CN1730841A

CN1730841A - Slope support method by compacting soil-lime to form cushion solid

Info

Publication number: CN1730841A
Application number: CN 200510019240
Authority: CN
Inventors: 贾燎
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-08-05
Filing date: 2005-08-05
Publication date: 2006-02-08
Anticipated expiration: 2025-08-05
Also published as: CN100427687C

Abstract

The present invention relates to geotechnical engineering, and is especially one kind of slope supporting method with densified lime soil to refill slope. Specifically, the operation process includes mixing lime and fiber into soil homogeneously, refilling the soil with lime and/or fiber to slope and rolling to densify the slope. The present invention has low cost, simple construction, high safety of the refilled slope, and is suitable for treatment of temporary and permanent slopes.

Description

Compacted lime soil backfill solid slope supporting method

Technical Field

The invention relates to a method for supporting a dense lime soil solid side slope in a foundation pit in the field of geotechnical engineering, in particular to a method for supporting a foundation pit in a soft soil area.

Background

In engineering construction, when a foundation pit or a road side slope is excavated by soft foundation soil, support measures need to be taken for the side slope so as to ensure that the excavated side slope is kept stable. At present, the main technical means commonly used for slope support include methods such as powder-injection pile gravity retaining wall support, cantilever pile support, pile anchor support and the like, which are mature and effective technical methods, but have certain defects:

the powder-sprayed pile gravity type retaining wall supporting method comprises the following steps: when sludge with water content over 70 percent or peat in soil is too large or acid soil is encountered, the method has the problems of difficult pile forming or low pile forming strength, and has the defects of long construction period, unstable quality, high manufacturing cost and the like;

the method comprises the following steps of cantilever pile support, pile anchor support and the like: the two methods have the advantages that the calculation model is clear, the method is suitable for supporting the deep foundation pit with the depth of more than six meters, the problems of long construction period and high construction cost exist, and the method is very waste when used for shallow foundation pits of soft foundations.

In a word, the above methods have certain limitations, and the problems of long construction period, high construction cost, more mechanical equipment required by construction, complex construction process and the like are common defects of the methods.

In the prior art, the traditional method of compacting with lime soil as a road base course is favorable, and the principle is that the compressibility of the compacted lime soil is improved. However, the shear strength index of compacted lime soil is also remarkably improved, and in this regard, the compacted lime soil has not been fully recognized and valued by the geotechnical engineering industry for a long time and has not been effectively utilized.

Disclosure of Invention

The invention aims to provide a compacted limestone soil solid-replacement side slope supporting method which can use local materials, has good technical stability, short construction period and low manufacturing cost.

The invention aims to realize a method for supporting a compacted limestone soil backfill solid side slope, which is characterized by comprising the following specific operation steps:

1) taking out soil on site, mixing 5-20% of quicklime in soil, stirring, and digesting for 8-24 hr;

2) and (4) filling the mixed soil to the slope position, and rolling and compacting according to the designed size to form a filling and replacing entity.

The invention has the following advantages:

1. the used blended materials of quicklime and fiber materials are common building materials, are available in all places, are convenient to obtain materials, are low in price, are wide in application range and low in engineering cost, and the manufacturing cost is only 30-50% of that of the traditional method;

2. the construction equipment is simple, and only an excavator is needed to cooperate with construction;

3. the construction is convenient, and the construction period is short;

4. the safety performance of the filling and replacement entity built by the invention is good.

The invention is suitable for excavating below ten meters in depth, has temporary slope releasing condition, and can be widely applied to temporary slope support and permanent slope treatment with the safety level below two levels.

Drawings

FIG. 1 is a schematic view of a first supporting method using the present invention

FIG. 2 is a schematic view of a second supporting method using the present invention

FIG. 3 is a schematic view of a third supporting mode made by the invention

FIG. 4 is a structural diagram of the analysis of the overall stability of the front slope before replacement and filling calculated by the arc sliding method

FIG. 5 is a structural diagram of analysis of the stability of the slope after replacement and filling calculated by the arc sliding method

Detailed Description

The concrete operation of the invention is that the soil is taken out on site, quicklime is mixed into the soil, the mixture is evenly mixed and digested, the mixed soil is filled into the slope position, and the mixed soil is rolled and compacted according to the design size to form the filling and replacing entity. And (3) adding 1-8% of fibers into the digested mixed soil for 8-24 hours, uniformly mixing, filling the mixed soil mixed with the fibers to a side slope, and rolling and compacting according to the designed size to form a filling and replacing entity.

The soil taken in situ is general cohesive soil, silt soil, silty clay, silt, mucky soil, sandy soil, gravel soil, backfill soil or the soil mixed with construction waste and industrial waste.

For sandy soils with a clay content below 20%, it is necessary to incorporate clay or silt into them to achieve a clay content above 20% in order to increase the proportion of particles of secondary minerals in the soil.

Mixing soil with calcium lime, and covering with film in rainy day.

The specific proportion of the quicklime mixing amount is determined according to the water content of the soil:

the water content of the soil is lower than 70 percent, the mixing amount of the quicklime is 5 to 10 percent,

the water content of the soil is 70-100%, the content of quicklime is 10-12%,

the water content of the soil is higher than 100 percent, the content of quicklime is 12 to 20 percent,

mixing soil with quicklime, uniformly mixing, and digesting for 8-24 hours, wherein the digestion reaction process is as follows:

the quicklime digestion reaction process not only changes the water content of the soil on the surface, but also changes the physical and chemical structure of the soil, namely, changes the bound water, the combination of silicate mineral particles and water in the soil is broken, and Ca (OH) is generated in the later period₂The strong alkalinity of the silicate activates the activity of the silicate and generates a complex and slow chemical reaction process along with the silicate, the aluminate and water, so the digestion process not only plays a role in draining water, but also plays a role in the physicochemical action of structural reorganization on mineral particles such as silicate, aluminate and the like in soil.

