Compared with the really new project of opening up roads and meeting water bridges in the mountains, there are still more small projects in the municipal area, right? For projects such as highway repair and maintenance, here is a guide to the on-site construction of embankment filling and trench excavation.
01 embankment reclamation construction
1.1 Construction of embankment filling
1.2 Substrate treatment
The base treatment before the embankment is filled can make the embankment filled in closely with the original surface, increase the bearing capacity, avoid the sliding of the embankment along the base, prevent the embankment from sinking caused by turf and tree root rot, ensure the quality of the embankment filling, and ensure that the embankment has sufficient strength and stability.
(1) When the horizontal slope of the ground of the dense and stable soil base is not steeper than 1:10, the embankment is built directly on the ground
(2) Local cross-slope, i> 1:5, when steep, weeding, debris, digging steps, step width is not less than 2m, height is not less than 1m, if i > 1:2.5, special treatment of the outer slope angle (foot guard)
(3) When the basal subsoil is humus soil, it must be removed manually or mechanically to replace the topsoil, and the general replacement thickness is not less than 30cm.
(4) Within the scope of embankment construction, pits, holes, base holes, etc. on the original ground should be backfilled and compacted.
(5) When the stability of the embankment is affected by surface water or groundwater within the base area of the embankment, measures such as interception and drainage should be taken, or permeable materials such as flakes, blocks or sand and gravel that are not easy to weather should be filled at the bottom of the embankment. When the route passes through paddy fields, ponds or depressions, according to the specific conditions such as stagnant water and silt layer, drainage and drainage, dredging and refilling (roads below the second level can be filled with gravel or stone and other pressures, squeezing silt, see the figure below), drying or ashing, etc.; when the soil is wet and soft and deep, it should be treated according to the soft soil foundation.
Basal treatment scheme for paddy field or pond lots:
1.3 Selection of filler materials
The Technical Specifications for the Construction of Highway Subgrades stipulates
(1) Embankment fillers shall not use silt, swamp soil, frozen soil, organic soil, turf-containing soil, domestic garbage, tree roots and soil containing decaying substances. When using saline soil, loess and expanded soil to fill the embankment, it should be selected after testing for the geological and hydrological environment.
(2) Soil with a liquid limit greater than 50% and a plasticity index greater than 26, as well as soil with a water content exceeding the specified, shall not be directly used as embankment filler. When it is necessary to apply, technical measures must be taken to meet the design requirements and can only be used after inspection.
(3) Steel slag, fly ash and other materials, can be used as embankment filler, other industrial waste residue should be used before use of the content test of harmful substances, to avoid harmful substances exceeding the standard, pollution of the environment.
(4) The planting soil after mashing can be used for the surface layer of the slope of the embankment.
The most stable fillers in the subgrade filler are mainly stony soil, sandy soil and steel slag, etc., these types of materials have a large coefficient of friction, should not be compressed, good water permeability, and their strength is affected by water is very small, which is the best material for filling embankments. The fillers with poor stability in the subgrade filler mainly include high-liquid limit clay, silty soil, etc., which should not be used as soil for highway subgrade.
Expressway and primary highway embankment fillers should be taken to the field to take soil samples and geotechnical tests, and the relevant indicators should meet the requirements of the following table.
Embankment fillers for Secondary and Secondary Highways are also selected as specified in the table below.
1.4 Subgrade filling
(1) Horizontal layered filling: According to the design of the cross-section of the embankment, from bottom to top layer by layer. Depending on the nature of the filler (water permeability), it is filled up layer by layer from the original ground and compacted in layers.
(2) Longitudinal layered filling method: Longitudinal layered filling is suitable for bulldozers or scrapers to take soil from the road graben to fill the embankment with a short distance, layer by layer according to the direction of the longitudinal slope, layer by layer bulldozer and compact compaction.
(3) Horizontal filling method: from the longitudinal or transverse direction of the embankment, according to the full height of the gradual advance of filling. Routes are often used to cross deep valleys or pass through steep slopes and muddy areas, but they are not easy to compact and have uneven settlement.
1.5 Subgrade compaction construction
The role of subgrade compaction is to improve the compactness of the filler, reduce porosity, enhance the contact surface between the packing particles, increase the cohesion or inlay extrusion force, improve the internal friction resistance, reduce deformation, and provide a good foundation for the normal use of the subgrade.
(1) Soil subgrade compaction
1, compaction principle - under the action of pressure, the soil body to overcome the cohesion and friction between the soil particles, so that the original structure is destroyed, the solid particles rearrangement.
2. Compaction mechanical operation mode
1) Slow rolling, compaction speed of 2 ~ 4km / h is appropriate
2) Avoid turning around and crushing, and use the longitudinal way of advancing and retreating
3) Crushing should be carried out in longitudinal branches
4) After the longitudinal branch is pressed, the second section of rolling is carried out, and the longitudinal joint overlaps 1 to 2m.
