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Earth Retention Using the TRD Method

Ed Garbin1, Ph.D., P.E., A. M. ASCE, James Hussin

2, M. ASCE, Chikashi Kami

3

1Chief Engineer, Hayward Baker Inc., 6850 Benjamin Road, Tampa, FL 33634; PH

(813) 884-3441; FAX (813) 884-3820; [email protected], Hayward Baker Inc., 6850 Benjamin Road, Tampa, FL 33634; PH (813)

884-3441; FAX (813) 884-3820;[email protected] Civil Engineer Deputy General Manager, Tenox Corporation, 13-7, Akasaka,

6-Chome, Minato-KU, Tokyo, Japan; PH +81 (3) 35825168; FAX +81 (3) 35824714;

[email protected]

ABSTRACT

The Trench Remixing Deep (TRD) method of wall construction is an innovative

method of deep soil mixing developed in Japan that employs a tool resembling a

vertical chainsaw to simultaneously cut and mix soil and grout in place withoutcreating an open trench. Ideally suited for projects requiring a high quality wall or forconditions where typical construction methods would be difficult, TRD has been used

to construct earth retention walls with great success.

This paper covers the design and construction of the TRD method to construct high

quality earth retention walls.

INTRODUCTION

The TRD method of in-situ wall construction results in a highly uniform vertical wall.

The tooling consists of a tracked rig mounted full-depth post equipped with arevolving chain with cutter teeth that chip away the in-situ soil from the trench face

while mixing it with binder slurry as the post advances horizontally. Slurry

composition varies according to specified wall properties. The slurry consists of watermixed with cementitious binder, typically Portland cement and/or ground granulated

blast furnace slag (GGBFS), and clay (typically bentonite) when low permeability is

required.

The TRD method has been used in the United States since 2006 and for the past 20

years in Japan, where the technology was developed. Previous use of the TRDmethod in Japan has been extensive and highly successful (Aoi et al. 1996 and Aoi et

al. 1998). The TRD methods unique vertical mixing process results in a high degree

of wall uniformity, which is its foremost advantage over other in-situ mixing

methods. This quality is demonstrated in this paper with sample data from theextensive quality control (QC) testing program at Herbert Hoover Dike (HHD) at

Lake Okeechobee, Florida.


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THE TRD CONSTRUCTION PROCESS

Wall continuity and full vertical mixing are the primary differences between TRD and

other wall construction techniques. The TRD process is continuous, with a full-depth

cutter post that extends to the wall tip elevation. The cutting teeth vertically mix the

entire soil profile to a high degree of homogeneity as they revolve around the cutterpost, thus eliminating any natural layering that may have been initially present. The

TRD machine horizontally advances the cutter post along the wall alignment as it

mixes, leaving a wall free of joints (Figure 1).

Figure 1. Illustration of the TRD walling method. Post is inserted full-depth

(left) and then mixing proceeds horizontally (right).

The TRD method provides a high degree of control over the walls verticality andpositioning, whether at shallow or extreme depths [over 46 m (150 ft)]. The TRD

machine is also able to install battered walls at up to 45 degrees from horizontal. It

can cut through rock layers having a compressive strength of 20 MPa (~3000 psi) andcan key into bedrock having a strength of 70 MPa (~10000 psi). Further, the TRD can

cut through boulders up to 1 m in diameter, and has been used to cut through granite.Over the past 20 years in Japan, more than 1,486,448 m (16,000,000 ft

2) of wall has

been constructed to depths as great as 56.7 m (186 ft) (AK Chemical, 2006).

DESIGN

Earth retention systems constructed with the TRD method are designed as soldier pileand lagging walls, with the mixed soil-cement acting as the lagging. Horizontal


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spacing of the soldier piles is governed by the strength of the soil-cement and the soil

and water pressures acting on the wall. In the past, a maximum spacing of about 1.5m (5 ft) has been used. For permanent wall applications, modified H beams with

interlocking flanges have been installed acting as a steel reinforcing cage. If the

required depth of excavation is such that predicted wall movements exceed tolerable

levels, one or more levels of tieback anchors may be incorporated into the design.

Several limitations inherent in traditional soldier pile and lagging walls are avoided

by using the TRD. For example, soil arching between the soldier piles prior tolagging is not a concern with the TRD method, since the entire wall is constructed,

full-depth prior to excavation. Where excavation below the water table is not feasible

using traditional soldier pile and lagging walls, a TRD wall can be designed with lowpermeability to prevent inflow, though if the TRD wall is not keyed into an aquiclude,

basal stability and flow beneath the wall must be evaluated during the design.

CONSTRUCTION

The wall construction process continuously produces a soil mix wall along a straight

or curved line. Structural steel reinforcement is added, typically by inserting steel Hbeams or a similar steel section in the wet soil mix wall immediately behind the cutter

post (Figure 2).

Figure 2. Steel beam being inserted vertically into the wet soil mix wall (left), and

tops of soldier piles visible in TRD wall (right).

The post is initially inserted into the ground in sections, much the way that a drill rig

advances drill steel (Figure 3).


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Figure 3. Sequence of initial installation of the cutter post.

After reaching a corner location, the post is removed by disconnecting the top of the

post from the post drive unit and then pulling the post, generally in one piece, with a

crane (Figure 4) to minimize the removal and reinsertion time.

Figure 4. Removal of cutter post in one section.


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The post is laid on the ground and as each segment is unbolted it is reinserted along

the next wall alignment as initially installed (Figure 3).

