greggdrilling.com

PROJECT PROFILES

In November of 2006, Gregg Drilling was contracted to provide site investigation services for the Dumbarton and Antioch bridges located in the San Francisco Bay Area.  The Dumbarton Bridge connects Newark, Alameda County to East Palo Alto, San Mateo County.  It is the southern most highway bridge to span the San Francisco Bay and is also the shortest at 1.63 miles.  The Antioch Bridge crosses the San Joaquin River, linking Antioch to Sacramento County and is part of California State Route 160.  It was the first toll bridge built across a San Francisco Bay tributary and was originally opened in 1926.  New regulations require that all bridges be re-evaluated under current seismic design criteria.  CALTRANS turned to the Earth Mechanics Inc., a local California consultant for the expertise to perform this evaluation.  In turn, Earth Mechanics subcontracted the major portion of the site investigation to Gregg Drilling. 
 

Dumbarton Bridge
 

For the Dumbarton Bridge, boreholes and Cone Penetration Tests (CPT’s) were completed on land where possible using standard truck and track mounted mud rotary drill rigs and 25 ton CPT rigs.  In addition to Standard Penetration Test (SPT) and California modified samples, vane shear testing and PS logging were also completed at select locations.  The vane shear tests were conducted in the bay mud clays to determine in-situ values of the undrained shear strength.  On-land CPT’s were supplemented by seismic testing using the Seismic Cone Penetration Test (SCPT) to 100ft below the ground surface.  Obtaining shear wave velocity from both PS logging and SCPT allows computation of a site specific seismisity analysis. 

To complete the over-water work, Gregg utilized its custom designed drill ship, the Quin Delta.  With a flat bottom and shallow draft of only three feet, the Quin Delta was able to sit on the mud at low tide and complete drilling and CPT operations.  In total, 21 CPT’s were completed to 100 ft or refusal and 10 boreholes were drilled down to 250 ft.
 

Quin Delta drill ship conducting site investigation at low tide.
 

At the Antioch bridge location, boreholes and CPT’s were completed on-land totaling 21 CPT’s with seismic testing to 100 feet.  PS logging was also carried out in the boreholes to provide shear wave velocities in conjunction with those collected from the SCPT.  Over-water work included 14 CPT’s to 100 feet and a number of boreholes to 200 feet complete with PS logging.

The thorough and complete evaluation of these two bridge sites illustrated the wide range of site investigation tools and equipment available.  From in situ tests such as the CPT, SCPT, vane shear, and PS logging to more invasive testing such as drilling and sampling, geotechnical engineers have a large selection of site investigation tools available.  It was shown that by supplementing the in situ tests with a number of boreholes and samples, the site investigation program was completed in a short amount of time and at a reduced cost compared to more traditional methods.

SALTON SEA LAKEBED PROJECT
 

California’s largest lake, the Salton Sea, was once flourishing as a sport-fishing and recreational area as well as a habitat for endangered wildlife.  Now, it is quickly turning into a pungent-smelling, desolate, lake dying from enemies such as salt, fertilizer, California water agencies, and the sun.  The Salton Sea straddles Riverside and Imperial Counties and is located only 35 miles north of the Mexican border, in the middle of a hot and dry desert area.  This feat of nature was created in 1905 when a silt build up blocked the Colorado River’s flow to the Gulf of California.  The river diverted from its course and flowed into the Salton Sink.  The lake that resulted was five times larger than it is now and attracted over 400 species of birds, some now endangered.  Numerous species of sport fish were introduced and the lake flourished.  When the river’s silt closed off in-flow to the lake, the water level began to decrease due to evaporation under the intense desert sun.  Since the lake has no out-flow channel, the minerals and salts remain and increase in concentration as the water level is depleted.

Salton Sea - Map courtesy of Salton Sea Database Program, University of Redlands, Redlands, California

How does the lake maintain its current level?
At 227 feet below sea level, the sea is officially designated as a sump for agricultural drainage.  Agricultural runoff from farms throughout the Imperial and Coachella valleys drain into the lake, replenishing water lost due to evaporation.  This results in more salts, nutrients and contaminants retained by the lake as pure water is removed by evaporation.  The Salton Sea is currently 25% saltier than the Pacific Ocean and boasts large amounts of fertilizer and minerals.  The nutrients fuel plant and algae growth which at first, allowed the fish population to boom, but now is causing their demise.  Fertilizers cause large algae blooms, which deplete the water of oxygen when they die and decompose.  In summer, oxygen levels in the water disappear in all but the top few inches due to the heat, high salt content, and decomposing algae.  This causes massive fish die-offs, affecting birds and wildlife surviving in the area.  Salt itself also aides fish extinction because an increasing content will soon hinder the ability for fish to reproduce.  To add to these problems, representatives of Southern California’s largest water agencies agreed on September 5^th, 2003 to transfer 65 million gallons of water from the Imperial Irrigation District to the San Diego County Water Authority.  If approved by the agencies’ boards, this would reduce the inflow of water that maintains the Salton Sea.  This will, in effect, only add to the problems outlined above by speeding up the process.

