design assumption of loading equally, was quite uneven; the contact pressure inevitably was produced once the settlement developed; the pore-water pressure reflected the water head from the underground confined water; the foundation settlement was 127 mm and the settlement difference was 6 mm between the opposite sides of the raft. The analytical work demonstrates the influence of the various factors contributing to the observed behaviours of the foundation, and the safety of the observed foundation is still under control. For the first time, in situ testing of the pile foundation of a super-tall building embedded in deep, soft soil was conducted; the results provide a comprehensive insight into the working performance of a pile foundation.