TRD QUALITY CONTROL

Quality control (QC) of TRD constructed walls begins with a pre-constructionlaboratory mix design program, mixing pre-selected grouts with full depth soil/rock

samples. During construction, QC continues with careful monitoring of the grout

components and the specific gravity (SG) of the neat grout at the batch plant. Thisensures consistency between batches, and helps to achieve the highly uniform wall

typical of the TRD method. SG is monitored in real-time using a mass flow sensor

mounted on the TRD rig, with the data displayed in the cab and also recorded for laterincorporation into QC reports (Figure 5). This same sensor also measures and records

the flow rate, volume and temperature of the grout being pumped through the system.

It is typical to also verify SG several times each shift using a mud balance, as a check

test for the instrumentation.

Figure 5. Plot of SG Data from the HHD project

Additionally, the wet soil mix material from the trench is sampled and subjected to

flow table testing in order to assess the mix viscosity. Maintaining the flow tablevalue within a certain range ensures proper material flow around the cutter post,

which is essential for uniform full-depth mixing. The flow table testing apparatus and

sample test results from the HHD project are shown in Figure 6.


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Figure 6. Flow table test apparatus and test results from the HHD project.

Wall verticality is controlled by the operator and monitored in real-time usinginclinometers installed inside the TRD cutter post at various elevations. Additionally,

the position of the cutter post can be tracked using a differential GPS, as well as with

routine surveys using a total station. This inclinometer and GPS data are displayed in

the cab and also recorded.

The strength and permeability of the cured soil mix material may be ascertained by

testing specimens that have been collected wet and cast into standard cylinder molds.Careful control and monitoring of the grout quality during batching and quantity

during mixing with the soil produces a homogeneous wall with the desired properties.

(Figures 7).

Figure 7. Deep grab sample laboratory strength and permeability test results

from the HHD project demonstrates wall homogeneity over depth & length.

In addition, the material may be cored using rotary drilling techniques to retrievesamples for visual inspection, or to allow for the use of a down hole camera. Highly

destructive by its nature, coring is not recommended except on a limited basis, as it


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can adversely impact the integrity of the wall. Where coring has been performed,

down hole cameras have verified the high homogeneity and continuity of the TRD-constructed walls with depth (Figure 8).

Figure 8. Down hole camera images at depths of 2.4-4.2 m (8-14 ft) [above], and

12.4-15.5 (45-51 ft) [below], from the HHD project, showing evenly distributedrock fragments from the bedrock layer.

PAST PERFORMANCE

Since the early 1990s, approximately 400 projects have been performed using the

TRD method. Approximately two thirds have been structural retaining walls and onethird were cut off walls. The retaining walls have ranged from 550 mm (21.6 in) to

800 mm (31.5 in) wide and as deep as 56.7 m (186 ft). The walls have been

constructed in a wide range of subsurface conditions, including clay, silt, sand,gravel, boulders, peat, mudstone, limestone, weathered rock, and granite. The

excavations were for various types of projects including housing, schools, offices,hotels, museums, airports, underground parking, roads, railroads, subways, tunnels,power plants, treatment plants, pump stations, utilities, canals, reservoirs, and dams.

An example of a TRD earth retention wall project is presented in Figure 9.

LIMITATIONS

The TRD is a versatile tool which has been successfully used to install walls in a

multitude of geologic conditions, ranging from soft soils to hard rock. TRD may notbe cost-effective for shallower trenches or soils that can be readily excavated by

traditional methods. Deep walls, excavation below the water table, boulders and hard

rock, and other conditions that would impede traditional methods are ideal for TRD.Depth is limited to roughly 60 m (~200 ft). Wall thicknesses of 550 mm to 800 mm

(1.8 ft to 2.6 ft) are possible with presently available equipment.


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Figure 9. Isogo Pumping Station for a reservoir in Yokohama City, Japan. Top

of TRD wall with exposed soldier pile (left) and TRD wall exposed after

excavation (right).

CONCLUSIONS

The TRD method has a successful 20 year track record of shallow and deep earth

retention for a wide range of construction projects and subsurface conditions. For

earth retention applications, steel beams are inserted in the freshly constructed wall toprovide the required lateral strength. The TRD method of wall construction provides

the highest quality continuous mixed-in-place wall of any method available.

REFERENCES

AK Chemical Co., Ltd., (2006). TRD Performance Records in Japan & USA.

Internal Publication, Prepared for Hayward Baker.Aoi, Minori, Fumio Kinoshita, Shigeki Ashida, Hiroaki Kondo, Yuji Nakajim,

Motohiko Mizutani. (1998). Diaphragm Wall Continuous Excavation

Method: TRD Method. Korbelco Technology Review, No. 21.

Aoi, M., T. Komoto and S. Ashida. Application of TRD Method to WasteTreatment on the Earth. M. Kamon (ed.), Environmental Geotechnics:

Volume 1 (1996): 437-440, Rotterdam, Balkema.

Cedergren, Harry R., (1988). Seepage, Drainage and Flow Nets. 3rd Edition. JohnWiley & Sons, Inc.

Evans, J.C., (2007). The TRD Method: Slag-Cement Materials for In Situ Mixed

Vertical Barriers. Conference Proceedings, GeoDenver 2007.Fordham, E., 2006, Flow Modeling as a Tool for Designing and Evaluating a

Seawater Barrier Demonstration Project, MODFLOW and More 2006:

Managing Ground-Water Systems - Conference Proceedings, Poeter, Hill &Zheng eds., International Ground Water Modeling Center, p. 796-800.

Gularte, F., Fordham, E., Watt, D., Weeks, J. and Johnson, T., (2007) First use of

TRD Construction Technique for Soil Mix Cutoff Wall Construction in the

United States Proceedings of GeoDenver 2007.

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