Grouting for Ground Improvement: Innovative Concepts and Applications

This paper presents a mathematical model for describing the jet grouting process, using fundamental theories of jet hydrodynamics and soil mechanics. The proposed model assumes that the velocity distribution in the cutting jet is equivalent to that of a submerged free jet with boundaries corresponding to the dimensions of the cavity excavated in the ground. It was found that jet penetration distance in soil is governed by the nozzle diameter and the ratio of the pressure difference across the nozzle to the soil bearing resistance. The model predicts that the limit of jet penetration is reached when the average dynamic pressure at the jet tip becomes equal to the ultimate soil resistance. Soil resistance to jet penetration is observed to be about 40% of a circular surface punch. Comparison with full-scale jet grouting trial data suggests that the proposed model is reasonable for fine-grained soils, but is likely to give a lower bound estimate of the jet cutting distance in coarse-grained soils.

The type and level of injection pressure used during permeation grouting with microfine cement suspensions can influence the extent of improvement in permeability and strength of grouted sand, the mass of cement particle deposition, and the grout flow rate. Laboratory experiments were conducted using constant pressure, variable pressure, and oscillating pressure with different pressure levels, ranges, and cyclic durations. Microfine cement grout at three different w:c ratios was injected into sand-packed columns of two different lengths; the longer column length allowed assessment of property improvement with distance from the injection point. Effluent flow rates decreased as the grouting process continued and the response was dependent on the type and level of injection pressure. Although a relatively large mass of cement particles may be deposited in the intergranular space, the grouted sand may not necessarily exhibit corresponding improvements in permeability and strength. Results from the longer columns showed sand grouted with oscillatory injection pressure exhibited somewhat greater mean strength, lower mean permeability, and larger mean cement content than sand grouted with increasing pressure or constant pressure.

Fractured rock grouting commonly adopts the GIN principle as a means of controlling grout penetration. Assumptions of negligible fracture flow velocities within the method, however, are questionable. Theoretically, penetration length for the common Bingham fluid grout idealization can be shown to be a function of the grout rheology, fracture geometry and the grout injection rate. This paper investigates the effects of fracture aperture and injection rate on grout penetration length using a 1-D fracture idealization; an approximation reasonable for channeled flow in rough fractures, but not applicable to radial flow. These preliminary results indicate that for realistic grout properties and injection rates the GIN approximation may significantly over-estimate the achievable penetration.

The grout used in this study was a N-Sodium Silicate solution, mixed with an organic reactant (dimethyl ester (DME)) at room temperature. Gelling time and syneresis tests were performed on the neat grout with different amounts of organic rectant and the optimum percentage of DME was obtained. Grout mixes with 5, 7, and 9% of DME were injected into medium dense sand with USCS classification of SP (d₅₀ = 0.45 mm). Unconfined compression tests (strain rate=1%/min), and creep tests (stress levels from 25% to 60% of the unconfined compressive strength) were performed on grouted sand with varying grout compositions. The compressive strength of silicate grouted sand (14 days) varied from of 300 to 1900 kPa (41 to 271 psi), and the Young's modulus was in the range of 200 and 500 MPa (29 to 72.5 ksi). Creep failures in grouted sand were observed at various stress levels based on the composition of the grout and a new model is proposed based on current results and other published data. The results from this study are compared to four decades of published data in the literature. Both strength and modulus were in the range of data reported in the literature.

Support of existing structures, equipment, and utilities requires means and methods that will lend this support without causing any harm. Several methods of grouting can offer support, but only a few can resist compressive loads while also resisting lateral earth pressures. This is particularly so when historic and sensitive structures are in consideration and deformation tolerance is minimal. Several case histories will be presented to illustrate the type of structures that can be supported, along with the processes and procedures that make for a successful project. Jet grouting and chemical grouting technologies will be highlighted.

Structures such as dams and quarries create differential piezometric heads in their vicinity when operational. In certain geological conditions, such heads may, in association with other factors, create sudden water flows — under or around a dam, into a deep quarry. Grouting is often proposed as an emergency solution to such events which can be of catastrophic significance, in many ways. This paper provides a nine-step guide to managing the design and construction of the grouting involved in such emergency situations.

