Improved soil for backfill engineering and preparation method thereof

Abstract

The invention discloses improved soil for backfill engineering and a preparation method of the improved soil, and relates to the technical field of backfill materials for constructional engineering. The improved soil is formed by mixing weathered glutenite and plain soil according to the mass ratio of 8: 2; the weathered glutenite is a crushed glutenite material formed by natural weathering, the particle size of the weathered glutenite is 5-50 mm, and the porosity of the weathered glutenite is 25%-30% according to ASTM854-92 standard measurement; the grain size of the plain soil is less than or equal to 2mm, and the plasticity index is 10-15; the technical effects of high bearing capacity, high drainage speed, low settlement risk and controllable cost after the room core backfill area is compacted are achieved; the defects that an existing plain soil backfill material is low in bearing capacity, sensitive in water content and high in lime soil cost are overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of backfill materials for construction engineering, and particularly relates to improved soil for backfill engineering and a preparation method thereof. BACKGROUND

[0002] In the construction engineering construction, the house core backfill is a key process for guaranteeing the stability and safety of the building structure, and the performance of the backfill material directly determines the bearing capacity, settlement resistance and durability of the house core area. According to the requirements of the “Standard for Construction Quality Acceptance of Building Foundation Engineering” (GB50202-2018), the characteristic value of the bearing capacity of the plain soil foundation shall be greater than or equal to 100 kPa, and the bearing capacity of the foundation shall be inspected at least once per 300 square meters. At present, the backfill material commonly used in the house core backfill engineering is plain soil (i.e. natural undisturbed soil), but the plain soil has significant drawbacks:

[0003] Low bearing capacity: the plain soil has a single particle size distribution, and the overall structural strength after compaction is insufficient, and the actual detection shows that the bearing capacity is mostly in the range of 100-150 kPa, which is difficult to meet the requirements of high-rise or heavy-load buildings on the bearing capacity of the house core area, and is prone to cause ground settlement and cracking in the later period;

[0004] High sensitivity to water content: the plain soil is extremely sensitive to changes in water content, and when the water content is higher than the optimum water content by more than 2%, the cohesion between soil particles decreases, and the soil is prone to flow and plasticize, and the compaction quality is difficult to control; when the water content is lower than the optimum water content by more than 3%, the voids between soil particles increase, and the compaction degree cannot meet the standard, further reducing the bearing capacity;

[0005] Poor erosion resistance: the plain soil has weak impermeability, and the permeability coefficient is usually less than or equal to 1 x 10 -4 cm / s, and if there is water leakage in the house core area, water can easily penetrate into the interior of the plain soil, causing the soil to soften, and the bearing capacity can be reduced by 30%-40%, increasing the risk of settlement.

[0006] In order to improve the backfill performance of the plain soil, the existing technology commonly uses lime soil (plain soil mixed with lime in a certain proportion) as the backfill material, but the lime soil has the problem of high cost. According to industry cost analysis data, the comprehensive unit price of lime soil (2:8) is about 135-140 yuan / m 3 , and for an area of 1200 m 3 , the total cost of lime soil backfill is about 162,000 yuan, which is significantly higher than the cost of plain soil backfill. In addition, the procurement, transportation and mixing processing of lime raw materials require additional investment, and the mixing of lime and plain soil needs to be strictly controlled in terms of proportioning and curing conditions (usually water curing for 7-14 days), which further increases the engineering construction cost and complexity, and is not conducive to large-scale popularization and application.

[0007] Therefore, it is urgent to develop a core backfill material with high bearing capacity, low water content sensitivity, strong anti-settling ability and low cost to solve the problems of the prior art. SUMMARY

[0008] The application aims to provide an improved soil for backfill engineering and a preparation method thereof, and solve the above technical problems.

[0009] To achieve the above object, the application provides the following technical scheme: an improved soil for backfill engineering, which is prepared by mixing weathered sandy gravel and soil in a mass ratio of 8:2; the weathered sandy gravel is a crushed material of naturally weathered sandy gravel, the particle size of the weathered sandy gravel is 5-50 mm, and the porosity of the weathered sandy gravel is 25%-30% as determined by ASTM854-92 standard; the particle size of the soil is ≤2 mm, and the plasticity index of the soil is 10-15.

[0010] Preferably, the bearing capacity of the weathered sandy gravel after compaction is ≥200 kPa, the impermeability coefficient is ≤1×0.0001 cm / s, and the permeability coefficient is ≥1×0.01 cm / s.

