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METHOD STATEMENT GMS Ben Luc Long Thanh Expressway Project Package A5 Civil Works Km 32+450 to Km 35+900 DEEP MIXING METHOD (SOIL CEMENT COLUMN) AND SAND CEMENT STABILIZED MAT TABLE OF CONTENTS I DEEP[.]

DEEP MIXING METHOD (SOIL CEMENT COLUMN) AND SAND

CEMENT STABILIZED MAT

TABLE OF CONTENTS

I DEEP MIXING METHOD (SOIL CEMENT COLUMN)

II SAND CEMENT STABILIZED MAT

I DEEP MIXING METHOD (SOIL CEMENT COLUMN)

1 Scope of works

Deep mixing or the soil cement column method is the process of improving properties

of existing soils, which are essentially soft clay, by mixing stabilizing material: cement with existing soil Soil cement columns can be installed by mechanical mixing method

by means of wet mixing (slurry type) The mixing of stabilizing material to the existing soils at various levels shall create soil columns with a predetermined strength, depth and diameter

Ground improvement includes constructing deep soil mixing columns, disposing/delivering, transporting and treating the entire disposal soil, creating block and compressing soil, monitoring the settling part of soil

Prior to ground improvement, the Contractor is required to receive a written approval

by the Engineer regarding equipment and materials to be used and implementation methods for the work

2 References and standards

Based on technical specifications – Package A5

TCXDVN 385: 2006 “Stabilization of Soft Soil by the Soil Cement Column Method”

3 Requirements of materials

Stabilizing material shall be cement at the quantities given in the table below:

Stabilizing material Quantity per cubic meter of existing soil (kg/m 3 )

Cement shall material Cement in accordance with TCVN 5439-2004 The material shall be stored in containers to prevent damage from moisture before application Water shall be in accordance with the requirements for water for concrete as specified

in section - Concrete and Concrete Structure

4 Design of pilot mix

The contractor shall perform soil investigation and trial mix tests to determine the soil profile and he appropriate cement content for the soil cement column in accordance with requirements stated in the following sections

At a ratio of two (2%) of cement soil columns improved by deep mixing method, a set

of undisturbed soil samples shall be collected at depths of 3, 6, 9, 12, 15m and 18m through rotary wash boring, and the following laboratory test shall be performed on each sample

sieve analysis for all samples

- Unconfined compression test on all samples.

For the soil collected from depths of 3, 6, 9, 12, 15 and 18m, trial mixes shall be prepared to determine the unconfined compressive strength and modulus of the mixture of existing clay with cement through unconfined compression test The test shall be performed with at least 15 samples for each mixture proportion as given in the table below Unconfined compression tests shall be made when the test samples are cured at 7 days, 14 days and 28 days At least three samples shall be tested for each different curing time If volume of sample soil is insufficient to conduct the above trial mix, additional borehole shall be installed nearby area

Materials Quantities (kg/m 3 of existing soil)

The water cement ratio (W/C) shall range between 0,8 and 1,0 the contractor, based on the results from the trials, shall determine a ratio that with be subject to the Engineer’s approval The design unconfined compressive strength from unconfined compression test at 28 days (Qd) shall be as shown on the Drawings

target strength to determine a mix proportion) = 3 x Qf

However, the actual quantity of stabilizing material to be used in the field shall not be less than minimum values shown in the table above

Unconfined compression test shall be made in accordance with ASTM D 2166-85 The test sample shall have minimum diameter of 50 mm and a height of 2 times the diameter The casing shall be the type that can be removed without disturbing of the sample The sample shall be cured by covering with plastic sheet to prevent dehydration of water

In the mixture test, the stabilizing material shall be of the same type and characteristics as to be used in the field as shown below:

Field Soil Cement Column Mixture Test

proportion to be used in the field with existing clay The report shall describe the mixing method, storage and curing procedure and the test results The report shall also include:

Tables summarizing unconfined compressive strength, modulus and unit weight of mixed samples at different curing times

Graph showing unconfined compressive strength of mixture against quantity of stabilizing material and graph showing unconfined compressive strength against curing time

5 Technology line

Based on geological conditions, the route nature of the work, the Contractor shall select foundation treatment solutions by combination between mechanical and manpower construction of wet and deep mixing technology, ensuring schedule, quality and the highest effectiveness of the work

