WO2021072941A1 - 一种滨海淤泥软土地基二次强夯碎石置换加固方法 - Google Patents

一种滨海淤泥软土地基二次强夯碎石置换加固方法 Download PDF

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WO2021072941A1
WO2021072941A1 PCT/CN2019/123609 CN2019123609W WO2021072941A1 WO 2021072941 A1 WO2021072941 A1 WO 2021072941A1 CN 2019123609 W CN2019123609 W CN 2019123609W WO 2021072941 A1 WO2021072941 A1 WO 2021072941A1
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Prior art keywords
ramming
foundation
rammer
water pressure
replacement
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PCT/CN2019/123609
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English (en)
French (fr)
Inventor
刘文连
李鸿翔
李泽
张国海
韩鹏伟
贺加乐
吴胤龙
眭素刚
唐果
闫鼎熠
秦勇光
郝勇
高楠
张劼
周志恒
张腾龙
华明亮
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中国有色金属工业昆明勘察设计研究院有限公司
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Publication of WO2021072941A1 publication Critical patent/WO2021072941A1/zh

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    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E02D3/02—Improving by compacting
    • E02D3/046—Improving by compacting by tamping or vibrating, e.g. with auxiliary watering of the soil
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E02D3/02—Improving by compacting
    • E02D3/08—Improving by compacting by inserting stones or lost bodies, e.g. compaction piles
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
    • E02D3/02—Improving by compacting
    • E02D3/10—Improving by compacting by watering, draining, de-aerating or blasting, e.g. by installing sand or wick drains

Definitions

  • the invention belongs to the technical field of coastal soft soil foundation treatment, and specifically relates to a method for replacing and strengthening coastal silt soft soil foundations with secondary dynamic compaction gravel.
  • the coastal soft soil foundation is mainly formed by marine deposits.
  • the stratum contains a thick layer of fine sand or silt, and a certain thickness of silt is distributed on the upper part of the sand layer; the fine sand or silt layer makes the foundation have
  • the possibility of seismic liquefaction is higher, and the higher water content and higher liquid limit of the silt soil layer result in greater compressibility and slow drainage and consolidation speed. Therefore, coastal soft soil foundations have three major characteristics: low bearing capacity, high compressibility, and high seismic liquefaction possibility.
  • the bearing capacity of coastal soft soil foundations has become increasingly prominent.
  • the traditional methods of soft soil foundation treatment mainly include preloading method, pile foundation method and dynamic compaction method.
  • the preloading method accelerates the drainage and solid process of soft soil by preloading preloading, and the pile foundation method transfers the upper load through artificial piles.
  • the dynamic compaction method is a treatment method to compact soft soil through compaction work.
  • the preloading method and pile foundation can solve the low bearing capacity and high compressibility of the coastal soft soil foundation, they can not eliminate the seismic liquefaction of the sand layer; while the conventional dynamic compaction method is used to deal with the buried soft soil foundation. Problems such as hammering, frequent feeding and high swelling, and the one-time dynamic compaction has a poor drainage and consolidation effect on the silt layer in the soil between the piles. Due to the particularity of coastal soft soil foundations, the use of traditional dynamic compaction methods to reinforce coastal soft soil foundations is not ideal. It will cause problems such as long construction period, high cost, difficult control of post-construction settlement and limited seismic liquefaction elimination.
  • the technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for replacing and strengthening the coastal silt soft soil foundation with secondary dynamic compaction and gravel replacement.
  • the first and second dynamic compaction replacement is performed on the coastal soft soil foundation. Reinforcement, to achieve compaction of the sand layer to reduce its water content and porosity, to eliminate the possibility of seismic liquefaction of the sand layer, and replace shallow silt with gravel to form a gravel replacement pile composite foundation to enhance the bearing capacity of the foundation
  • crushed stones replace the piles to compact the soil between the piles to reduce the porosity and moisture content of the soil.
  • the drainage between the first and the second dynamic compaction accelerates the drainage and consolidation process of the silt soft soil layer. Effectively improve the bearing capacity of the foundation, eliminate the possibility of liquefaction of the lower sand layer, and realize the efficient dynamic compaction replacement and reinforcement of the silt soft soil foundation.
  • Step 1 Draft the basic parameters of coastal soft soil foundation, including: the number of coastal soft soil foundation soil layers, the name and thickness of each layer of soil; groundwater level information; the length, width and area of the coastal soft soil foundation site; dynamic compaction replacement The design of the gravel pier is long.
