NEW SOIL TREATMENT METHODS IN JAPAN. H. Miki Public Works Research Institute, Tsukuba-Shi, Japan

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1 NEW SOIL TREATMENT METHODS IN JAPAN H. Miki Public Works Research Institute, TsukubaShi, Japan J. Iwabuchi Japan Association of Representative General Contractors (JARGC), Central Research Institute for Construction Technology, Tokyo, Japan S. Chida Chida Engineering Co., Tokyo, Japan ABSTRACT This paper reports of several new soil treatment methods in Japan, which include 1) a liquefied soil stabilizing method to reuse construction sludge and excavated surplus soils, 2) a highspeed continuous soil treatment system using pipeline mixers and a lightweight banking method which utilize insitu surface soil without purchase and carrying of fill materials. Liquefied soil stabilizing method involves adding stabilizer to slurried soil, and enables the laying of soil with stable quality that requires no compacting at construction sites. The application of this method has recently been increasing in Japan for backfilling underground multipurpose ducts or other underground structures. This method has a major advantage in that muddy construction sludge, dredged material and various other types of soils generated from excavation can be effectively used, thus both the waste disposal cost and the production cost of stabilized soil slurry can be reduced. An attempt to use lightweight foam mixed soil throughout the entire road embankment crosssection on a soft ground was shown to be applicable, in which insitu surface soil was used to make a high lightweight soil embankment, which means that the insitu surface soil is expanded to attain the required volume of the embankment. Pipeline mixers were used to produce lightweight foam mixed soil in this case. KEY WORDS SOIL STABILIZATION / CONSTRUCTION SLUDGE / SURPLUS SOIL / PIPELINE MIXER / LIGHTWEIGHT BANKING METHOD / MATERIALS RECYCLING 1. BACKGROUND OF SOIL RECYCLING IN JAPAN The results of a survey for the fiscal year of 2000 indicate that approximately 208 million m 3 of soil was generated from construction work around the country, of which only about 30% was reused for construction work. To promote the use of such soils, it is essential to solve the differences in timing and quality. Particularly, technology to use low quality soil with high water content needs to be developed.

2 Present conditions and issues regarding the effective use of soil generated from construction work are summarized below. (a) The amount of soil that needs to be carried out of construction sites is far larger than the amount of soil used, meaning that there exists a surplus of soil. (b) On the other hand, large amounts of new materials, such as sand from mountains, are used, and this has a significant impact on the natural environment. (c) A large amount of surplus soil is transported to inland reclamation sites, and part of such soil is inappropriately disposed of. (d) Proper measures are needed to correct the problems of polluted soil and soil mixed with waste. (e) Sludge generated from construction work and polluted soil exacerbate the shortage of final disposal sites. (f) One important point when promoting the effective use of soil generated from construction work is to develop technologies to use low quality soil with low cone index values, such as mud. 2. LIQUEFIED SOIL STABILIZING METHOD 2.1. Outline The liquefied soil stabilizing method (LSS) involves adding stabilizer to slurried soil, and injecting the slurry directly from the transport vehicle or pressurefeeding the slurry from the plant. This method enables the laying of soil with stable quality that requires no compacting at construction sites. The application of this method has recently been increasing; for example, it is used for backfilling underground multipurpose ducts, the foundation work for structures, filling cavities and lightweight embankment. This method has a major advantage in that sludge generated from construction work, dredged material and various other types of soils generated from excavation can be effectively used. Even the muddy sludge generated from construction work can be used as high quality slurrying material, thus both the waste disposal cost and slurrying cost can be reduced Reuse of muddy soils According to the soil classification standard in the Technical Manual for Utilization of Excavated Soils from Construction Works issued by the former Ministry of Construction, muddy soils are defined as those having a cone index of about 200 kn/m 2 or less and as the sludge generated from construction works. When disposing of them, the procedures specified by the Waste Disposal Law must be followed. Since such excavated soils and/or sludge contain a large quantity of fine grains, the soils cannot readily be reused as earthwork materials without any treatment. For recycling such soils, various technical methods such as addition of sand, solidification by plaster, lime or cement stabilization, and reuse of the soils as raw materials for cement have been developed, in addition to the dewatering/drying method. In this report, the technical background and reasoning for classifying the Liquefied Soil Stabilizing Method (LSS) as solidification by cement stabilization will be introduced as a technical method of reuse of muddy soils.

2.3. Concept and histry of LSS In order to ensure that the stabilizer may be mixed evenly with cohesive soil containing a large quantity of fine grains, mixing can be facilitated by turning the

Therefore, such mixture can not be compacted, but can only be used to fill spaces closely due to its liquidity, thus achieving its purpose by strength developed after hardening, like placing concrete

As an extension of this concept, the project Technical Development of Liquefied Soil Utilization was conducted from 1992 to 1995 jointly by Public Works Research Institute, the former Ministry of

Prevention of Generation and Reuse of Construction Byproducts by the former Ministry of Construction.