Is there hope?
Yes!  The Salton Sea Authority, which is a coalition of Riverside and Imperial county governments and water districts, decided in January 2003 to take restoration plans into their own hands.  A number of ideas were proposed to improve water quality and preserve the valuable habitat.  It was also important that all designs account for possible seismic movement since the east side of the lake borders the San Andreas Fault.  The plans revolve around creating a dike or dam to separate the lake into north and south sections.  Desalination plants would reduce the salt content in the north lake, providing a recreational area and marine lake environment.  The southern section would also benefit from water quality improvement, and could be turned into shallow wetlands for water birds and other wildlife.  The plan would entail dam construction, wildlife preserves and one of the world’s largest desalination plants.  Initial estimates come in at almost $2 billion due to the hefty price tag on desalination.  To assist with the cost of implementation, some of the water could be sold to California residents at $470/acre-foot.  This is half the cost of desalinating ocean water but 60% more than just transferring water from the valley and not improving the Salton Sea.  Enough water for 1 to 2 million people could be provided by this project, creating a win-win situation for the water agencies and the environmental conservationists.  There are still some opponents to the plan who say that it is too centered on reducing the sea’s salinity and stabilizing its elevation instead of other, more serious, water quality factors.

Action is taken
Regardless of this opposition, in June 2003, Congress gave the Salton Sea Authority $10 million for feasibility studies and design efforts.  After more than 30 years of research, the Authority was eager to take action.  They contracted Tetra Tech and URS Corporation, environmental and engineering firms, to conduct investigations. Before engineers could get started on possible designs, exploration of the seabed for strength, stability and possible building materials had to be conducted.

The specialized nature of the project required engineers to engage Gregg Drilling and Testing of Signal Hill, California to perform the over-water drilling operation.  Gregg used a jack-up boat with a deck load capacity of 25,000 as a stable platform upon which they mounted their drilling rig.  The benefit of the jack-up boat is that it is easily maneuvered to different locations across the lake and can be raised off the water surface to avoid disturbance by large waves.  The jack-up boat was used to successfully drill and test sub-bottom soil in water up to 50 feet deep.  A total of 28 locations were tested and sampled using standard penetration tests (SPT), cone penetration tests (CPT), and Shelby tube samplers.

Jack-up boat used for Salton Sea project by Gregg Drilling & Testing, Inc.

The boreholes and CPT ranged from 30 to 50 feet in depth with one borehole extending to 200 feet below mudline.  Cone Penetration Tests (CPT) conducted in 15 locations provided a continuous soil behavior type profile of the sub-bottom environment.  This was accomplished by pushing a cone penetrometer, attached to a data acquisition system, into the subsurface using a hydraulic ram.  The cone penetrometer contains electronic sensors to measure tip resistance and sleeve friction, while a small filter behind the tip measures pore water pressure.  The CPT provides a rapid, reliable, and economical means of determining soil stratigraphy, relative density, strength, and hydro-geologic information without generating soil cuttings.  Geologists and engineers looked for strong and stable soils in the planned construction area to support large structures, and around the lake for possible fill materials for the proposed earthen structures (to reduce material importing costs).  If the sub-bottom sediments are found to be soft fine-grained soils, extensive excavation and backfilling will be required to support construction of a dam. 

Drilling and testing was completed in just over four weeks with samples sent to a URS geotechnical laboratory for further study.  The data and information collected will provide valuable information for Salton Sea restoration designers and planners.

The Cook Inlet near the Port of Anchorage, Alaska is attracting attention as it is now the center of an estimated $200 million dock expansion. The Port of Anchorage Intermodal Expansion Project (PIEP) is a major transportation infrastructure project that will include road and rail access, cruise ship, ferry, barge, and bus terminals, as well as an expansion to accommodate 1000-foot vessels. The project will greatly expand the current 100 acre port by an additional 83 acres, provide dock widening, 100-foot. cranes, and deepen the harbor by 10 feet to allow access to larger ships. This expansion will help the port deal with the projected 200% increase of activity over the next 20 years. The project, estimated to take six years to complete, has become the largest near-term marine transportation project in the United States.

Example of an open cell dock design.

Prospective Designs
A development proposal has been submitted by Peratrovich Nottingham & Drage Inc. outlining the construction of a dock based on their open-cell system technology. The model utilizes sheet pile membranes to create a bulkhead that would hold nine million tons of compacted gravel when completed. This would allow for a land based installation and cost savings of over 30% compared to traditional designs. This design has been successfully implemented at neighboring Port Mackenzie and other areas in Alaska.
 

Another option was provided by the engineering firm originally contracted, Tryck Nyman Hayes Inc. They have developed a design for a pile-supported dock similar to current West Coast ports. In this traditional design, the dock would be supported by piles driven deep into the ocean floor.
 

