2. Construction method

2.1 Prepare the lower bearing layer

(1) The surface of the lower bearing layer of lime-stabilized soil is smooth, solid, and free of holes. Elevation and crown meet design and specification requirements.

(2) Use vibratory road rolling to conduct rolling inspection of the roadbed. During the rolling process, if the soil is found to be too dry and the surface layer is loose, sprinkle water appropriately before loading the soil; dig out 10cm of existing holes or local potholes and then replace them with lime soil and compact them.

(3) Repair drain channels on the roadbed slopes on both sides of the construction section.

2.2 Construction stakeout

(1) Restore the center line on the soil foundation, stake out the middle piles at a spacing of 10m, and set indicator piles 0.5m outside the edges of the shoulders on both sides, and stake out the second soil at the same time sideline.

(2) Use red reflective paper on the indicator piles on both sides to mark the design height of the edge of the lime-stabilized soil roof.

2.3 Preparing materials and paving soil

2.3.1 Preparing materials:

(1) Fly ash is transported to the roadbed near the construction section 3 days in advance. The fly ash transported to the site must contain enough moisture to prevent dust. When it is dry and windy, water should be sprinkled on the surface of the pile to keep it moist. The fly ash stacked in batches should be covered with plastic paper to avoid excessive moisture from rain; the lime soil layer should be transported directly to the construction site after the lime soil layer is paved; the soil for lime soil should be transported from the soil yard to the construction site, and the soil should be excavated first in the soil yard. Trees, turf, silt and other impurities should be removed, and oversized particles in the soil should be screened out.

(2) Calculation of the quantity of lime soil aggregate:

Per square meter of lime soil aggregate:

Quantity of earth = length × width × thickness × maximum dry density × soil aggregate percentage × compaction degree/soil density × compaction degree.

Quantity of lime = length × width × thickness × maximum dry density × lime aggregate percentage × compaction degree/lime density.

Quantity of fly ash = length × width × thickness × maximum dry density × percentage of fly ash aggregate × compaction degree/density of loose fly ash.

(3) Sprinkle water on the roadbed before applying soil to make the surface moist, but it should not be too wet to cause mud.

When loading soil into trucks, control the quantity of materials in each truck to be basically equal, and prepare materials according to the calculated earthwork volume and unloading distance to avoid insufficient or excessive materials in some road sections.

(4) In order to facilitate the maintenance of the lime soil roadbed, the paving of lime-stabilized soil will begin after the subgrade handover and acceptance is completed. The paved soil must include the width of the road shoulder, and the total paving width is 30.18m.

2.3.2 Paving soil

(1) Before paving, determine the location of three sections and measure the top elevation of the lower bearing layer, the elevation after spreading soil and the elevation after rolling Elevation, check the thickness of the loose soil layer to meet the expected requirements. Calculate the paving area of ??each vehicle, then use white ash to make gray line squares on the completed and inspected roadbed, and unload the soil neatly into the squares. When the bulldozer is placing soil, use a level gauge to measure and set an elevation control point, and bulldoze and release the soil based on the height of the control point. After the bulldozer completes rough leveling and pressure relief, the elevation is measured. A grader is used to level the road to the specified elevation and crown, and the compaction and moisture content are tested. The surface of the finely leveled paved soil should be smooth and free of potholes, and the road crown elevation should meet the specified requirements.

(2) The soil paving operation should be completed the day before lime and fly ash are paved. The paving length is controlled according to the daily progress requirements, so that the addition of fly ash and lime, mixing, and rolling can be completed the next day.

(3) During the spreading process, soil clods, oversized particles and other debris should be removed.

(4) If there are more clods in the soil, crush it with a mixer.

2.4 Sprinkle water and stuffing material

According to the detected moisture content, if the moisture content of the leveled soil is too small, sprinkle water stuffing material on the soil layer 12 hours in advance [supplement the moisture content] V=ρ*(w0 -w)/(1-w) In the formula: ρ-density of soil before rolling (kg/m3); w-natural moisture content of soil; w0-optimal moisture content of soil]. Sprinkle water evenly to prevent local excess water. It is strictly forbidden for sprinklers to stop or turn around in the watering section.

2.5 Spread the center line, side lines and grid lines

Before paving fly ash and lime, use white ash to stake out the center line, side lines and grid lines according to the instructions.

2.6 Paving lime and fly ash

(1) Paving lime and fly ash: first spread fly ash, mix and stabilize the pressure, then spread lime, lime Increase dose by 1%.

(2) Based on the calculated amount of fly ash loosened per linear meter, use 3cm × 3cm angle steel to make a trapezoidal yard square, and square the fly ash at the midline of the half-width soil. Fly ash is transported to the construction section by car, and the fly ash is coded into trapezoidal gray strips according to the amount of ash per linear meter. According to actual construction needs, the fly ash is coded into two gray strips. The gray strips must be straight. After supervision and acceptance, the fly ash shall be dispersed manually and evenly according to the required width. If the moisture content of the fly ash is small, water shall be sprinkled appropriately.

(3) After the fly ash is mixed, leveled and rolled, a grid line is spread, and a small transport truck is used to transport the bagged lime to the construction site. Calculate the amount per square meter according to the grid area. The required amount of lime is placed in the grid. After the placement is completed and the supervision engineer completes the quantity acceptance, they will be spread evenly within the square manually.

