Analysis of Deep Excavation with Column Type of Ground Improvement in Soft Clay

This paper presents the design and construction of a deep excavation for building foundations in saturated soil. This deep excavation was of particular interest because it was located above and beside the Shanghai Metro tunnels. The twin Shanghai Metro tunnels had to be in full operation during the deep excavation. Potential large deformation of the twin tunnels was one of the main concerns during the design and construction for the deep excavation. The paper discusses in detail the criteria and measures for controlling the soil and tunnel deformation. The measures included cast-in-place concrete diaphragm walls with bracing structural members, pumping consolidation, cementsoil mix pile systems, and rational excavation procedures. A simplified theoretical method was proposed to estimate the increment in undrained shear strength in a soft clay layer due to pumping consolidation. Furthermore, conventional finite element methods were used to predict the soil vertical and horizontal displacements induced by the excavation. Using the design and construction methods discussed in the paper, the settlement and horizontal displacement of the tunnels were successfully controlled within 5.0 mm and 9.0 mm, respectively. The curvature of longitudinal deformation curve of the tunnels was less than 1/15 000. The horizontal displacement of the braced diaphragm walls was less than 0.12% of the total excavation depth. Key words: Metro tunnels, saturated soft soil, deep excavation, design, construction, ground improvement, case studies.

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Uplift and Settlement Prediction Model of Marine Clay Soil e Integrated with Polyurethane Foam

Open Engineering ◽

10.1515/eng-2019-0054 ◽

2019 ◽

Vol 9 (1) ◽

pp. 481-489

Author(s):

D.C. Lat ◽

I.B.M. Jais ◽

N. Ali ◽

B. Baharom ◽

N.Z. Mohd Yunus ◽

...

Keyword(s):

Polyurethane Foam ◽

Clay Soil ◽

Ground Improvement ◽

Soft Soil ◽

Soft Clay ◽

Effective Thickness ◽

Marine Clay ◽

Uplift Pressure ◽

Pu Foam ◽

Improvement Method

AbstractPolyurethane (PU) foam is a lightweight material that can be used efficiently as a ground improvement method in solving excessive and differential settlement of soil foundation mainly for infrastructures such as road, highway and parking spaces. The ground improvement method is done by excavation and removal of soft soil at shallow depth and replacement with lightweight PU foam slab. This study is done to simulate the model of marine clay soil integrated with polyurethane foam using finite element method (FEM) PLAXIS 2D for prediction of settlement behavior and uplift effect due to polyurethane foam mitigation method. Model of soft clay foundation stabilized with PU foam slab with variation in thickness and overburden loads were analyzed. Results from FEM exhibited the same trend as the results of the analytical method whereby PU foam has successfully reduced the amount of settlement significantly. With the increase in PU foam thickness, the settlement is reduced, nonetheless the uplift pressure starts to increase beyond the line of effective thickness. PU foam design chart has been produced for practical application in order to adopt the effective thickness of PU foam within tolerable settlement value and uplift pressure with respect to different overburden loads for ground improvement works.

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Performance of soft clay stabilized with sand columns treated by silica fume

MATEC Web of Conferences ◽

10.1051/matecconf/201816201007 ◽

2018 ◽

Vol 162 ◽

pp. 01007

Author(s):

Zeena Samueel ◽

Hussein Karim ◽

Mohammed Mohammed

Keyword(s):

Silica Fume ◽

Carrying Capacity ◽

Construction Projects ◽

Ground Improvement ◽

Soft Clay ◽

Road Construction ◽

Reduction Ratio ◽

Area Replacement Ratio ◽

Second Category ◽

Improvement Ratio

In many road construction projects, if weak soil exists, then uncontrollable settlement and critical load carrying capacity are major difficult problems to the safety and serviceability of roads in these areas. Thus ground improvement is essential to achieve the required level of performance. The paper presents results of the tests of four categories. First category was performed on saturated soft bed of clay without any treatment, the second category shed light on the improvement achieved in loading carrying capacity and settlement as a result of reinforcing with conventional sand columns at area replacement ratio = 0.196. The third set investigates the bed reinforced by sand columns stabilized with dry silica fume at different percentages (3, 5 and 7%) and the fourth set investigates the behavior of sand columns treated with slurry silica fume at two percentages (10 and 12%). All sand columns models were constructed at (R.D= 60%). Model tests were performed on bed of saturated soil prepared at undrained shear strength between 16-20 kPa for all models. For all cases, the model test was loaded gradually by stress increments up to failure. Stress deformation measurements are recorded and analyzed in terms of bearing improvement ratio and settlement reduction ratio. Optimum results were indicated from soil treated with sand columns stabilized with 7% dry silica fume at medium state reflecting the highest bearing improvement ratio (3.04) and the settlement reduction ratio (0.09) after 7 days curing. While soil treated with sand columns stabilized with 10% slurry silica fume provided higher bearing improvement ratio 3.13 with lower settlement reduction ratio of 0.57 after 7-days curing.