In 2003, LSS was designated by the Ministry of the Environment as a Green Procurement item. 2.4.

3 2.3. Concept and histry of LSS In order to ensure that the stabilizer may be mixed evenly with cohesive soil containing a large quantity of fine grains, mixing can be facilitated by turning the cohesive soil into slurry by increasing its water content. In this case, voids in the mixture thus obtained will be saturated with water. Therefore, such mixture can not be compacted, but can only be used to fill spaces closely due to its liquidity, thus achieving its purpose by strength developed after hardening, like placing concrete into a form. This was the original concept of developing LSS. As an extension of this concept, the project Technical Development of Liquefied Soil Utilization was conducted from 1992 to 1995 jointly by Public Works Research Institute, the former Ministry of Construction and Central Research Institute, Japan Association of Representative General Contractors as a part of the Comprehensive Technical Development Project Development of Techniques for Prevention of Generation and Reuse of Construction Byproducts by the former Ministry of Construction. This project enabled the Liquefied soil stabilizing method to be generalized nationwide, and a cumulative total of 3,200,000 m 3 of LSS has now been applied. In 2003, LSS was designated by the Ministry of the Environment as a Green Procurement item Required property of LSS Liquefied soil is used mainly for backfilling narrow spaces between structures and/or vacant spaces in ground where compaction cannot be used. The liquefied soil must have sufficient strength for transmitting the structural load on the liquefied soil to the surrounding ground and the liquidity to fill spaces by itself. Here, strength means greater shearing strength than that of surrounding ground and compressive strength to avoid consolidation by overburden pressure, also including the density effect capable of dispersing the load. Regarding liquidity, sufficient liquidity to fill narrow spaces is related to the value of the mortar flow test (JHS A / Photo 1) and this is used as the liquidity index of liquefied soil to be placed at site. The largescale model test (Kuno, 1996) as shown in Photo 2, for example, was conducted to examine the relation between the flow gradient of the liquefied soil placed and the flow test results. As a result, the relation shown in Table 1 was obtained. Photo 1 Flow Test Photo 2 LargeScale Model Test

Table 1 Flow Gradient of LSS Flow value Flow gradient (mm) (%) Case 1 120 11.3 Case 2 160 2.3 Case 3 (Linear) 220 1.9 Case 3 (Bend) 2.

surface, may occur. From experience, it is known that there is less material segregation at the bleeding rate of less than 1% in three hours after placement.

4 Table 1 Flow Gradient of LSS Flow value Flow gradient (mm) (%) Case Case Case 3 (Linear) Case 3 (Bend) 2.0 On the other hand, since LSS has high liquidity, the phenomenon of material segregation in which coarsegrained soils settle in slurry and the bleeding phenomenon in which water floats up to the surface, may occur. From experience, it is known that there is less material segregation at the bleeding rate of less than 1% in three hours after placement. In order to ensure the quality, a bleeding test (JSCE1986) was conducted to confirm that the bleeding rate is less than 1%. Thus, the principle of LSS is to design the mix proportion to be suitable for individual backfilling specifications while satisfying the strength and liquidity as well as bleeding rate mentioned above for the given construction sludge Mix design and production of LSS The method of determining the mix proportion is given here for the case when construction soil containing a large quantity of fine grains is used as the principal material. First, four or five slurries of different specific gravity are prepared, to which 100 kg of cement is added. The bleeding rate, flow value and unconfined compressive strength are determined by soil tests for each of LSS and the values thus obtained are plotted against the specific gravity of slurry as shown in Figure 1. Figure 1 Determination of Slurry Density Photo 3 Placement of LSS Regarding the specifications for backfilling, the unconfined compressive strength must be N/mm 2 in consideration of reexcavation, and the flow value for liquidity must be mm. Then, the specific gravity of muddy water capable of satisfying the specifications for 100 kg of cement is calculated to range from 1.52 to The sludge and/or excavated soils from the construction site are stirred to ensure that the specific gravity of slurry falls within this range. LSS satisfying the specifications can be

produced by adding 100 kg of cement to the slurry and mixing. LSS thus produced is transported to the backfilling site and placed as shown in Photo 3. 2.6.

