SBIR-STTR Award

Lateral earth pressure is fundamental to much of soil mechanics, and vital to the solution of may practical problems including computerized solutions for bearing capacities and for stability of tunnels, slopes and walls. Unfortunately, the key role of lateral stress has tended to be passed over in engineering investiga- tions because of difficulties in its measurement. Assumed values or values based on some very loose empirical correlations frequently are used despite an acknowledged and demonstrable error that usually will result in overdesign. The problems in measurement for the most part derive from the sensitivity of soil stress to introduction of a measuring device. The several approaches to this and other measurement problems will e analyzed and evaluated, with special attention to probable effects on soil behavior as it pertains to accuracy and reliability of each type of test. An existing database of ko stepped blade, dilatometer, and pressure- meter data will be used to help select one or at most two approaches or test procedures for further investigation, improvement, and use during Phase II.

Lateral in situ soil stress being fundamental to many soil mechanics and foundation engineering, is an entered parameter in many computer programs generating these solutions for purposes of analysis an ddesign. Yet seldom, if ever, is the in situ lateral stress actually known, nor has it been measured. The problem has been the lack of an instrument with which to accurately and efficiently perform such measurmeents. The successful development of such a method or methods therefore may be expected not only to provide these essential data that now must be estimated or guessed at--it may also lead to new concepts in analysis and design of soil and foundation structures, and almost certainly will lead to modifications and improvements on the old ones. The Phase I study reviewed the current technology on in situ lateral earth pressure measurmenet and identified the stepped blade as having the greateds potential for achieving the stated goals of the project solicitation. Problems relating to measurment of in situ lateral earth pressures relate to the sensitivity of soil stress to the introduction of a measuring device. The self-borin pressurementer addresses these sensitively by attempting to minimize displacemnt while the dilatometer applies empirical relationships to account for influence on soil stress resulting form insertion of the device. The stepped blade provides a direct measure of the influence on soild stress, eleiminating the need for empirical relationships that may not be appropriate for a specific soil. Also, in addition to providing a means of measuring lateral earth pressure, results obtained witht he stepped blade can provide a basis for estimating other soil parameters, providing a better means to understand soil behavior in situ.

Keywords:
soil stress in situ lateral stress ratio measurement