Present study attempts to investigate the possible reasons behind the failure of a cantilever retaining wall with relief shelves, which is located in the heart of Hyderabad city, India. A pressure relief shelf is a finite width, thin horizontal cantilever platform extending into the backfill, which are constructed monolithic with the stem of the retaining wall. Number of such shelves is constructed at regular spacing along the height of the wall. From the limited theoretical studies, it is noted that the provision of relief shelves, extending beyond the rupture surface in the backfill, can considerably reduce the earth pressures on the retaining wall and subsequently increase the stability of the retaining structure. The height of the failed retaining wall ranges from 10 to 13.9 m and retains a loose to medium dense sandy soil backfill, and constructed with 5 relief shelves. After few years of construction, a portion of retaining wall of about 20 m length had collapsed and adjoining 20 m length had severely distressed, immediately after the end of a monsoon. The preliminary post-failure investigation revealed that quality of concrete used in construction was satisfactory, and the construction joints were intact. Cracks due to failure had propagated almost up to the full thickness of reinforced concrete wall. To get more insight about the causes of failure, numerical analysis of retaining wall with pressure relief shelves is carried out using widely used geotechnical numerical code, FLAC3D. From the preliminary analysis, it is noted that, though the lateral thrust on the retaining wall in the presence of relief shelves is reduced by 43-48%, use of inappropriate magnitude and distribution of lateral earth pressure in the design calculations might have attributed to the failure of the wall.

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Site investigations were performed on a damaged river dike, which was located in the central and southern part of Iwate prefecture. The field investigation results show that subsidence related failure probably had taken place in the dike body with low penetration resistance and high water table. Further investigations also revealed that the dike body had low liquefaction resistance and the volume change after liquefaction was rather large. Numerical investigation through two dimensional effective stress analyses show that due to main shock and aftershock, there is a likelihood of liquefaction in dike body and the re-liquefaction possibilities are high even under small ground motion.

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In this paper, the three-dimensional finite element software, 3-D PLAXIS, is used to back study possible failure reason of a deep excavation project in soft clay. The building project is located in Taipei covering an area of 200 m by 200 m. General ground condition consists approximately 29 m of soft with SPT-N of 1 to 5 only. The average elevation of the construction site is plus 4.4 m. It’s planned to excavate down to minus 9.5 m. It is planned to leave a berm into 1(V) by 2.5 (H) slope along with installation of shotcrete and 70 cm of drilled shafts along the east side of the site. Two horizontal layers of H pile will then be installed when reaching the second basement level. Slope failure occurs on the east side during excavation. Comparison between the 3D FEM analytical results and instrumentation measurement data showed asymmetric excavation and misjudgment of the elevation of bedrock are the possible reasons to cause the failure of the excavation.

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This paper presents result of analysis for operation of TBM made from the monitoring records obtained during the excavation for the DTSS in Singapore. The long distance and deep tunnel excavation of 7.3km was carried out for this project. The subsoil at the excavation depth of TBM is generally Old Alluvium underlying a relatively thin fill layer for 85% of whole distance. There were some exceptions where relatively thick layer of Kallang formation is lying at 15% at last excavation area. Tunneling was done totally within the Old Alluvium. However TBM were encountered five incidents. Four cases are caused by abrasion and operation. One case was caused by the unforeseen geological condition. According to the result of analysis for TBM operation data, added soil investigations help the understanding of geological conditions in detail and reducing risks for tunneling collapse with ground settlement.

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In this paper, results of forensic analysis of a cantilever retaining wall for road approach embankments which showed distress in the form of translation, vertical settlements and rotation is presented. Extensive geotechnical soil investigation and field measurements of distress are collected. The paper presents prominent causes of failure of cantilever retaining wall using forensic geotechnical investigation. Back analysis of the cantilever retaining wall is performed using classical conventional methods and finite elements analysis. From the results of the conventional analysis and finite element methods, it is observed the retaining wall designs based on prescriptive guidelines may not lead to satisfactory designs and considerations of deformations is important. Back analysis of failure showed that the mechanism of failure is a combination of sliding and overturning and the deformations are in conformity with the predictions obtained from the numerical analysis.

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There are around 10 major bridges are being under construction in the Nagapattinam Tiruthuraipoondi B.G railway line. These bridges are supported by pile foundations with varying founding depths depending up on the soil stratum. Bored cast in suit piles were cast and pile load tests were conducted at five locations for the estimated pile capacity (capacity was estimated as per IS 2911). Almost in all the locations, the pile load test were failed, which means the pile settlement was beyond the specified settlement under the test load. The failure was assessed and reported in this paper. The estimated pile capacity (design load) and test load (working pile load test) was 278MT and 417MT respectively. The pile has got yielded (settled) beyond 12mm, when the test loads of 220MT (which is 80% of the working load) in progress. The pile got settled around 25mm when the working load was in progress and finally reached to 38mm after 12hrs. After unloading, the pile has got rebound only 3mm, which motivate us to do the complete re-assessment of the soil strata in the study area. The forensic investigation on this failure has clearly evident that the failure had happen due to inadequate geotechnical investigation and improper pile installation. The cause will be discussed in this paper.

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A warehouse that had been built in thick sot soil ground with long PC piles of point supported and used as steel products center was divided into two parts. The western half was retained as it was with piled foundation and reused as automobile disassembly yard. The eastern half was used as macadam stock yard after dismantling ware structure as well as foundation piles. Within a few months after the operation of stockyard, the columns of the adjacent disassembly yard were found being settled. Overhead travelling cranes in the disassembly yard was also found being deformed. A question why the structure that is supported by point bearing piles should have settled was sent to the first author. This paper describes the process of geotechnical study and field monitoring including GPS to disclose the mechanism.

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