Payum Vossoughi Presentation

8/12/2019 Payum Vossoughi Presentation

1/27

University of California, Davis

Civil & Environmental Engineering

ECI284 Term Project

Study of GroundImprovement Techniques

with an Emphasis on Deep

Soil Mixing

Payum Vossoughi

Instructor: Professor Boris Jeremic

March 2012


2/27

Presentation Outline

Introduction/Motivation

Overview of available ground improvement techniques

Emphasis on Deep Soil Mixing (DM)

Laboratory testing

Numerical analysis

Statistical analysis

Conclusion


3/27

Introduction/Motivation

How do we keep our civil infrastructure safe from liquefaction?

Liquefaction mitigation strategies:

1.) Modify designreduce damage to acceptable levels

2.) Do nothing alternativeaccept risk

3.) Abandon projectchoose another site

4.) Ground improvement

Increased density of underlying soil deposits

Reduced excess pore pressure build-up (maintain ru< 1.0)


4/27

How does a project engineering choose a ground improvement

technique(s) to implement?

Case studies

Numerical & statistical analyses

Laboratory tests on soil specimens (QA/QC)

Benefit vs. cost analysis

Constructability issues + engineering judgment

Purpose: Increase confidencein ground improvement techniques to

better protect civil engineering infrastructure from future natural

disasters related to liquefaction

Introduction/Motivation cont

- NSPE Code of Ethics:

Engineers, in the fulfillment of

their professional duties, shall

hold paramount the safety,

health and welfare of the public


5/27

Overview of AvailableGround Improvement

Techniques


6/27

Ground Improvement techniques based on soil characterization


7/27

Methods of Ground Improvement: Vibro Methods

Advantages Disadvantages

Densifies soil

Increases lateral stress

Reinforces soil mass

Provide drainage of excess pore Most effective technique for

liquefiable soils that fall within

the typical grain size range

Widely used

Economical

Ineffective for soils with high fines content

(>20%)

Inefficient for liquefiable soils with a limited

thickness at a significant depth Difficult to penetrate stiff strata (cemented,

cobbles)

Settlement of surrounding ground

Vertical conduit for environmental

contaminants

Construction of a vibro-replacement stone column

(Idriss & Boulanger 2008)


8/27

Methods of Ground Improvement: Deep Dynamic Compaction


Densifies soil


Economicallarge areas

Simple; no insertion required

Effective for only upper 10 meters

Difficult to densify soil surrounding large

cobbles/boulders

Decreasing effectiveness with decreasing

permeability (>20% fines)damping effect

of generated dynamic shear stresses

Disturbing to local structures + occupants

Crawler cranes can drop tamper masses weighing up to 33 tons from heights of 30 meters



9/27

Methods of Ground Improvement: Compaction Grouting


Densifies soil


Reinforces soil mass

Works well in low-overhead +

constricted spaces

Can target specific depth interval

Effective with high fines soil (>20%)

+ large particles (cobbles, boulders)

Ineffective for small depths

(


10/27

Methods of Ground Improvement: Jet Grouting


Construction of overlapping soil-cement columns

(in-ground shear walls)

Reduces earthquake-induced shear strains of

treated zones

Increases composite shear strength of treated

zones

Prevents migration of excess pore between

untreated and treated zones

Works well in low overhead

Can target specific depth interval

Works well in high fines soil (large applicability

range)

Hydraulic fracture

Overlapping soil-cement

columns are brittle =

tendency to crack with

earthquake shaking

High-pressure jets of air, water and/or groutoverlapping soil-cement columns


h d h h


11/27

Other Ground Improvement Techniques Worth Mentioning Drainage systems

Coarse aggregates or geosynthetic composites

Design goal: control max. rulevels

Limited to high k soils

Prevent void redistribution or water film generation

at interfaces

Permeation Grouting

Reduces the potential for contraction during cyclic

shearing

Optimization and QC through computer automation

Minimal disturbance; clean sands

Generally expensive (special circumstances)

Explosive Compaction

Propagation of dynamic shear stresses

Deep deposits; clean sands

Non-uniform densification Permitting requirement (large disturbance)

