AU2020103401A4

AU2020103401A4 - Self-compacting Liquid Cement for Backfilling Trench

Info

Publication number: AU2020103401A4
Application number: AU2020103401A
Authority: AU
Inventors: Peng Chen; Shiming He; Jiang Li; Jun Liu; Yongyan WANG; Jing Yang; Hekun Yu; Yucheng Zhou
Original assignee: Beijing Building Mat Engineering Co Ltd; Beijing Urban Construction Science Tech Promotion Association; Beijing University of Civil Engineering and Architecture
Current assignee: Beijing Building Materials Engineering Co Ltd; Beijing Urban Construction Science Technology Promotion Association; Beijing University of Civil Engineering and Architecture
Priority date: 2020-11-11
Filing date: 2020-11-11
Publication date: 2021-01-28
Anticipated expiration: 2028-11-11

Abstract

The self-compacting liquid cement for backfilling trench is characterized in that its basic formula is comprised of 100-400 kg of cement, 500-900 kg of local soil, 200-400 kg of stone chips or powder, 50-100 kg of fly ash, accelerating agent or early strength agent accounting for 1-3% of cement weight and a proper amount of water in each cubic meter. Then mixing above materials evenly with a blender and concreting the trench with them. The beneficial effect of the invention is that the invention can avoid the vibration procedure and form by self-weight, which can reduce construction noise, thereby improving the working environment of workers and the living environment of surrounding residents. It can solve the problem of not easy or unable to vibrate and improve the concreting speed, shorten the construction period and reduce the labour intensity of workers. Using local material, it saves material cost as well the cost of earthwork transportation. In addition, it can use industrial waste such as fly-ash, stone chips, etc., which has obvious cost advantages over concrete mortar. Therefore, the invention has significant benefits on economy, society and environment. -1/1 Conventional preparation works and entrance of the construction equipment Installment and debugging of the forced blender. and setting of the necessary dust-proof shed Installation and commissioning of ground pump in situ Site soil selection or screening |Material yard planning and connection of temporary water and electricity Entrance of stone chips or stone Entrance of cement and additives powder and fly-ash Mix and test according to the design proportion Passing the laboratory retest Mixing and producing cement slurry formally Conveying and concreting by pump Figure 1 Flow chart of mixing process of self-compacting liquid cement of the invention

Description

-1/1

Conventional preparation works and entrance of the construction equipment

Installment and debugging of the forced blender. and setting of the necessary dust-proof shed

Installation and commissioning of ground pump in situ

Site soil selection or screening

|Materialyard planning temporary and connection water and electricity of

additives Entrance of cement and and chips of stone powder or stone fly-ash Entrance

Mix and test according to the design proportion Passing the laboratory retest

Mixing and producing cement slurry formally

Conveying and concreting by pump

Figure 1

Flow chart of mixing process of self-compacting liquid cement of the invention

AUSTRALIA

PATENTS ACT 1990

PATENT SPECIFICATION FOR THE INVENTION ENTITLED:

Self-compacting Liquid Cement for Backfilling Trench

The invention is described in the following statement:-

Self-compacting Liquid Cement for Backfilling Trench

TECHNICAL FIELD

The invention belongs to the material for backfilling trench in the construction of

building foundation, in particular to a new type of self-compacting liquid cement. It can

be used for backfilling trench of building foundation pit, local replacement of foundation

or cavity backfill, etc. Self-compacting refers to its high fluidity, non-segregation,

uniformity and stability. That is, when concreting, it can rely on its own flow to achieves

compaction without vibration, which is especially used for parts that are difficult to

concrete or even unable to concrete.

BACKGROUND

At present, most of the construction engineering backfills trench with plain soil or 2:8

soil-lime or 3:7 soil-lime. But in actual construction, soil is directly poured by earthwork

truck or forklift truck, and some foundation pit trench is more than ten meters deep,

which can be filled overnight. The supervisor also neglects the supervision, which led to

the poor quality of trench backfilling. Taking a certain building in Beijing as an example,

less than two years after the method was used, the soil filling part of the trench appeared

subsidence caused by the immersion of water, which even led to the fracture of various

pipelines buried in the part, resulting in the building power failure, water and gas

stoppage and other serious consequences. In order to repair and compact the trench, a

small single pipe rotary jet drill was used for high-pressure jet grouting with cost more

than 3 million yuan, and the building party was forced to sue the construction party, resulting in huge loss. This is a typical case of contract dispute caused by the construction quality of trench backfilling.

Moreover, due to the narrow trench, the backfill cannot be compacted in layers. Due to

the high price of low-grade concrete and mortar, and the higher price of expansive

concrete or foamed concrete, graded sand is selected as backfill material, and the "water

tamping method" is adopted accordingly, that is, filling with material and flushing with

water at the same time to make it dense, which is also not desirable. In one case, a post

pouring belt is set on the bottom plate, and the water can be pumped out through the

pumping well in the pit; in the other case, there is no post pouring belt, however, the

buoyancy of the water on the structure cannot be ignored. It is a failure case that the

bottom plate cracks due to using water tamping method to backfill the trench.

