Geotechnical Engineering Online Library

Internal erosion through or beneath levees frequently occurs during flood events, resulting in sand boils. Determining the extent of damage from the seepage channels that caused the sand boils remains difficult, and many sand boils are simply monitored in subsequent floods. There is a need for a nondestructive methodology to map the voids caused by seepage channels so that needed repairs can be identified prior to the next flood. The objective of this study is to identify the electrical response of internal erosion pathways with electrical resistivity tomography (ERT). A case study using ERT on the Hager Slough Levee, which has experienced sand boils since the 1990s, is presented. Three ERT surveys were conducted along the levee in an area of apparent damage (i.e., crown settlement and sand boils) and where nearby boring logs were available. Laboratory resistivity tests provide support for the field ERT interpretations. The results indicate that ERT may be used to identify zones of damage within and beneath a levee. If used in practice, ERT has the potential to improve remediation of levees by identifying needed repairs.

An underground reinforced concrete tank was constructed for a project in the southwest region of India. The tank was 90 m x 35 m in plan and 7.3 m deep resting on partly filled-up and partly native soil. During the peak monsoon, a sudden uplifting of the base slab by about 300 mm and subsequent failure of the foundation raft and a partition wall was observed. Laboratory testing was executed and hydrogeological survey was carried out using ground penetrating radar, seismic refraction and infiltrometer testing, and an analytical study was carried out to identify the root cause of the tank uplifting. Based on this study, it was observed that the uplifting and structural failure was essentially due to the peculiar land terrain and soil properties and the development of excess hydraulic head below the bottom of the tank. After considering different options, the rectification measures were carried out by provision of dewatering wells along the tank periphery to release the excess hydrostatic pressure and stabilize the foundation raft. The structural repair of the top of the foundation raft and partition wall was carried out to strengthen the reinforced concrete members. The rectification measures worked well to increase the structural stability of the tank and to prevent build-up of excess hydrostatic pressure preventing uplift and subsequent damage in the future.

Three areas in Egypt and Saudi Arabia were selected as pilot sites for studying karst foundation problems. Globally, the dissolution of carbonate rocks results in extensive karst landforms that can pose significant challenges to civil engineering projects. Most karst caves and sinkholes are structurally controlled by major faults and joints. Detection of karst limestone foundation bedrock (caves, sinkholes and open fractures) in the three studied sites has been conducted using geological and geophysical studies. The geological studies are based on review of published geologic maps for the three sites. The geophysical studies included a 2D electrical resistivity survey and ground-penetrating radar (GPR). Karst limestone foundation bedrock treatments have been performed in several projects worldwide and include engineering fill, engineering fill with geosynthetics, concrete filling and cement grout low pressure injection. Upper Egypt’s El Minia-Maghagha caves, underlying newly constructed settlement areas have been treated using high-slump concrete filling. Engineers treated foundations in northwestern Riyadh City and in eastern Al Hofuf City, Saudi Arabia, using engineering fill, high slump concrete filling and low pressure cement grout injection. This article summarizes the classification of encountered karst foundation bedrock according to Ford and Williams (1989) engineering classification, introduces the optimum methods for detecting karst features and presents engineering treatments of karst limestone landforms.

Macroseismic observations in the meizoseismal area of the Achaia-Ilia, Greece, Mw 6.4 earthquake of 8 June, 2008, have shown that soil liquefaction occurred at a number of sites up to distances of 25 km from the causative fault. In one of these sites (SITE-I at coastal zone of Kato Achaia) the occurrence of liquefaction was extensive and was followed by lateral spreading. In another nearby site (SITE-II) only marginal liquefaction (or nonliquefaction) was observed. Following the macroseismic observations, a geotechnical investigation was carried out at SITE-I and SITE-II which included exploratory boreholes with continuous sampling, SPT measurements, CPT soundings, surface wave measurements (SASW, MASW, ReMi) and laboratory testing. Based on the results of geotechnical investigation, the soil stratigraphy and pertinent soil properties were evaluated in the liquefaction/nonliquefaction locations. The assessment of peak ground acceleration at the area of SITE-I and SITE-II was based on attenuation relations and shaking table tests performed to simulate the observed behavior of an overturned (during the main shock), barrel-shaped, plastic, water filled container sitting on the ground surface at SITE-I. It is believed that the data presented in this paper can be used to 1) check the validity of current liquefaction susceptibility criteria/liquefaction triggering relationships, and 2) establish a well documented liquefaction case history that can be part of future liquefaction databases.