  • Step 2 Preliminarily level the construction site, remove the 0.5-1.0m thick miscellaneous fill on the ground surface, and measure the site base elevation.
  • Step 3 Backfill 1.0-1.5m thick strongly weathered crushed stone on the initial level ground.
  • the maximum particle size of the crushed stone is not more than 300mm and the unevenness coefficient is greater than 5.
  • Step 4 Determine the location and number of ramming points for dynamic ramming replacement on the site.
  • the ramming points are arranged in a square or quincunx shape.
  • the distance between the ramming points can be 3.0-6.0m, and all the ramming points of the foundation are numbered.
  • Step 6 Perform the first dynamic compaction on all the compaction points of the foundation dynamic compaction replacement, specifically:
  • the crane is in place, and a point rammer with a diameter of 1.5m ⁇ 2.0m is used to align the rammer at the position of the ramming point, and the height of the hammer top before ramming is measured.
  • the ramming energy can be 3000 ⁇ 4000kN ⁇ m, according to the weight of the rammer and the ramming point.
  • the design height of the rammer lift is calculated by the hammer diameter and the height of the hammer top.
  • the design height of the rammer lift for the first dynamic compaction is calculated as follows:
  • H 1 first dynamic rammer to increase the design height; It is the ramming energy of the first dynamic compaction, which can be 3000 ⁇ 4000kN ⁇ m, m 1 is the mass of the primary dynamic compaction hammer; g is the acceleration of gravity;
  • 3Use a crane to lift the rammer to the design height, release the rammer hook to make the rammer fall freely to complete the ramming, measure the height of the top of the rammer, and calculate the amount of ramming each time;
  • the replacement material uses medium weathered to slightly weathered crushed stone, the largest particle size of the crushed stone
  • the content of crushed stones with a maximum diameter of 300mm and 300mm is not greater than 30%, the unevenness coefficient of crushed rocks is greater than 5, and the mud content is less than 5%;
  • step 2 ⁇ step 4 for each ram point more than 15 times to make the pier length meet the design depth requirement, and complete the first dynamic ramming construction of each pier point;
  • Step 7 Drain the foundation to reduce the pore water pressure, use the pre-buried pore water pressure gauge to measure the pore water pressure value of the site, and monitor the dissipation law of the pore water pressure of the foundation, specifically as follows:
  • the pore water pressure in the foundation reaches the maximum value
  • the rammed pier is composed of crushed stones to form a drainage channel
  • the groundwater in the silt soil layer is drained by the rammed pier and collected in the rammed pit;
  • N p is the number of pore water pressure gauges buried
  • m is the number of pore water pressure measurements
  • Step 8 Perform a second dynamic compaction on all the compaction points of the foundation dynamic compaction replacement, specifically:
  • the second ramming is in no particular order, and the construction sequence is from the center of the ramming point to both sides;
  • the crane is in place, and a point rammer with a diameter of 2.0m is used to align the rammer at the ramming point position, and measure the height of the hammer before the rammer.
  • the ramming energy can be 5000 ⁇ 6000kN ⁇ m, according to the weight of the rammer, the diameter of the rammer and
  • the height of the hammer top calculates the design height of the rammer lift; the design height of the rammer lift of the second dynamic compaction is calculated as follows:
  • H 2 second dynamic rammer to increase the design height It is the ramming energy of the second dynamic compaction, which can be 5000 ⁇ 6000kN ⁇ m, m 2 is the mass of the secondary dynamic compaction hammer; g is the acceleration of gravity;
  • 3Use a crane to lift the rammer to the design height, release the rammer hook to make the rammer fall freely to complete the ramming, measure the height of the top of the rammer, and calculate the amount of ramming for each ramming;
  • the replacement material uses medium weathered to slightly weathered crushed stone, the largest particle size of the crushed stone
  • the content of crushed stones with a maximum diameter of 300mm and 300mm is not greater than 30%, the unevenness coefficient of crushed rocks is greater than 5, and the mud content is less than 5%;
  • Step 9 Carry out full compaction construction within the scope of the foundation, specifically:
  • 3Full ramming uses a rammer with a diameter of 2.4m, a weight of 20 tons and air holes, and uses a ramming energy of 2000kN ⁇ m to carry out the full ramming construction of all ramming points;
  • the full ramming is carried out in two sequences, the first ramming is 3 times, the second ramming is 2 times, the overlap between the ramming points of the full ramming is not less than 1/3 of the bottom diameter of the hammer;
  • Step 10 Use geological radar or geological drilling to detect the pier length of the gravel replacement pier, determine the pier length of the dynamic compaction gravel replacement pier, and monitor the number of replacement piers not less than 5;
  • Step 11 Carry out the plate load test of the replacement pier body of the dynamic compaction replacement foundation to determine the characteristic value of the bearing capacity of the dynamic consolidation replacement pier body.