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Numerical evaluation of dewatering effect on deep excavation in soft clay

Geotechnical Aspects of Underground Construction in Soft Ground ◽

10.1201/9780203879986.ch13 ◽

2008 ◽

Author(s):

L Li ◽

M Yang

Keyword(s):

Numerical Evaluation ◽

Soft Clay ◽

Deep Excavation

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Enhancing Base Stability of Deep Excavation in Soft Clay with Grout Piles

Grouting and Deep Mixing 2012 ◽

10.1061/9780784412350.0140 ◽

2012 ◽

Author(s):

Hung-Jiun Liao ◽

Chih-Chen Lin ◽

Chao-Jie Jeng

Keyword(s):

Soft Clay ◽

Deep Excavation ◽

Base Stability

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Analysis and Process Control of the Deformation for Deep Excavation in Soft Clay

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.580-583.395 ◽

2014 ◽

Vol 580-583 ◽

pp. 395-400

Author(s):

Hui Liu ◽

Wei Bin Li ◽

Hong Tao Liu

Keyword(s):

Process Control ◽

Soft Clay ◽

Back Analysis ◽

Control Model ◽

Prediction System ◽

Deep Excavation ◽

Dynamic Prediction

Mechanisms of the distortion of deep excavation in soft clay are recommended on the beginning. Plane FEA method is combined with back-analysis from displacement on this paper to establish a dynamic prediction system of the distortion of deep excavation, which is proved to be viable by practice. Combining with the idea of process control, a process control model of the distortion of deep excavation is established on this paper. It is divided into three parts: advance control, observation and dynamic prediction, process control in the construction.

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Ground deformation and base instability of deep excavation in soft clay subjected to hydraulic uplift

10.14711/thesis-b1198259 ◽

2012 ◽

Author(s):

Yi Hong

Keyword(s):

Ground Deformation ◽

Soft Clay ◽

Deep Excavation

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Monitoring of Electric Current during Electrokinetic Stabilisation Test for Soft Clay Using EKG Electrode

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.773-774.1560 ◽

2015 ◽

Vol 773-774 ◽

pp. 1560-1564 ◽

Cited By ~ 1

Author(s):

Saiful Azhar Ahmad Tajudin ◽

Ian Jefferson ◽

Aziman Madun ◽

Mohd Hazreek Zainal Abidin ◽

Mohamad Faizal Tajul Baharuddin ◽

...

Keyword(s):

Electric Current ◽

Ground Improvement ◽

Soft Clay ◽

Current Trend ◽

Monitoring Data ◽

Voltage Gradient ◽

Kaolinite Clay ◽

Pure System ◽

Inert Electrode ◽

Fluid Compartments

Electrokinetic Stabilisation (EKS) method has the potential to overcome problems on highly compressible clay. This study presents the monitoring results from an experimental study of EKS on soft clay soil. Inactive kaolinite clay, inert electrode and distilled water (DW) were used as a pure system mechanism before any chemical stabilisers are utilised for stabilisation. Therefore, this monitoring data will provide a baseline study to improve efficiency of the EKS approach for ground improvement application. An inert electrode of Electrokinetic Geosythentic (EKG) developed at the Newcastle University was utilised to apply a constant voltage gradient of 50 V/m across a soil sample of 400 mm length. The distilled waters were used at the pore electrolyte fluid compartments and supplied under zero hydraulic gradient conditions for periods of 3, 7 and 14 days. Throughout, monitoring data of electric current for all treatments were measured. Results showed that the electric current trend in this pure system was attributed to the electrochemical effects in the clay-water electrolyte system.

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Deformation characteristics of a 38 m deep excavation in soft clay

Canadian Geotechnical Journal ◽

10.1139/t11-075 ◽

2011 ◽

Vol 48 (12) ◽

pp. 1817-1828 ◽

Cited By ~ 59

Author(s):

Guo B. Liu ◽

Rebecca J. Jiang ◽

Charles W.W. Ng ◽

Y. Hong

Keyword(s):

Soft Clay ◽

Field Performance ◽

Lateral Wall ◽

Diaphragm Wall ◽

Deep Excavation ◽

Wall Panel ◽

Soft Clays ◽

Measured Ratio ◽

Increasing Demand ◽

Ground Settlements

To meet the increasing demand for underground space for economical development and infrastructural needs, more and more deep excavations have been constructed in Shanghai. In this paper, field performance of a 38 m deep multistrutted excavation in Shanghai soft clay is reported. The deep excavation was retained by a 65 m deep diaphragm wall. Inclinometers as well as settlement and heave markers were installed to monitor the performance of the deep excavation. This project provides an unusual opportunity to study the differential heaves of center columns and diaphragm walls during excavation. Because of the significant stress relief resulting from the 38 m deep excavation, maximum heaves of the center column and diaphragm wall panel were about 30 and 16 mm, respectively. The measured ratio δp/H (heave/final excavation depth) of column is less than 0.1% whereas the observed δp/H of the diaphragm wall panel is about 0.04%. The maximum distortion between the column and the diaphragm wall panel is smaller than 1/500, which is within the limit range proposed by Bjerrum in 1963. Owing to careful construction control, stiff strutting system, and compaction grouting, the measured lateral wall deflections and ground settlements at this site are generally smaller than other shallower excavations in soft clays in Shanghai, Singapore, and Taipei.

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