Lime soil subbase construction technology standard

2. Standard for the construction technology of limestone subbase

2.1 Applicability

This standard is applicable to the construction of urban road subbase in collapsible loess area in Shaanxi, and the construction of other road subbase can be implemented with reference.

2.2 Normative references

CJJ1 Code for Construction and Quality Acceptance of Urban Road Engineering

CJJ44 Code for Construction and Quality Acceptance of Urban Road Subgrade Engineering

CJJ194 Code for Design of Subgrade of Urban Road

JTG 034 "Technical Code for Construction of Highway Pavement Base Layer"

2.3 Terminology

2.3.1基层base course

A structural layer located below the surface level. It mainly bears the vehicle load transferred by the surface layer and distributes the load to the cushion or soil foundation. When the base layer is divided into multiple layers, the bottom layer is called the subbase.

2.3.2石灰稳定土lime soil

The slaked lime powder or quicklime powder is mixed into various crushed or originally loose soils, and the mixture obtained after mixing, compacting and curing.

2.4 Preparation for construction

I. Technical Preparation

2.4.1 carefully study the construction drawings, familiar with the construction site, and at the same time familiar with the road lime soil subbase various construction specifications and construction technology, understand the lime soil subbase construction points and quality inspection standards.

2.4.2 Before construction, the technical person in charge of the project shall make a detailed safety technical disclosure to the construction personnel, and the construction personnel shall make a detailed safety technical disclosure to the team operators, and implement the construction points that should be paid attention to in each link.

2.4.3 Raw material test

1. Check the content of lime calcium oxide and magnesium oxide to determine the lime grade.

2. Determine the soil extraction site and perform the following tests on the representative soil samples in the material yard: particle analysis, liquid limit and plasticity index.

2.4.4 According to the requirements of the design documents, determine the best water content and maximum dry density of lime soil according to the lime content.

2.4.5 Before construction, the construction of the 100~200m experimental section is carried out to determine the combination of machinery and equipment, the compaction coefficient and the construction method.

II. Material Preparation

2.4.6 Raw materials shall comply with the following requirements:

1. The soil shall meet the following requirements:

1) It is advisable to use sub-clay and clay with a plasticity index of 10~15. Sandy soils with a plasticity index greater than 4 can also be used.

2) The organic matter content in the soil should be less than 10%.

3) The graded gravel, sand or miscellaneous fill of the old road should be tested first. The maximum particle size of graded gravel, sand and other materials should not exceed 0.6 times the thickness of the layer, and should not be greater than 10cm.

2 Lime should meet the following requirements:

1) It is advisable to use 1~3 grade new ash, and the technical indicators of lime should comply with the provisions of Table 2.4.6-1.

Table 2.4.6-1 Lime technical indicators

category project

Calcareous quicklime

Magnesia quicklime

Calcareous slaked lime

Magnesia slaked lime

Grade

Ⅰ

Ⅱ

Ⅲ

Ⅰ

Ⅱ

Ⅲ

Ⅰ

Ⅱ

Ⅲ

Ⅰ

Ⅱ

Ⅲ

Available calcium plus magnesium oxide content (%)

≥85

≥80

≥70

≥80

≥75

≥65

≥65

≥60

≥55

≥60

≥55

≥50

Sieve residue of 5mm round hole sieve with undigested residue content (%)

≤7

≤11

≤17

≤10

≤14

≤20

—

—

—

—

—

—

Water content (%)

—

—

—

—

—

—

≤4

≤4

≤4

≤4

≤4

≤4

Fineness

0.71mm方孔筛的筛余（%）

—

—

—

—

—

—

≤1

≤1

≤1

≤1

0.125mm方孔筛的筛余（%）

—

—

—

—

—

—

≤13

≤20

—

≤13

≤20

—

Classification boundary of magnecite lime, magnesium oxide content (%)

≤5

＞5

≤4

＞4

Note: Quicklime with the sum of silicon, aluminum, and magnesium oxide content greater than 5%, the effective calcium plus magnesium oxide content index, I. equal ≥ 75%, II. equal ≥ 70%, III. equal ≥ 60%;

2) Finely ground quicklime, can be used directly without digestion; block ash should be completed 2~3d before use, undigested quicklime blocks should be screened out, the particle size of the digested lime shall not be greater than 10mm.

