GEO-TECHNICS AMERICA, INC

E-QUAKE^TM Drains Prevent Liquefaction
During St. Lucian Earthquake

At 8:03 A.M. on June 8, 1999, an earthquake with local magnitude of 5.4 rocked the small island of Saint Lucia, British West Indies. The United States Geological Society (USGS) estimated that the earthquake’s epicenter was located approximately 60 miles (100 km) northeast of Saint Lucia’s capital city of Castries.

The earthquake, the largest in islanders’ memories, disrupted classes at local schools, sent office workers rushing out of buildings, and knocked groceries off of shelves at local stores. Estimated ground accelerations across the northern portion of the island were on the order of 0.12g.

Although there were signs of liquefaction and structural damage in the Castries area, neither seismic settlements nor structural failures were observed at the Hyatt Regency Resort and Casino presently under construction near Pigeon Point. Rochamel Construction Limited, the developer, utilized a state-of-the-art ground improvement technique, E~QUAKE Drains, developed by Geotechnics America, Inc. to prevent liquefaction of underlying loose sands during earthquakes.

Hyatt Regency Hotel and Casino

To take advantage of the beautiful vistas of the Atlantic Ocean and Caribbean Sea, Rochamel Construction chose the causeway from the mainland to Pigeon Point for the location of the Hyatt Regency Hotel and Casino.

Development of the causeway posed significant geotechnical problems. The causeway was originally constructed some thirty years ago by back-dumping loose sands from the mainland into the sea. This back-dumping continued until the causeway extended to, and provided access for, Pigeon Point. This method of construction resulted in a thick layer of loose saturated sands that was likely to liquefy (turn to "quicksand") during an earthquake.

During earthquake shaking, loose deposits of sand densify. If water between individual sand particles is not allowed to drain, excess fluid pressures are generated. Once these pressures become too great, the sand loses inter-particle contact (shear strength) and behaves as a liquid. This liquefaction of the sands causes large structures to sink into the earth, underground structures to "float" to the ground surface, and dams and levees to wash away.

E-QUAKE Drains (Invented by GTA)

To address this potential liquefaction problem, Rochamel Construction contracted Geo-Technics America, Inc. to install over 500,000 linear feet (152,400 m) of E-QUAKE Drains across the site. E-QUAKE Drains are high discharge-capacity pipes that provide a short drainage path for the dissipation of excess pore pressures as fast as these pressures are generated during an earthquake. Water expelled from the sand flows radially into the drains and then vertically into a reservoir above the ground water table. By maintaining the excess pore pressure ratio, r_u, less than 0.6, liquefaction and intolerable seismic settlements are prevented.

E-QUAKE Drains are a very economical alternative to traditional liquefaction mitigation processes. E-QUAKE Drains can be installed in approximately half of the time as stone columns and at less than one-third the cost. In addition, there is little disturbance to other site activities. In St. Lucia, the E-QUAKE Drain installation has been performed in conjunction with the piling installation with no delays in the construction schedule.

The design of the E-QUAKE Drain system for this project was performed using the finite element computer program FEQDrain (Report No. UCB/EERC-97/15) distributed by the Earthquake Engineering Research Center, University of California at Berkeley. Based on the magnitude of the design earthquake and the permeability and compressibility of the liquefiable soils at this site, E-QUAKE Drain spacing for the project was on 4' (1.22m) centers.

E~QUAKE Drain Installation

The installation of the E-QUAKE Drains is performed using specially designed excavator-mounted equipment (see photo at right). The drain is inserted from the bottom into an open-ended steel pipe (mandrel) attached to the excavator’s leads. The pipe, with the E-QUAKE Drain inside, is driven through the liquefiable soil to underlying bedrock using a vibratory hammer. Once it reaches the design depth, the pipe is withdrawn leaving the E-QUAKE Drain in place (see photo below). E-QUAKE Drains may be installed to depths exceeding 150' (45 m) and on materials with bearing pressures as low as 1.7 psi (11.5 kPa).

Initial cost savings and long-term protection

The use of E-QUAKE Drains on the Hyatt Regency project in St. Lucia saved the owners millions of dollars in initial cost compared to stone columns or injection grouting. The recent earthquake proved the effectiveness of E-QUAKE drainage as a method for mitigating liquefaction potential.

During the June 8^th earthquake, excess pore pressures generated from the ground shaking drained into the E-QUAKE Drains, raising the water level in the drains and in some cases spilling water onto the ground surface as designed.

In addition to the cost savings of the E-QUAKE Drain system, future guests of the facility can be confident that Rochamel Construction has protected the Hyatt Regency from future earthquakes with a state-of-the art system for liquefaction mitigation.

For additional information about the St. Lucian project, other GTA contracting services, or for assistance with your next ground improvement project, call us at (770) 719-9495, fax us at (770) 719-1907, or email us at RussJoiner@msn.com

E-QUAKETM Drains Prevent Liquefaction During St. Lucian Earthquake

E-QUAKE^TM Drains Prevent Liquefaction
During St. Lucian Earthquake