JET GROUTING METHODS USED TO IMPROVE THE CONSTRUCTABILITY OF TRENCHLESS PROJECTS

Brennon T. Morioka1, Ph.D., P.E. James K.P. Kwong2, Ph.D., P.E.,

Jeff K. Kalani3 ABSTRACT The use of jet grouting methods for ground improvement was a key factor in the success of microtunneling beneath the busiest parts of downtown Honolulu and horizontal directional drilling (HDD) across Honolulu Harbor. Located in and near the Honolulu Harbor area, general subsurface conditions along a 0.9-km long, 1,372-mm diameter and a 2.3-km long, 914-mm diameter gravity sewer alignments, and a 1.5-km long, 864-mm and 1,219-mm diameter force mains included coralline, lagoonal, estuarine, volcanic, and fill deposits. Jet grouting aided in microtunneling operations, groundwater control for jacking and receiving shafts, utility protection, resolving unexpected utility conflicts within shafts, and pipeline and manhole support in settlement sensitive areas along major, highly congested utility corridors. For the HDD harbor crossing, jet grouting to about –40 m elevation allowed for protection of existing container yard pier piles against potential ground loss due to running and flowing ground conditions below the end-bearing piles. QA/QC measures employed to evaluate the effectiveness of the ground improvement program included monitoring of jet grouting operations, coring of jet grout columns and strength tests. Keywords: trenchless technology, microtunneling, horizontal directional drilling, jet grouting, ground improvement, sewers, force mains, shaft construction

1 Sr. Geotechnical Engineer, URS Corporation, Honolulu, HI; brennon_morioka@urscorp.com 2 Vice President, URS Corporation, Honolulu, HI; james_kwong@urscorp.com 3 Geotechnical Engineer, URS Corporation, Honolulu, HI; jeff_kalani@urscorp.com

INTRODUCTION Jet grouting ground improvement methods have been specified on two successful microtunneling projects in downtown Honolulu and one project completed using both microtunneling and HDD. The first microtunneling project outside the Downtown Honolulu area involved the reconstruction of about 0.9 kilometers (3,000 feet) of 1,372-mm (54-inch) reinforced concrete gravity collection sewer installed along a major city highway (Honke et al., 1997). The second microtunneling project, which was constructed in the heart of Downtown Honolulu, the most congested area in Hawaii, involved the installation of a new 914-mm (36-inch) reinforced concrete gravity sewer pipeline, approximately 2.3 kilometers (7,500 feet) long (Kwong et al., 1998, Kwong et al., 1999). The second sewer reconstruction project also involved the construction of thirty-six manholes, extensive utility relocation, and twenty-four hour by-pass systems. The third trenchless project was completed using both microtunneling and HDD installation methods. HDD was used to construct two parallel force main lines beneath Honolulu Harbor, the most traveled waterway in Hawaii, from the Downtown Honolulu end of the harbor and under a shipping container yard and pier on Sand Island. High density polyethylene (HDPE) pipes 864-mm (34-inches) in diameter were pulled across the harbor through 1,219-mm (48-inch) steel casings approximately 0.7 km (2,300 feet) in length. Microtunneling methods were used to install an additional 0.8 km (2,500 feet) of 1,219 -mm (48-inch) glass-fiber reinforced pipe from the HDD exit point in the container yard to the Sand Island Wastewater Treatment Facility (WWTF). Jet grouting methods were specified for the microtunneling projects to serve multiple purposes (Kwong et al., 1999; Morioka et al., 2001). Jet grout columns were used to support the new sewer line and manholes to prevent future settlements of the collection system that may occur in the highly compressible underlying soils and to change very soft soils to cemented zones, eliminating the possibility of MTBM settlement and uncontrollable deviation from line-and-grade. Jet grout bottom plugs and jet grouted zones around and between gaps in the sheetpile shoring systems caused by utility conflicts, as well as at all MTBM ingress/egress locations, were used for groundwater control within the jacking and receiving shafts. Jet grouted zones also provided resistance against lateral deflections to protect a nearby existing, historical, rock seawall from jacking loads. Jet grout was also installed to depths of 43 meters (140 feet) below Mean Sea Level (MSL) at and above the anticipated HDD drill path beneath end-bearing pile supported pier to reduce the potential of settlements of the pier due to running or flowing conditions around the slurry filled, opened reamed hole during hole enlargement and prior to pipe pullback operations. SUBSURFACE CONDITIONS The geologic formation and history of the Hawaiian Islands is one of dynamic change and fluctuation. The resulting regional geology in the coastal areas of Oahu consists of a volcanic basalt island core that is flanked by beaches and coral reefs, which are locally dissected by erosional channels, estuaries, lagoons, and new lava flows. The mixing and interfingering of coral, beach sands, estuarine and lagoonal deposits with lava flows, and occasional deposits of alluvial silts and clays carried down from the mountains have created a local geology that is highly complex.