Removal and Replacement

Excavate and replace with compacted fill

High degree of confidence

Practical for shallow liquefiable layers;

groundwater needs to be controlled

Low khigh k interface drain system

Exposed soil bulbs resulting from permeation grouting

Sediment boils resulting from explosive compaction


f


12/27

Methods of Ground Improvement: Deep Soil Mixing


Construction of overlapping soil-cement

columns (in-ground shear walls)

Reduces earthquake-induced shear strains

of treated zones

Increases composite shear strength of

treated zones Prevents migration of excess pore between

untreated and treated zones

Works well in high fines soil (large

applicability range)

Requires overhead clearance

Stiff strata can impede augers

Inefficient for liquefiable soils

with a limited thickness at a

significant depth

Overlapping soil-cementcolumns are brittle = tendency

to crack with earthquake

shaking

Cementitious materials/grout are injected through auger stems and mixed with native soils



13/27

Additional Information Regarding Deep Soil Mixing DM was put into practice inJapanin the middle of 1970sto improve soft marine deposits, and then spread into China, South

East Asia, and recently to the other parts of the world.

The maximum improvement depth on land is typically 30 meters in comparison to 50 meters for off-shore applications

The 2 principal hardening agents used in DM are cement and lime

The curing process for cement-treated soils is much longer for cohesive soils (approx. 56 90 days) compared to non-cohesive

soils (approx. 28 days). The strengths achieved in non-cohesive soils are larger.

Cement powderscan achieve higher strengths than cement slurries when used

to treat clayey soils. Cement powders have lower water contents

Typically SPT N-values of soils to be treated:

Cohesive: N < 4 blows (heavier equipment --- N < 10 blows)

Granular: N < 10 blows (heavier equipment --- N < 30 blows)

Alternative approach: dryjet mixing

Minimizing of hardening agent (cement or lime) Minimizing waste slurry and spoil

Reducing resources consumed/project expenses + increased sustainability

Markets for DM:

1.) Roads and Railways 4.) Foundation support -

2.) Water/sewage treatment works 5.) Temporary works

3.) Tunneling 6.) Seismic engineering


14/27

Laboratory Testing on

DM Stabilized Soil

Emphasis on Deep Soil Mixing


15/27

QA/QC

Kaolin clay stabilized with

ordinary Portland cement.

4 moulding techniques ,4binder contents -- 160 total

specimens obtained

28 days curing - unconfinedcompression test (axial strain

rate =1%/min);

Wet density also measured

Laboratory Testing on Stabilized Soil

(Kitazume 2012)


16/27

Laboratory Testing on Stabilized Soil cont

Tapping technique

Most uniform

Densest

Highest shear strength Most correlated

Minimal pockets/cavities

Static Compaction

Least uniform

Loosest Lowest shear strength

Least correlated

Maximum pockets/cavities

Strength increases approx. linearly

with increasing wet density(regardless of moulding technique)

Future Research: Perform similarstudies using

Different soils

Different laboratories

Wet Density

Parameter

Unconfined Compressive

Strength Parameter

(Kitazume 2012)


17/27

Numerical Analysis of

Lattice Shaped GroundImprovement in Japan



18/27

Oreintal Hotel in Kobe, Japan

Hyogo-Ken Nanbu earthquake1995

Dimensions: 134 m x 59m (plan) & 60m tall

Liquefaction potential in the upper loose fill

Lattice shaped ground improvement (16 m)

Treatment area ratio* = 20%

Unconfined compressive strength after

curing (6 weeks) = 46 MPa.

