What Are the Best Methods for Trench Excavation?

Earthwork excavation is a key process in the early stages of the project and during the construction process. Engineering that loosens, breaks, digs, and transports soil and rock. According to rock and soil properties, earthwork excavation is divided into earthwork excavation and stone excavation.

Earth excavation

Earthwork excavation is a key process in the early stages of the project and during the construction process. Engineering that loosens, breaks, digs, and transports soil and rock. According to rock and soil properties, earthwork excavation is divided into earthwork excavation and stone excavation.

Earthwork excavation is classified into open cut, hole excavation and underwater excavation according to whether the construction environment is open, underground or underwater. In hydraulic engineering, earth excavation is widely used in site leveling and slope cutting, excavation of foundations of hydraulic structures (sluices, dams, spillways, hydropower plant buildings, pumping stations, etc.), underground caves (hydraulic tunnels, underground Factory building, various flat holes, vertical shafts and inclined shafts) excavation, excavation and dredging of rivers, channels, ports, mining of filling materials, building stones and concrete aggregates, temporary buildings such as cofferdams or masonry, concrete structures Dismantling, etc.

Chinese name

Earth excavation

Term belongs

Architectural term

Application area

Construction works, tunnel works, etc.

Excavation principle

Slotted support

Excavation by layers, over-excavation is strictly prohibited

Classification

Excavation of shallow foundation pits; excavation of deep foundation pits

Before construction, it is necessary to study and select the excavation method according to the project scale and characteristics, natural conditions such as terrain, geology, hydrology, and meteorology, construction diversion methods and project progress requirements, construction conditions, and possible construction methods. Open excavation includes full excavation, sub-site excavation, layered excavation, and segmental excavation. Full excavation is suitable for engineering projects with shallow excavation depth and small scope. When the excavation range is large, sub-site excavation is required. If the excavation depth is large, layered excavation is adopted. For excavation of stone, deep hole ladder blasting (see deep hole blasting) is often used to divide the layer according to the ladder. Excavation in sections is suitable for projects such as larger channels and spillways. For tunnel excavation, there are excavation methods such as full-section excavation, branch excavation, and tunnel guide method.

Earthwork excavation includes loosening, crushing, excavation, slag transportation and other procedures. Stone excavation, except for soft rock can be excavated with a ripper to excavate, generally blasting is required to loosen and break. Manual and semi-mechanical excavation, using simple tools such as spade picks, air picks, wind drills, etc., with lifting or simple small transportation tools for operation, suitable for small water conservancy projects. Some irrigation and drainage ditches are constructed directly using a trencher and can be formed at one time. Earth and stone excavation of large and medium-sized water conservancy projects, multi-purpose machinery construction.

With the increasing development of water conservancy projects, the earth-rock excavation volume of some large-scale projects in the world often reaches tens of millions of cubic meters, even exceeding 100 million cubic meters.

(1) in

Earthwork grading coefficient (m): refers to the ratio of the base height h to the base width b of the slope of the soil wall, ie m = h / b

1. In construction, grading should start from the upper surface of the cushion;

2. The earthwork quota of the pipeline, the calculation of the earthmoving grading factor for trench excavation is as follows:

(1) The excavation depth is within lm, and grading is not considered;

(2) The excavation depth is 1.0lm 2.00m, and the slope shall be sloped according to l: 0.5;

(3) The excavation depth is 2.0lm 4.00m, and the slope shall be graded according to l: 0.7;

(4) The excavation depth is between 4.01m and 5.00m, and the slope shall be sloped at 1: 1;

(5) The excavation depth is greater than 5m, and the slope is calculated according to the soil stability theory calculation.

note:

When calculating the amount of work, the repeated amount of work caused by grading at the junction of the trenches will not be deducted.

Due to poor soil quality, when excavation and soil replacement are used for foundation treatment, the slope point should start from the actual digging depth.

When excavating earthwork, troughs, and pits, if different soil types are encountered, they should be calculated separately based on geological survey data.

The slope grading coefficient can be determined according to the weight of each soil type and depth

The data in this table is not applicable everywhere, but general rules, according to the 2009 new specification handout:

When the soil type is single, the excavation depth of ordinary soil (Class I or II) is greater than 1.2 meters and grading is started (K = 0.50).

When the soil is mixed with soil, the excavation depth is greater than 1.5 meters to start grading, and then the grading coefficient K is calculated according to the weight of different soils.

Specification of grading height and proportion in the construction manual for grading coefficient

Soil category	Regulation of grading depth (m)	Higher than wide ratio
		Artificial digging	Mechanical digging
			Pit operation	Pit operation
Class I or II soil	Over 1.20	1: 0.5	1: 0.33	1: 0.75
Three types of soil	More than 1.50	1: 0.33	1: 0.25	1: 0.67
Four types of soil	Over 2.00	1: 0.25	1: 0.10	1: 0.33

Note: 1. When the soil types in the trench and foundation pit are different, they are calculated according to their soil types and grading ratios with different soil thicknesses.

2. When calculating the grading engineering quantity, the repeated engineering quantity at the junction is not deducted. The grading can only be done when the grading depth is met. The grading height should be calculated from the lower surface of the cushion to the design outdoor floor elevation.

A good earth excavation construction scheme can make the construction better and higher quality. The earth excavation construction scheme generally includes: earth excavation construction preparation, survey setting out, excavation requirements, and earthmoving.

Earthwork preparation

(1) Survey the site and remove the ground and obstacles on the ground.

(2) Protect the measuring reference pile to ensure that the position and size of the earth excavation elevation are accurate.

(3) Prepare excavation machinery, personnel, construction electricity, water, roads and other facilities.