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Layout of construction machinery for cement deep mixing construction

The construction technique of soil cement piles (or soil cement column, soil cement pier) is done by drilling, deep mixing, in wet state Use driller and dedicated equipment (drilling rod, drilling augers, etc.) to drill into soil with drilling diameter and depth in accordance with technical design During drilling process, soil is not taken out of drilling hole, but its structure is broken on spot The soil is crushed by wings of auger, equally mixed with cement binder by jet pumping equipment into the soil (by air compressed pressure for dry compound or high-pressure pumping mortar for wet binder)

Based on the actual situation on site, the contractor will arrange for one machine pilot column construction at locations designated by Engineers Pilot column construction with different cement content in accordance with the design requirements were introduced

After receiving the test results, and Engineer approved construction on a large-scale, the contractor will also arrange 03 machines for large scale construction and other ancillary equipment

6 Pilot soil cement column

After obtaining appropriate content of cement from testing results, before constructing soil cement columns, the Contractor shall construct a set of three preliminary test columns (trial columns are non-working piles) for verification Tow test columns shall have a diameter of 0,7m and a depth of 20m and one test column shall have a diameter

of 0,7 m and a depth of 10m to demonstrate ability of machines, tools and equipment Location of pilot soil cement columns are instructed by the Engineer

Any pile which fails the above test shall be replaced by one or more piles by the Contractor or as directed by the Engineer and an additional test shall be conducted for the replaced pile If, in the opinion of the Engineer, it is impractical or inadvisable to install substitute piles in place of a failed pile, the Contractor shall submit proposals to rectify the defect The proposal is subject to the acceptance of the Engineer

Construction sequence of pilot cement deep mixing:

mixing blades are rotating to desegregate and disturb the soil to reduce the strength of the ground so as to make the mixing tools penetrate by their self-weight The binder slurry is injected during penetration and mixed with the disaggregated soil When the blade reaches the elevation at the bottom of column, stop but mixing blade is still rotated at least 2 minutes, ensuring the bottom of the pile was mixed thoroughly and uniformly After that, reverse rotation drill and withdraw (spray and cover with cement) to elevation at the top of column The process of drilling and injection of cement slurry to be an operational cycle to make sure soil and cement grout mixed together and the full amount cement slurry

move to the next

Experiment on pilot cement deep mixing column:

entire test column (preliminary test column of 10m length) from the ground

The column shall be inspected for size, shape and uniformity of the stabilization along the entire length of the column The Contactor shall submit the pulling method to the Engineer for approval before operation

using tension pile or ground anchorage system

including diameter and depth of column must be determined However, in case that the test for unconfined compressive strengths cannot be satisfactorily attained, pile load test may be required to determine the capacity of column The pile load test of column shall be conducted at 28 days of curing time

shall be made a interval not more than 1m with age of 28 days old having

a value of no less than Qd If the requirements are not met, Judgment shall

be made by the Engineer

column to determine the unconfined compressive strength of time 7 days,

14 days and 28 days old Reserve the fourth cylinder and test at 56 days if the 28 day result does not meet the required strength

tube D75mm The drill samples were then preserved original conditions and the moisture must be preserved until the experiment in the maintenance closet specialized in the laboratory

samples is twice the a diameter of the sample Sample surface before the experiment to be flattened by a thin plaster layer

to make sure implementation within the column section After taking core drilling is completed, the Contractor shall fill the drilled holes with cement slurry

completed column improved by deep mixing method The column shall submit the proposed method on the exposure of column top for inspection

to the Engineer for approval before operation

- Pile load test on column

soil cement column of age over 28 days applying 1.5 times of deign working load shown in the drawing The pile top shall be properly prepared for the test The method of testing shall be approved by the engineer prior to execution of the work Pile load test shall be performed with capacity of not less than 31 ton for 0.70m diameter cement column when the maximum settlement at pile head shall be less than 10% of column diameter

7 Construction method of large scale construction

Construction steps

drawing To identify pile’s center points, use a total station to get intersection of two theodolites Prior to identifying pile’s center points on site, location of coordinates have to be identified on paper After identifying, other measures are applied to check again to avoid errors

locations A, A1, B, B1 as shown in the chart and marked by four steel sticks The purpose of applying these reference points is to pinpoint center points of the piles when lowering drilling auger These points have to be protected and maintained until lowering and checking stability of drilling auger

