Discussion

SESSION 5

Professor CJ.F.P. JONES, University of Newcastle upon Tyne Dr. Bolton has stated that a check for sliding failure for a mass retaining wall will not be required in the new Code of Practice. Sliding of a gravity structure leads to active conditions in the backfill; but if the mass structure is a reinforced soil wall, checking for forward sliding on any form of foundation is essential. Reinforced soil structures are internally stabilized, and any forward sliding can lead to a reduction of internal sta bility, which in the limit can lead to collapse.

D. R. CARDER and A. BROOKES, Transport Research Laboratory London Regional Office of the Department of Transport commissioned the TRL to undertake measurements of termporary prop loads and wall move ments at the A40 Long Lane Improvement Scheme; the results are presented with their permission. The co-operation received from the site staff of Mott-MacDonald Civils and Fairclough Civil Engineering Ltd is also gratefully acknowledged. Figure 1 shows the temporary raked props which were installed at alter nate nominal spacings of 7 m and 5 m to support a bored pile retaining wall during excavation of the berm in front of the wall and during the subsequent construction of a permanent prop slab. The upper end of the prop seating under the capping beam was about 7.5 m above formation level for the permanent prop slab. The props comprised steel tubes 13 m in length which were prestressed to a nominal load of260 kN. Three props were instrumented with vibrating-wire strain gauges and thermocouples to determine loads and temperatures. Measurements were also made of the lateral movement of the top of the wall using a Geomensor electronic distance measuring system. Results from all three props were similar and the loads measured on prop B during construction are shown in Fig. 2. Loads rapidly increased during berm excavation and over the following few days. The average loads measured on props A, B and C after completion of the permanent prop slab