Especially when there are bad geological conditions, it is necessary to backfill in time.

Since the trench is narrow, the water ramming method is adopted, and the consequences

will be very serious. For example, in the coal seam with a consequent foundation pit, a

large amount of water pouring into the foundation may cause water immersion and

cracking of the foundation of adjacent buildings, and even cause landslide and collapse

seriously.

What's more, if the filling of trench is not dense, removing blindly the anchor rod will

lead to the collapse of foundation pit, the fracture of adjacent pipelines, "the flood of

Gold Mountain", "the thick smoke rolling into the sky", or serious damage to the nearby

buildings.

The uncompacted backfill of trench and the long-term subsidence and immersion are also

the causes of the subsidence of the adjacent road, causing vehicle damage and human

death.

Therefore, it is very necessary to require the construction party to adopt appropriate

materials and methods for backfilling, which can ensure the quality, safety, fast,

economic benefit and environment protection.

SUMMARY

The purpose of the invention is to provide a self-compacting liquid cement for backfilling

trench, so as to solve the above problems caused by the uncompacted filling of trench

existing in the prior art

The technical scheme of the invention is as follows.

The self-compacting liquid cement for backfilling trench is characterized in that its basic

formula is comprised of 100-400 kg of cement, 500-900 kg of local soil, 200-400 kg of

stone chips or powder, 50-100 kg of fly ash, and a proper amount of water in each cubic

meter. Then mixing above materials evenly with a blender and concreting the trench with

them. Fly-ash has the same function of low-grade cement and can improves the

pumpability of mixture.

It further includes accelerating agent or early strength agent, accounting for 1-3% of

cement weight. The role of accelerating agent is to promote the rapid solidification of

mixture and improve its early strength; the early strength agent can improve its early

strength and shorten the setting time. If necessary, high-grade cement can be used without

accelerating agent and early strength agent thereby simplifying the formula and process.

The cement comprises ordinary portland cement, portland slag cement, portland fly-ash

cement or complex portland cement; the soil taken in situ includes silt, cohesive soil,

sandy soil or sandy pebble soil; the stone chips are the by-product of stone sorting, used

to adjust the pumpability, specific gravity and strength of the cement soil mixture.

If sand pebble soil is adopted in the field, the stone chips and fly-ash can be not added by

test certification, so the formula and process are simplified.

The newly mixed liquid cement should meet the following requirements: slump of

260mm, slump expansion of 600mm and adjustable specific gravity range of 1.01 -1.90.

Moreover, the strength tested at 28 days should be above 0.8MPa and the permeability

coefficient is 1.0 x 1O0-cm/s.

The process adopts on-site mixing and soil collecting. And it mixes with automatic

metering forced blender and uses ground pump to concrete and convey.

A special concrete mixing station is entrusted for mixing, and then the mixture is

transported to the site by concrete tank truck for direct concreting or by ground pump or

truck pump.

The beneficial effect of the invention is that the invention can avoid the vibration

procedure and form by self-weight, which can reduce construction noise, thereby

improving the working environment of workers and the living environment of

surrounding residents. It can solve the problem of not easy or unable to vibrate (if the

trench is too narrow and deep) and improve the concreting speed, shorten the

construction period and reduce the labour intensity of workers. Using local material, it

saves material cost as well the cost of earthwork transportation. In addition, it can use

industrial waste such as fly-ash, stone chips, etc., which has obvious cost advantages over concrete mortar. It can ensure the quality, safety, fast and economic benefit and environment protection of the trench backfilling and overcome the adverse effect of the traditional backfilling method on the surrounding environment. Therefore, the invention has significant benefits on economy, society and environment.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is the flow chart of mixing process of self-compacting liquid cement of the

invention.

DESCRIPTION OF THE INVENTION

Referring to Fig.1, the invention adopts the construction technology of self-compacting

liquid cement for backfilling trench, and the main process includes:

1.The construction site shall be provided with conventional preparation works, and the

construction equipment enters the site then.

2.The forced blender shall be in place, installed and debugged, and setting up the

necessary dust-proof shed.

3.Installation and commissioning of ground pump in situ.

4. Site soil selection or screening.

5. Material yard planning and connection of temporary water and electricity.

6. Stone chips or stone powder and fly-ash enter the site, cement and additives enter the

site as well. These materials have passed the laboratory retest.

7. Mix and test according to the design proportion. Its basic formula is comprised of 100

400 kg of cement, 500-900 kg of local soil, 200-400 kg of stone chips or powder, 50-100

kg of fly ash, and a proper amount of water in each cubic meter. Then mixing above

materials evenly with a blender and concreting the trench with them. Testing the newly mixed liquid cement, and it should meet the following requirements: slump of 260mm, slump expansion of 600mm and adjustable specific gravity range of 1.01-1.90. Moreover, the strength tested at 28 days should be above 0.8MPa and the permeability coefficient is

6 1.0x10-cm/s. The test sample can be prepared according to the requirements of the test

procedures.