JET GROUTING REQUIREMENTS Specification requirements The plans and specifications for the first two microtunneling projects required jet grout columns to be installed with a minimum 1.2-meters (4-feet) diameter and 690 kPa (100 psi) unconfined compressive strength (UCS). All the described microtunneling projects specified jet grouting methods be used to install shaft bottom seals in soils, and for MTBM ingress and egress. The HDD portion of the third project also called for jet grout columns to be installed to depths up to 43 meters (140 feet) below MSL at and around the HDD drill path beneath the pile support pier at the shipping container yard. Minimum UCS values for this jet grouted zone was 4,826 kPa (700 psi). This jet grouted zone was to provide a degree of ground stability around the reamed hole area to reduce the potential of running or flowing ground into the open reamed hole and the amount of potential settlement below the existing end-bearing piles. The geotechnical reports for these projects indicated jet grouting methods would not be effective in cemented soils or rock, and placement of a tremie concrete plug and other grouting methods would be required to control groundwater inflows into shafts. For the two Downtown projects, a sequence of alternating and overlapping primary and secondary jet grout columns was designed to provide support for the pipeline and produce a more uniform material at the tunneling zone for the microtunnel boring machine (MTBM) to improve steerability (Figure 1). The specific design requirements for jet grout column installation for pipe support are provided in Kwong et al. (1999) and Morioka et al. (2001). The overlapping of jet grout columns, installed using single fluid jet grouting methods, provided a generally continuous and more consistent tunneling zone of soil-cement through which the MTBM could excavate and make steering adjustments, in otherwise very soft estuarine and lagoonal silts (typical SPT and California sampler N-values of 0 to 5 blows per foot). The size of the jet grout columns appeared to provide sufficient lateral coverage, such that the MTBM would remain within the jet grouted zone, as long as the MTBM did not deviate from the alignment in excess of the specified line and grade tolerances. Microtunneling considerations Successful installation of the specified jet grout columns appeared to have increased the efficiency of microtunneling operations (Morioka et al., 2001). Line and grade were maintained within the specified tolerances without observable, significant steering adjustments in these projects. Jet grouting the microtunneling zone also aided in maintaining lower and fairly constant jacking forces (Morioka et al., 2001). Jacking forces during tunneling within jet grouted zones typically ranged between 270 to 450 kN (30 to 50 tons) as compared to 530 to 890 kN (60 to 100 tons) in non-grouted alluvium, coralline deposits, and coral reef materials. Soil improvement was also required behind the jacking pit reaction/thrust block locations where soft and loose subsurface materials were present to reduce potential lateral ground deformation or bearing failure behind the thrust block during pipe jacking operations (Kwong et al., 1998). Figure 2 shows the line and grade observations for a drive with and without jet grout in the same drive. Tunneling in a loose, unfused portion of volcanic cinder deposits (flowing sands) posed initial steering difficulties resulting in significant line deviations, as illustrated in Figure 2.

However, the operator was able to steer the machine back on line once the MTBM entered the jet grouted zone, as steerability improved due to the availability of ground resistance from the jet grouted soils. Sewer pipe and manhole support The geotechnical explorations indicated that highly compressible, subsurface deposits underlie numerous portions of the two Downtown Honolulu sewer alignments and a short segment of the Sand Island project. Concerns existed that the placement of compacted backfill at shaft excavations and groundwater drawdown from future construction activities would induce new loads on the compressible soils beneath the manholes and pipelines. This would potentially result in settlements that may create sags and reverse flows within the new gravity sewer collection system, as well as potential cracking at manhole/pipe connections if no preventative measures were taken.

