SoilModification

Print This Page!

SOIL MODIFICATION
CASE HISTORIES

Curtis Bay Waterfront, Old Industrial Site
Fairfield Peninsula, Baltimore Harbor

Situation: Excessively wet and oil contaminated land needed for re-developement.

The Problem: For industrial land owners, the process of closing old industrial sites including the mitigation of free phase petroleum hydrocarbons in the soil and ground water that resulted from prior facility operations poses unique challenges.

In meeting these challenges, BP Amoco looked to Environmental Resources Management, Inc. (ERM) to design and manage the closure of one of its sites, the former Amoco Baltimore Asphalt Terminal, located in Baltimore, Maryland. Originally constructed in 1922 as a bulk transport terminal for gasoline and kerosene, the facility eventually operated solely as an asphalt refinery before operations ceased in 1982, after which the facility served as an asphalt storage terminal.

The closure plan prepared by ERM was approved by the Maryland Department of Environment (MDE) Oil Control Progam (OCP). The primary objective of the plan was to remove, to the best extent practicable, free product from soil and ground water to achieve the site closure and increase property value for future development. The closure plan required the excavation of approximately 15,000 cubic yards of soil containing free product. The excavated soil was to be managed on site and placed within a clay-lined berm formerly used for storage tanks. The cleanup criterion required one part per million (ppm) or less of leachable total petroleum hydrocarbons (TPH) diesel range organics (DRO). To perform this work, ERM turned to RECON of Houston, Texas, a leading contractor who specializes in soil stabilization and remediation.

The Solution: ERM and RECON determined that soil stabilization with pebbled quicklime was the most effective method to achieve the criterion for clean-up of free product, and also pr o vide optimum dr ying and stabilization for the soil. This soil modification practice is a common and highly proven method with identical uses in road construction and site development where wet, plastic soil is improved beneath pavement subgrades or building slabs.

The process relies on the use of quicklime (calcium oxide, CaO), which reacts with the existing soil moisture to cause lime hydration to help dry the soil. During hydration, the soil.s high pH levels cause the calcium ions from the hydrated lime to attack and separate the clay par ticles by decreasing the levels of water. Subsequently, this reduces the amount of water the soil can then absorb. Clay particles are agglomerated and their texture rapidly changes to a granular form with larger particle properties and less surface area, resulting in greatly reduced soil plasticity. The new modified condition significantly reduces soil leaching capacity. Stabilized soil is also easier for contractors to maneuver than wet soil, and improves compaction properties.

The multi-weather attributes of lime stabilization allows for application in the colder winter climate by which quicklime can still react. For this operation the lower temperatures provided additional advantages in keeping the viscosity of the free product high, and minimizing odors. As summarized by Karl Peckhaus of RECON, .Quicklime was used to solidify the saturated soil during the winter months. Its long-lasting reaction time and drying ability virtually eliminated petroleum hydrocarbon leaching all together.. With the importance of environmental dust control for site work contractors, Peckhaus was also quick to point out, .During the soil stabilization phase, RECON maintained a virtually dust-free environment by using 1/4. by 1/2. quicklime product.

The Results: Samples of the stabilized soil were collected throughout the project to document and verify the stabilization results. In all cases, the soil passed a .paint filter test. by which it proved to be dry enough (lowered moisture content) so that free liquids were no longer present (or at negligible levels) in the soil. TPH-DRO results were below one part per million (ppm), which achieved MDE.s cleanup criterion. In fact, all leachable results were non-detect except for one, for which the laboratory reported a leachable result of 0.90 ppm.

Verification monitoring results since show that free product is not being detected in the remaining monitoring wells indicating that the corrective measures, as approved by MDE, have removed significant levels of free product. Structurally, the stabilized soil provided an all-weather working platform capable of supporting typical construction traffic.
According to Leonard Rafalko of ERM, .The use of quick¬lime as the stabilizing agent was instrumental in allowing the project to meet regulatory criteria, and BP Amoco.s schedule for site closure.. Since the work was completed, MDE.s State Superfund, Oil Control, and Voluntary Cleanup programs have issued a No Further Action or No Further Requirements Determination for the site.

US ARMY CORPS OF ENGINEERS
Houston, Texas

Sims Bayou is a major stormwater conveyance feature that comes under the auspices of the U.S. Army Corps of Engineers (USACE). When a deep failure plane - caused by the presence of low-strength soils combined with a seasonal upward hydraulic gradient - developed along a stretch of the bayou's 20-foot high embankment, the USACE selected the single-fluid jet grouting technique to stablize the slope.

Jet Grouting is a replacement mixing technology that uses a high-pressure jet of grout to erode and mix the soils in-situ, creating a blended soil/grout matrix with improved engineering properties.

Jet Grouting Program
The intent of the jet-grouting program was to intercept the active failure plane and prevent further soil movement into the bayou. Deleterious material was excavated and the work area was backfilled to construct a stable working platform. Jet grouting was accomplished using Remedial Construction Services, L.P. (RECON's) state-of-the-art equipment, including an automated grout batch plant, high-pressure pump, and hydraulic drill equipped with a single-fluid jet grout drill string. RECON installed 120, 30-inch diameter jet grout columns to a depth of 32 feet, creating a stablized zone of soil approximately 100 feet long and 10 feet wide. The project was successfully completed within the 240-day schedule.