  • 2 to 3 replacement pier bodies can be randomly selected for the plate load test, and the plate load of the replacement pier body The number of tests shall not be less than 2, and the method of plate load test for replacement piers shall be carried out in accordance with the relevant regulations in the "Code for Design of Building Foundations" GB 50007-2011.
  • Step 12 Carry out the plate load test of the soil between the piers of the dynamic compaction replacement foundation to determine the characteristic value of the bearing capacity of the soil between the piers of the dynamic compaction replacement.
  • the plate load test of the soil between the piers is only carried out at a depth of about 2 to 3m.
  • the maximum load and bearing capacity characteristic values of the soil between the piers can be randomly selected from 3 to 4 locations of the soil between the piers for the plate load test.
  • the number of the soil between the piers is not less than 3, and the number of the soil between the piers is not less than 3.
  • the method of the soil slab load test shall be implemented in accordance with the relevant regulations in the "Code for Design of Building Foundations" GB 50007-2011.
  • the present invention has the following beneficial effects compared with the prior art.
  • the present invention implements the first and second dynamic compaction replacement and reinforcement of the coastal soft soil foundation to achieve compaction of the sand layer to reduce its water content and porosity, so as to eliminate the possibility of seismic liquefaction of the sand layer.
  • Block stones replace shallow silt soil to form a gravel replacement pile composite foundation to enhance the bearing capacity of the foundation, while rubble replace the piles to compact the soil between the piles to reduce the porosity and moisture content of the soil. Drainage between the second dynamic compaction accelerates the drainage consolidation process of the silt soft soil layer, effectively improves the bearing capacity of the foundation, eliminates the possibility of liquefaction of the lower sand layer, and realizes the efficient dynamic compaction replacement and reinforcement of the silt soft soil foundation.
  • the reinforcement method of the present invention can effectively, quickly and economically reinforce the coastal silt soft soil foundation to improve the bearing capacity of the coastal silt soft soil foundation, control the post-construction settlement of the foundation, eliminate the liquefaction characteristics of the sand layer, and solve the bearing capacity of the silt soft soil foundation
  • Low force, difficult reinforcement treatment, slow drainage and consolidation speed, and high reinforcement treatment cost are difficult to improve the ultimate bearing capacity of the silt soft soil foundation after the reinforcement treatment, effectively reduce the post-construction settlement of the upper building, and eliminate the lower sand
  • the possibility of layer liquefaction achieves both economical and safe objectives.
  • FIG. 1 Schematic diagram of the process of the present invention
  • Figure 2 is a cross-sectional view of the coastal silt soft soil base layer in the embodiment
  • Figure 3 is a plan view of the seashore silt soft soil foundation site in the embodiment.
  • Figure 4 is a plan layout diagram of the location of the ramming points of the secondary dynamic compaction replacement foundation
  • Fig. 5 is a schematic diagram of the buried position of the pore water pressure gauge in the embodiment
  • Fig. 6 is a plan layout diagram of the ramming point of the full ramming construction in the embodiment
  • Figure 7 is a schematic diagram of the grid layout and the number of measuring points after the actual measurement of the elevation after the full ramming is completed in the embodiment
  • Figure 8 Schematic diagram of the measurement position of the length of the foundation replacement pier in the embodiment
  • Fig. 9 is a schematic diagram of the position of the slab load test of the foundation replacement pier in the embodiment.
  • Fig. 10 is a schematic diagram of the position of the soil plate load test between the foundation piers in the embodiment
  • Step 1 Draft the basic parameters of coastal soft soil foundation, including: the number of coastal soft soil foundation soil layers, the name and thickness of each layer of soil; groundwater level information; the length, width and area of the coastal soft soil foundation site; dynamic compaction replacement The design of the gravel pier is long.