The quicklime digestion time cannot be too long because the simultaneous chemical action when exposed to air is also:

thus, the content of calcium hydroxide is reduced, the moisture in the soil is increased, and the lime soil compacting agent has adverse effect.

After digestion, the lime soil becomes loose, 1-8% of fiber is mixed into the mixed soil, and the mixture is uniformly mixed. The fiber is plant fiber such as rice straw, wheat straw, bamboo branch, etc. 50-200 mm long, or other cheap short mineral fiber or artificial fiber. The shear strength of the soil can be greatly improved by 2-5 times by mixing the fiber.

And (3) replacing and filling the mixed soil mixed with the fibers to the side slope position, and carrying out layered rolling compaction according to the designed geometric shape of the side slope retaining wall, wherein the thickness of each layer is 300-500 mm, the rolling strength is not less than 80kPa, and the larger the rolling strength is, the better the effect is.

The method for determining the geometric dimension of the compacted lime soil backfill entity and checking the safety degree comprises the following steps:

the calculation formula is as follows:

T = Σ_{i = 1}^{n 1} (Q_{i} + W_{i}) \sin α_{i}

k_hd＝R/T

in the formula:

t-glide force

R-sliding resistance

C_ki’The ith earthA standard value of cohesive force (kPa) determined by a total stress method for the bottom surface of the strip;

φ_ki-the internal friction angle (°) normalized value of the bottom surface of the ith swath determined by the total stress method;

l_i-arc length (m) of the bottom surface of the ith soil strip;

Q_i-the value of the standard of overload (kN/m) of the top surface of the ith soil bar;

W_i-weighted average of the deadweight of the ith soil strip (kN/m);

α_i-the angle (°) between the tangent to the bottom midpoint of the ith swath and the horizontal;

n, n 1-total number of branches, number of branches on active side;

k_hd-anti-skid stability safety factor.

k_hdThe foundation pits with importance levels of one, two and three should respectively satisfy not less than 1.30, 1.15 and 1.05. (see Hubei province local Standard Foundation pit engineering technical Specification (DB42/159 and 2004) page 16).

Aiming at different soil conditions, the invention adopts different retaining walls. When the soil layer of the side slope is soft and the soil texture of the pit bottom is hard, the solid backfill 4 shown in figure 1 is adopted; when the soil layer of the side slope is hard and the soil quality of the pit bottom is soft, the solid replacement and filling body 5 shown in figure 2 is adopted; when the soil layer of the side slope and the soil quality of the pit bottom are soft, the combined body of the solid backfill body 4 and the solid backfill body 5 shown in figure 3 is adopted. In the figure, 1-ground, 2-soft and hard soil and 3-soft soil.

The following examples illustrate specific applications of the present invention:

the excavation depth of the second-level foundation pit is 3.35 meters, and the geological conditions are as follows:

① layers of plain filling soil with thickness of 4.46 m, which is newly filled cohesive soil mixed with sundries such as broken stone, and has uneven and loose soil texture, c is 6kPa, phi is 14 degrees,

② layers of sludge with thickness of 1.7 m, gray black, flow plastic, saturation, average water content of 60%, c 10kPa, phi 5 deg,

③ layered clay with thickness of 5.3 m, yellow brown to grey brown, plasticity, and wet, c 21kPa, phi 11 deg.

By adopting the method to fill and replace the sludge on the side slope and the pit bottom, the actual measurement shows that the cohesive force c value of the filling and replacing entity for 3 days is 11kPa, and the value of the internal friction angle phi is 11 degrees. The calculation results of K before and after the replacement are shown in figures 4 and 5, and it can be seen from the figures that before the replacement, the anti-skid stability safety coefficient K (4) is 1.114 < 1.15, which does not meet the requirement, and after the replacement, the anti-skid stability safety coefficient K (i) > 1.15, which meets the requirement.

It can be seen that the stability requirement is not met before the filling and is completely met after the filling. There is also a large increase in the values of c and Φ over time.

Claims

1. A compacted lime soil backfill entity side slope supporting method is characterized by comprising the following specific operation steps:

1) taking out soil on site, mixing 5-20% of quicklime into soil, stirring, digesting for 8-24 hr,

2. The method of claim 1, wherein 1-8% of fiber is added into the digested mixed soil for 8-24 hours, the mixture is mixed uniformly, the mixed soil mixed with the fiber is filled into the slope, and the mixed soil is compacted according to the designed size to form the solid.

3. The method of claim 1 or 2, wherein the soil is selected from the group consisting of clay, silt, silty clay, silt, sandy soil, gravelly soil, backfill soil, and construction waste and industrial waste.

4. The method as claimed in claim 1 or 2, wherein the clay content is less than 20% and the sandy soil and crushed rock soil are mixed with clay soil or silt soil to make the clay content higher than 20%.

5. The method as claimed in claim 2, wherein the fiber is plant fiber such as straw, wheat straw, bamboo branch, etc. 50-200 mm long, or other cheap short mineral fiber or artificial fiber.