Figure 1. Jet grout for pipe/manhole support, groundwater control, and microtunneling

To reduce the potential for future settlement of the new manholes and sewer pipes, the compressible soils beneath the manhole subgrade and the sewer line were stabilized by installing jet grout columns that extended into a firm bearing layer (Figure 1) to maximum depths of 24 meters (80 feet) below ground surface. Primary columns were installed to behave as a type of deep foundation support system (Kwong et al., 1999; Morioka et al., 2001). The columns were designed to carry the load of the newly installed sewer pipe under full flow conditions, in addition to the weight of the soil above the pipe, the jet grouted zone around the pipe, and the jet grout column itself.

Shaft construction and groundwater control considerations Groundwater control was also a key factor in the construction of shaft and trench excavations and in determining appropriate excavation support systems. Due to the requirement that precluded dewatering methods for groundwater control using wells, a watertight support system was required (Kwong et al., 1998). Lowering of the groundwater table outside of any excavation limit was strictly prohibited due to the very loose and soft, highly compressible subsurface conditions of the downtown, high-rise areas, and the stringent environmental regulations on dewatering discharge.

Coralline Jet Grout Zone Deposits Cinders Lagoonal Alluvium

-60

-30

0

30

0 50 100 150Distance (m)

Line

Grade

Figure 2. Line/grade observations in jet grouted and non jet grouted materials

For the downtown project, continuous interlocking sheetpiles in conjunction with overlapping jet grout columns with appropriate internal bracing systems were specified. Also, because the excavations did not penetrate into impervious deposits, the soils below the base of the shaft were treated utilizing jet grouting methods in order to establish a groundwater cut-off at the base of the excavation, to prevent excavation instability, and to avoid excessive groundwater inflows. In selecting, designing, and constructing shoring systems for the shaft excavations, the contractors had to consider the presence of low to moderate strength sand, gravel, and clay layers below the groundwater table in designing against potential bottom heave and boiling, as well as the presence of strong, cemented, coral reef formations with cobble- and boulder-sized fragments. Where conflicting adjacent existing utilities were too close to allow the installation of sheetpiles, and too costly to be relocated, jet grouted columns were installed to strengthen and close the shaft walls and cut off groundwater inflows prior to shaft or trench excavation. Excavation of these shafts and support/protection for some of these utilities were accomplished by the innovative use of combined steel micro-piles installed within 1.2- to 2.4-meter (4- to 8-feet) diameter jet grout columns beneath the ducts. Double fluid methods were used to install the larger diameter jet grout columns. In areas of conflicting utilities, the contractor was also instructed to pre-drill and break-up cemented soils and rock, prior to jet grouting beneath large utilities.

In addition, the close proximity of an eighty year-old, river rock seawall near a jacking pit dictated the installation of jet grout columns behind the thrust block that successfully reduced the amount of lateral deflection that may have resulted in cracking of the rigid seawall. The jet grout column layout (Figure 3) was designed to resist against shearing forces through the columns and translation and deflection of the grouted mass. Jet grout stabilized soils were also used to control groundwater inflows for MTBM ingress/egress locations around the shaft excavations. A jet grouted zone beyond the anticipated excavation limits of the MTBM was installed to provide groundwater infiltration control at the MTBM ingress/egress locations within the sheetpile walls, as well as to reduce the amount of flowing and running ground into the excavation. Ground loss below the groundwater table and the shallow amount of ground cover of 2.4 to 4.6 meters (8 to 15 ft) was a serious concern of the engineers and owner, should this condition propagate towards the ground surface.

Figure 3. Jet grout layout for rock sea wall protection and inclinometer data Jet grouting below pier pile foundation system Jet grout was used to help stabilize the influence zone below a pile-supported pier for HDD beneath the Honolulu Harbor crossing (Figure 4). The pier was supported by end bearing piles in medium dense to dense, coralline deposits. The drill path was expected to contain high contents of gravels and sands with coralline cobbles and boulders or cemented zones. Cobbles and boulders falling into the 1,524-mm (60-inch) open-reamed hole would create potential obstructions during pullback activities. In addition, if ground loss as a result of running and/or

flowing ground conditions developed around the open hole and propagated up towards the pile tips, a loss in load carrying capacity of the end-bearing piles could result in excessive settlements of the piles. The pier supported by the piles contained crane rails for the 890 kN (100-ton) Gauge Cranes that load and unload the cargo ships. The cranes were extremely settlement sensitive and, for this reason, no settlement of the crane rails was allowed by the third-party, pier owners. The jet grouted zone, installed by double fluid jet grouting methods (selected by the contractors), around and above the drill path was designed to compensate for the absence of ground material as close as 3.0 meters (10 feet) below the pile tips. Figure 5 shows jet grouting operations on the pier area.