+

Determine the location of column

geometric dimensions and other technical specifications

1.0m/minute and loose the soil in the column, pier

Center point

 Drilling and grouting slurry to design elevation: During the penetration, the mixing blades are rotating to disaggregate and disturb the soil to reduce the strength of the ground so as to make the mixing tools penetrate

by their self-weight The binder slurry is injected during penetration and mixed with the disaggregated soil

least 2 minutes, ensuring the bottom of the pile was mixed thoroughly and uniformly After that, turn drilling auger backwards and take out drilling rod then pump mortar in Taking out drilling rod needs to be combined with mixing and compacting mortar inside the pile thanks to structure of drilling auger Speed to take out drilling auger tb: 0.5m-1.0m/minute The process of drilling and injection of cement slurry to be an operational cycle to make sure soil and cement grout mixed together and the full amount cement slurry

finished, stop all jet pumping equipment Start cleaning up mortar scattering around the drilling hole and move driller to the new location of the pile

P

8 Frequency of testing

The number of column to be tested shall be as follows:

sample for each 600m3 of soil / binder production with a minimum of one sample per day Each sample shall be of sufficient size to produce four (4) specimens for testing The specimens shall be cylindrical with a nominal diameter of 75mm and length 150mm Test one cylinder for unconfined compressive strength at 7 days, one at 14 days, and one at 28 days Reserve the fourth cylinder and test at 56 days if the 28 day result does not meet the required strength Determine unit weight on each cylinder as part of the unconfined compressive strength testing process

shall be performed at a ratio of two (2)% of total number of column improved

by deep mixing method

– out test shall be conducted one preliminary test column (non-working column prior to the commencement of working columns)

conducted at a ration of one (1)% of total number of column improved by deep mixing method If the Contractor changes a path of his construction method, additional test shall be conducted

directed by the Engineer

nd with the same equipment as to be for the working piles

9 Allowable deviation

The Contractor shall construct each column to the depth, spacing, vertical alignment, location and with unconfined compressive strength as specified in the Drawing and the Specification In such case that and column constructed with smaller diameter or specified strength, the Engineer shall have the right to order construction of additional column or reconstruct the defective column at the expense of the Contractor

Allowable deviation shall be as follows:

more than 100 mm in any direction

Unconfined compressive strength shall not be less than Qd kPa

II SAND CEMENT STABILIZED MAT

This work shall consist of a stabilized mat composed of soil mixed with Portland cement and water, constructed in multi-layers on a prepared and accepted subgrade in accordance with these Specifications and the lines, levels, grades, dimensions and cross sections shown on the Drawings and subject to approval by the Engineer

1 Materials

1.1 Soil

Soil shall be sand with a fines content of less than 25% The soil shall be free from contamination by topsoil, vegetation and other organic matter, and any deleterious materials Salt and gypsum content shall be less than 2% Organic content shall be less than 2%

1.2 Cement

Cement shall conform to the requirements for Cement in accordance with TCVN 5439-1991 The materials shall be stored in containers to prevent damage from moisture before application

1.3 Water

Water shall be clear and free from harmful matter, and shall conform to TCXDVN-302-2004 Any indication of unsoundness, marked change in time of setting or a reduction of more than 10% in strength of mortar mixtures made with distilled water shall be cause for rejection

2 Construction method

2.1 Mix design

The Contractors submit to the Engineer for his approval samples of materials to be used in the Mat together with the Contractor’s Proposed mix design The Proportion of cement and moisture content required with be determined by means of cylinders tests but in the cement content shall not be less than 3% by dry weight Cylinders tests with

be carried out in accordance with AASHTO test method T134 for cement stabilized mixes subject to modification to use he compaction effort defined in AASHTO test method T180 The mix will be so selected that the strength shall be at least equal o the design strength as indicated in this specification section or as shown on the Drawings The design compressive strength (Qd) of the cement stabilized mat shall be an unconfined compressive strength of not less than 0.2Mpa at 28 days of curing tested in accordance with AASHTO test method T208