Soft Soil Foundation Research Articles

Calculation and Analysis of Nonlinear Algorithm for Stability of Nanosilica Powder Soft Soil Pile Foundation.

In order to reasonably evaluate the stability of the embankment supported by the rigid pile composite foundation, a nonlinear algorithm calculation and analysis method for the stability of the nanosilica powder soft soil pile foundation is proposed. First, the soft soil foundation reinforced by the composite structure of “piles (prestressed pipe piles, (cement fly-ash gravel, CFG) piles)—pile caps—geotextile pads” is analyzed through the soft soil embankment test section of the Wenfu high-speed railway. Second, the compressive modulus under one-dimensional confining compression is calculated using the layered summation method. Finally, the deep lateral deformation of the pile foundation soil is measured by an inclinometer to evaluate the actual displacement of the pile foundation soil. In the standard method, the empirical coefficient 1.1–1.7 is multiplied on the basis of the calculation result of this method to correct the calculation error. Combined with the test results, it is shown that nanosilica powder can give full play to its excellent characteristics: promoting hydration speed and hydration degree through the reaction of pozzolan refining and consuming Ca(OH)2 crystals produced by cement hydration. Soft soils and modified soft soils: a certain amount of nanosilica powder can significantly improve the strength of soft soil at different ages.

Construction parameters of graded sand-gravel foundation on seismic response law of nuclear safety grade underground corridor

The treatment of soft soil foundation under nuclear safety grade corridors with graded sand and gravel materials has a good development prospect. It is of great engineering value to explore the influence of construction parameters of graded sand and gravel foundation on the seismic response of gallery structures. Taking the safety grade underground corridor of a nuclear power plant as the engineering background, the equivalent linear method is used to consider the nonlinear dynamic characteristics of graded sand and gravel. The energy transfer boundary is applied at the truncation boundary to simulate the dissipation effect of scattered wave fluctuation energy and the ground motion input. The thicknessless contact element is introduced to consider the contact effect between the corridor structure and the graded sand and gravel foundation, so as to establish the calculation model of the dynamic interaction between the graded sand and gravel foundation and the corridor structure. Furthermore, the influence of the relative compactness and the foundation treatment depth on the seismic response of the corridor structure is studied, and the calculation results of the acceleration response spectrum and relative displacement of the corridor structure are analyzed. The calculation results show that the two construction parameters have different degrees of influence on the seismic response of corridor structure. The research results can provide reference for the engineering design and construction of underground corridors, and provide technical support for the application of graded gravel materials in soft soil foundation treatment.

Structural analysis of piled raft foundation in soft soil: An experimental simulation and parametric study with numerical method

The high infrastructural demand and the unavailability of proper foundation soil have increased the evolution of combined piled raft foundation (CPRF) in the current generation. The use of CPRF in soft soils has increased immensely in the last few decades. But there is a lack of laboratory experiments to understand the behaviour of CPRF in soft/clayey soil, and hence, this study considers an innovative approach to understand different behaviour of CPRF using clayey soil through laboratory experiments. Two different types of small-scaled CPRF models are prepared with 2 × 2 and 3 × 3 pile groups, and the spacing among the piles as well as the thickness of clayey soil are also altered. Several aspects are studied through the experiments such as load-settlement behaviour, load improvement ratio, behaviour of piles in CPRF, load sharing behaviour, axial forces, raft-soil contact behaviour, bending moment in the raft, etc. Based on the experimental test results, a numerical model is also prepared, and then a parametric study is performed numerically considering a 10-storey residential building. The effect of different pile lengths in CPRF is also checked and the parametric study is conducted with several types of pile arrangements.

Design selection and dynamic response analysis of CFG pile composite foundation in soft soil areas

The construction of roads along rivers plays a crucial role in the construction of economic belts and social and economic development along rivers. Roadbeds are the foundation of highway construction, while the soft soil foundation is widely distributed on both sides of rivers, resulting in some difficulties for roadbed construction and highway use. Despite diverse technical methods for the treatment of general roadbeds, the treatment of soft soil roadbeds should be further explored. In this paper, various advantages of applying CFG (Cement Fly-ash Gravels) pile treatment to the soft foundation in Bailinhe Road, Yichang are investigated. Specifically, the soft soil roadbed treated by CFG pile is numerically simulated, the changes in engineering index response before and after foundation treatment are analyzed, and then the dynamic analysis under vehicle dynamic load is performed. The results demonstrate that the reinforcement effect of the CFG pile significantly weakens the influence of vehicle dynamic load on roadbeds.