  • the number of coastal soft soil foundation soil layers is 6 layers; from top to bottom, they are: the first layer is miscellaneous fill soil with a thickness of 0.6m, the second layer is silty clay with a thickness of 3.0m, and the second layer is silty clay with a thickness of 3.0m.
  • the third layer is silt with a thickness of 2.0m, the fourth layer is silty fine sand with a thickness of 4.3m, the fifth layer is medium-coarse sand with a thickness of 3.0m, and the sixth layer is silty clay with a thickness of 8.0m.
  • the section of the silt soft soil base layer is shown in Figure 2; the groundwater level is -1.2m below the ground surface; the length of the coastal soft soil foundation site is 40m, the width is 30m, and the area is 1200m 2.
  • the plan view of the silt soft soil foundation of the embodiment is shown in Figure 3; The design pier length of the dynamic compaction replacement gravel pier is 12.0m.
  • Step 2 Preliminarily level the construction site, remove the 0.5-1.0m thick miscellaneous fill on the ground surface, and measure the site base elevation.
  • the construction site of the foundation of the embodiment was initially leveled, the 0.6m thick miscellaneous fill on the ground surface was removed, and the reference elevation of the measurement site was 6.0m.
  • Step 3 Backfill 1.0-1.5m thick strongly weathered crushed stone on the initial level ground.
  • the maximum particle size of the crushed stone is not more than 300mm and the unevenness coefficient is greater than 5.
  • Step 4 Determine the location and number of ramming points for dynamic ramming replacement on the site.
  • the ramming points are arranged in a square or quincunx shape.
  • the distance between the ramming points can be 3.0-6.0m, and all the ramming points of the foundation are numbered.
  • the pore water pressure gauge is buried near the central area of the compaction area of the dynamic tamping replacement foundation in the embodiment, the pore water pressure gauge is a vibrating wire pore water pressure gauge, the model is RC011-KYJ, and the number of pore water pressure gauges buried is 3 , The elevation of the first pore pressure gauge is -3.0m below the surface, the elevation of the first pore pressure gauge is -4.5m below the surface, and the elevation of the first pore pressure gauge is -7.0m below the surface, 3 The buried elevation intervals of the pore water pressure gauges are 1.5m and 2.5m, respectively. The pore water pressure gauges are buried in position as shown in Figure 5.
  • Table 1 The benchmark value of pore water pressure at the measurement points of the silt soft soil foundation in the embodiment
  • Step 6 Perform the first dynamic compaction on all the compaction points of the foundation dynamic compaction replacement, specifically:
  • the construction sequence of ramming points in the first sequence is ramming all the ramming points 10 times ⁇ All ramming points in the second sequence are tamped 10 times ⁇ all ramming points in the first sequence are tamped more than 8 times ⁇ all ramming points in the second sequence are tamped more than 8 times;
  • the crane is in place, and a point rammer with a diameter of 1.5m is used to align the rammer at the location of the ramming point, and the height of the hammer top before the ramming is measured.
  • the ramming energy is 3000kN ⁇ m, based on the weight of the rammer, the diameter of the rammer and the top of the hammer.
  • the elevation calculates the design height of the rammer lift.
  • the design height of the rammer lift for the first dynamic compaction is calculated as follows:
  • H 1 first dynamic rammer to increase the design height; It is the ramming energy of the first dynamic compaction, taken as 3000kN ⁇ m, m 1 is the mass of the one-time dynamic compaction hammer, taken as 30 tons; g is the acceleration of gravity, taken as 10m/s 2 ;
  • the replacement material uses medium weathered to slightly weathered crushed stone, the largest particle size of the crushed stone
  • the content of crushed stone with a diameter of 250mm and a maximum particle size of 300mm shall not exceed 25%, the uneven coefficient of crushed stone shall be greater than 5.5, and the mud content shall be 3%;
  • Step 7 Drain the foundation to reduce the pore water pressure, use the pre-buried pore water pressure gauge to measure the pore water pressure value of the site, and monitor the dissipation law of the pore water pressure of the foundation, specifically as follows:
  • the pore water pressure in the foundation reaches the maximum value
  • the rammed pier is composed of crushed stones to form a drainage channel
  • the groundwater in the silt soil layer is drained by the rammed pier and collected in the rammed pit;
  • N p is the number of pore water pressure gauges buried
  • m (1,2,3,...,N)
  • N is the number of pore water pressure measurements
  • the buried pore water pressure gauge is used to measure the pore water pressure value of the site of the example.
