To deal with the penetrability problem of cement grout in sandy soil and the durability problem of sodium silicate grout, a new permanent type grout has been developed in Japan during the past years. It has the durability of cement grout and the penetrability of solution grout. So this new permanent type grout can be used to improve the liquefaction resistance of in-situ sandy soil under existing buildings. This paper will present some of the strength and permeability properties of this new grout and its grouted sand. They include the chemical and physical stability of grout and the long-term permeability of grouted sand. The dynamic response of the grouted sand under triaxial cyclic test was studied as well. The test results have shown that this grout can provide the strength needed to increase the liquefaction resistance of sandy soil underlying the existing buildings.
In an effort to develop soil improvement agent that is more cost effective and has better performance, the blast furnace slag was recently used to develop new super fine cement (SFC) for soil improvement purpose. Advantages of the super fine cement include better water-resistant and improved soil strength resulted from a well-graded grain size distribution. Moreover, because the SFC is recycled from the manufacture process of iron, not only the price of the SFC cement is very compatible with other Portland cement but also recycling slag is a typical case of waste reduction.
In this paper, the authors will first present the material properties of the developed SFC cement. A case history will then be presented to describe the applications of this new cement in deep soil mixing pile wall construction. Finally, performance of the SFC cement would be summarized as conclusions of this paper.
To increase the base stability of braced excavations in soft clay, grout piles are frequently used to improve the base soil. Although the strength of base soil has crucial effect on the base stability of excavation, it is mostly determined by means of empirical equations so far. To rationalize the empirical equation commonly used, this paper will evaluate the apparent shear strength of grout piles improved clay based on the results of a model test simulating deep excavation in soft clay. The size effect of the model test was minimized by keeping the base stability numbers (= gH/Su) of the model test and the field excavation being equal. The undrained shear strength Su of soil used in the model test was reduced according to the size reduced from the prototype. The composite undrained shear strength of grout piles improved clay is evaluated by comparing the basal heave behavior of soil with grout piles improvement and that of soil with 100% ground improvement. Test results indicate that the contribution of grout piles to the undrained shear strength of the base soil underlying a deep excavation is only a small fraction of the grout pile strength. The contributed grout pile strength is smaller than the value which is usually adopted in the empirical equation for the undrained shear strength of grout piles improved clay.
Jet grouting is often used in deep excavation projects to improve the strength of soft ground. It not only increases the stability of excavation, but also limits the lateral displacement of retaining walls. However, it is often found that jet grouting may induce lateral outward displacement of diaphragm walls. The amount of displacement may exceed 10cm, leading to crack of diaphragm wall in extreme cases. Contrary to general belief, the outward movement of diaphragm wall is not induced by the seemingly high grouting pressure infact, difficulties in expelling waste disposal from the grout hole that leads to expansion of the soil mass is perhaps the governing mechanism. This paper presents to case of history a deep excavation. Both the construction characteristics of jet grouting as well as displacement patterns of diaphragm wall are addressed. The mechanism that leads to the outward movements of diaphragm wall is also delineated via a theoretical approach.
The finite element method is used in this study to investigate behavior of two bermed excavations. The results show that the finite element method can reasonably predict the short-term behavior of ground movement induced by bermed excavation. But the longer-term lateral deflection of retaining wall after excavation can not be reasonably simulated without considering the progressive failure behavior of berm and the interaction behavior between grout piles and clay.
Most coastal industrial parks in Taiwan were mainly completed through hydraulic fill reclamation. Most sites were reclaimed by dredging. Their subsoil conditions are mainly composed of grey silty sand locally laminated with grey silty clay and/or sandy silt. The liquefaction potential of saturated silty sand at various depths underlying each site is high due to high ground water table and potentially large earthquake ground shaking. The main purpose of this paper is to briefly illustrate the mechanism, arrangement, efficiency, and practical experience of various ground improvement method, such as sand compaction pile method, dynamic consolidation method, stone column method, and deep liquefaction compaction method. The objective for the whole article also intends to provide useful references for design and construction of similar projects in the future.
To deal with liquefaction of reclaimed land and to provide the oil tank foundation with enough bearing capacity, stone columns were widely adopted in the large reclaimed land development projects recently. The construction of stone columns is a state of the art practice due to the unforeseen ground conditions which are unknown on the design stage, but must be resolved during construction immediately. A case history of stone column construction on the difficult ground is selected to illustrate this phenomenon. This case shows that the results of stone column compaction pressure are significantly influenced by the arrangement of construction sequence. Five sets of CPT results and plate load test results from different pilot test field on a reclaimed land base are presented in this paper also. Test results indicate that the strain modulus of stone column ranges from 1400 tf/m2 to 3700 tf/m2. The stress concentration factor n of 1.8 between stone columns and the surrounding soil was obtained from this pilot test.
The construction of Second Bangkok International Airport has been planned since 1960 to accommodate the rapid growth of air traffic in this region. The 41 years project, which has passed more than 30 governments, was finally approved for the construction in 1991 and is scheduled to open in December 2004 with capacity to deal with 30 million passengers and 1.46 million tons of cargo per year. Due to the underlying high compressibility and low strength soft marine clay, ground improvement by Prefabricated Vertical Drains with preloading embankment is selected to reduce the post-construction settlement prior to the permanent airport facilities construction. This paper discusses the design concept and construction method of the on-going ground improvement project at Airside Pavements for the new airport construction. The ground improvement performance is evaluated through the monitoring data and the change of soil properties.