Comparative Study on Field Tests of Two Kinds of Shallow Treatment of Soft Soil Foundation

Through the vacuum preloading test with three different arrangements and the in-situ curing treatment at different depths, the treatment effect reached the expectation, indicating that both the vacuum preloading method and the in-situ curing method can achieve good reinforcement effect. Among them, the local curing method has remarkable effect on treating waste engineering mud, and its bearing capacity is far beyond expectation, which can be used as the foundation of high-grade highway. After the test, it is found that the real air filtration test area can also improve the treatment effect by reducing the distance between drainage plates, and the local curing treatment can further optimize the admixture content to achieve better reinforcement effect and further reduce the project cost. For the construction site with general bearing capacity requirements, vacuum filter tube or air pipe can be used to meet the requirements. For sites requiring higher bearing capacity, true air filter tube treatment can be used, and higher grade roadbed can be used in situ curing treatment.

Brief Analysis of the Application of Soft Soil Foundation Treatment Technology and Expansion Joint Technology in Roads and Bridges

Brief Analysis of the Application of Soft Soil Foundation Treatment Technology and Expansion Joint Technology in Roads and Bridges

Effect of Metakaolin on Strength Properties of Lateritic Soil Intended for Use as Road Construction Material

An excellent all-weather road is essential in providing reliable transportation services that comprise social and economic development elements. However, in most cases, the road has to be constructed on a soft foundation soil where large deformations usually occur, which causes increases in maintenance costs and leads to interruption of traffic service, especially during the wet season. It is necessary to stabilize or improve the in-situ soils. This study explores the potential of using metakaolin to improve the geotechnical properties of lateritic soil for road construction materials. The soil classifies as A-6(4) and CL according to the American Association of State Highway and Transport Officials and the Unified Soil Classification System. The soil was treated with 5, 17.5 and 30 % concentrations of metakaolin by dry weight and was compacted using three compaction energies: British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests were carried out to evaluate the effect of metakaolin on the soil investigated. Results showed a general improvement in the engineering properties of the soil with an increase in metakaolin content, particularly when compacted at the BSH energy level. However, the results did not meet the 1500-3000 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification for road base courses. However, 30 % lateritic soil/metakaolin blended soil compacted using WAS and BSH energy levels suffice for use as sub-base in road construction, having met the 750-1500 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification. The Peak CBR value for the treated soil, compacted using the three energy levels of BSL, WAS, and BSH, occurred at 30 % metakaolin concentration with corresponding soaked CBR values of 17, 23 and 31 %. The Nigerian General Specification recommends a nominal strength criterion of a soaked CBR value of 30 and 80 % to be attained by material to be used as sub-base and base course in road construction. Based on the above criterion, only the 30 % metakaolin treated blend compacted at the BSH energy level met the 30 % requirement for sub-base materials.

Field Test on Deformation Characteristics of Pile-Supported Reinforced Embankment in Soft Soil Foundation

In this work, the settlement deformation of the soft-soil subgrade and the deformation law of the geogrid were studied based on field tests carried out on the pile-supported reinforced embankment of the Rongwu Expressway in the Xiong’an New Area. The settlement and deformation law of the reinforcement area and the underlying layer of the pile-supported reinforced embankment, the settlement law of the transverse and longitudinal sections of the subgrade, and the deformation law of the bidirectional geogrid were analyzed. The results show that reducing the pile spacing and embankment height can effectively reduce the foundation settlement. The change in the pile spacing mainly affected the settlement in the reinforcement area, while the embankment height mainly affected the substratum settlement; the differential settlement in the subgrade cross-section was mainly caused by the settlement in the reinforcement area. The settlement at the center of the subgrade was obviously higher than that at the shoulder. In terms of the geogrid deformation law of the subgrade cross-section, the geogrid deformation at the center line of the subgrade was the largest. With the increase in the distance from the center line, the geogrid deformation gradually decreased. In terms of the deformation law of the biaxial geogrid, the tensile deformation of the geogrid in the center of two piles was greater than that in the center of four piles. The transverse tensile deformation of the geogrid was greater than the longitudinal tensile deformation. The tensile stress of the reinforced materials was calculated according to four specifications, and the applicability of various methods was evaluated.