  • the pore water pressure gauge is buried in position as shown in Figure 5. The measurement is performed every 12 hours, and a total of 5 measurements are made for 60 hours in history.
  • the pore water pressure has dissipated, as shown in Table 3: That is, when the measurement reaches the fifth time, the pore water pressure change rate of measuring point 1, measuring point 2, and measuring point 3 are 13% and 14 respectively. % And 8%, the rate of change of the three measuring points is less than 20%, stop measuring the pore water pressure value and proceed to the next step.
  • Step 8 Perform a second dynamic compaction on all the compaction points of the foundation dynamic compaction replacement, specifically:
  • the construction sequence is from the center of the ramming point to the ramming points on both sides; specifically as shown in Figure 4:
  • the central ramming point of the embodiment is H35, and the construction sequence is ramming Point H35 is the center and tap all the ramming points on the top, bottom, left and right in order from inside to outside;
  • the crane is in place, and a point rammer with a diameter of 2.0m is used to align the rammer at the ramming point position, and measure the height of the hammer before the rammer.
  • the ramming energy can be 5000 ⁇ 6000kN ⁇ m, according to the weight of the rammer, the diameter of the rammer and
  • the height of the hammer top calculates the design height of the rammer lift; the design height of the rammer lift of the second dynamic compaction is calculated as follows:
  • H 2 second dynamic rammer to increase the design height It is the ramming energy of the second dynamic compaction, which can be 6000kN ⁇ m, m 2 is the mass of the secondary dynamic compaction hammer, which is 40 tons; g is the acceleration of gravity, which is 10m/s 2
  • the replacement material uses medium weathered to slightly weathered crushed stone, with the largest particle size of the crushed stone
  • the content of crushed stone with a maximum diameter of 250mm is 20%, the uneven coefficient of crushed stone is greater than 5.5, and the mud content is 3%;
  • Dynamic compaction construction specifically: repeat steps 2 to step 4 13 times for all ramming points of the site, and the number of ramming times for each ramming point is not less than 10 times; the ramming amount of the ramming point H35 in the center of the foundation is shown in Table 4 ,
  • the 12th ramming sinking volume is 9cm
  • the 13th ramming sinking volume is 7cm, that is, the ramming sinking volume of the 12th and 13th strokes are both less than 10cm
  • the second dynamic compaction construction of the ramming point is completed.
  • Step 9 Carry out full ramming construction within the scope of the foundation, specifically as follows: 1 Excavate the floating soil with a depth of 1.0 ⁇ 1.5m, and backfill the site with strong weathered crushed stone to the reference elevation. The maximum particle size of the strong weathered crushed stone is not Larger than 300mm, the uneven coefficient of the crushed stone is greater than 5, and the mud content is not greater than 5%; 2The full ramming is carried out in two sequences, the first sequence is 3 times, the second sequence is 2 times, the ramming point of the full ramming The overlap between each other is not less than 1/3 of the diameter of the bottom of the hammer; 3For full ramming, use a rammer with a diameter of 2.4m, a weight of 20 tons and an air hole, and use a ramming energy of 2000kN ⁇ m for full ramming of all ramming points. ;
  • 3Full ramming uses a rammer with a diameter of 2.4m, a weight of 20 tons and air holes, and uses a ramming energy of 2000kN ⁇ m to carry out the full ramming construction of all ramming points;
  • the post-ramming elevation is measured with a 10m ⁇ 10m square grid.
  • the grid layout and measuring point number are shown in Figure 7.
  • the measured elevation of each measuring point is shown in Table 5.
  • Step 10 Use geological radar or geological drilling to detect the pier length of the gravel replacement pier, determine the pier length of the dynamic compaction gravel replacement pier, and measure the number of replacement piers to be no less than 5;
  • the embodiment uses geological drilling to monitor the pier length of the gravel replacement piers, and selects 6 replacement piers for borehole measurement.
  • the measurement positions of the lengths of the 6 replacement piers are shown in Figure 8.
  • the pier lengths of the 6 replacement piers The measured values are shown in Table 7.
  • the measured pier lengths are all larger than the designed pier length by 12.0m.
  • Numbering Pier length (m) Numbering Pier length (m) 1 12.38 4 13.35 2 13.50 5 12.75 3 12.18 6 13.20
  • Step 11 Carry out the plate load test of the replacement pier body of the dynamic compaction replacement foundation to determine the characteristic value of the bearing capacity of the dynamic consolidation replacement pier body.