Compaction of mechanical rolling routes
Selection and operation of compaction tools:
The choice of compactor tools and reasonable operation are another comprehensive factor affecting the effect of soil-based compaction. There are many types of soil compaction tools, which are roughly divided into three types: rolling type, compaction type and vibration type. Rolling type (also known as static rolling type), including smooth surface mill (ordinary two-wheel and three-wheel roller), sheep foot mill and air tire mill. In addition to the stone rammers and rammers used by people, the mobile equipment includes rammers, rammer plates, pneumatic rammers and frog rammers. There are vibrators, vibratory rollers, etc. in the vibratory type.
Different compactor tools, suitable for different soil and different soil thickness and other conditions, these are the main basis for compaction tools, under normal conditions, for the compaction effect of sandy soil, the vibration type is better, the ramming type is second, and the compaction type is poor. For clay soils, it is advisable to choose the rolling type or ramming type, and the vibration type is poor or even ineffective. Different compaction tools, under optimal moisture content, are adapted to a certain optimal compaction thickness and the usual number of compaction passes.
Static rolling type: (glossy mill, sheep foot mill, air tire mill) clay soil
Rammer type: clay soil
Vibratory type: sandy soil
Practical experience proves that when the soil foundation is compacted, under the conditions that the type of tool, the thickness of the soil layer and the number of stroke times have been selected, the compaction operation should be light and then heavy, slow and then fast, and the edge and then the middle (when the ultra-high road section is needed, it is necessary to be low and then high from the inside to the outside.
When compacting, the adjacent wheel tracks should overlap 1/3 of the wheel width, keep the compaction uniform, do not leak pressure, and for the corners that cannot be pressed, they should be supplemented by manpower or small machinery. During the whole process of compaction, the moisture content and compactness are often checked to meet the requirements of the specified compaction degree.
Soil foundation compaction standards:
Soil-based field construction, subject to various conditions, can not reach the maximum dry capacity γ0 obtained by the indoor standard solidification test should be appropriately reduced. The dry bulk weight measured at the site is γ, which is the relative value of the ratio of γ0 value obtained by the indoor standard solidification test, which is called the compaction degree K. Compaction K is the subgrade compaction standard specified in the current code. The maximum dry density γ0 is determined by standard decommissioning tests.
Control of the rolling process:
In order to effectively compact the subgrade fill soil, the following control must be made of the rolling process:
The degree of compaction required for the subgrade depends on the type of fill and the grade of the road and the height of the embankment fill. Usually according to the provisions in the table, the maximum dry density and the corresponding optimal moisture content are determined by standard solidification test, and the minimum dry density required for construction is calculated.
The appropriate thickness and the required compaction number of various compactors to roll different soil types are related to the actual water content of the filled soil (the optimal water content is ± within 2%), and the required compaction degree should be determined according to the required compaction degree when doing the test section. High-grade highway subgrade fill compaction should be carried out by vibratory roller or 35~50t tire roller. When using a vibratory roller to roll, the first time should be hydrostatic pressure, the second time begins to use vibration compaction.
The moisture content of the filled soil is strictly controlled during the compaction process. When the water content is too large, the soil should be turned over to the required water content and then rolled; if the water content is too small, it is necessary to evenly dry the water before rolling. In general, when the moisture content of natural soil is close to the optimal moisture content, it should be compacted immediately after filling the soil.
Control of the rolling process
1 The construction site took soil for standard solidification test to obtain the maximum dry density and the best moisture content
2 Determine the degree of compaction required by the site k
3 Paving (thickness)
4 Crushing - pre-pressing leveling - moderate speed - first slow and then fast, first light and then heavy - first two sides and then middle
5 Detect compaction k
6 The next floor is paved
1.6 Factors affecting the compaction effect
1) The moisture content of the soil
Under certain functional conditions, when the humidity of the controlled soil is the optimal value, the compaction effect is the best and most economical;
Moisture content is a decisive factor affecting the compaction effect;
Under the action of a certain compaction function, the change of water content will lead to a change in the dry density of the soil, and the maximum dry density can be obtained when the water content is optimal;
2) The influence of soil quality on compaction
The soil quality is different, the maximum dry bulk weight and the optimal moisture content are different, and the compaction effect of sandy soil is better than that of cohesive soil;
3) Compaction function
The impact of the compaction function (referring to the weight of the compaction tool, the number of rolls or the height of the hammer drop, the action time, etc.) on the compaction effect is another important factor in addition to the moisture content.
Under the same conditions, the higher the function, the higher the compactness of the soil foundation.
The compaction function is increased above a certain limit, and the effect is improved more slowly. However, by increasing the compaction function too much, exceeding the limit strength of the soil will lead to soil destruction.
4) Rolling temperature
The temperature should not be too high or too low, the appropriate temperature can reduce the water viscosity in the soil, easy to compact.
5) The influence of compaction thickness on compaction effect.
The compaction thickness has a clear effect on the compaction effect. Under the same compaction conditions (soil quality, humidity and function are unchanged), the density (or compaction) of different depths of the soil layer is measured, and the compactness decreases with the depth, and the surface layer is the highest 5cm. The effective depth of compaction varies from compaction tool to compaction tool.