Stochastic Medium Model for the Settlement Calculation of Prefabricated Vertical Drains of Soft Soil Foundations in the Coastal Area of South China

The prefabricated vertical drain (PVD) is an essential means to mitigate the settlement of soft soil foundations in coastal areas of South China. The commonly used elastoplastic analytical method cannot directly reflect the interaction of different PVDs and the resulting displacement of soft soil. At the same time, these elastoplastic analysis and numerical simulation methods are greatly influenced by the values adopted for rock and soil material parameters. In this paper, we present a stochastic medium model that can directly reflect the interaction of different PVDs and the resulting displacement of soft soil. It is not affected by the characteristics of rock and soil themselves and can also reflect the actual deformation process of soft soil. According to engineering practice, the settlement curves of soft soil foundations in coastal areas of South China with PVDs exhibited distinct normal distribution characteristics, which was consistent with the description of settlement by the stochastic medium model. Hence, based on the stochastic medium model, this paper analyzed the settlement mechanism of PVDs and established a stochastic medium model for the settlement calculation of PVDs. A function for the soft soil foundation in the coastal area of South China cross-section settlement curve was presented by back analysis of the PVD model. We chose the stochastic medium model based on this methodology to explore the interaction between different PVDs. The above models were then applied to an expressway in South China. Comparing actual settlement monitoring values to calculated values obtained with the PVD model, the error between the two models was less than 15%. This research provides a new settlement calculation method of PVDs in soft soil foundations in the coastal area of South China and a new basis for designing soft soil foundations.

Discussion on Soft Soil Foundation Treatment Technology in Water Conservancy Construction

Discussion on Soft Soil Foundation Treatment Technology in Water Conservancy Construction

Brief Analysis of Soft Soil Foundation Treatment Technology in the Construction Engineering

Brief Analysis of Soft Soil Foundation Treatment Technology in the Construction Engineering

Study of Bag Grouting Pile Reinforcing Deep Soft-Soil Foundation with an Interlayer of Hard Materials on High-Speed Railway Ballast Track

High-speed railways are built in deep soft-soil foundations interlayered with hard materials. However, the hard layers cannot be penetrated by conventional foundation treatment. Moreover, the project cost is sometimes prohibitive, which is an issue for post-construction subsidence control. The bag grouting pile is a special grouting-pile-reinforcement technique for treating soft-soil foundations interlayered with hard materials. This paper conducted tests on the Ningbo-Taizhou-Wenzhou ballast track passenger railway, combining a conventional mixing-pile-foundation (not through hard layer) processing station and the bag-grouting-pile-processing subgrade line. Using field tests combined with numerical calculation, the lateral displacement, settlement and pile–soil stress were tested to obtain the working properties of the grouting-pile-composite foundation. The variation in the law of lateral displacement, settlement, and pile–soil stress of the foundation was studied. The results showed that the post-construction subsidence of bag-grouting-pile- and conventional mixing-pile-foundation control was less than 15 cm and 30 cm, respectively, which met the design requirements. The results also showed that the design scheme was reasonable (load-sharing ratio of bag-pile-foundation pile soil-based test was reasonable). The numerical calculation showed a change in pile diameter. It also showed that pile spacing could not improve subsidence-control properties, bag grouting pile can promote pore-pressure dissipation and accelerate consolidation, and pile spacing can be increased to cut project costs incurred by the pile-bearing capacity.

Treatment Analysis of Soft Soil Foundation in Bridge Construction

Treatment Analysis of Soft Soil Foundation in Bridge Construction

Correction to: Application of visualization modeling technology in the determination of reinforcement range of deep soft soil foundation

Correction to: Application of visualization modeling technology in the determination of reinforcement range of deep soft soil foundation

Study on the Application of Construction Technology in Soft Soil Foundation of Building Construction Project

Study on the Application of Construction Technology in Soft Soil Foundation of Building Construction Project

A STUDY ON EFFICIENCY OF PERFECTLY MATCHED LAYER (PML) FOR SEISMIC SOIL-STRUCTURE INTERACTION

The direct method is a finite element approach used in soil-structure interaction (SSI) analysis. The main assumption of this method is the transformation of the infinite soil domain to the truncated soil domain applying different boundary conditions. The objective of this study is to examine the efficiency of The Perfectly Matched Layers (PML) for SSI analysis. For this purpose, the soil-structure problem with different planar-sized truncated soil domains with constrained boundary (CB) and non-reflecting boundary (NRB) were analyzed using 3 different soil stiffness. The results obtained from these analyses were compared with PML and fixed-base reference model results. According to the findings, if the truncated soil domain planar sizes are larger than 10 times the foundation widths for traditional boundary conditions, the effect of the soil domain size is negligible. When the foundation soil stiffness is assumed to be medium and hard, it was observed that PML results are very close to other boundary condition model results, but greater differences were observed in results between PML and other models for soft foundation soil conditions. From the parametrical study, it was concluded that PML provides superiority in terms of computational cost and practical application.