Figure 4. Jet grouted zone below pier piles

Figure 5. Jet grout activities on Container yard Pier, Honolulu Harbor

QA/QC PROGRAM Jet grout testing program Prior to production column installation on these projects, the contractors were required to demonstrate that the jet grouting construction methods and equipment used for this project were suitable for the anticipated ground conditions and would satisfy the depth, diameter, overlapping, and material property requirements outlined in the project specifications and shown on the contract drawings. A more detailed description of a typical test program is provided in Morioka et al. (2001). Jet grout test programs were performed at selected locations along the alignments of each project. The test program sites were selected based on the types of anticipated subsurface ground conditions to be encountered to evaluate the effectiveness of jet grouting methods in the various soil materials and depths. The upper 1.5 meters (5 feet) of the test columns were exposed to determine actual in-situ column dimensions and conditions. An example of exposed, top portion of the jet grout test columns from the various test programs are shown in Figures 6 and 7. Bulk specimens from exposed columns and core samples from selected columns and selected locations within and between columns were collected for laboratory testing. Results from the UCS testing program for representative samples at selected depths are presented in Figure 8.

Figure 6. Exposed test column from Downtown Honolulu project

Core samples at the edge and in the overlap zones were used to demonstrate the quality of the grouted material in the installed columns. Core samples were examined for continuity, segregation, and quality of grouted material. In general, core recovery ranged from 85 to 100 percent and Rock Quality Designation values were typically on the order of 70 to 100 percent. Photographs of core samples from a 23-meter (75-foot) jet grouted primary column from the second Downtown Honolulu project are shown in Figure 9.

(a) (b)

Figure 7. Exposed test column from Sand Island project (a) 0.9-m diameter test column by double fluid methods,

(b) Top portion of 1.0-m diameter columns installed by single fluid methods

0

5

10

15

20

25

30

35

0 5,000 10,000 15,000 20,000 25,000Unconfined Compressive Strength (kPa)

Alluvium (SM to MH)

Coralline Sand & Gravel (GM to GP)

Estuarine/Lagoonal (SM, GM, MH)

Coralline Sand & Gravel (DF)

Mixed with:

Figure 8. Selected QA/QC test core strength results

(DF – double fluid methods, others single fluid methods)

Figure 10 shows QA/QC cores from the Sand Island project in coral detritus and partially cemented reef formations. Figures 10(a) and 10(b) illustrate the jet grout material intermixed in voids, cavities, and joints in the coral formation within the expected grout zone. Appropriate adjustments in jet grouting parameters, such as lift rate, rotation, grout pump pressures, air flow and pressures, number of grouting nozzles, and cement grout specific gravity are very important

in achieving the desired results in variable ground conditions and when large ranges in depths and groundwater pressures are expected. Field permeability tests were also performed in the test core holes to evaluate the permeability of the grouted zones. Calculated in-situ hydraulic conductivities of jet grout soils ranged from 1x10-6 to 1x10-7 cm/sec (2x10-6 to 2x10-7 ft/min). Ground heave measurements were also observed during the test programs to determine the amount of ground movement during column installation. Observed ground heave measurements from the test programs were less than 50 mm (2.0 inches) for the columns installed up to 1.2 meters (4 feet) below ground surface. However, observed ground heave during deeper production column installation, between 3.0 to 4.6 meters (10 to 15 feet) below ground surface, was less than about 13 mm (½-inch).

S TA 4 5 + 1 42 0 ’ to 2 5’3 0 ’ to 3 5’

S a m p le# :D e pth :

S TA 4 5 + 1 43 5 ’ to 4 5 ’

S a m p le# :D e pth :

S TA 4 5 + 1 44 5 ’ to 5 5 ’

S a m p le# :D e pth :

S TA 4 5 + 1 46 0 ’ to 6 5’7 0 ’ to 7 5’

S a m p le# :D e pth :

S TA 4 5 + 1 45 ’ to 1 0 ’1 5 ’ to 2 0’

S a m p le# :D e pth :

Figure 9. Representative test core samples from Downtown Honolulu project

(c)