[0011] Preferably, the soil is a naturally undisturbed soil excavated on a construction site, which is used after removing impurities (such as stones and roots), and the optimum water content of the soil is 15%-18% as determined by the ring knife method, and the particle size of the soil after screening and crushing is ≤2 mm, which can fill the larger pores between the weathered sandy gravel particles.

[0012] Preferably, the permeability coefficient of the improved soil is 5×0.001-1×0.01 cm / s.

[0013] A preparation method of the improved soil for backfill engineering, comprising the following steps:

[0014] S1, raw material pretreatment; the weathered sandy gravel is screened by a vibrating screen, and the weathered sandy gravel is classified and screened by a 2YZ-1848 vibrating screen, the screen mesh aperture is 50 mm in the upper layer and 5 mm in the lower layer, the large particles with a particle size >50 mm and the fine powder with a particle size <5 mm are removed, the weathered sandy gravel particles with a particle size of 5-50 mm are retained, and the screening efficiency is not less than 95%; the soil is screened by a 5 mm screen mesh to remove impurities, and then crushed to a particle size of ≤2 mm by a PEX250×1000 jaw crusher, and the impurity content is checked by a 300 mesh screen after crushing, and the impurity content is ≤1%;

[0015] S2, raw material mixing; the pretreated weathered sandy gravel and soil are weighed in a mass ratio of 8:2, and then put into a JS500 forced mixer, the stirring speed is 180 r / min, and the stirring time is 10-15 min until the uniformity deviation of the mixture is ≤3%, so as to ensure that the two raw materials are uniformly mixed;

[0016] S3, compaction molding; the mixed improved soil is layered and laid, each layer is 20-30cm thick, is rolled 3-5 times using a vibrating roller, and the compaction degree is controlled to be greater than or equal to 96% by a sand pouring method.

[0017] Preferably, the mixed and uniform improved soil mixture is transported to the house core backfill area, is layered and rolled using a YZC18 vibrating roller (working frequency 28-32Hz, amplitude 1.5-2.0mm), each layer is 20-30cm thick, is rolled 3-5 times, and the compaction degree is detected to be greater than or equal to 96% by a sand pouring method (according to the Technical Specification for Highway Subgrade Construction JTGF10-2006), and the house core backfill construction is completed.

[0018] Compared with the related art, the improved soil for backfill engineering and the preparation method thereof provided by the present application have the following beneficial effects:

[0019] 1. The weathered sandy conglomerate itself has high bearing capacity characteristics, and the soil fills the large pores between the weathered sandy conglomerate particles, so that the improved soil forms a dense structure after compaction. Through static load test detection, the bearing capacity after compaction can reach 220-250kPa, which is increased by more than 45% compared with the soil, and the bearing capacity is significantly improved.

[0020] 2. The high permeability of the weathered sandy conglomerate and the synergistic effect of the soil filling the pores make the permeability coefficient of the improved soil more stable, and the drainage speed is greatly improved compared with the soil, effectively improving the drainage speed and significantly reducing the settlement risk caused by water leakage.

[0021] 3. The improved soil is mixed with the weathered sandy conglomerate and the on-site soil, without the need for additional purchase of high-priced raw materials such as lime, and the preparation cost is more economical.

[0022] 4. The improved soil has strong adaptability to water content, does not need a complex curing process, and can be directly compacted using a conventional vibrating roller, which can effectively improve the construction efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a whole system flowchart of the present application;

[0024] Fig. 2 is a raw material pretreatment step framework diagram of the present application. DETAILED DESCRIPTION

[0025] Example 1:

[0026] Please refer to Figs. 1-2 , the present application provides a technical solution, including raw material pretreatment:

[0027] The weathered sandstone and gravel in the surrounding mountain of the building project is selected, and is sieved by a 2YZ-1848 type vibrating screen (upper layer 50 mm screen, lower layer 5 mm screen), and the sandstone and gravel particles with a particle size of 5-50 mm are reserved, and the qualified rate of the particles after the sieving is 97%;

[0028] The raw soil excavated on the construction site is selected, impurities are removed through a vibrating screen with a pore size of 5 mm, and is crushed to a particle size of ≤2 mm by using a PEX250x1000 type jaw crusher, the plasticity index of the raw soil is 13, and the optimum water content is 16%;

[0029] Raw material ratio mixing:

[0030] The weathered sandstone and gravel 800 kg and the raw soil 200 kg are weighed according to the mass ratio 8:2, are put into a JS500 forced mixer (rotating speed 180 r / min), are stirred for 12 min, and the uniformity deviation of the mixture is 2.3% detected by random sampling;