Earthwork excavation

All surface weeds, stones, debris, humus soil, tree roots, etc. within the scope of the project should be cleaned, compacted and compacted, and the thickness of the cleaning should not be less than 0.3m. Outbound to the scrap yard.

Earthwork excavation

The earth excavation referred to here is mainly earth excavation within the scope specified by the tenderer. The excavated earth is transported to the place designated by the tenderer, and the height of the earth mound shall not exceed the 1985 Yellow Sea elevation of 12.20 meters.

(1) Preparation for construction

Preparation of construction materials: Earthwork excavation is affected by weather, geological conditions, and existing buildings. The following work should be done before excavation:

a Review and analysis of construction drawings and formulation of construction plans.

b Understanding of local hydrological and meteorological conditions.

c Understanding of the geological conditions of the construction site.

d Buried conditions of buildings and pipelines within the construction scope.

e Draw the plan and cross section of the earth excavation.

(2) Measure and stake out

The temporary control points are used to stake out the excavation edge and excavation depth. When setting out the excavation line, you should add 30 ~ 1250px outside the design line and mark it clearly. The dimensions of the excavation at the bottom of the foundation pit, in addition to the requirements of the building outline, shall also consider the requirements of drainage facilities and installation formwork.

(3) Earthwork excavation requirements

Preparation for construction

a Before excavation of earthwork, the underground and above-ground obstacles in the construction area should be removed and treated according to the requirements of the construction plan.

b The location of the building or structure or the location control line (pile), standard horizontal pile and slotted gray line size must pass the inspection and pass the pre-inspection procedure.

c During night construction, there should be sufficient lighting facilities; obvious signs should be set in dangerous areas, and the excavation sequence should be arranged reasonably to prevent mis-excavation or over-excavation.

d When excavating foundation pit trenches and pipe trenches with a groundwater level, measures should be taken to reduce the groundwater level based on local engineering geological data. Generally, it should be lowered to 0.5m below the excavation surface before excavation.

e The roads, bridges, and unloading facilities that construction machinery passes through the site should be inspected in advance, and preparations such as reinforcement or widening should be performed if necessary.

f Selection of earthmoving machinery should be comprehensively considered according to the topography and operating conditions of the construction area, the type and thickness of soil, the total amount of work and the construction period, so that the efficiency of the construction machinery can be used to determine the construction plan.

g The layout of the operation route in the construction area should be determined according to the size, mechanical properties, transportation distance, and terrain fluctuations of the work area.

h In areas where mechanical construction is inoperable, trimming slope slopes, cleaning tank bottoms, etc., should be equipped with manual labor.

i Tools: Excavating machinery includes: excavators, bulldozers, shovel (both pointed and flat), trolleys, small white wires or 20-gauge lead wire and steel tape measure, and slope rulers.

jFamiliar with the drawings and complete technical knowledge.

Operation process

aprocess flow:

Determine the order and slope of excavation average digging in sections and layers trimming and clearing.

Determination of b slope:

The excavation slope of this project is in accordance with the design requirements. If stability cannot be ensured during construction, contact the design side and change the excavation plan.

c mechanical excavation

The excavation sequence, route and excavation depth should be reasonably determined. This project uses an excavator in conjunction with an earthmoving machine to perform the excavation. The earthwork excavation should be carried out sequentially from top to bottom in layers. Make a certain slope at any time to facilitate drainage. During the excavation process, the condition of the slope should be checked at any time. Excavation of a foundation pit shall not be carried out below the design elevation. If it cannot be dug accurately to the design base elevation, a layer of soil may not be dug above the design elevation so that it can be excavated manually after leveling. When using a backhoe to shovel the temporary soil layer excavator, it should be about 1250px.

d Manual excavation

For earthwork that cannot be dug by mechanical construction, it should be excavated at any time in cooperation with humans, and the soil should be transported to the place dug by the machine with a cart in order to be dug away in time. When repairing and clearing the bottom, at the height of 1250px above the bottom of the groove, copy out the horizontal line, nail the small wooden rafters, and then excavate the temporary soil layer by hand. The cement mixing pile head should be excavated along the pile. At the base elevation, the cement mixing pile is cut according to the requirements of the cut height, and the pile top is leveled. At the same time, draw the line (with a small wire or lead wire) from the axis (center line), check the size from the groove edge, determine the groove width standard, and trim the groove edge. Finally, the earthwork at the bottom of the tank is removed.

Rain and winter construction

a Earthwork excavation should generally not be carried out during the rainy season, otherwise the working face should not be too large and should be completed piece by piece and piece by piece.

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Quality and safety control measures

a Carefully stake out according to the drawings. The slope after earthwork excavation should meet the design requirements to avoid collapse due to the steep slope. To ensure the quality of the slope, the backhoe should be dug close to the slope line to ensure the slope is level And try to avoid the occurrence of undercut and overcut.

b. After excavation and completion of cleaning, the station number, coordinates, elevation, etc. should be restored in a timely manner, and eye-catching signs should be made.

c In rainy days, a interception ditch should be set up on the top of the excavation slope, and a drainage ditch and a water collection well should be set up in the excavation area.

d During the excavation process, the design slope line shall be maintained to be excavated layer by layer to avoid landslides caused by excessively steep temporary slopes in the excavation project, and the observation of slope stability shall be enhanced.

e It is forbidden to pile heavy objects on the top of excavated slopes to avoid landslides.

Earthmoving

The earthwork for this project is transported by a 5t dump truck, transported to the place designated by the tenderer, and stacked according to the tenderer's requirements. During the construction period, the spoil ground shall be managed. It is strictly forbidden to transport earthwork outside the project to the spoil ground of the project. The roads involved in engineering transportation pollution shall be promptly cleaned up in accordance with the requirements of the road administration department.