5 produced by adding 100 kg of cement to the slurry and mixing. LSS thus produced is transported to the backfilling site and placed as shown in Photo Application examples As described above, it is important to control the specific gravity of slurry for LSS. With this background, two cases of reuse are introduced below. (1) Reuse of general construction slurry This plant receives 1,000 to 1,500 m 3 /day of sludge with no cement contained. The sludge is generated from shield tunneling works, underground diaphragm wall construction and various types of piledriving works. The plant also receives sludge containing some cement, which is generated from deep ground jet mixing and soil/cement wall construction. As sludge with consistent properties will yield LSS of better quality, an experienced engineer inspects the received sludge for any changes in properties. When the place and type of construction changes, the properties of sludge change and then soil classification tests are conducted. A scene of sludge stirring is shown in the left side of Photo 4; during stirring, the specific gravity and sand content of the sludge are confirmed by measuring instruments. The machine shown in the top center of this photo is a vibrating screen in which adjusted slurry and foreign matter of more than 7mm in grain size that have been pumped up by a sand pump are removed. Under the vibrating screen, there is a slurry storage tank in which twostage stirring vanes rotate to prevent coarsegrained soils from settling. In the top right of the photo is a sand stock yard from which the required quantity of sand is charged into a mixer car when producing highdensity LSS. The mixing plant consists of a tank with specific gravity meter for monitoring the condition of incoming slurry, flow meter to measure the amount of slurry produced, a flow jet mixer type of mixing device, and a control room in which various quality tests are conducted. Photo 4 LSS Plat with Sludge Stirring Photo 5 LSS Plant with Shield Sludge (2) Reuse of shield mud only This plant receives only highdensity sludge obtained by removing water from raw sludge at the site of shield tunneling works. In case of shield works, since excavation is made deep underground and the soil strata typically consist of Diluvial silt/clay layers, stable soil material is obtained. The sludge carried into the plant is high density, having generally

6 been concentrated to the density of 1.5 g/cm 3. Therefore, the system is designed so that construction sludge of 1.2 g/cm 3 or less in density generated from earth drilling works is stored for adjusting the highdensity sludge and is added whenever necessary. A general view of the plant is shown in Photo 5. Although the common LSS plants are equipped with a soil stock yard and a mud stirring facility, this plant has no such facilities and so appears neatly arranged. As shown, construction sludge is received at the mouth for highdensity sludge and at that for general sludge, then fed to a highdensity sludge tank and a general sludge tank, respectively. In these tanks, there are 5stage stirring vanes for suppressing settling, which are rotated in such a manner that the slurry may be stirred upward. In the liquefied soil production process, the required quantity of slurry is fed from both tanks to the tank shown in the center of Photo 5 for adjusting the specific gravity. In case of highdensity LSS production, materials for density adjustment are separately fed into the tank and mixed with the slurry to achieve the required density. In the top left of Photo 5 is a mixing plant equipped with a 1 m 3 biaxial forced action paddle mixer and a 2 m 3 liquefied soil storage tank. The slurry carried in is controlled by computer in the shipment control room, sent through pneumatic tubes to the mixer, then finally the product is transported by an agitator car located below the mixer. 3. PIPELINE SOIL TREATMENT SYSTEM 3.1. Outline For the purpose of utilization of dredged mud, pipeline soil mixing methods are getting popularized in Japan. The pipeline treatment system has been developed as a kind of the pipeline soil mixing methods. The system is comprised of so called Kanro Mixer installed on the way of dredging pipe line and feeder devices for mixing materials. The system can be utilized for not only the consolidation of mud but making the foam mixed soil, producing the grainy soil and so on Process to produce lightweight foam mixed soil Figure 2 shows the continuous processing approach employed for the construction of the lightweight embankment. 1. Water is added to the untreated soil material and the mixture is transferred to the mud conditioning tank. 2. In the mud conditioning tank, the specific gravity of the mud is measured and extra water added as required. 3. The mud is then transferred to the agitator tank for churning. 4. The mud is pumped at fixed pressure by a pressure pump. 5. The mud is kneaded together with cement milk in the primary line mixer located along the pump line, then pumped out under pressure. 6. The mud and cement milk mixture is combined with foam in the second line mixer, then pumped out under pressure.

7 Mud Water Density control tank Slurry plant Agitator Mud pump Preparated mud Foam mixed soil Pipe line mixer(2) Pipe line mixer(1) Cement slurry Figure 2 Production system for foam mixed light weight soil Foam 4. LIGHTWEIGHT BANKING METHOD USING INSITU SURFACE SOIL 4.1. Outline Foam mixed soil has been used extensively in Japan for road widening and backfilling projects, but never throughout the entire road crosssection. An attempt to use lightweight foam mixed soil throughout the entire embankment crosssection on soft ground was done in which cohesive soil taken in situ from the surface of the ground was used to make a high lightweight soil embankments, which means that the insitu soil is expanded to attain the required volume Concept of a new lightweight banking method An attempt to use lightweight foam mixed soil throughout the entire embankment crosssection on soft ground was done in which cohesive soil taken in situ from the surface to the depth of 2m was used to make a 7m high lightweight soil embankments, which means that the insitu soil is expanded up to about four times to attain the required volume (Figure 3). The ground is a soft ground of around ten meters in depth, consisting of alluvial cohesive soils having an intermediate sand layer (Figure 4).

