Soft Clayey Ground Research Articles

Measurements and analysis of load sharing between piles and raft in a pile foundation in clay

This research presents the monitoring results and their interpretation on load sharing of the pile foundation during the construction of a high-rise (124 m in height) building in Bangkok, in soft clayey ground. Axial forces in several piles, pore water pressure and earth pressures beneath the raft in a tributary area were monitored through the construction period of the building. The raft of the pile foundation in soft clayey ground can share the load up to 10-20% even though the foundation was designed using the conventional approach in which the raft resistance is ignored. The benefit from the return of ground water table as the uplift pressure is recognized. A series of parametric study by 3D-FEA were carried out. The potential of utilizing the piled raft system for the high-rise building with underground basement in soft clayey ground was preliminarily confirmed.

Dynamic Centrifuge Model Tests on Pile Foundation of Plate-shape Building in Soft Clayey Ground and its Numerical Analyses

Dynamic Centrifuge Model Tests on Pile Foundation of Plate-shape Building in Soft Clayey Ground and its Numerical Analyses

Assessment of Strength Development in Stabilized Soil with CBR Plus and Silica Sand

This paper investigates the potential use of a nano polymer stabilizer, namely CBR PLUS for stabilization of soft clay and formulation of an optimal mix design of stabilized soil with CBR PLUS and silica sand. The highway settlements induced by the soft clay are problematic due to serious damages in the form of cracks and deformation. With respect to this, soil compaction and stabilization is regarded as a viable method to treat shallow soft clayey ground for supporting highway embankment. The suitability of stabilized soil was examined on the basis of standard Proctor compaction, California Bearing Ratio (CBR), unconfined compression, direct shear and permeability falling head tests. Furthermore, the chemical compositions of the materials were determined using X-Ray Fluorescence (XRF) test. The objectives of this paper are (i) to stabilize the compacted soil with CBR PLUS and silica sand in the laboratory; and (ii) to evaluate the strength and CBR of the untreated and stabilized soil specimens. It was found that the optimal mix design of the stabilized soil is 90% clay, 1% CBR PLUS, 9% silica sand. It is further revealed that, stabilization increases the CBR and unconfined compressive strength of the combinations by almost 6-fold and 1.8-fold respectively. In summary, a notable discovery is that the optimum mix design can be sustainably applied to stabilize the shallow clay without failure.

Assessment of strength development in stabilized soil with CBR PLUS and silica sand

Abstract This paper investigates the potential use of a nano polymer stabilizer, namely CBR PLUS for stabilization of soft clay and formulation of an optimal mix design of stabilized soil with CBR PLUS and silica sand. The highway settlements induced by the soft clay are problematic due to serious damages in the form of cracks and deformation. With respect to this, soil compaction and stabilization is regarded as a viable method to treat shallow soft clayey ground for supporting highway embankment. The objectives of this paper are: i) to stabilize the compacted soil with CBR PLUS and silica sand in the laboratory; and ii) to evaluate the permeability, strength and California bearing ratio (CBR) of the untreated and stabilized soil specimens. The suitability of stabilized soil was examined on the basis of standard Proctor compaction, CBR, unconfined compression, direct shear, and falling head permeability tests. Furthermore, the chemical composition of the materials was determined using X-ray Fluorescence (XRF) test. It was found that the optimal mix design of the stabilized soil is 90% clay, 1% CBR PLUS, 9% silica sand. It is further revealed that, stabilization increases the CBR and unconfined compressive strength of the combinations by almost 6-fold and 1.8-fold respectively. In summary, a notable discovery is that the optimum mix design can be sustainably applied to stabilize the shallow clay without failure.

Hardening performance of reclaimed gypsums for stabilizing agent to improve soft clayey ground

For a prospective solution of effective recycling of gypsum board wastes, the present study was conducted to evaluate applicability of reclaimed gypsum as stabilizing agent for improvement of soft clayey ground. A series of unconfined compression tests and needle penetration tests were conducted to understand the fundamental properties of reclaimed gypsum and gypsum treated soils and the durability in water. An important finding was strength decrease in relation to mixing time of gypsum and soil. This may attribute to excessive mixing that caused breakage of the promptly hardened gypsum treated clay. In addition, from sounding and laboratory tests on the stabilized ground by shallow mixing method with different execution conditions, it was found that the strength of stabilized ground appeared in an early stage and that the hardening effect of cement that was used in combination with gypsum continued in a longer period. Regarding an environmental aspect, a specific amount of cement could have restrained leaching fluorine satisfactorily under the standard level in the field by adopting suitable mixing proportions based on the laboratory mixing test results. For practical application, the mixing procedure was a major factor of strength growth when hemihydrate gypsum was used to stabilize soft clayey ground.