2.7 Mixing and sprinkling

(1) Use a stabilized soil mixer to mix. The mixing is carried out in two steps. After the fly ash is laid, the lime-soil mixer performs the first step. Mix once.

After the first mixing is completed, the lime is laid after leveling the tractor and stabilizing the pressure. After the laying is completed, the second mixing is carried out. Check the moisture content of the lime before mixing. If the moisture content loss is too large, sprinkle an appropriate amount of water. The mixer should be mixed closely behind the sprinkler truck. The mixing depth reaches the bottom of the stable layer and penetrates into the underlying layer by about 5-10mm. Designate a dedicated person to follow the mixer, check the mixing depth at any time and cooperate with the mixer operator to adjust the mixing depth to avoid interlayering of plain soil. When the moisture content is too high and the stabilized soil mixer slips, mix it with rotary pear first. The number of mixing passes is determined based on the uniformity and moisture content of the aggregate.

(2) After mixing, check the moisture content of the mixture. The moisture content should be about 1% greater than the optimal moisture content. If the water content is low, use a nozzle-type sprinkler truck to spray water evenly on the mixed mixture. The watering distance should be longer. The starting point of the water truck and the U-turn point at the other end should be more than 2m beyond the mixing section. The sprinkler truck should not turn around or stop on the road section where mixing is being carried out or where mixing is planned for the day, and excessive local water volume should be prevented.

(3) During the mixing process, the mixing depth should be checked in time at 10cm of the mixing overlap, and checked every 5 meters. The sign that the mixing is completed is that the mixture has a consistent color, no gray strips, ash balls, and flower surfaces, no "nests" or "bands" of thick and fine particles, and the moisture content is appropriate and uniform. When uneven mixing or interlayering occurs, promptly notify the mixer to return and re-mix

(4) After mixing is completed and local uneven parts are manually leveled, the tractor should stabilize the pressure. When stabilizing the pressure, pay attention to overlapping to prevent leakage. pressure.

2.8 Shaping

(1) After setting out the center line, measure and set the elevation control point reinforcement according to the loose paving coefficient to set the grader leveling datum plane. The grader will level the road from both sides toward the center of the road. On super-high flat curve sections, the grader will level the road from the inside to the outside. If necessary, go back and scrape again. The excess dust during scraping shall not be discarded on the slope. If the water content of the surface layer is low during the last leveling, use a sprinkler to spray water once to facilitate rolling and molding. At the same time, the leveling machine will work with the soil to ensure that it is better to scrape than patch.

(2) For local low-lying areas, use a tooth rake to loosen the surface layer more than 5cm, and use freshly mixed two-ash grade aggregate to make it smooth.

(3) Each reshaping must be carried out according to the specified slope and road crown, and special attention should be paid to the smoothness and smoothness of the joints.

(4) During the shaping process, no vehicles must be allowed to pass.

2.9 Rolling

(1) Rolling combination: a combination of vibratory roller, three-wheel roller and rubber tire roller.

(2) The rolling sequence and number of passes: first use a vibratory roller for static pressure, then use a vibratory roller for low vibration and 2 times for high vibration, then use a three-wheel roller for static pressure 2 times, and finally Rubber tire roller 2 times. When rolling from both sides of the road shoulder to the center of the road, the rolling process should be driven straight and at low speed, with an overlap of 1/2 wheel width. The rear wheels must exceed the joint of the two sections. When the rear wheels cover the full width of the road, That’s one pass (press 2 more times on both sides). The rolling speed of the road roller is preferably 1.5~1.7km/h for the first two passes, and 2.0~2.5km/h thereafter. The compaction degree should be detected in time during rolling, and the rolling plan should be adjusted in a timely manner according to the growth situation. The dirt shoulders are rolled together with the sub-base. The rolling work must be completed continuously without stopping in the middle. .

(3) During the rolling process of lime soil, it is strictly prohibited for the roller to turn around or brake suddenly on the completed or ongoing road section to ensure that the surface is not damaged.

(4) For pulping that occurs during the rolling process, it should be opened in time to dry, and rolled to the specified compaction degree. Due to the high temperature, in order to prevent peeling, the rolling time should be controlled before 10 am or after 4 pm. If serious peeling is found, use a rotary tiller to mix in time and re-compact until the specified compaction degree.

(5) For rolling within 10 meters of the bridge head, the surface of the stabilized soil should always be kept moist during the rolling process.

(6) Treatment of joints and bridgeheads: Immediately cut off the ends of the rolled lime fly ash vertically where the mixing is uneven, the elevation error is large, or the flatness is not good. Keep joints straight and neat. At the connection point of the next working section, 2m shall be left for general soil and mixing, and shall be leveled according to the thickness of the loose paving during leveling.

2.10. Health care

Immediately after the rolling is completed The curing period should be no less than 7 days. If the construction of the next structural layer is not carried out after the 7-day curing period, curing should be continued to keep the surface of the lime soil moist at all times. Prevent the lime soil from losing strength due to lack of water. During the health care period, it is not allowed to dry and wet. During the health care period, traffic is closed except for sprinklers. Health care is carried out by sprinkling water and covering with non-woven geotextile.

2.11 Lime Soil Testing Project