  • 2 to 3 replacement pier bodies can be randomly selected for the plate load test, and the plate load of the replacement pier body The number of tests shall not be less than 2, and the method of plate load test for replacement piers shall be carried out in accordance with the relevant regulations in the "Code for Design of Building Foundations" GB 50007-2011.
  • Step 12 Carry out the plate load test of the soil between the piers of the dynamic compaction replacement foundation to determine the characteristic value of the bearing capacity of the soil between the piers of the dynamic compaction replacement.
  • the plate load test of the soil between the piers is carried out at a depth of about 2 to 3m to determine the pier.
  • the maximum load and bearing capacity characteristic values of the soil slab load test can be randomly selected from 3 to 4 positions of the soil between the piers for the slab load test.
  • the number of the slab load tests for the soil between the piers is not less than 3, replace the pier body plate load
  • the test method refers to the relevant regulations in the "Code for Design of Building Foundations" GB 50007-2011.
  • the plate load test of the soil between the piers was carried out after the replacement of the foundation by dynamic compaction of the embodiment.
  • the plate load test of the soil between the piers was carried out at a depth of 2.5m. The positions of the soil between the three piers were randomly selected for the plate load test.
  • the location of the soil slab load test is shown in Figure 10; the method of the replacement pier body slab load test refers to the relevant regulations in the "Code for Design of Building Foundations" GB 50007-2011; through the test statistics: the load of the soil slab load test 1 between the piers The characteristic value of force is 423.00kPa, the characteristic value of bearing capacity of soil slab load test 2 between piers is 386.00kPa, and the characteristic value of bearing capacity of soil slab load test 3 between piers is 406.00kPa.
  • the present invention implements the first and second dynamic compaction replacement and reinforcement of the coastal soft soil foundation to achieve compaction of the sand layer to reduce its water content and porosity, so as to eliminate the possibility of seismic liquefaction of the sand layer.