8. Formal mixing and producing cement slurry. It should be mixed evenly, generally for

2-3 minutes.

9.The pump is used for concreting.

Further, the material includes accelerating agent or early strength agent, accounting for 1

3% of cement weight. The role of accelerating agent is to promote the rapid solidification

of mixture and improve its early strength; the early strength agent can improve its early

test certification, so the formula and process are simplified.

metering forced blender and uses ground pump to concrete and convey.

truck pump.

The followings are two comparison examples of the technical effect between the present

invention and the two prior art construction schemes.

A foundation pit in Fengtai District, Beijing, with a depth of 21.8m and a circumference

of 800m, is composed of filling and silt in the upper part of 6m and sandy pebble stratum

in the lower part. The water level is Im below the foundation pit. The foundation pit

supporting system is designed as a pile anchor system with a pile diameter of 800mm and

a pile spacing of 1.5m. The anchor rod is a pile and an anchor, with a spacing of 1.5m.

There are 5 sets of 23-26m in length. The waist beam is made of two 28B "I"-beams.

The width of the trench is 0.8m.

Although a rotary drilling rig with good verticality is used in the construction process, it

is inevitable that the pile verticality is not easy to guarantee. The phenomenon of "big

belly" and concrete over pouring appeared in many places. It is found that the width of

most trench is less than 0.4m after the steel beams are tensioned and locked. In addition,

the length of the cut-off steel strand is 10-20cm. It is obviously impossible for people to

stand in such a narrow trench to backfill and tamp layer by layer. The construction unit

also put forward the idea of recycling steel beam. Removing the anchor rod blindly when

the filling of trench is not compact will obviously lead to deformation and even collapse

of the foundation pit supporting pile, and seriously damage the pipelines or buildings near

the road. Therefore, three schemes are put forward, in which the former two schemes adopt the existing technology, and the third scheme adopts the technical scheme of the present invention. The technical effects of the three schemes are compared.

Scheme 1

Plain soil backfilling and layered backfilling and layered compaction are adopted.

Obviously, the traditional scheme cannot be implemented. In such a narrow space, people

cannot go in and therefore, the idea of dismantling and recycling steel beams cannot be

realized.

Scheme 2

Backfilling with graded sand and stone and adopting the water tamping method. This

method is rarely used in Beijing area, especially for such a large and deep foundation pit,

and there is no precedent. It needs a large amount of water, while there is no water in the

stratum. With so much water poured into the stratum, the stability of the foundation pit

may suffer serious damage, and the buoyancy damage of the building cannot be

accurately estimated. Therefore, the scheme is finally given up.

Scheme 3

Backfilling with self-compacting liquid cement of the invention. The scheme can ensure

the safety of backfill and will not damage the existing support system. It can realize the

idea of removing the anchor rod and it can save more than 50% of the cost compared with

low grade or mortar concrete. According to the theoretical calculation, 14,000m3 can save

2 million yuan of direct cost. With saving muck of 14,000 m 3, it can save 350,000 yuan

for freight and consumption. The direct income of steel beam recovery is 1 million yuan.

It can be seen that the economic benefits, social benefits and environmental benefits are

obvious in the scheme.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A self-compacting liquid cement for backfilling trench is characterized in that its basic

them.

2. The self-compacting liquid cement for backfilling trench according to claim 1, is

characterized in that it further includes accelerating agent or early strength agent,

accounting for 1-3% of cement weight. The role of accelerating agent is to promote the

rapid solidification of mixture and improve its early strength; the early strength agent can

improve its early strength and shorten the setting time.

3. The self-compacting liquid cement for backfilling trench according to claim 1 is

characterized in that the cement comprises ordinary portland cement, portland slag

cement, portland fly-ash cement or complex portland cement; the soil taken in situ

includes silt, cohesive soil, sandy soil or sandy pebble soil; the stone chips are the by

product of stone sorting, used to adjust the pumpability, specific gravity and strength of

the cement soil mixture.

4. The self-compacting liquid cement for backfilling trench according to claim 1 is

characterized in that if sand pebble soil is adopted in the field, the stone chips and fly-ash

can be not added by test certification, so the formula and process are simplified.

5. The self-compacting liquid cement for backfilling trench according to claim 1 is

characterized in that the characteristics of the newly mixed liquid cement should meet the following requirements: slump of 260mm, slump expansion of 600mm and adjustable specific gravity range of 1.01 -1.90. Moreover, the strength tested at 28 days should be above 0.8MPa and the permeability coefficient is 1.0 x 10-cm/s.

6. The self-compacting liquid cement for backfilling trench according to claim 1 is

characterized in that the process adopts on-site mixing and soil collecting. And it mixes

with automatic metering forced blender and uses pump to concrete and convey.

7. The self-compacting liquid cement for backfilling trench according to claim 1 is

characterized in that a special concrete mixing station is entrusted for mixing, and then

the mixture is transported to the site by concrete tank truck for direct concreting or by

ground pump or truck pump.

-1/1- 2020103401

Figure 1

Flow chart of mixing process of self-compacting liquid cement of the invention