Figure 10. Representative test core samples from Sand Island project Daily QA/QC monitoring program Throughout the jet grouting operations, QA/QC monitoring was performed by the construction management design team to observe and record installation parameters used for the production columns. Morioka et al. (2001) provides a more detailed description of daily jet grouting observations and records. Analyses of QA/QC core tests appeared to demonstrate certain trends in UCS values obtained, depending on in-situ material type and depth. As illustrated in Figure 8, jet grouting in granular, coralline deposits typically resulted in higher UCS values. Estuarine and lagoonal deposits, consisting predominantly of silts and clays, typically produced the lowest UCS values upon QA/QC testing. The more granular alluvial deposits, although consistently lower in strength when compared to jet grout cores from coralline deposits, produced UCS values higher than the silty and clayey estuarine and lagoonal deposits at similar depths. In most cases, decrease in strength values was observed in tests performed on core samples retrieved from greater depths. In general, jet grout UCS values in coralline materials were reported to be as high as 15,000 kPa (2,175 psi), 6,000 kPa (870 psi) in granular alluvium, and 4,300 kPa (600 psi) in the estuarine and lagoonal deposits. Surface settlement surveys were also performed periodically along the alignment at the pier location because of the settlement sensitive nature of the crane rails situated on the pier. In general, survey data obtained prior to jet grouting, and before and after HDD operations,

(a) (b)

indicated little to no settlement at the pier surface. The jet grout was installed prior to drilling of the pilot holes. SUMMARY AND CONCLUSIONS Based on the observations during construction of the three projects described in this paper, jet grouting can be a useful and multi-purpose ground improvement technique to reduce potential construction difficulties relating to microtunneling, shaft installation and HDD. Jet grouting methods aided in the construction activities for reducing groundwater infiltration from both the excavation walls and shaft bottoms, particularly where the shaft wall cannot be closed, due to the presence of existing utilities and other pipelines, to a depth of 12 meters (40 feet) below ground surface and for improving excavation bottom stability by increasing strength characteristics of the in-situ soils. Steering control during microtunneling was improved by producing more uniform tunneling conditions where mixed face and/or adverse tunneling conditions pre-existed. Jet grouting provided stabilized potential problematic ground conditions, to reduce potential adverse effects to an existing pier pile foundation system prior to HDD and adequate protection of existing utilities and historic structures near shaft excavations. Finally, jet grouting was useful in providing long-term pipe support against excessive settlements due to consolidation of the highly compressible soils in the project areas. Adequate QA/QC efforts were found to be vital in the evaluation and aid in the proper installation of effective jet grout columns, particularly for the deep columns, such as the 21 meter (70 feet) long grouted length installed to depths of up to 24 meters (80 feet) below ground surface for pipeline support and microtunneling, and where jet grouting had to be performed in an unprecedented depth of 40 meters (130 feet) below sea level. The benefits of ground improvement with jet grouting techniques are many and can be very cost-effective when used on large projects and/or for multiple construction purposes. However, adequate, performance-base specifications, an experienced contractor work fore, and careful monitoring and control of jet grouting procedures are vital to the success of jet grouting in highly diverse and difficult geological conditions, such as those described. Test programs should be adequately defined and planned to ensure compatibility of the equipment and installation methods with the full range of anticipated ground conditions. REFERENCES [1] Kwong, J., S. Klein, G. Nagle, and S. Duke (1998). “Microtunneling in Downtown

Honolulu,” Proceedings from Pipelines in the Constructed Environment, ASCE Specialty Conference, San Diego, 1998.

[2] Kwong, J., S. Klein, G. Nagle, G. Okita, and S. Duke (1999).“Microtunneling Under

Honolulu,” Civil Engineering, ASCE, March, Volume 69, No. 3. [3] Morioka, B.T., J.K.P. Kwong, and J.K. Kalani (2001). “ Jet Grouting for Microtunneling

and Shaft Construction in Highly Congested Utility Corridors,” Proceedings from 2001 – A Geo-Odyssey, Foundations and Ground Improvement, ASCE Specialty Conference, Blacksburg, VA, June 9-13, 2001.

ACKNOWLEDGEMENT Jet grouting and relating work for the downtown Honolulu projects was performed by Hayward Baker (first project) and Layne GeoConstruction (second project) and Frank Coluccio Construction (general contractor); jet grouting for the HDD crossing was performed by Layne GeoConstruction for Modern Continental Construction (general contractor).