  • Block stones replace shallow silt soil to form a gravel replacement pile composite foundation to enhance the bearing capacity of the foundation, while rubble replace the piles to compact the soil between the piles to reduce the porosity and moisture content of the soil. Drainage between the second dynamic compaction accelerates the drainage consolidation process of the silt soft soil layer, effectively improves the bearing capacity of the foundation, eliminates the possibility of liquefaction of the lower sand layer, and realizes the efficient dynamic compaction replacement and reinforcement of the silt soft soil foundation.

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Abstract

本发明公开了一种滨海淤泥软土地基二次强夯碎石置换加固方法，通过对滨海软土地基进行第一次、第二次强夯置换加固，实现通过击实功将砂层压密降低其含水率和孔隙率，以消除砂层地震液化可能性，通过碎块石置换浅层淤泥土形成碎石置换桩复合地基以增强地基承载力，同时碎块石置换桩体挤密桩间土体以降低土体的孔隙率和含水率，通过第一次和第二次强夯之间进行排水加速淤泥软土层的排水固结过程，有效提高地基的承载力、消除下部砂层的液化可能性，实现淤泥软土地基的高效强夯置换加固，解决淤泥软土地基承载力低、加固处理难度大、排水固结速度较慢、加固处理费用高等难题。

Description

一种滨海淤泥软土地基二次强夯碎石置换加固方法 技术领域
本发明属于滨海软土地基处理技术领域，具体地说，涉及一种滨海淤泥软土地基二次强夯碎石置换加固方法。
背景技术
随着我国沿海地区经济的快速发展，对基础设施建设需求不断加大，沿海地区进行了大规模的公路、铁路和工业厂房的建设，而这些建筑物大部分均修建于滨海软土地基之上，滨海软土地基主要由海相沉积而形成，其地层中包含有较厚的细砂层或粉砂层，同时砂层上部分布有一定厚度的淤泥；细砂层或粉砂层使得地基具有较高的地震液化可能性，而淤泥土层含水量较大、液限较高导致其压缩性较大、排水固结速度缓慢。因此，滨海软土地基具有三大特点：低承载力、高压缩性和较高的地震液化可能性，滨海软土地基的承载力问题日益突出。
传统处理软土地基的方法主要有预压法、桩基础法和强夯法，预压法是通过堆载预压加速软土的排水固体过程，桩基础法是通过人工成桩将上部荷载传递到深部的持力层，强夯法是通过击实功将软土压密的处理方法。
预压法和桩基础虽然可以解决滨海软土地基低承载力、高压缩性的不足，但其均无法消除砂层的地震液化；而使用常规强夯法处理滨海软土地基会碰到的埋锤、频繁加料和高隆起等问题，并且一次性强夯对桩间土中的淤泥层的排水固结效果不好。由于滨海软土地基的特殊性，使用传统强夯方法加固滨海软土地基效果并不理想，会产生工期长、造价高、工后沉降难于控制和地震液化消除有限等问题。
有鉴于此特提出本发明。
发明内容
本发明要解决的技术问题在于克服现有技术的不足，提供一种滨海淤泥软土地基二次强夯碎石置换加固方法，通过对滨海软土地基进行第一次、第二次强夯置换加固，实现通过击实功将砂层压密降低其含水率和孔隙率，以消除砂层地震液化可能性，通过碎块石置换浅层淤泥土形成碎石置换桩复合地基以增强地基承载力，同时碎块石置换桩体挤密桩间土体以降低土体的孔隙率和含水率，通过第一次和第二次强夯之间进行排水加速淤泥软土层的排水固结过程，有效提高地基的承载力、消除下部砂层的液化可能性，实现淤泥软土地基的高效强夯置换加固。
为解决上述技术问题，本发明采用技术方案的基本构思是：
一种滨海淤泥软土地基二次强夯碎石置换加固方法，具体步骤如下：
步骤1、拟定滨海软土地基的基本参数，包括：滨海软土地基土层的数量、每层土的名称、厚度；地下水位信息；滨海软土地基场地的长度、宽度和面积；强夯置换碎石墩的设计墩长。
步骤2、初步平整施工场地，清除地面表层0.5～1.0m厚的杂填土，测量场地基准高程。
步骤3、在初平地面上回填1.0～1.5m厚的强风化碎块石，碎块石最大粒径不大于300mm、不均匀系数大于5。
步骤4、确定场地强夯置换的夯点位置和数量，夯点按正方形或梅花形布置，夯点间距可取3.0～6.0m，，对地基的所有夯点进行编号。
步骤5、量测强夯开始前地基的孔隙水压力基准值，具体为：在强夯置换地基的夯区中心区域附近埋设孔隙水压力计，孔隙水压力计埋设不少于3个，确定每个孔隙水压力计的高程、每个孔隙水压力计埋设高程间距为2.0～3.0m，埋设好孔隙水压力计以后测定强夯开始前每个测点的孔隙水压力基准值
Figure PCTCN2019123609-appb-000001
其中i＝(1,…,N p)，N p是孔隙水压力计埋设的数量。
