Jack Shuilong Shen

Geohazards induced by anthropic activities of geoconstruction: a review of recent failure cases

Many hazards occurring due to underground construction works can be attributed to anthropic activities. It is important to know what new knowledge on both geology and construction operation are needed to prevent these hazards from leading to catastrophic failures. In this paper, nine anthropic hazards due to the underground construction in recent years at Asian countries are discussed. Each case study discussed the project description, geological conditions, the collapse and its consequence, and analysis of failure mechanism according to field investigations. Furthermore, to explore the cause of the collapse and to prevent similar hazards from leading to failures, the collapsed excavations of the selected case studies were studied extensively. Based on the field investigations undertaken in this study, underground construction collapse which can be attributed to human-induced activities are overexcavation, water leakage, soil deterioration, faults in design and implementations, erosion, and inadequate ground improvement. The understanding of the effect of these human-induced activities can be used as a guideline for avoiding hazards in future projects.

Recycled concrete aggregate/municipal glass blends as a low-carbon resource material for footpaths

Construction and Demolition (C&D) materials comprising recycled concrete aggregate (RCA), fine recycled glass (FRG) and a blend comprising 85% RCA with 15% FRG (85RCA/15FRG) were evaluated for their viability as footpath base layers. The geotechnical laboratory evaluation assessed the performance of the C&D materials in footpath bases and included particle size distribution, particle density, water absorption, pH, organic content, modified Proctor compaction, Los Angeles Abrasion and California bearing ratio (CBR) tests. Total concentrations and Australian standard leaching procedure tests were performed on several heavy metals to assess the leaching potentials of contaminants released from the recycled materials. Following the completion of the geotechnical and environmental laboratory evaluation, a footpath was constructed to demonstrate the performance of the 85RCA/15FRG blend as a footpath base material. Field tests comprising nuclear gauges for density and moisture measurements and Clegg hammer tests for field CBR measurements were undertaken to assess the performance of the base materials in the field. The 85RCA/15FRG blend was found to be an optimum one in the laboratory and field evaluation works, as the blend provided adequate bearing strength and furthermore enhanced the workability of RCA, through the introduction of glass fines. Energy savings assessment demonstrated that the use of 85RCA/15FRG blend as footpath base material furthermore has the potential for saving embodied energy. This research indicates that this low carbon concept, utilizing RCA and FRG blends as base materials, is a viable alternative engineering material for future footpaths.

Evaluation of the uplift behavior of plate anchor in structured marine clay

ABSTRACT The uplift behavior of a plate anchor in a structured clay (soft Ariake clay) is investigated through a series of laboratory tests and method of finite element analysis. The tests are adopted to identify the factors influencing the behavior of the anchor, including the thixotropic nature of Ariake clay, consolidation time, and embedment ratio of the anchor. A finite element method (FEM) is used to analyze and predict the uplift behavior of the anchor plate well in the elastic region and the yield load. The results from both the laboratory tests and the FEM analysis suggest that the embedment ratio for a deep anchor in Ariake clay is close to 4. Further increase in embedment ratio improves the capacity to a lesser extent. FEM overestimates the failure load of the uplift anchor in soft Ariake clay by about 20%. This may be ascribed to the hypothesis in the FEM analysis that there is continuous contact between the clay and the anchor until failure. Vesic’s theory for deep anchors, which may be used to predict the ultimate pullout resistance of the plate anchor in reconstituted Ariake clay, is verified to be applicable. In this paper, the plastic flow zone around the anchor is discussed using FEM which makes the behavior of anchor more understandable during the design stage.

Evaluation of Environmental Risk Due to Metro System Construction in Jinan, China

Jinan is a famous spring city in China. Construction of underground metro system may block groundwater seepage, inducing the depletion risk of springs. This paper presents an assessment of the risk due to metro line construction to groundwater in Jinan City using Analytic Hierarchy Process (AHP) and Geographic International System (GIS). Based on the characteristics of hydrogeology and engineering geology, the assessment model is established from the perspectives of surface index and underground index. The assessment results show that the high and very high risk levels of surface index exceed 98% in the north region; and high and very high risk levels of underground index exceed 56% in urban center and southern region. The assessment result also shows that about 14% of the urban area belongs to very high risk level; regions of high risk are 20% in urban area, 9% in Changqing County and 43% in Pingyin County. In the high risk region, metro lines R1 to R3, which are under construction, and metro lines L1 to L5, which are planned, have very high and high risk. Therefore, risk control measures are proposed to protect the groundwater seepage path to spring.

Investigation of the geological and hydrogeological environment with relation to metro system construction in Jinan, China

Jinan City is located in Eastern China, where porous water and karst water are well developed. The geographic position, geological environment, and terrain of Jinan provide many springs, most of which are distributed in urban areas. When metro lines are constructed in Jinan, six types of stratum combinations are typically encountered. Dewatering needs to be considered to avoid the occurrence of water-inrushing, quicksand and piping hazards, which can change the groundwater seepage environment and reduce spring discharge. In addition, the existence of metro lines can block the recharge channels of karst water. The effects of a metro system are felt on springs in three zones: shallowly buried areas of limestone, deeply buried areas of limestone and spring discharge areas. This paper proposes countermeasures to mitigate the impacts of metro lines on groundwater seepage and to protect springs. These measures include waterproof curtains, dewatering on demand, groundwater head monitoring, artificial recharge, tunnel waterproofing, and groundwater flow path systems.

Soil Characterisation Based on Pipejacking Parameters and Spoil Characteristics

Possessing a few geological boreholes distributed along the tunnel alignment is likely to lead to an inability of understanding the complex geological structure of worksite and optimising the tunnelling parameters. This lack of geological borehole will result in a high potential of geo-hazards for tunnelling works. This study proposes an alternative method to dynamically determine the major and other components of ground by taking the pipejacking parameters and spoil characteristics into account. The validity of the proposed method is verified via a case study.

Performance Evaluation of Jacking Force Models for Tunnel Bore Conditions Characterisation

Since the ability of many available jacking force models to characterise the tunnel bore conditions is limited. A simple approach to characterise the tunnel bore conditions is proposed and applied to a case study where four sewer pipelines of the Shulin district sewer network in Taipei County, Taiwan were constructed to verify its validity. Four jacking force models are benchmarked in this study. Based upon the given soil properties and pipe dimensions as well as the pipe buried depth, the calculated normal contact pressure (σ′) from each model and the measured frictional stress (τ) in each baseline section are utilised for the back-analysis of the frictional coefficient (μavg). The μavg values outside the range of 0.1–0.3 recommended for lubricated drives can be ascribed to the increasing pipe friction resulting from the excessive pipe deviation or ground closure or the gravel formation not being long enough to establish lower face resistance. JMTA has indicated a further potential use in assessment of the interface performance during pipe-jacking works.