3) The digested lime that has been stored for a long time or after the rainy period should be tested first, and whether it can be used and used according to the content of active oxides should be determined.

3. The water shall comply with the provisions of the current national standard "Concrete Water Standard" JGJ 63. It is advisable to use drinking water and clean neutral water without impurities such as oil, and the PH value should be 6~8.

III. Preparation of construction facilities

2.4.7 Construction machinery: pavers, excavators, bulldozers, graders, vibratory rollers, three-wheel rollers, loaders, dump trucks, water wheels, mixers, pickaxes, shovels, etc.

2.4.8 Measurement and experimental equipment

1. Measuring equipment: GPS, total station, theodolite, level.

2. Experimental equipment: three-meter ruler, flatness meter, ring knife, ash dose test equipment, steel tape measure, etc.

IV. Preparation of operating conditions

2.4.11 The roadbed has passed the acceptance, its surface should be smooth and solid, compaction, flatness, longitudinal elevation, center line deviation, width, cross slope, slope and other indicators must comply with the relevant regulations.

1. Clean the roadbed before construction and sprinkle water appropriately.

2. Restore the middle line of the road in the construction section, with a pile every 20m in the straight section and a pile every 10m in the flat curve.

2.5 Construction technology

I. Construction process

2.5.1 Plant mixing method construction process

II. Operational Process

2.5.2 Measurement and pay-off: measure and release the center line of the road, set up a pile every 10 meters, and release 0.3m-0.5m control piles outside the edge line on both sides.

2.5.3 The construction process of the plant mixing method is as follows:

1. Lime soil mixing: After the raw materials enter the site for inspection, the lime dose is increased by 0.5% compared with the dose determined by the laboratory test, and when the raw materials change, the ash soil mix must be re-adjusted. The water content of the limestone soil should be considered according to the weather conditions at the time, sunny and windy weather is generally slightly larger by 1% ~ 2%, and the water content and ash dose of the limestone should be monitored in time, and the inspection can only be allowed to go out after passing the inspection.

2. Lime soil transportation: the use of vehicles with covering devices for transportation, according to the demand, distance and production capacity of the reasonable configuration of the number of vehicles, transport vehicles according to the established route in and out of the site, prohibiting sharp braking, sharp turns, U-turns, speeding.

3. The paving requirements for limestone soil are as follows:

1) The roadbed should be moist before paving. According to the design thickness, calculate the number of imaginary squares of ash per linear meter, set up a square grid on the site according to the load capacity of each vehicle, and command the unloading. The discharge pile should be arranged according to the plum pile shape to facilitate paving operations.

2) When the grader is leveled, a special person will follow the machine for elevation measurement.

3) When using a paver for paving, the elevation point should be arranged in advance, and the elevation should be controlled by a ruler rod or wire rope.

4) The coefficient of ash paving is determined by test.

5) When paving lime soil mixed with coarse aggregate, the coarse aggregate should be uniform.

4. When paving, use excavators, bulldozers, and loaders to push the flat, in the process of "rather high than low" principle, when the elevation of the large surface is basically leveled, the grader is used to level it.

5. After the initial leveling with the grader, the quality inspector will detect the water content in time, and adjust the water content by sprinkling or drying if necessary.

6 graders for fine leveling 1~2 times, and timely detection of elevation, cross slope, flatness, the local elevation of slightly lower ash surface is strictly forbidden to directly take a thin layer of patchwork, should be used manually or mechanically to loosen about 100mm and then make up.

7. Rolling shall comply with the following provisions:

1) The paved limestone soil should be rolled into a day, and the rolling principle is "slow and fast", "light and heavy", "low and high" in principle.

2) The water content during rolling should be within the range of ±2% of the optimal water content.

3) Straight line and non-super-high flat curve sections, from both shoulders to the center of the road rolling, set super-high flat curves, from the inner shoulder to the outer shoulder to roll. When rolling, it should overlap 200~300mm, and the rear wheel must exceed the seam of two sections.