Numerical Analysis of the Carrying Capacity of a Piled Raft Foundation in Soft Clayey Soils

Piled raft foundations are a common type of foundation for high-rise buildings. Unlike shallow foundations, deep foundations (piles) pass through weak or soft soil deposits and can reach stiff soil or bedrock to support the weight of the structure. In this paper, the performance of a medium embedment depth piled raft foundation in soft soil is presented. A numerical model was developed and a parametric study was conducted in order to simulate the case of such a foundation system and to investigate its performance in soft clay. This parametric study investigated the effect of the geometry of a piled raft foundation and the stiffness ratio between the pile material and clay on the performance of the foundation system in soft soil. Additionally, the failure mechanism of such a foundation system under load was examined. An analytical model was developed to predict the ultimate carrying capacity based on the observed failure mechanism. A semi-empirical model is proposed for determining the Improvement Factor (IF) of a given soil, pile, and geometric condition. Findings of the study indicate that the performance of piled raft foundations on soft soils is significantly affected by the piles’ spacing. As the ratio S/D increases, the ultimate carrying capacity of a piled raft foundation decreases. However, when this ratio exceeds 10 (S/D> 10), piles have little or no effect on the ultimate carrying capacity of this foundation system. A piled raft foundation system fails by bearing at the base of the piles and also by shear at the side of the pile group on hyperbolic plans. Doi: 10.28991/CEJ-2022-08-04-01 Full Text: PDF

Deformation mechanism and soil evolution analysis based on different types geogrid reinforced foundation

Geogrids are extensively used to improve the bearing capacity of low strength soil and reduce the settlement of soft soil foundations. This study aims to compare the bearing capacity and deformation characteristics of geogrid reinforced foundation with different types of geogrids (uniaxial, biaxial, triaxial) and different reinforcement layers (N = 1, 2, 3) in reduced-scale transparent soil model tests. The images of the foundation model are captured by the laser transmitter and digital camera. These images are further analyzed to study the foundation deformation of different cases by digital image processing technique. The results show that triaxial geogrid reinforced foundation has a better bearing capacity than the uniaxial geogrid and biaxial geogrid reinforced foundation. In the process of foundation settlement, the slip crack surface and ground heave gradually develop with the bottom-up diffusion of horizontal and vertical displacements of the soil. Local shear failure first occurred in the bottom of the foundation, and then transformed into general shear failure. These results visualize and quantify the soil displacement transfer and spreading behavior in geogrid reinforced foundations. This paper illustrates the effects that geogrid reinforcing at a microscopic scale under strip footing loads.

Application of visualization modeling technology in the determination of reinforcement range of deep soft soil foundation

Application of visualization modeling technology in the determination of reinforcement range of deep soft soil foundation

Numerical Study of Recycled-Plastic-Pin- and Geosynthetic-Platform-Supported Embankment over Soft Soil

Embankment construction over soft soils is extremely challenging because of excessive settlement of the soil and the potential for bearing failure. Many of the available conventional methods for solving these problems require a tremendous amount of time and resources. Researchers are therefore striving to create a sustainable alternative to conventional practices. Utilizing recycled plastic pins (RPP) in conjunction with geosynthetics is a novel approach to improve soft foundation soil. This study uses finite element analysis to evaluate the effectiveness of RPP and geosynthetic platform for improving soft foundation soil. PLAXIS 2D software was used for the numerical analysis. Field measurements were used to calibrate the model for settlement and pressure variations. The performance of the RPP-supported embankment was evaluated with maximum consolidation settlement, differential settlement, and soil arching effect. Furthermore, a comprehensive parametric study was carried out to investigate the influence of RPP size and spacing, load transfer platform, stiffness of geosynthetics, and shear strength of embankment fill. It was observed that the load efficacy increases, and the differential settlement efficacy decreases with the increase of embankment load. The settlement improvement factor is found negligible for the values of area ratio inverse higher than 30. The cohesion rather than the friction angle of embankment fill was found more influential in transferring the embankment load to RPPs. Furthermore, the maximum settlement decreases, and maximum tension in geosynthetics increases with the increase of geosynthetic stiffness.