Quality Control and Quality Assurance
Prior to production work, six test columns were installed within the area of the permanent system. After being allowed to cure, all six columns were excavated and visually inspected to verify that the required column diameter could be achieved in the highly plastic Gulf Coast clays. One unconfined compressive strength (USC) test was performed for every ten production columns to ensure that the specified minimum USC of 250 psi in 28 days had been achieved.

Site Restoration
In addition to the jet-grouting program, RECON performed the following items of work at the site:

Installation of silt barriers to protect Sims Bayou during construction;

Installation of a cellular concrete mattress from the base of the jet-grouted section to below the waterline to prevent erosion of the slope into the bayou.

Installation of relief wells and drainage structures, and

Restoration of the slope to its pre-failure condition, including turfing and tree planting.

SABINE PASS LNG PROJECT
Cameron Parish, Louisiana

To expedite permit processing of a new tank farm, the owner selected a site with little public opposition however, a site poorly suited for construction. In general terms, the site was a dredge spoil pile. These soils have little bearing capacity and consolidate extensively when subjected to loads. Remedial Construction Services, L.P. (RECON’s) challenge was to develop an approach that:

Stabilized over a million cubic yards of zero strength soils;

Constructed 300,000 cubic yards of dikes with an above grade height of 30 feet;

Accelerated 7 feet of consolidation from 7 years to 12 months; and

Constructed a temporary dock.

Stabilization
The largest hurdle consisted of stabilizing 500,000 cubic yards during the first 6 months of the project to allow the tank contractor access to the site. The remaining materials could be stabilized within 12 months. To meet this schedule, RECON needed an innovative technique; otherwise 20 soil mixing rigs and over 192,000 tons of concrete would be required.

RECON’s approach was to use a technique developed for the stabilization of massive impoundments in the environmental industry – use a high calcium oxide ash to consume the soil moisture and allow the soils to be placed and compacted to the required 25 psi unconfined compressive strength. RECON processed 3,500 cubic yards per day during the first six months of the project, meeting the project schedule.

The top 8 feet of stabilized soils were used for construction of the secondary containment dikes. These dikes averaged 15 feet above existing grade. Preliminary calculations indicated that these dikes, once built, could subside as much as 7 feet. To accelerate subsidence, over six million linear feet of wick drains were installed on 4 foot spacing to a depth of 90 feet. The water flowed into a French drain system at the toe of the dike. To continuously monitor the dikes, over 50 nests of vibrating wire piezometers, settlement platforms, and inclinometers were installed.

Dock Construction
The area selected for the construction of the dock had low to zero- strength soils to depths of 70 feet. The dock design required:

A bulkhead with 16 feet of draft,

A platform for a 200-ton crane, and

A truck turn-around and materials staging area.

The bulkhead was constructed using 65 foot sheet piles. These piles were tied back with 50 foot long Dywidag Threadbar® rods to a series of A-frame battered pipe piles, each 85 feet long. The battered piles had a concrete pile cap cast-in-place which anchored the rods.

The crane platform consisted of thirty-five 18-inch square concrete piles, each 60 feet in length. A concrete pile cap 2-foot thick was cast on top of the concrete piles. The cap doubled as the working platform for the crane.

The staging area consisted of a heavy haul road constructed using a geotextile fabric and 24-inches of crushed stone base. The entire area was stabilized using RECON proprietary methods to a final depth, 5 feet below ground surface. The stabilized soils were overlain with 8-inches of crushed stone base.

Stabilized over a 1,000,000 cubic yards of zero strength soil to a 25 psi base for a tank farm

CENTRAL ALABAMA WATER INTAKE CENTER
Statesville, Alabama

This project used jet grouting to construct in-situ mixed columns of soil and grout to accomplish the following tasks in support of a microtunneling operation:

Stopping a major leak of water and fluidized sand into the microtunneling jacking shaft.
Grouting quick soils within 25 feet of jacking shaft to create a stable drilling corridor.
Installing stabilized columns to underpin a footing located above the drilling corridor.

Remeidal Construction Services, L.P. (RECON) installed twenty-two, 36-inch diameter columns, to depths greater than 80 feet. The unconfined compressive strength (UCS) of the grouted soil could not exceed 1000 psi in 28 days, to accommodate microtunneling through the solidified mass.

Jet Grouting is a replacement/mixing technology where a high-pressure “jet” of grout is used to erode and mix in-situ soil to create a blended mass of grout and soil with improved engineering properties. The columns were installed using RECON’s state-of-the-art equipment, including an automated grout batch plant, high-pressure pump, and hydraulic drill equipped with a 2-fluid Jet Grout drill string.

Difficulties presented during this project included:

A rapid mobilization and construction schedule.
Breaking and adding rods during drilling and grouting, because of the required depths.
The jet grout columns were drilled at varying angles, to work around the pump station foundation and structure.