The East Side Access Project will connect the Long Island Railroad to a new terminal beneath Grand Central Station in Manhattan, NY. Contract CQ026 in Queens, NY involved construction of a "bathtub" work excavation, approximately 30.5 x 91 m in plan, excavated through the granular overburden to rock at depths between 18.3 and 24.4 m below working grade. Design of the excavation was complicated by several factors related to construction in an urban setting, notably that one area of the excavation would extend down and uncover an existing subway tunnel that would remain active during the work, excavation would proceed to 15 m below the groundwater table, and that plumes of contamination existed nearby that could not be disturbed by off-site drawdown. The primary means of support of excavation were a structural slurry wall extending to rock and connecting to an existing slurry wall (installed during construction of the active subway), and steel sheetpiles which had been installed over the existing subway. In order to ensure that the joints between the different means of excavation support did not allow water infiltration, zones of soil immediately outside of the joints were permeation grouted prior to the start of excavation to complete the watertight bathtub. Additionally, a groundwater cutoff bulkhead was required around all four sides of the existing active subway structure. Permeation grouting was used to close the gaps and joints and create the bulkhead around the existing structure to limit offsite drawdown and the movement of contamination. The permeation grouting was re-designed after bid time to allow all of the grouting to be performed from outside of the excavation. This reduced the risks associated with the performance of the grouting and allowed the contractor to accelerate his schedule. This paper discusses the design, re-design and execution of the permeation grouting program, including significant quality assurance and quality control measures.

Seepage barriers can be formed using jet grouting techniques from a wide variety of geometries. Forming interconnected panels and columns are common for vertical barriers, and other shapes may be warranted when sealing sheetpiling or other existing structures. When forming horizontal barriers, from vertical drilling, short columns or disks are used to interconnect and create the seepage barrier. This paper will review where the jet grouting technologies are viable, how they are implemented, and discuss the performance that can be achieved. Several case histories will be presented to illustrate these issues.

Jet grouting can be used to consolidate, treat, or waterproof deeply buried material with more precision than is possible with ordinary pressure grouting. However, in radioactive contaminated soil, bringing contaminated material back to the surface must be avoided. Industrial jet grouting is typically a very messy operation with large volumes of soil, water and grout returning to the surface. Over the last 9 years, special techniques were developed specifically for the Idaho National Laboratory (INL) to adapt this jet grouting technology to operate in radiologically contaminated environments. In a recent project at the INL an advanced jet grouting technique was performed using a molten thermoplastic wax grout in place of the traditional cement and water slurry. An old radioactive waste burial site at the INL contained large sections, or "blocks", of a nuclear reactor made from solid beryllium metal. After being in the reactor for many years, they were highly radioactive and INL scientists were concerned that corrosion chemistry could release radioactive carbon 14. Beryllium waste is of a special interest to the INL because it contains approximately 19% of the C-14 inventory at the burial site. Beryllium exposed to moisture corrodes rapidly, releasing C-14. The beryllium waste targeted for grouting represented approximately 90% of the C-14 that was releasable (mobile) in the environment. Past monitoring confirmed the C-14 release and it was considered good management practice to immobilize the C-14 and reduce the potential environmental threat to the vadose zone and groundwater. Jet grouting was selected as the means of isolating the blocks from the water environment. Jet grouted columns would be placed around the perimeter and throughout each disposal area. However, the scientists feared that cement based grouts could have undesirable chemical reactions with the Beryllium over time. A novel molten wax grout known as WAXFIX, previously demonstrated at the INL, was selected because it could better isolate the beryllium from water and thus prevent further chemical reaction.

A grouting program has been carried out beneath a main output transformer at Ontario Power Generation (OPG) Pickering B Nuclear Generating Station (Pickering B NGS) Unit 8 Main Output Transformer (MOT 8). The objectives of the program were to fill voids and compact loose zones below the MOT foundation in order to reduce the risk of further unpredictable, and possibly large, settlements due to the collapse of voids. The construction period extended from April 5 and to May 24, 2006, during which 79 grout holes were drilled into the soil beneath the MOT. The program was divided into two phases: Primary, which addressed most of the voids and loose fill zones and Secondary, which filled remaining small voids and loose zones between primary treatment areas. The grout consisted of a mixture of cement, bentonite, water, and other admixtures. The total volume of grout introduced into the soils below the MOT was approximately 29.2 m³, representing approximately 3 per cent of the volume of granular fill below the treatment area. Approximately 93 per cent of this volume was introduced during the primary phase. The amount of grout introduced in the program is significant and is consistent with the theory that granular backfill has been lost from beneath the MOT through an ongoing process of erosion. It is estimated that about 100 mm of potential settlement was arrested by the grouting treatment, based on the total volume of grout injected and gross area of treatment. During construction, cumulative settlement of approximately 3.4 mm occurred on the south side of the MOT slab, with cumulative uplift of about 3.6 mm on the north side. Since the completion of construction, the settlement trend has been generally flat. Based on the measurements of grout volume injected, the significant difference in the performance of the ground between primary and secondary grouting, and the small amount of settlement that occurred during treatment, the grouting program successfully met its objectives.