According to the type of compaction tool, soil and the basic requirements of soil foundation compaction, the thickness of the roadbed layered compaction has a specific specified value. Under normal circumstances, the compaction should not exceed 20 cm, 12-15t glossy surface roller, should not exceed 25cm, vibratory roller or rammer, should be limited to 50 cm.
6) Strength of the lower bearing layer of the foundation
The foundation strength is insufficient, the first layer of the embankment is difficult to achieve a high degree of compaction, therefore, before filling the embankment, the first thing to roll the embankment, if the foundation has a weak layer, the foundation should be treated with gravel.
7) Rolling tools and methods
The effective depth of pressure transmission is different depending on the compaction machine; the pressure transmission of ramming machine tools is the deepest, followed by vibration type, and the shallowest type of rolling type.
When the mass of the compactor is small, the longer the load action time, the higher the compactness of the soil, and the growth of the compactness decreases with the increase of the action time; when the compacting tool is heavier, the compaction of the soil increases rapidly with the increase of the load action time, and beyond a certain time limit, the deformation of the soil base increases and is destroyed. The higher the rolling speed, the worse the compaction effect.
Compaction standards:
2) Control and inspection of subgrade compaction operations
Determine the maximum dry density and optimal moisture content of the irrigated soil without species;
Check and control the water content of the filled soil;
3) Selection of compaction machinery
Rolling type: glossy mill (two-wheel and three-wheel roller), sheep foot mill and air tire mill, etc
Ramming type: artificial ramming, ramming hammer, rammer plate, pneumatic rammer and frog rammer, etc.
Vibratory type: vibrator, vibratory roller, etc.
Different compaction tools, suitable for different soil and different soil thickness and other conditions.
For sandy soils: the vibration type is better, the ramming type is second, and the crushing type is poor.
For clay soil: rolling or ramming type is better, vibration type is poor or even ineffective.
Compaction method: first light and then heavy, first slow and then fast.
The key to layered compaction is to control the number of rolling passes, which are on average 4-6 times for low clay compaction and 10-12 times for clay soil.
02 Road Graben excavation construction
Trench excavation is the largest and most common construction content in subgrade construction, and it must have a variety of machinery for construction.
2.1 Characteristics of trench excavation
(1) Before excavation, the trench should be excavated first, and all the ground water and groundwater that may affect the stability of the slope should be diverted.
(2) When excavating, it should be carried out from top to bottom according to the cross-section, and the construction should not be reversed.
(3) In the road graben with a proposed retaining wall for geological defects, the road graben should be excavated in sections.
(4) The abandoned soil of the road graben should be neatly stacked on one or both sides of the roadbed as required.
(5) Soft land belts or other soil sections that do not meet the requirements should be subject to various stability measures.
2.2 Excavation of soil grabens
Trench excavation is the excavation of natural soil above the design elevation within the subgrade and transported to a filled area or other designated location.
(1) Horizontal digging method
At one or both ends of the route, excavate longitudinally along the route. When the layer is doubled, the lower layer is left with excavation and drainage channels for the upper operation. It is suitable for short and shallow earth and stone road grabens on gentle ground, and is constructed with digging and loading, vehicle transportation machinery.
(2) Longitudinal digging method
Dig the working passage longitudinally along the road graben, and then gradually dig horizontally to both sides. This method is convenient for arranging earthmoving transportation and unfolding work sections, when the excavation depth is large, the height can be divided into several levels to arrange multiple groups of shifts to excavate on different levels and staggered working surfaces before and after, which is suitable for large excavation and long grabens.
(3) Mixed tunneling of longitudinal and horizontal channels
If the excavation section is wide and the excavation volume is large, the longitudinal channel can be excavated on the basis of the longitudinal channel to improve work efficiency.
(4) Segmented excavation
If you excavate a long road graben, you can choose one or several suitable places along the longitudinal direction of the graben, dig the thinner side of the graben horizontally, divide the graben into several sections in the longitudinal direction, arrange multiple groups of excavation sections, and excavate at the same time.
Principles and precautions for trench excavation:
1. Slope top slope surface inspection
Dangerous rocks, cracks or other unstable conditions must be properly handled. When excavating, the surface humus soil is first pushed away to the designated abandoned soil field, and then the soil is allocated to the filled embankment section for filling, and if the test finds that there is unqualified soil, it is also discarded to the abandoned soil field.
2. Excavation sequence
Excavation from top to bottom, from the center to both sides, layer by layer downhill excavation, it is strictly forbidden to dig the bottom of the excavation. Brush slope treatment is carried out at any time during the excavation process to make the slope form at one time. Digging deep into the graben also repairs the descending steps. In the direction and inclination of the rock layer is not conducive to slope stability and construction safety, it is changed to excavate along the layer, do not dig the rock layer, and take measures to weaken the construction vibration. In the above-mentioned areas with retaining walls, short excavations or horse mouth excavations were adopted, and temporary support measures were set up.
3. On the slope with slope protection, when the protection can not follow the excavation, temporarily leave a certain protective layer, and then brush the slope to dig enough when the protective layer is used.
Issues to be aware of:
1． Dig a trench first
2． Discarders cannot discard at will
3． Timely setting up support projects
2.3 Excavation method of stone road graben
Blasting method, soil loosening method.