Geotextiles with natural fibers like coir, jute, sisal, hemp, etc. are used in many non-critical civil engineering applications like erosion control. The main advantage of geotextiles with natural fibers is that they are ecofriendly and biodegradable. They can be successfully used in limited life applications of geotechnical engineering. This paper deals with some case histories on the use of woven and stitched non-woven coir blankets for erosion control and slope stabilization, executed by the authors.
The ground freezing method is a ground improvement technique used as temporary work such as in shield tunnel construction. This chapter introduces two projects using the ground freezing method in Japan. One is a case adopted to remove the existing steel sheet piles under the subway tunnel structure; the other is a case adopted as shield arrival protection work of a discharge tunnel in the thermal power plant station. In the former case, it was necessary to excavate an adit under the existing subway tunnel structure in order to remove the existing steel sheet pile. The ground freezing method was adopted as a protection work for excavation of the adit. In the latter case, a newly developed CO2 ground freezing method was adopted for the first time in the world, in order to cut off water at arrival point of the shield to build discharge tunnels. The ground freezing method of the CO2 has advantages such as lower temperatures and smaller freezing facilities as compared with the conventional method, in addition to reducing environmental loads. In this case, the construction period was shortened utilizing the advantage of CO2 system.
The historical ruins, which consisted of rocks or soils, are treated for their preservation. In many cases, the ground improvement techniques are being used for the preservation of them. One tower of Angkor ruins was deemed as the most dangerous tower among them for restoration work. The compacted sandy formation was found from −1.5 m from the original ground surface and to +3.5 m above the ground. The safety factor for the ground bearing capacity in rainy season was calculated with S.F = 1.1. When its bearing strata were reconstituted, it was designed to have a sufficient safety factor value of S.F > 1.5. To achieve this purpose, the original sandy soils were mixed with slaked lime and compacted by tamping with geotextile. The material soil used for the platform was a mixture of different soils of original sandy soil, clayey soil, and lateritic soil at weight ratios of 70, 15, and 15%. Slaked lime was added to the mixed soil 1 at a rate of 0.1.
Cement deep mixing (CDM) was selected as a ground improvement technology and designed to treat the soft ground of a 2224 m long section of levee along the west bank of the Mississippi River for emergency repair. The project owned by the United States Army Corps of Engineers (USACE) was a part of the Louisiana Hurricane Protection Project. A series of overlapping CDM columns (panels) oriented in the transverse direction of the levee was installed. The primary purpose of these panels was to provide shear resistance to the levee against lateral loads at high flood water conditions. In addition, these panels were designed to support the additional vertical load generated by the increased height of the levee and to control the long-term settlement of the remediated levee, which might otherwise occur due to the compression of the soft foundation soils. A total of 41,500 m3 of CDM was produced.
In order to study the improvement of embankment stability on soft ground, two test embankments were constructed to failure. One test embankment was reinforced with high-strength, nonwoven geotextile as base reinforcement. The reinforcement consisted of one layer of high-strength geotextile placed directly on the natural ground surface at the bottom of the embankment fill. For comparison, another full-scale, unreinforced embankment using the same fill material as that of the reinforced one was also constructed to failure at the adjacent site. The height at failure of the reinforced embankment was 6 m while that of the unreinforced embankment was 4 m. This paper presents the instrumentation program, construction procedure, monitored data, and stability analysis of the test embankments. The study indicated that the high-strength, nonwoven geotextile as base reinforcement, can considerably increase the ultimate height of embankments on soft clay. It was also shown that the rapture occurred at large deformation of foundation subsoils.
This paper examines the characteristics of highly expansive black cotton soils of India and presents some experiences with foundation design and construction. Foundation failures in these soils are attributed mainly to the differential movement of the structure as a result of uneven ground movements due to alternate swelling and shrinkage of the soil. The use of under-reamed piles in black cotton areas has resulted in economy of as high as 30-60% when compared to strip footings. It is also quick and needs no exta backfilling thus providing for better and more uniform conditions for floor finishes adjacent to the walls.
Excavation to install and repair buried municipal services causes inconvenience and economic loss. Innovative alternatives are proposed which include bundling communications and power cables in common utility ducts and designing networks to benefit from no-dig technology.
When a schisty material is tectonically compressed in a direction parallel to the schistosity a kind of buckling of the layers occurs, so-called kink band. A model is proposed for this phenomena which shows that the angle of the kink band with the normal to the layers is equal to the angle of dilatancy between the layers. It seems that the elements in the kink, between the hinges, may be in any length.
Synopsis : Industrial waste management should be conducted rationally based on sound environmental geotechnology. Utilization of the industrial wastes as construction materials has been recommended, and many attempts on geotechnical waste utilization have been undertaken. This paper firstly introduces the recent governmental policy including the Japanese legal system and the present condition on industrial waste generation and management in Japan. An overview of researches and developments in last decade on utilization of various types of industrial wastes is provided systematically. Treatment techniques and utilization of surplus soil and waste sludge/slurry from construction works are discussed in detail. The paper concludes by mentioning the future outlook and our duties on waste utilization for a better environment.