4) The rolling speed of the roller should be 1.5~1.7km/h for the first two times, and 2~2.5km/h should be used after the initial stabilization of the ash. First, the vibrating roller is used to roll 3~6, and finally the three-drum roller is used for static pressure 2~3 times, and finally the wheel trace marks are eliminated, so that the surface can achieve solid, smooth, no peeling, no waves and other undesirable phenomena, and the compaction degree meets the specification or design requirements.

5) When the work is interrupted or sectional construction, 300~500mm should be reserved at the lime soil stubble to not be compacted, and the newly paved lime soil should be connected, and the water should be sprinkled and moistened when rolling. Layered continuous construction should be completed within 24h.

7. The following provisions shall be complied with:

1) After the limestone soil survives, it should be sprinkled with water, covered and cured, and kept moist until the construction of the superstructure, and the health period should not be less than 7 days.

2) The maintenance period of limestone soil should be closed to traffic.

2.5.4 Longitudinal and transverse joints should be provided with straight stubble. The seams shall comply with the following requirements:

1. Longitudinal stubble joints should be avoided, and when longitudinal stubble is required, longitudinal joints should be located at the center line of the road.

2. The joints should be made into a stepped shape, and the width of the steps should not be less than 1/2 layer thick.

3 Transverse seams should be minimized.

III. Seasonal Construction

2.5.5 The construction in the rainy season shall comply with the following provisions:

1. Avoid the construction of limestone subbase in the rainy season.

2. The paving length should be shortened in the rainy season, and the paved limestone will survive on the same day.

3. The spare lime and soil mounds should be piled into large piles, covered with plastic sheets, etc., and drainage ditches should be dug around to prevent excessive moisture of the aggregates transported to the road, and measures should be taken to protect the lime from rain.

2.5.6 Winter construction shall comply with the following provisions:

1. The limestone subbase should not be constructed in winter, and the daily minimum temperature during the construction period should be above 5 °C.

2. The limestone base should be completed one month to one and a half months before the arrival of the first heavy freezing (-3~-5 °C).

2.6 Quality Standards

2.6.1 The master control project shall comply with the following provisions

1. The quality inspection of soil raw materials shall meet the following requirements:

1) shall comply with the provisions of paragraph 1 of Article 2.4.6 of this Code.

2) Lime shall comply with the provisions of paragraph 2 of Article 2.4.6 of this specification.

3) The water shall comply with the provisions of paragraph 3 of Article 2.4.6 of this Code.

Inspection quantity: according to different materials into the factory batch, each batch inspection 1 time.

Inspection method: check the inspection report and re-inspection.

2. The degree of compaction should meet the following requirements:

1) The subbase of urban expressways and trunk roads is greater than or equal to 95%.

2) The subbase of other grades of roads is greater than or equal to 93%.

Number of inspections: 1 point per 1000 square meters, each compacted layer.

Inspection method: check the inspection report (sand filling method or irrigation method).

3 subbase specimens for 7 unconfined compressive strength, should meet the design requirements.

Number of inspections: 1 group per 2000㎡ (6 blocks).

Test method: on-site sampling test.

2.6.1 General items shall comply with the following provisions

1. The surface should be smooth and solid, without the concentration of thick and fine aggregates, without obvious wheel tracks, shifts, cracks, smooth stubble, and no skin and bulk materials.

2. The allowable deviation of the subbase shall be in accordance with the provisions of Table 2.6.1-1.

Table 2.6.1-1 Allowable deviation of lime-stabilized soil base and subbase

project	Allowable deviations	Frequency of inspection	Test Method
range	score
Midline Deviation (mm)	≤20	100m	1	Measured with a theodolite
Longitudinal elevation (mm)	±20	20m	1	Measure with a level
Flatness （mm）	≤15	20m	Road width (m)	＜9	1	Use a 3m ruler and feeler gauge to measure two feet in a row, and take the larger value
9～15	2
＞15	3
Width (mm)	Not less than the design provision +B	40m	1	Measure with a steel ruler
Hengpo	± 0.3% and no reverse slope	20m	Road width (m)	＜9	2	Measure with a level
9～15	4
＞15	6
Thickness (mm)	±10	1000㎡	1	Measure with a steel ruler

2.6.3 Other items shall comply with the following requirements:

1. The stubble is smooth and stable, and the formed base shall not have the phenomenon of "spring".

2. In order to prevent the uneven mixing of lime soil, the mixing time of lime soil should be extended, and the water content should be strictly controlled.