8 WL ahu aas aac aas Fo amm ixed so il Cement m ixed so i l F ig.2 Closs sect ion of des igned embankment Figure 3 Cross section of designed embankment GL WL Ground su rface ƒá ƒó C Cv 2.00 Hasu ike ( ahu ) z Sand ( aa s ) Ar iake c lay (aac) z Sand ( aa s ) Mix design ƒá?f un i t w e igh t ( kn/m3 ), ƒó?f f r ic t ion ang le (??j?a C?F cohes ion (kn/m2 ) (z=0 a t +0.9m GL ), Cv?F coe f f ic ien t o f con so l ida t ion ( cm2 / day )?}?],P y w ƒ, ƒf ƒ,æ y? è? The foam mixed with soil design involves choosing a hardening agent that satisfies the design requirements (specific weight = 8 kn/m 3, uniaxial compression strength = 600 kn/m 3 ) using soil from the site, and choosing the type and quantity of the foaming agent. Table 2 summarizes the characteristics of the soil used. Based on the results of the trials, the mix ratio shown in Table 3 was adopted. 表 1 Figure 4 Soil strata model and soil constants Table 2 Properties of site soil (surface soil) 現地発生土の土質特性 Water content (%) Wet Density (g/cm 3 ) Grain size distribution (%) Sand Silt Clay

Foaming agent Surfactantbased A Target density (g/cm 3 ) Table 3 Design mix proportion of foam mixed soil Target strength qu (kn/m 2 ) Dry soil (kg/m 3 ) Water (kg/m 3 ) Added cement (kg/m 3 ) Foam

9 Foaming agent Surfactantbased A Target density (g/cm 3 ) Table 3 Design mix proportion of foam mixed soil Target strength qu (kn/m 2 ) Dry soil (kg/m 3 ) Water (kg/m 3 ) Added cement (kg/m 3 ) Foam content (l/m 3 ) Foaming agent content (l/m 3 ) Flow value (mm) 160 mm or greater 4.4. Construction Method Foam mixed with soil made with site soil has many benefits apart from reducing the load on the ground; it also makes purchase and carrying of fill materials unnecessary, and allows greater flexibility with respect to strength and specific weight values. In the trial, a highspeed continuous processing system was employed instead of conventional batch production in an attempt to reduce costs. The ground is stabilized from a depth of two to four meters. The soil of top two meters at the surface was used to produce lightweight fill. The embankment was constructed by first building a trapeziumshaped mound of height 0.7 m around the periphery of the embankment, then filling it with the foam mixed soil. Ten stages were built in this way to achieve a total height of seven meters. Geogrid layers were laid at intervals of 2.1 m (three stages) to add reinforcement to the structure. The sloping faces are sprayed with a sedmudchemical mixture to create vegetation cover. Figure 5a) shows the construction process in progress while Figure 5b) shows the completed embankment. a) Embankment construction in progress b) Completed embankment (10 stages) 4.5. Monitoring results Figure 5 Construction process in progress Settlement of the embankment measured were only 29 mm in the base plane. Likewise, lateral displacement was virtually nil, thanks to the shallow stabilization on the ground surface; the maximum observed lateral displacement was 40 mm.

10 5. CONCLUSIONS Among the technologies for using soil and/or construction sludge generated from construction work, liquefied soil stabilizing method (LSS) is promising in Japan. This method has a major advantage in that sludge generated from construction work, dredged material and various other types of soils generated from excavation can be effectively used. Even the muddy sludge generated from construction work can be used as high quality slurrying material, thus both the waste disposal cost and slurrying cost can be reduced. For the purpose of utilization of dredged mud, pipeline soil mixing methods are getting popularized in Japan. The system can be utilized for not only the consolidation of mud but making the foam mixed soil. An attempt to use lightweight foam mixed soil throughout the entire embankment crosssection on soft ground was shown to be applicable in which cohesive soil taken in situ from the surface of the ground was used to make a high lightweight soil embankments, which means that the insitu soil is expanded to attain the required volume. REFERENCES Kuno, G., Miki, H., Mori, N., Iwabuchi, J. (1996) Application of the Liquefied Stabilized Soil Method as a Soil Recycling System. Proceedings of the Second International Congress on Environmental Geotechnics, pp Miki, H., Mori, M., and Chida, S. (2003) Trial embankment on soft ground using lightweight foammixed insitu surface soil, XXIInd PIARC World Road Congress, Durban, CD ROM Miki, H. (2005) Geosynthetic Reinforcement for Marginal Soils and Soft Foundations: Japanese Perspectives, GeoFrontiers 2005, ASCE, CD ROM

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