Effects of coarse inclusions on strength behavior of a compacted residual soil were investigated through a laboratory direct shear test program. Factors investigated included inclusion content, size, shape, orientation and spacing, and saturation of matrix materials. It was found that critical inclusion content, below which inclusions have no effect, for this clayey matrix material was between 10% and 20%. The important factors controlling a strength increase of soils are inclusion surface angularity and roughness, inclusion spacing, and height of inclusion perpendicular to shear plane.
A new simple laboratory permeability test is proposed; an undisturbed soil sample encased in a thin wall (Shelby) tube may be tested directly for horizontal mass permeability. Through a row of small holes drilled on each side of the tube, water with a constant head is supplied from one end to the other across the diameter of the soil sample until a steady state seepage is established through the soil encased in the sample tube. From the rate of discharge measured, the coefficient of permeability may readily be computed over each divided section or over the entire length of the thin wall sample, thus providing an important information on horizontal mass permeability of a thick compressible stratum to evaluate more logically and reliably the rate of settlement of a structure on a soft clay foundation.
Block vibration tests were conducted on two test blocks measuring 3.0m × 1.5m × 0.7m and 1.5m × 0.75m × 0.70m, cast on level ground. The blocks were excited into vertical vibrations and the amplitudes of vibration at different frequencies of excitation were measured using acceleration transducers mounted on appropriate faces of the block. Dynamic shear modulus at this site was also determined by conducting in-situ tests. The natural frequencies and the vibration amplitudes of the test blocks were calculated by (i) the linear spring method, (ii) the elastic half space method and (iii) the impedance function method. A comparison was then made of the observed and computed natural frequencies and the vibration amplitudes of the blocks. The results of this comparison showed that for the cases of vertical vibrations, the natural frequencies in this case could be reasonably predicted by either of the methods used. The calculated and observed amplitudes, however, showed a wide variation.
Pile supported embankments have been constructed in Malaysia in soft ground areas. The success of the construction is mixed; it is successful with piles smaller than 300mm diameter but failure occurred when piles from 400mm to 500mm sizes were employed. The Swedish Method of design is adequate for the smaller piles provided that horizontal forces are catered for, the Method is inadequate for the larger piles as it results in spacings on the high side. Various models representing pile supported embankment behaviour are reviewed. A preferred design method based on the stone column analogy model is then proposed catering for the larger size pile supports.
Before the excavation work of the ground in caissons was mechanized, pneumatic caissons were inefficient, labor-intensive means of subsurface construction. Excavating machines called caisson shovel were developed and they have been used efficiently for excavating the ground in large caissons since 1971. Through the improvements made to the various appliances associated with the use of caisson shovels, pneumatic-caisson technology has been remarkably renovated. Innovative unmanned excavation systems have been developed recently and they were utilized successfully in deep caissons. As a result of those renovations realized in pneumatic-caisson practices, the dreadful image associated with the cruel labor in the compressed-air work of the conventional pneumatic caissons was wiped out.
The design of two large dams, Mangla and Kalabagh has given the profession a very useful insight on the behaviour and engineering characteristics of the soft rocks in general and sheared clays in particular. Mangla was designed when the concept of long-term stability of slopes underwent radical changes. The design of the project had to be modified during construction as it was realized that shearing in clays was far more extensive than what had been assumed during the design stage. Design parameters were revised and residual strength of clays was adopted instead of peak strength, owing to which major design changes had to be incorporated. The research conducted at Mangla on the properties of these over-consolidated clays is a landmark and has provided an important guidance for dealing with such foundations in the future projects. The experience of design, construction and monitoring during operation of Mangla dam and later the design of Kalabagh dam, afforded the profession an excellent opportunity for the study of these soft rocks. The special design features adopted for these large projects will also be of considerable help for the designers dealing with similar foundation conditions.
Laboratory model pile tests were performed to evaluate ultimate uplift capacities and critical relative displacements (CRD). The uplift capacities are significantly affected by pile surface conditions and the depth of pile embedment. The test results show that the CRD is not constant and is independent of the pile size, but is most closely related to the magnitude of the critical pile-soil adhesion along the pile shaft. An empirical relationship between these two quantities was established from the experimental results. This empirical equation was then verified by comparison with the reported results of conducting field tests on piles. A method has been proposed to calculate the value of adhesion coefficient for smooth metal piles in clay.
Japan has a 400 years' history of shallow sea reclamation for new land. However, the application of Soil Mechanics Engineering to reclamation started just recently. In reclamation works, two types of fill–material, the pit sand and the dredged seabed soil, are generally employed. The water content of dredged soil used as fill–material is rather high due to the intrusion of seawater while dredging and as a result, an extremely soft ground is made–up. As such there arise the problems of insufficient bearing capacity and subsidence of the reclaimed ground. Some measures for ground improvement are required to solve these problems. This paper deals with the technology on reclamation, seabed dredging, revetment construction, the problems of reclaimed ground as viewed from Soil Mechanics Engineering and their solutions. These are discussed together with Japan's unique nature of technological development in the field of reclamation engineering.
