Geotechnical Research

Geotechnical Engineering Research

Research Overview | Treasure Island Project | In-Situ Testing | Drilling Parameter Recorders | International Cooperation

Invitation to Participate in a Strong Ground Motion Prediction Exercise (pdf)

Research Overview

Unless you plan to spend your career working on the space station, everything you design as a civil engineer has to eventually be connected to the earth. Research in geotechnical engineering at UNH concentrates on field and laboratory measurements of the material properties required to predict how different soils will behave under the loads applied by a structure. In some cases, the structure will be made of soil (earth dams, for example) so you will need soil properties to design the structure itself.

As computer models of soils grow more sophisticated and complex, more and different soil properties have to be fed to them as input, including not only stresses and strains at failure, but also at working-stress levels. One problem we are working on is the development of more sophisticated field tools that are capable of measuring soil properties at a wide range of strain levels, and doing so rapidly and economically.

Treasure Island Project

As a special problem in predicting soil behavior, we are interested in how soils react to earthquake loading. UNH geotechnical faculty and students have been involved for several years in designing, installing and monitoring instruments for a field site on Treasure Island in San Francisco Bay. We are currently working on a new design for a groundwater-pressure sensor (piezometer) system intended to pick up water pressure increase produced by earthquakes in loose sands such as those under Treasure Island (if the pressure buildup becomes high enough, it may lead to liquefaction of the sand layer and collapse of structures supported on this layer).

The current estimate of probability for a major earthquake in the San Francisco Bay Area before the year 2030 is over 70%; we are currently engaged in planning a prediction exercise where seismologists and geotechnical engineers will give their best estimate of ground shaking and liquefaction potential for Treasure Island assuming that an earthquake occurs on the nearby Hayward Fault. The idea is to quantify and discuss uncertainties involved in predicting earthquake effects using currently available methods.

In-Situ Testing

Evaluation of soil properties in situ has gained more acceptance in the past two decades with recent technological developments and a better understanding of the mechanics of certain in situ tests. The main objectives of in situ testing is to allow testing of soils which are difficult or impossible to sample for laboratory testing, obtain better spatial evaluation of soil properties, test soil deposits in their natural environment and, involve a larger volume of soil than possible with conventional laboratory testing. Research at UNH has focused on several in situ tools but especially on the self-boring pressuremeter and the Marchetti flat plate dilatometer. These instruments have been modified and improved for the measurement of lateral stresses and modulus values.

Since 1988, UNH has been leading a program of National Geotechnical Experimentation Sites (NGES), which comprises sites available to the geo-community for the purpose of advancing the state-of-the-art in areas such as in situ testing, field instrumentation, prediction of soil behavior, and foundation prototype testing. An integral part of the NGES program is a database and web site designed to document the activities and disseminate the results from each test site. These sites have helped foster cooperation and information exchange and stimulate our ability to develop and evaluate new geotechnical tools and techniques to improve geotechnical practice, enhance research and provide educational opportunities.

Every day in the United States, an astonishing number of subsurface investigations and installations take place using various types of boring machines and penetration rigs. It is conceivable than more than 1 million boreholes are drilled on an annual basis in the US. Unfortunately, very little geotechnical information is retrieved from these borings since the great majority of boreholes are carried out to perform such tasks as installation of monitoring wells, water wells, deep foundations and instrumentation.

Drilling Parameter Recorders

A solution to what appears as an insurmountable problem is readily available: Drilling Parameter Recorders (DPR). These DPR’s consist of computerized systems which monitor a series of transducers installed on conventional drilling rigs to collect data on all aspects of drilling including advance rate, downthrust and pull-up pressures, rod torque, rotation rate, mud/water pressure and flow, depth and time. The data from the different parameters are acquired automatically. The data is displayed in real time and stored on electronic medium for further analysis. Correlations can be developed between the DPR measurements and mechanical properties of soils and rocks. The measurements can also lead to improvement to drilling equipment and techniques. The DPR system, currently being used in the Bedrock Bioremediation project, will also help with comparisons to various geophysical test results and direct examination of bedrock cores. These comparisons will help determine how these methods could be used most effectively, separately or in combination, to gain the most information possible about lithology and fracture patterns in a bedrock aquifer.

International Cooperation

Geo-environmental research activities begun at UNH more than a decade ago with a project dealing with the safe disposal of a mixture of bottom ash and sludge at a local landfill. Recently, a cooperation between the Laboratoire Central des Ponts et Chaussées in France and the Recycled Materials Resource Center at UNH has been initiated with research efforts on water movement in pavement and highway structures. This project will focus on possible hydraulic scenarios that exist within these structures for both conventional and recycled materials. These hydraulic conditions are important from both a mechanical and an environmental perspective.