Vertical drainage capacity of new electrical drainage board on improvement of super soft clayey ground

As an advanced polymer composites electro-kinetic geosynthetics, the electro-osmotic vertical drainage (EVD) board could drain water quickly and accelerate consolidation process. However, the drainage rate was mainly impacted by the vertical drainage capability. Therefore, vertical drainage capability at the top of EVD board was theoretically analyzed. Basic requirements for drainage at the top of the board were summed up, as well as the formula of anode pore pressure when losing the vertical drainage capability. Meanwhile, a contrast test on the top and bottom drainage capacities was conducted. In use of the advanced EVD board, the voltage potential and pore pressure of anode were measured. Moreover, the derived formulas were verified. The result shows that the decrease of electric force gradient had an observable impact on the drainage capability. There was nearly no difference between the energy consumption for the two drainage methods. Although a little less water was discharged, the top drainage method had more advantages, such as high initial drainage velocity, few soil cracks, low anode water content and high soil strength. All of these show that the super soft soil ground could be consolidated quickly in use of the advanced EVD board through the top drainage. The top drainage method could efficiently improve the drainage effect, decrease the energy consumption and speed up the project proceeding.

일정변형률 시험을 이용한 재성형 광양 해성점토의 압밀특성 연구

최근 들어 연약지반상에 구조물을 건설하는 경우가 증가하고 있으며, 사회기반 시설의 유지관리 및 건설 비용의 절감을 위해 사전압밀공법 및 연직배수공법과 같은 기존의 방법을 이용하여 지반 개량이 행해지고 있다. 이와 같이 연약점성토 지반상에 다양한 개량공법이 적용 될 때, 점성토의 낮은 투수계수로 인한 장기간에 걸친 압밀침하가 중요하게 된다. 압밀침하와 관련된 기존 연구결과에 따르면, 기존의 표준압밀시험의 재하기간은 압밀정수 산정에 최소한 10일 이상의 시간을 요하게 된다. 따라서 이 연구에서는 서남해안의 대표적인 연약지반으로 구성된 광양만 재성형 해성점토를 이용하여 표준압밀시험과, 일정변형률 압밀시험의 변형률 속도를 변화시킨 실험을 수행하였다. 실내시험결과를 통해 등변형률 속도에 따른 압축특성, 변형률-유효응력관계, 재하속도에 따른 간극수압 변화특성, 압밀정수와 등변형률 속도의 관계를 비교/분석하였다. Recently, the case to construct the structure on the soft clayey ground has increased and in order to the reduction of the cost of construction and maintenance on the social infrastructure facilities we have been trying to improve the soft clayey ground using the existing methods such as the pre-loading method and the vertical drain method. Like this, when various ground improvement methods are applied on the soft clayey ground, a long-term consolidation settlement will be key issue due to low permeability coefficient of cohesive soil. According to existing research results that relate to the consolidation settlement, the loading periods for existing the standard consolidation test (Oedometer test) to obtain the consolidation parameters are needed for minimum ten days or more. Therefore, in this study, the standard consolidation test (24 hours step-loading) and constant strain rate consolidation test changed by strain rate was performed using the remolded marine clay on Gwangyang bay composed of a soft clayey ground of the south-west coast. From the laboratory test results, the characteristics of compression, strain-effective stress relations by constant strain rate and the variation characteristic of the pore water pressure by different of loading speed and the relation between consolidation parameters and constant strain rate are compared and analyzed.

Lateral displacement of soft ground under vacuum pressure and surcharge load

Surcharge load (e.g. embankment fill) will induce settlement and outward lateral displacement, while vacuum pressure will induce settlement and inward lateral displacement of a ground. Ideally, combination of surcharge load and vacuum pressure can reduce or minimize the lateral displacement. Laboratory large scale model (length: 1.50 m, width: ∼0.62 m, height: 0.85 m) tests and finite element analyses (FEA) were conducted to investigate the main influencing factors on lateral displacement of a soft clayey ground under the combination of vacuum pressure and surcharge load. For the conditions investigated, the results indicate that the outward lateral displacement increases with the increase of the ratio of surcharge load to vacuum pressure (RL) and the loading rate of the surcharge load (LR). Also, it is shown that for a given RL and LR condition, lateral displacement reduces with the increase of the initial undrained shear strength (Su) of the ground. To predict the lateral displacement of a ground under the combination of surcharge load and vacuum pressure, the loading conditions in terms of RL and LR, and Su value of the ground have to be considered.

