The material properties of cement-admixed soil vary spatially. Statistical parameters such as mean, coefficient of variation and scale of fluctuation were used to characterize the spatial variability of cement-admixed soil. In this paper, an advanced constitutive model for cement-admixed marine clay is firstly randomized by relating model parameters to mix ratios and hence binder concentration. This makes it possible to estimate behavior of spatially varying cement-admixed soil before construction. Then a random finite element analysis with fully-coupled consolidation analysis is performed to simulate the undrained behavior of cement-admixed soil with spatially varying properties in specimen-scale. Results show that existence of spatial variability reduces the overall strength of specimen and a “worst case” occurs when SOF is approximately one third of the diameter of specimen.

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Improving the ground beneath or beside existing structures is one of the most effective countermeasures against structural damage caused by seismic motion of the ground. Economical and mobile methods will be in high demand in Japan where seismic events with greater intensity are anticipated in the near future. The authors have developed a new in-situ soil mixing method using collapsible/expandable mixing blades and a special monitoring/auto-control system. This paper first describes the new technique in comparison with conventional soil mixing methods and describes the results of field tests. Lastly, an actual application is described in which a slope of loose deposits filling a valley is improved with inclined soil columns.

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More and more infrastructure have to be built on super saline soil in China, the salt content of which may be as high as 40wt.%. The salt corrodes the cement hydrate of the foundation. This paper reports preliminary research on anti-corrosion cementitious materials for concrete pile and stabilized soil pile. The results are as follows: Strength of magnesium oxychloride cement (MOC) and its hydrate Phase 518 (P5, the contributor of the strength) could develop and keep stable in the chloride brine, the ions other than those forming P5 did not affect P5 forming. So MOC possesses the characteristic of hydraulic cementitious material and the essential stability of corrosion resistance in the brine. Strength of GC (self-made binder) paste and stabilized soil stabilized with GC could develop and keep stable in the chloride brine. Both strength and height of diffraction peak of hydrated calcium silicate (CSH) of the specimen either curing in the brine or mixed with the brine were higher than that mixed with distilled water and standard curing. So the brine is favorable condition for GC hydrate growing rather than corrosion media. GM (self-made binder) didn’t include Ca2+, so eliminated the basic element to form expansive ettringite (AFt) when GM immerged in sulfur brine. Sulfur saline soil stabilized by GM curing in the sulfur saline could keep strength and volume stable. Strength of GM paste could keep stably in the sulfate solution.

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The paper presents a method to estimate the bearing capacity of a strip footing on a geosynthetic reinforced foundation bed (RFB) laid over soft compressible ground stabilized with granular trench. Madhav and Vitkar's solution for bearing capacity of granular trench-supported footing in soft ground, Vesic’s cavity expansion theory that considers the compressibility/stiffness of soft ground together with its undrained shear strength and the effect of kinematics (the effect of the transverse resistance in addition to the axial resistance of the reinforcement, Madhav and Umashankar) are incorporated in Meyerhof’s analysis for layered soils, to arrive at the ultimate capacity of the reinforced foundation bed-granular trench system. A parametric study quantifies the effects of various parameters on the bearing capacity of the strip footing. Consideration of compressibility/stiffness of soft ground together with kinematics of failure indicates relatively enhanced values of bearing capacity of footing over those corresponding to incompressible ground or reinforced two-layered system considering axial resistance of reinforcement alone. Predictions compare well with experimental results in literature.

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The technique of sand or stone columns is widely used to improve the load carrying capacity and reduce the settlement of soft soils. The technique consists of excavating holes of specific dimensions and arrangement in the soft soil and backfilling them with either stone or sand particles. The efficiency of the technique depends primarily on the type of the backfill material (sand or stone) and gradation as well as the placement relative density. In the present research, holes 50 mm in diameter and 300 mm in length were excavated in a bed of soft soil, 400 mm in thickness, of undrained shear strength between 16-19 kPa. The holes were backfilled with either sand or stone particles at loose and dense states. Each column was loaded gradually through a circular rigid footing 64.6 mm in diameter up to failure with continuous monitoring of the settlement. The outcomes of the model tests revealed that for both floating and end bearing types, the sand columns at low relative density exhibited higher bearing improvement ratios and lower settlement reduction ratios compared to stone columns. On the other hand, a reverse behavior was noticed, when the backfill material was placed at "dense state". The results shed the light on the importance of placement relative density of both backfill materials. The results are thoroughly analyzed in terms of the stress concentration ratio and stiffness ratio

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The construction of large diameter tunnels can be challenging, especially in soft soil conditions. Stability intervention by means of ground improvement has been identified as a possible method to allow for the safe construction of such tunnels. A 1-g physical model study of the stability of a tunnel with a cement-treated soil layer surrounding it, along with related failure loads and mechanisms, is reported here. The failure mechanism of such tunnels is found to be very different from conventional tunnels with no ground improvement as cement-treated soil is very brittle. Failure occurs locally, with cracks developing in the tensile region in the cement treated layer. These cracks consistently occur at the crown, springline and invert, over a range of improved soil layer thickness-to-tunnel diameter (t/D) ratio. These cracks are also distinctly flexural tensile in nature. Prior to the onset of cracking, the deformation of the tunnel is minimal. This in turn results in a negligible settlement trough. This implies that caution is needed on the use of ground movement as a measure of the strength mobilization, owing to the lack of warning signs. The stability of such tunnels is found to be related to the t/D ratio and strength of the improved soil layer, while the significance of the unimproved surrounding soil is found to be minimal. This leads to the formulation of a new stability equation.

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