Compaction grouting is a mechanical ground improvement technique that involves displacement of soil through pressure-injection of stiff mortar-like grout. This type of displacement grouting has been used for several decades to treat weak foundation soils and lift portions of settled structures, and more recently for a wider range of applications, including mitigation of liquefaction potential. Records of injected grout quantities are maintained during production, providing an indication of relative soil displacement with respect to treatment depth. Data have traditionally been collected manually, and typically include grout quantity, average pressure and injection rate for each treatment interval, or "stage". This type of quality control record is often used to estimate hypothetical soil improvement in terms of a displacement ratio; however continuous real-time records of pressure and flow are impractical to obtain through manual methodology. Use of data-logging instrumentation allows for effectively continuous and precise monitoring of pressure and flow during the compaction grouting process. Data collected in this manner not only provide an accurate record of injected grout quantity, but can also be used to identify grout-induced ground deformation, identify and diagnose equipment problems, and evaluate soil response. This paper presents several time-history records of displacement grouting pressure and flow, as well as discussion of associated conditions and possible implications.

Jet Grouting is an in-situ injection technique employed with specialized equipment, drill rig, drill rods and injection monitor with horizontal radial nozzles delivering high velocity fluids to erode, mix, and stabilize in-situ soils. This process is used on a wide variety of projects to improve the mechanical properties and/or reduce the permeability of the soil. Prior to commencing production jet grouting, a field test program is typically undertaken to evaluate and refine injection parameters and to assess jet grout element geometric, mechanical, and permeability properties. The test program typically involves the construction of test elements followed by a 3 to 14 day cure time, depending upon soil type and project requirements. Where possible, jet grout test elements are exposed by excavation and geometric properties are obtained by direct measurement and bulk samples are collected and delivered to a laboratory for unconfined compressive strength and permeability testing, as required. Where excavation is not possible, core drilling is employed to obtain soil cement samples from the jet grout test columns for strength testing. Coring jet grouted soil can be difficult and often yields results that are not representative of the in-situ condition and quality of the jet grouted element(s). Therefore, an alternative quality control evaluation method is needed. This paper will discuss the measurement of in-situ jet grout column diameters on a project site in Columbus, Ohio. The measurement and evaluation of jet grout column diameters were obtained using a wave-based analysis approach. This approach will be introduced and data will be presented to show that column diameters can be assessed in-situ with this method, even in different soil types. The measurements, data collection, and analysis are the result of an international collaboration and the authors believe the system may be useful for similar projects in the future for our industry.

Experience combined with analytical and empirical design has allowed the process to improve significantly over the past 30 years. Improved equipment from pumps to sleeve port injection pipes, improved electronic measuring devices from electromagnetic flowmeters to automated valves, and improved computers from reliability and data acquisition to storage and presentation have helped foster this development. On another front the recent developments of more sensitive rugged transducers have entered the market. These are being innovatively employed to provide the observational feedback so valuable in the grouting process. The ability to observe movements or deflections of the ground and critical structures when combined with computer storage, software, and presentation of data advance the injection process to a new level. This paper provides a review of several recent grouting projects where innovative "observational monitoring" techniques have improved grouting.

Traditional grouts consisted of fluid suspensions of cement and water and these continue to be sometimes used. Such mixtures are subject to sedimentation of the solids resulting in incomplete filling of the injected voids, and thus poor quality work. Grouting is now performed for an ever-expanding variety of objectives which require special grout properties varying from self-leveling fluid to stiff mortar-like low mobility. Established cement technology and material science now enable design of stable grout mixes with virtually any desired properties. The many available mix ingredients and admixtures are discussed, as is practical mix design of optimal grout for a variety of typical applications.

Pregrouting is an extremely important part of many rock tunneling projects. However, poor and unsatisfactory performances have been frequently recorded often with very severe consequences to one or more of the parties, both technically and financially. This paper provides recommendations with respect to specification drafting, drilling, water pressure testing, and grouting methodologies, and cementitious grout mix design principles. Even given that the logistical challenges facing tunnel pregrouting from underground will prevent all the sophistication and innovations of contemporary dam foundation grouting being practically implemented, there is still opportunity and need to change "traditional" approaches for the benefit of the tunneling industry.