 Troubled Past…
Stability issues are playing a pivotal role in this proposal because the region is prone to massive earthquakes. This area of Alaska experienced the second largest recorded earthquake in history in 1964, recording 9.2 on the Richter scale. Surprisingly, the earthquake itself caused less damage than the numerous tsunamis produced by the quake and resulting landslides.

It is essential that the new port incorporate design features to   withstand a large earthquake. San Francisco, a city that’s had its share of earthquakes, must design its docks to withstand a    magnitude 7.5 earthquake. In comparison, the new port in Anchorage will be designed to withstand a magnitude 9.0 earthquake, almost 800 times more intense. For this to be accomplished, the design must be based on a good understanding of the subsurface conditions and ground environment. To prepare a proper design, a $1.25 million geotechnical seismic study was conducted to collect more data on the strength and stiffness of the seabed near the Port of Anchorage.

Above:  During the 1964 earthquake, a section of waterfront slid into the sea producing tsunamis that destroyed this dock.
 

Left:  The tsunami's power is displayed.

Gregg's jack-up rig used for testing and sampling soil under the waters of the Kink Arm near Anchorage, Alaska.

A Call to California

In the summer of 2003, The Federal Maritime Administration sub-contracted Gregg Drilling and Testing Inc., of Signal Hill, California to test and sample the soil near the Port of Anchorage. Because the Cook Inlet experiences tidal fluctuations of up to 36 feet, drilling boats or barges could become grounded. Instead, a jack-up drilling platform (see picture on right), similar to those used for near-shore oil drilling and capable of working in water up to 83 feet deep, was used.

The Skate III jack-up rig is also designed for rapid assembly and easy transportation since the pontoons double as containers for the jack-up legs and other components. In two weeks the rig was shipped from California to Alaska, assembled, and ready for use. It has a jacking capacity of up to 100 tons and is easily moved from one location to another by lowering the platform to water level and acting as a barge powered by a tug boat. Gregg Drilling mounted their equipment on this platform, and with crews of 5 to 6 people working 24/7, completed in-situ soil testing and sampling in little over a month.
 

Cone Penetration Tests (CPT) conducted in 39 locations provided a continuous soil behavior type profile of the expansion area. This was accomplished by pushing a cone penetrometer, attached to a data acquisition system, into the subsurface using a hydraulic ram. The cone penetrometer contains electronic sensors to measure tip resistance and sleeve friction, while a small filter behind the tip measures pore water pressure. The CPT provides a rapid, reliable, and economical means of determining soil stratigraphy, relative density, strength and hydro geologic information without generating soil cuttings. Many other sensors such as resistivity, ultra violet, and seismic geophones can be added to the cone penetrometer. For this application, it was important to analyze soil behavior and liquefaction potential in response to dynamic loading from earthquakes, ice, vibrating machine foundations, waves and wind. Therefore, a seismic module was added to the cone penetrometer to conduct seismic tests in a few of the locations. In addition to CPT, various sampling methods such as standard penetration tests (SPT), Shelby tube, and piston samplers were utilized to obtain 190 samples from 20 different locations. Many of these were taken from 100 to 200 feet. below the ocean floor. All samples were sent to Terracon Consulting for further evaluation by professional geologists and geotechnical engineers.

The success of the Port of Anchorage seabed sampling program and the uniqueness of the drilling equipment quickly attracted the attention of the Alaska Department of Transportation. For nearly 30 years, the Department of Transportation has been contemplating a bridge across the Knik Arm linking the crowded Anchorage bowl with the largely undeveloped Matanuska-Susitna (Mat-su) side. The proposed bridge would eliminate the current two-hour drive circling the Knik Arm from the Port of Anchorage to Port MacKenzie. The state acted quickly to retain Gregg Drilling to mobilize the same equipment directly from the port so work could begin immediately.

In the middle of August, Gregg Drilling began site investigation in the two nautical miles that stretch between Carin Point and Port MacKenzie. Gregg Drilling was asked to drill a number of boreholes and collect samples in the often rough waters of the Knik Arm. Drilling conditions included clays, hard silts, loose flowing sands, gravels, cobbles, and a few boulders. Due to such variance in soil types, further work was required to gain a full understanding of the subsurface conditions. A CPT sounding was conducted to determine a continuous soil profile and a seismic CPT sounding was performed to a depth of 224 ft below the mud line. By the end of August, drilling became difficult as a mixture of bad weather and complicated drilling conditions plagued the crew. Work was postponed until the middle of September, allowing the rig to move to areas of deeper water, where more favorable tides were present. By the end of September, a total of seven boreholes had been drilled in the ocean floor spanning the Knik Arm. Samples and CPT data taken from the area will provide engineers with design parameters and allow planners to narrow cost estimates for the proposed bridge.

With the end of September approaching, it was time for Gregg’s drillers and engineers to head back home to warmer climes. Anticipation builds for port and bridge planners as Anchorage awaits test sample results and designs for some truly ambitious construction projects.