Settlement prediction for soft ground improved by columns

A simple method of calculating the consolidation settlement of soft subsoil improved by a floating cement-stabilised column–slab system subjected to embankment loading has been proposed, and the method has been applied to three case histories in Fukuoka, Japan. The proposed method adopts the methodology of treating a part of the soil–cement column improved layer with a thickness of Hc as an unimproved layer and calculating its compression using the properties of the soft soil only. Based on coupled finite-element analysis results using a unit cell model, two bilinear functions with variables of the improvement area ratio (α) and the improvement depth ratio (β) by the columns have been proposed to determine the value of Hc. Both the proposed method and the method currently used in Japan (proposed by the Japanese Institute of Construction Engineering (JICE)) were used to calculate the settlement (compression) of the soft layers for three case histories in Fukuoka, Japan. Comparing the calculated results with the field values shows that the proposed method yielded much better predictions than that of the JICE method. It is suggested that the proposed method can be used to design the improvement of soft clayey ground using the floating cement-stabilised column–slab system.

Evaluation of Long-Term Displacements of Pile Foundation Using Coupled FEM and Centrifuge Model Test

ABSTRACT Recently the introduction of performance-based design into infrastructure including pile foundation is on process. For performance-based design, it is necessary to develop a practical prediction method for long-term displacements of pile foundation. In this paper, soil-water coupled analyses with FEM-FDM method are conducted to evaluate the long-term displacements of pile foundation installed in soft clayey ground. The analytical target is the actual pile foundation of road viaduct planned to be constructed in Niigata Prefecture, Japan. As constitutive model for ground, subloading tij model is adopted, which is a simple elasto-plastic model for normally and over consolidated soils. Further more, centrifuge model tests are conducted to verify the validity of the numerical analyses. As the conclusion of a series of analyses and centrifuge model tests, following aspects are clarified; 1) the long-term behaviour of pile foundation; 2) the influence of the thickness of bearing layer to the behaviour; 3) the mechanism of pile-soil-pile system, especially about how the load is allotted to each pile, how the migration of excess pore water pressure occurs, migrates and dissipates, and how the uneven settlement is caused.

On the deformation behaviour of strip footings during the construction process of an adjacent diaphragm wall in soft clayey ground

AbstractThe installation process of diaphragm walls in soft clayey soil deposits can produce considerable deformations on the adjacent ground, affecting the serviceability of nearby structures. This article highlights the influence of the stepwise D‐wall construction process on the development of settlements of neighbouring strip footings. For the simulation of the construction process, a three‐dimensional finite element model of a plain diaphragm wall section and an adjacent footing is assumed. The stress‐strain behaviour of the ground is described by an advanced constitutive model, which especially takes into account the rheological properties of the soft clay, like creep, relaxation and a rate‐dependent stiffness. Numerous calculations are performed, considering the impact of the panel geometry and the installation sequence of the diaphragm wall. Furthermore, the loading as well as the bending stiffness of the strip footing is varied. With respect to the serviceability of the footing, recommendations for the D‐wall construction are finally given, aiming at a prevention oriented construction technique.

GROUND DEFORMATION INDUCED BY COMBINATION OF VACUUM PRESSURE AND SURCHARGE LOAD

Laboratory large-scale model (length: 1.50m, width: ~0.62m, height: 0.85m) tests and finite element analyses (FEA) were conducted to investigate the deformation characteristics of soft clayey ground under the combination of vacuum pressure and surcharge load. Both the model test and FEA results indicate that the combination of vacuum pressure with surcharge load can reduce the lateral displacement of the model ground. The outward lateral displacement increases with the increase of the loading rate (LR) of surcharge load and the ratio of surcharge load to vacuum pressure (RL). The results also indicate that by adjusting LR and RL, the lateral displacement of the ground can be minimized.

The influence of the construction process on the deformation behaviour of diaphragm walls in soft clayey ground

AbstractConventional numerical predictions of deep excavations normally neglect the construction process of the retaining structure and choose the earth pressure at rest as initial condition at the beginning of the simulation. The presented results of simulation and measurements during the construction process of the Taipei National Enterprise Center show, that such an assumption leads to an underestimation of the horizontal wall deflection, the surface ground settlements as well as the loading of the struts in case of normally to slightly over‐consolidated clayey soil deposits. The stepwise installation process of the individual diaphragm wall panels results in a substantial modification of the lateral effective stresses in the adjacent ground. Especially the pouring process of the panel and the fresh concrete pressure causes a partial mobilization of the passive earth pressure and a distinct stress level increase in the upper half of the wall. As a consequence of the increased stresses prior to the pit excavation, up to 15% greater ground and wall movements are predicted. Moreover, the increased stress level due to the installation process of the diaphragm wall leads to substantial higher strut loadings during the excavation of the pit. Copyright © 2006 John Wiley & Sons, Ltd.

