Every work of humans is constructed on, in, or with ground materials. Highway facilities certainly fall within these bounds. Even intelligent highway vehicle systems must have a sound foundation support system. Some exceptions are those things that fly, drift in space, float or fall down, and even these must start or end with some contact with the ground. Knowledge of the science, art, and technology of these materials (geotechnology) is necessary to enhance and exploit these resources.

To orient the general civil engineer and lay reader of this report, significant background discussions and explanations of the objectives and scope of the various geotechnical research projects and studies were presented at the beginning of each chapter. These discussions were followed by a review of the performance of each study and a delineation of significant results. The report is sprinkled with a number of success stories to demonstrate the value of the research efforts and to justify the significant expenditures of highway user tax funds. Chapter 7 attempts to show that the research and development products are not gathering dust on the shelves in the libraries of the world, but rather they are used often and productively. Numerous testimonials are immodestly delineated to demonstrate the acceptance of these products into the highway and civil engineering mainstream.

Geotechnology and geotechnical engineering are used almost interchangeably throughout the report. These terms are used to imply a wide range of technical disciplines that contribute to the understanding of soil and rock behavior, and are defined as the field of professional practice and research that draws heavily on the principles of soil and rock mechanics, foundation engineering, and engineering geology. These disciplines involve the study of highway structural foundations, tunnels, earth retaining structures, cut slopes, and pavement subgrades. The research reported in this document involves the application of geotechnology in site characterizations, design, construction, and performance monitoring and assessment.

At the same time that the science, art, and engineering principles of geotechnology have been extensively improved due to the quarter century of work reported herein, the public demands placed on this profession have increased significantly. The ability to design and build larger structures has brought heavier loads that must be supported by ground materials. Expectations on performance have also gone up, and the public will no longer tolerate failures or gross over-design to mask knowledge gaps and uncertainties. The decrease in available quality construction sites compounds the demand for bigger and better infrastructure facilities. Sites with poor or marginal geotechnical features can no longer be avoided because the options in site selection are fewer and further between. Underground options are sometimes the only choice at hand for extending or improving urban infrastructure facilities.

Expanding or upgrading urban highways in crowded environments has significant potential to influence adjacent structures. The prediction and control of ground movements from highway construction operations such as open-cut excavations, tunneling, dewatering, and vibrations from pile driving and blasting operations is becoming more and more important. The Boston Central Artery and Third Harbor Tunnel project is a good example of both a geotechnical nightmare and a researcher's dream because of the fascinating geotechnical problems and challenges. Some of the advancements reported in the earlier chapters of this report were developed by studying some of the Boston problems in the early phases of design and construction, and the later phases will certainly benefit from this new knowledge.

The author is sure that there will be some readers who will ask why it is still necessary to continue geotechnical research programs because it seems to them that we have done all there is to do. Why continue to do the "same old, same old" for the sake of just doing more. At the risk of dignifying this shallow thinking, the author suggests that these people reread the report and reflect on the many problems that continue to stymie the efficient and safe construction of this nation's transportation system over, through, and within heterogeneous ground materials.

These problems have not been approached with sufficient resources in the past, and will continue to grow and compound with increasing demands of a mobile and highly technically oriented society. Thoughts of reducing or downsizing geotechnical research efforts need to be reversed and expanded to properly address these urgent problems. Geotechnical engineering can and should play a major role in assessing the effects of construction on other structures adjoining the highway, by providing rational tools and methods for selecting the appropriate construction methods, predicting the ground movements, designing protective measures, and developing remedial correction schemes. If allowed, geotechnology will play a critical role in the construction, renovation, and upkeep of our Nation's highway system.