CHARACTERIZATION OF

SILT/SAND SOILS

An-Bin Huang, Ph.D., P.E.

Department of Civil Engineering

National Chiao Tung University

Hsin Chu, TAIWAN

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What is silt/sand (M/S) soil?

•Sand, silty sand, sandy silt, silt

•Well mixed, layered

•With occasional clay layers

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Clean sand vs sand+silt

•Dilatancy or compressibility

•Permeability

•Sampling

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Test sites and origin of soils

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Issues of interests

• Interpretation of CPT

•Effects of fines on undrained cyclic strength of M/S soils

•Natural versus reconstituted

• Fines content adjustment in simplified procedure

•Ground subsidence & design of piles

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Characteristics of Mai Liao Soil (MLS)

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Mineral Coarse, % Fines, %

Quartz 75.4 20.0

Clinochlore 10.9 29.4

Muscovite 8.6 48.1

Feldspar 5.1 5.1

Grain characteristics of MLS

•Alluvial soil from central mountain range.

•Parental rock• Sandstone

• Shale

• Slate

• Schist

• Mudstone

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Grain size distribution of MLS

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Comparison with binary packing

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DEM data from Ng et al. (2016)

FC = 0%

FC = 30%

FC = 50%

LAB TESTS ON RECONSTITUTED SPECIMENSSoil element tests

CPT calibration tests

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Factors considered

•Fines contents

•Densities

•Stress states

•Specimen preparation methods –

• Moist Tamping (MT)

• Water Sedimentation (WS)

• Dry Deposition (DD)

• Moist Pluviation (MP)

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Iso-consolidation on MLS specimens prepared by MT method

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(Huang & Chuang, 2011)

e vs cyclic resistance ratio

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MLS specimens made by WS method

Use of equivalent void ratio e*

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𝑒∗ =𝑒 + 1 − 𝑏 𝐹𝐶

1 − 1 − 𝑏 𝐹𝐶

(Thevanayagam, 2000)

𝑏 ≈ 0.6

(Huang & Chuang, 2011)

e* based critical state line

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State parameter Ψ vs CRR

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Ψ∗ vs CRR

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CPT calibration tests in MLS

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(Huang and Hsu, 2004)

Compare w/ NC, clean, uniform quartz sands

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(after Jamiolski et al., 1985; Mayne, 2006)

Compare w/ other sands

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Effects of pore pressure on qT

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Specimens by mist pluviation (MP)

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Compressed air

Pluviator

Unit: mm

Nozzle

Dry sand

(Huang et al., 2015)

Comparison of CTX test results

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(Huang et al., 2015)

Calibration chamber specimens by MP method

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MP chamber specimen

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UNDISTURBED SAMPLING

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Laval sampling

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Dimensions in mm

273

218

60

0

12

44

302

Section A-A

Rod B.Q. wire line

drilling rod

Collar

Locking pin

Internal guide

Overcoring tube

Internal guide

Steel teeth and cuttersHead valve

External guide

Sampling tube

Carbon steel ZW pipe

Steel teeth and cutters

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(La Rochelle et al., 1981)

Laval sampling & uni-directional freezinig

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(Konrad et al., 1995)

Expelled water & temp. vs time

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Vs1 profiles at Yuan Lin site

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Comparison of CTX results

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Gel-push sampler

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收 收 收

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Shutter

Gel chamber

Water chamber

Water injection

(Lee et al., 2006)

Sample trimming＆holding

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Comparison of Vs measurements

• Vs from field SCPTu

• Vs from bender element

tests in gel-push triaxial

test specimens

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INFERENCE OF CRR

FROM 𝑞𝑇 AND 𝑉𝑠

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qT1N –CRR correlation

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Slow CPT and pore pressure dissipation tests at Yuan Lin site

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FC, %

4389

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(Huang et al., 2009)

Comparison of qT setup

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Comparison of t50

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CRR-Vs1 correlation

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SUBSIDENCE IN M/S SOILS

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Field monitoring site

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Subsidence & GWT records

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Integrated PWP+ subsidence Monitoring

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Plastic pipew/ ribs

Corrugated pipe

Optical fiber FBG extensometer

Installation in a 100m deep borehole

Friction ring

Extensometer

Piezometer

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24 hour record of 8/28/1247

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sv = constant, repeated PWP fluctuation

±

±

±

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Concluding remarks

•Post-consolidation void ratio ec

•Use of e*

•Undisturbed sampling is relatively practical

•Drainage or fines content adjustment?

•Drainage verification in CPT

•Effects of repeated PWP fluctuations

•Effects of fines may be soil dependent?

•For M/S soils with FC > 50% ???

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Thank you