3. In order to prevent the shrinkage and cracking of the gray soil base, the health management should be strengthened, and the upper layer construction should be carried out as soon as possible.

2.7 Product Protection

2.7.1 The construction site is closed, and non-construction personnel and vehicles are not allowed to enter the maintenance section.

2.7.2 It is strictly forbidden for rollers and heavy vehicles to drive on the road section that has survived, and sprinkler trucks and other vehicles are not allowed to make a U-turn or brake sharply on the road surface.

2.7.3 Arrange a special person to be responsible for the basic health of the lime soil, sprinkling, moisturizing, and maintaining health for more than 7 days. Keep the surface of the ash base in a damp state at all times.

2.7.4 Protect the elevation control points and line control piles, and restore the damaged pile points in time.

2.8 Occupational Health and Safety Requirements

2.8.1 During the construction, a safety technology disclosure system must be established, and relevant safety technology education and training must be carried out for operators. Before the operation, the competent construction technician must make a detailed safety technical disclosure to the operator and form a document.

2.8.2 The construction site is closed and fenced, and non-construction personnel are prohibited from entering.

2.8.3 A full-time safety officer should be set up on site to be responsible for safety inspection and supervision at the construction site.

2.8.4 Construction personnel must wear corresponding safety protection equipment and labor protection supplies.

2.8.5 It is strictly forbidden for operators to operate in violation of regulations, and management personnel to command in violation of regulations.

2.8.6 Construction electricity should be carried out in strict accordance with the requirements of the "Technical Specifications for Temporary Electricity Safety on the Construction Site" (JGJ46), and in accordance with the requirements of "one machine, one gate, one box, one leakage, one grounding" and "three-phase five-wire" system.

2.8.7 Before construction and during the construction process of each team, check whether the power supply and electrical appliances are safe and normal to prevent fire accidents.

2.8.8 manpower and machine with earthwork operations, must be set up to command. During mechanical operation, it is strictly forbidden to cooperate with the operator in the range of mechanical operation and travel. When cooperating with personnel to work within the range of the machine, the machine must stop working.

2.8.9 Construction machinery should be well maintained daily to ensure the safe use of machinery.

2.8.10 mechanical operators must be certified to work, special personnel and special posts, it is strictly forbidden to drink and drive, fatigue driving.

2.8.11 It is forbidden to use vertical and frog tamping machines for base compaction.

2.8.12 Warning and traffic signs should be set up for the construction of sidewalks and bridges, and special personnel should be set up to maintain and direct traffic when necessary. Construction vehicles must comply with road traffic regulations.

2.9 Green construction requirements

2.9.1 Maintain the fence at the construction site every day to ensure that the fence is clean and tidy.

2.9.2 construction garbage should be transported out in a timely manner, and the garbage and bare ground that cannot be removed in time on the site should be covered with dust nets or temporarily greened.

2.9.3 Adopt low-noise mechanical equipment, and try to avoid construction at night, early in the morning, and during the noon break. And special isolation is carried out on noisy equipment (such as generators) to prevent noise from disturbing the people.

2.9.4 Formulate sprinkler and dust prevention measures, carry out daily maintenance of construction sidewalks, and sprinkle water to moisturize and suppress dust.

2.9.5 at the entrance and exit of the construction site to set up vehicle washing equipment, can not be set up and approved by the relevant departments, must be set up temporary vehicle cleaning equipment.

2.10 Quality Records

2.10.1 Product certificate.

2.10.2 Chemical test report (lime).

2.10.3 Lime test report.

2.10.4 Witness Records

2.10.5 Joint test report of soil liquid-plastic limit.

2.10.6 materials and components into the site inspection records

2.10.7 Test report of maximum dry density and optimal water content of soil

2.10.8 Inorganic mixture ash dosage standard curve test report.

2.10.9 Elevation Survey Review Record.

2.10.10 Soil compaction (ring knife method) test record.

2.10.11 Inorganic mixture ash dosage inspection record.

2.10.12 Concealed acceptance inspection records.

2.10.13 inspection batch quality acceptance records.

2.10.13 Test report of unconfined compressive strength of road base mixture.

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