Aftermath: minimal damage to the cast-in-

place pile foundation and superstructure

due to implemented DM walls

Numerical Analysis:

Case Study

* Treatment area ratio is defined as the ratio of the improved soil area to the whole site area (Namikawa 2007)

i l l i


19/27

3-D FE Analysis

Mesh = 8 node isoparametric elements

Two-phase u-U formulation (excess pore)

Boundary conditions: cyclic, viscous, undrained

Elastic and Elasto-Plastic Model

Accounts for partial damage

Can notsimulate cyclic mobility after the

initial liquefaction

Rayleigh Damping (solid phase)

Saturated sand densification model (Mohr Coulomb)

Distribution in stress

(Tensile --- cracking)

Distribution in the

number of Gauss points

that reach failure

Numerical Analysis:

Important Aspects to the Model

(Namikawa 2007)


20/27

Numerical Analysis:

Cases/Results

2 varying parameters in the

analysis of the improved soil

Without ground improvement Representative of case

study

(Namikawa 2007)

N i l A l i C l di R k


21/27

Improved soil in Case 1 satisfies both the liquefaction potential & internal stability criteria

Partial Failures (as witnessed in cases 2 & 3) do not greatly affect potential of liquefactionmitigation. Note, however, that internal stabilities are not satisfied for cases 2 & 3.

Primary factors affecting the potential of liquefaction mitigation:

A.) Treatment area ratio

B.) Elastic modulus of the improved soil

What if the site experiences another earthquake (of equivalent energy/shaking)?

If the induced failure region from the 1st earthquake is small (represented by a smalldamage volume ratio), the potential of liquefaction mitigation remains approximatelythe same for the 2ndearthquake.

Future Research Topics:1.) Investigate the influence of input wave characteristics

2.)Expand the numerical model to account for plastic deformations (nonlinear behavior)

Numerical Analysis: Concluding Remarks

(Namikawa 2007)


22/27

Statistical analysis of

DM implementation inSingapore


St ti ti l A l i


23/27

Marina Bay Financial Centre (MBFC)

Soil deposition:primarily marine clay & some sand

with seashell fragment. The design UCS is 0.8MPa.

Sampling conducted after 2 months of DM

installationsQA/QC

Nicoll Highway MRT Station (NCHS)

Soil deposition: thick layer of marine clay, thinner

layers of estuarine clay, fluvial sand cohesionless soil

& layer of land reclamation fill (ground surface).

The design UCS is 0.9MPa.

Sampling conducted after 2 months of the DM

installationsQA/QC

Site layoutMBFC project

Site layoutNCHS project

(Chen 2011)

Statistical Analysis:

Case Studies

St ti ti l A l i


24/27


Results from MBFC Project

97 Samples

156 Samples

73 Samples

75 Samples

84 Samples

Total = 485 Improvement in the uniformity

of the mixing as the project

proceeds. Phase 4 has the

smallest COV, corresponding to

the greatest uniformity

Operating parameters play a

significant role in DM statistical

analysis

Small pockets of high strength

can significantly skew mean

UCS upward

COV values fit within the

expected range: 0.20

0.60(Chen 2011)

Statistical Anal sis


25/27


Results from NCHS Project

112 Samples

28 Samples

16 Samples

17 Samples

51 Samples

COV range is lowerfor NCHS

compared to MBFC project

Histograms are left-skewed

with high mean values---

modified DM approach =

Jet Mechanical Mixing (JMM)

Ignoring the fill layer, the

naturally-occurring soil deposit

with the lowest mean UCS and

poorest mixing quality is the M

layer (or high plasticity clay)

The F1 layer (a sandy deposit)

shows the best improvement

(Chen 2011)

Statistical Analysis: Concluding Remarks


26/27

MBFC strength < NCHS strength

Increasing cement content increases strength (operating parameter)

MBFC COV > NCHS COV

Increasing presence of marine clay deposit increases COV (geologic condition)

MBFC blade rotation number < NCHS blade rotation number

Increasing penetration and withdrawal rates decreases mixing quality, and UCS (operating

parameter)

Constructed (actual) strength > design (target) strength for all phases/layers; both projects

High conservatism observed in construction

Lack of understanding regarding strength variability in DM columns

Future Research:

Improvements to DM construction method to effectively treat Singapore marine clay

Acquire better understanding of strength variability in DM columns

Statistical Analysis: Concluding Remarks

MBFC - DM NCHSJMM (mod. DM)(Chen 2011)


27/27

Payum Vossoughi Presentation

Documents

Transcript of Payum Vossoughi Presentation