[0031] Compaction forming:

[0032] The improved soil mixture is transported to the house core backfill area, is laid in layers, the thickness of each layer is 25 cm, is rolled by using a YZC18 vibrating road roller (working frequency 30 Hz, amplitude 1.8 mm) for 4 times, and the compaction degree is 97.2% detected by the sand replacement method;

[0033] Performance detection:

[0034] The improved soil after compaction is detected, and the results show that the static load test bearing capacity is 235 kPa, the permeability coefficient is 8x0.001 cm / s, compared with the raw soil (bearing capacity 140 kPa, permeability coefficient 6x0.0001 cm / s) under the same condition, the bearing capacity is increased by 67.9%, and the drainage speed is increased by 12.3 times. After 6 months of observation, the cumulative settlement is 3.2 mm.

[0035] Example two:

[0036] The present application provides a technical scheme: including raw material pretreatment:

[0037] The weathered sandstone and gravel cleaned in the river dredging project is selected, is sieved by a 2YZ-1848 type vibrating screen, and the particle size of 5-50 mm is reserved, and the qualified rate of the particles after the sieving is 96%;

[0038] The raw soil around the farmland is selected, and the plasticity index is 11 after pretreatment, the optimum water content is 15.5%, and the particle size is ≤2 mm;

[0039] Raw material ratio mixing:

[0040] The weathered sandstone and gravel 800 kg and the raw soil 200 kg are weighed according to the mass ratio 8:2, are put into a JS500 forced mixer (rotating speed 180 r / min), are stirred for 12 min, and the uniformity deviation of the mixture is 2.3% detected by random sampling;

[0041] Compaction:

[0042] Layered compaction, each layer 30 cm thick, using YZC18 vibratory roller to roll 5 times (frequency 32 Hz, amplitude 2.0 mm), compaction degree 96.5%;

[0043] Performance testing:

[0044] The test results show that the bearing capacity is 228 kPa, and the permeability coefficient is 7x0.001 cm / s. Cost accounting shows that the comprehensive unit price of the improved soil is 92 yuan / m 3 , which is 35% lower than that of lime soil (140 yuan / m 3 ), and the construction efficiency reaches 90 m 3 / day.

[0045] Example Three:

[0046] Set up different ratio comparison groups, other conditions same as example one:

[0047] 7:3 ratio group: bearing capacity 205 kPa, permeability coefficient 4x0.001 cm / s, cost reduction 28%;

[0048] 9:1 ratio group: bearing capacity 210 kPa, permeability coefficient 9x0.001 cm / s, but compaction degree only 93%, not meeting the requirements;

[0049] The results show that the 8:2 ratio achieves the optimal balance in bearing capacity, permeability and compaction degree.

Claims

1. An improved soil for backfilling projects, characterized in that: The improved soil is made by mixing weathered sandstone and plain soil at a mass ratio of 8:2; the particle size of the weathered sandstone is 5-50 mm and the porosity is 25%-30%; the particle size of the plain soil is ≤2 mm and the plasticity index is 10-15.

2. The improved soil for backfilling projects according to claim 1, characterized in that: The compacted weathered sandstone has a bearing capacity ≥200kPa, a permeability coefficient ≤1×0.0001cm / s, and a permeability coefficient ≥1×0.01cm / s.

3. The method for preparing improved soil for backfilling projects according to claim 2, characterized in that: Includes the following steps: S1. Raw material pretreatment: Weathered sandstone and conglomerate are screened using a vibrating screen to retain particles with a diameter of 5-50mm; Plain soil is screened through a 5mm mesh screen to remove impurities and then crushed to a particle size of ≤2mm using a jaw crusher. S2. Raw material mixing ratio: Weigh the pretreated weathered sandstone and plain soil at a mass ratio of 8:2, put them into a forced mixer, and mix for 10-15 minutes until the mixing uniformity deviation is ≤3%. S3. Compaction and shaping: The mixed improved soil is laid in layers, each layer being 20-30cm thick, and compacted 3-5 times with a vibratory roller. The compaction degree is controlled to be ≥96% by sand filling.

4. The method for preparing improved soil for backfilling projects according to claim 3, characterized in that: In S1, the impurity content of the raw soil after sieving is ≤1%.

5. A method for preparing improved soil for backfilling projects according to claim 3, characterized in that: In S2, the forced mixer is a JS500 model.

6. The improved soil for backfilling projects according to claim 1, characterized in that: The permeability coefficient of the improved soil is 5×0.001~1×0.01cm / s.

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