Soil consolidation associated with grouting during shield tunnelling in soft clayey ground

Soil consolidation associated with grouting during shield tunnelling in soft clayey ground

Discussion: Soil consolidation associated with grouting during shield tunnelling in soft clayey ground

Discussion: Soil consolidation associated with grouting during shield tunnelling in soft clayey ground

Soil consolidation associated with grouting during shield tunnelling in soft clayey ground

The effectiveness of grouting to reduce surface settlements during underground construction in clayey ground was investigated by a field trial and laboratory tests. The field trial was carried out during shield tunnelling work conducted in alluvial clay deposits in Koto-Ku, Tokyo. Grout was injected at some distance away from the tunnel, and both surface and subsurface settlements above the tunnel were monitored. Although the initial heave was achieved immediately after the grout injection, the ground continued to settle with time, owing to soil consolidation and grout shrinkage. A laboratory investigation was conducted to investigate the parameters that control the long-term behaviour of grouting in clay. It was found that better long-term grout efficiency can be achieved in overconsolidated clay than in normally consolidated clay, and the efficiency increased with increasing injection volume. Finite element analysis of the laboratory experiments confirmed that the amount and extent of excess pore pressures generated during injection govern the long-term grout efficiency. Finite element analysis of the field trial was also performed to simulate the long-term ground deformation after grout injection.

Soil consolidation associated with grouting during shield tunnelling in soft clayey ground

The effectiveness of grouting to reduce surface settlements during underground construction in clayey ground was investigated by a field trial and laboratory tests. The field trial was carried out during shield tunnelling work conducted in alluvial clay deposits in Koto-Ku, Tokyo. Grout was injected at some distance away from the tunnel, and both surface and subsurface settlements above the tunnel were monitored. Although the initial heave was achieved immediately after the grout injection, the ground continued to settle with time, owing to soil consolidation and grout shrinkage. A laboratory investigation was conducted to investigate the parameters that control the long-term behaviour of grouting in clay. It was found that better long-term grout efficiency can be achieved in overconsolidated clay than in normally consolidated clay, and the efficiency increased with increasing injection volume. Finite element analysis of the laboratory experiments confirmed that the amount and extent of excess pore pressures generated during injection govern the long-term grout efficiency. Finite element analysis of the field trial was also performed to simulate the long-term ground deformation after grout injection.

Experimental Study on Deformation of Soft Clay Improved by Low Replacement Ratio SCP Under Backfilled Caisson Loading

In designing structures, especially harbor structures on soft clayey ground, deformation of the foundation ground may sometimes appear as a vital factor for rational design. Both the short and long term behavior of soft clay improved by sand compaction piles with low replacement ratios, which is subjected to backfilled caisson loading, were investigated through a series of centrifuge model tests. In model tests, the construction sequence from the installation of the caisson to backfilling was simulated in-flight. Effects of replacement ratio, improvement width, SCP location and loading rate on the behavior of the caisson were studied. It was found that settlement of the model ground can be effectively reduced by a higher replacement ratio, and long term settlement of caisson after backfilling is highly influenced by the settlement of the ground behind the SCP portion. A wider improvement area towards the fill is more effective in reducing the lateral displacement of the caisson both during and after backfilling, and the degree of consolidation of the clay part in SCP ground has a significant effect on short term lateral deformation.

DEFORMATION DUE TO SECONDARY INJECTION DURING SHIELD WORK IN SOFT CLAYEY GROUND AND ITS SINKAGE PREVENTION EFFECTS

The effects of secondary injection during shield work on the prevention of ground subsidence were examined, using the measurement results of ground displacement during shield work in soft clayey ground. In order to investigate the deformation of soft ground during shield work, the finite element analyses were carried out by taking account of the consolidation of soft clayey soil due to the disturbance of micro-structure of soil. In case of soft clayey soil, the secondary injection could become the cause of ground subsidence because of the disturbance of micro-structure of soil associated with the fracturing phenomena during secondary injection. The guidelines for the design and execution procedures of secondary injection in soft clayey ground were also proposed.

Positive and negative skin friction on a pile in soft clayey ground at Haneda : Takahashi, K; Katayama, T; Souda, S Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991V1, P747–752. Publ Japan: Coastal Development Institute of Technology, 1991

Positive and negative skin friction on a pile in soft clayey ground at Haneda : Takahashi, K; Katayama, T; Souda, S Proc International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST'91, Yokahama, 3–6 September 1991V1, P747–752. Publ Japan: Coastal Development Institute of Technology, 1991