步骤6、对地基强夯置换的所有夯点进行第一次强夯，具体为：
①将强夯墩点分为2-3序，采用隔空分序跳打的方式完成全部夯点施工；
②起重机就位，采用直径1.5m～2.0m直径的点夯锤，使夯锤对准夯点位置，测量夯前锤顶高程，夯击能采用3000～4000kN·m，根据夯锤重量、夯锤直径和锤顶高程计算夯锤提升的设计高度，第一次强夯的夯锤提升设计高度按下式计算：
Figure PCTCN2019123609-appb-000002
式中：H 1第一次强夯夯锤提升设计高度；
Figure PCTCN2019123609-appb-000003
是第一次强夯的夯击能，可取3000～4000kN·m，m 1是一次强夯夯锤的质量；g是重力加速度；
③使用起重机将夯锤起吊到设计高度，解除夯锤挂钩使夯锤自由下落完成一遍夯击，测量锤顶高程，计算每遍夯沉量；
④将夯锤从夯坑中取出，当夯坑深度大于50cm时及时向夯坑内填加置换料将夯坑填平，置换料使用中风化至微风化的碎块石，碎块石最大粒径不大于300mm，最大粒径300mm的碎块石的含量不大于30％，碎块石不均匀系数大于5，含泥量小于5％；
⑤每个夯点重复步骤②～步骤④15遍以上，使墩长达到设计深度要求，完成每个墩点的第一次强夯施工；
⑥对各序的每个夯点重复步骤②～步骤⑤，连续进行夯击，各序之间不设时间间隔连续进行夯击施工，对最后两击的夯沉量也不做限定；
步骤7、进行地基的排水降低孔隙水压力，使用预先埋设的孔隙水压力计测定场地的孔隙水压力值，监测地基孔隙水压力的消散规律，具体为：
①步骤6的第一次夯击完成时地基内的孔隙水压力达到最大值，夯墩由碎块石组成而形成排水通道，淤泥土层内的地下水由夯墩排水汇集在夯坑内；
②使用抽水设备抽排夯坑内的积水；
③使用埋设的孔隙水压力计测定场地的孔隙水压力值，每间隔8～12小时测量一次，并按下式计算孔隙水压力实测值相对与基准值的变化率：
Figure PCTCN2019123609-appb-000004
式中：其中i＝(1,…,N p)，N p是孔隙水压力计埋设的数量，m＝(1,2,3,…,N)，m是孔隙水压力测量次数，
Figure PCTCN2019123609-appb-000005
是强夯之前地基中第i个测点的孔隙水压力的基准值，
Figure PCTCN2019123609-appb-000006
是第一次夯击完成以后第i个测点第m次测量获得的地基孔隙水压力值，
Figure PCTCN2019123609-appb-000007
是第一次强夯完成以后第i个测点第m次测量获得的地基孔隙水压力值相对于初始基准值的变化率。
④当所有测点的
Figure PCTCN2019123609-appb-000008
均小于20％时，孔隙水压力消散完毕，停止测量孔隙水压力值，进入下一步骤。
步骤8、对地基强夯置换的所有夯点进行第二次强夯，具体为：
①第二次夯击不分序次，施工顺序从最中心的夯点向两侧施工；
②起重机就位，采用直径2.0m直径的点夯锤，使夯锤对准夯点位置，测量夯前锤顶高程，夯击能采用5000～6000kN·m，根据夯锤重量、夯锤直径和锤顶高程计算夯锤提升的设计高度；第二次强夯的夯锤提升设计高度按下式计算：
Figure PCTCN2019123609-appb-000009
式中：H 2第二次强夯夯锤提升设计高度；
Figure PCTCN2019123609-appb-000010
是第二次强夯的夯击能，可取5000～6000kN·m，m 2是二次强夯夯锤的质量；g是重力加速度；
③使用起重机将夯锤起吊到设计高度，解除夯锤挂钩使夯锤自由下落完成一遍夯击，测量锤顶高程，计算每遍夯击的夯沉量；
④将夯锤从夯坑中取出，当夯坑深度大于50cm时及时向夯坑内填加置换料将夯坑填平，置换料使用中风化至微风化的碎块石，碎块石最大粒径不大于300mm，最大粒径300mm的碎块石的含量不大于30％，碎块石不均匀系数大于5，含泥量小于5％；
⑤对场地的所有夯点重复步骤②至步骤④10～30遍，每个夯点的夯击遍数不小于10遍，当最后两遍的夯沉量须小于10cm时，完成夯点的第二次强夯施工；
步骤9、进行地基范围内的满夯施工，具体为：
①挖除深度1.0～1.5m深度的浮土，并用强风化碎块石回填整平场地至基准标高，强风化碎块石最大粒径不大于300mm、碎块石的不均匀系数大于5、含泥量不大于5％；；
③满夯夯击使用直径2.4m、重20吨并带有气孔的夯锤，以夯击能2000kN·m进行所有夯点的满夯施工；
②满夯分两序进行，第一序夯击3遍，第二序夯击2遍，满夯的夯点之间相互搭接不小于1/3锤底直径；
④满夯完毕以后以10m×10m或20m×20m的方格网实测夯后标高。
步骤10、采用地质雷达或地质钻孔的方式检测碎石置换墩的墩长，确定强夯碎石置换墩的墩长，监测置换墩数量不少于5个；
步骤11、进行强夯置换地基的置换墩体的平板载荷试验，确定强夯置换墩体的承载力特征值，可随机选取2～3个置换墩体进行平板载荷试验，置换墩体的平板载荷试验数量不少于2个，置换墩体平板载荷试验的方法参照《建筑地基基础设计规范》GB 50007-2011中的相关规定执行。
步骤12、进行强夯置换地基的墩间土的平板载荷试验，确定强夯置换墩间土的承载力特征值，墩间土的平板载荷试验仅在深约2～3m的深度处进行，确定墩间土的平板荷载试验的最大荷载和承载力特征值，可随机选取3～4个墩间土的位置进行平板载荷试验，后墩间土的平板载荷试验数量不少于3个，墩间土平板载荷试验的方法参照《建筑地基基础设计规范》GB 50007-2011中的相关规定执行。
采用上述技术方案后，本发明与现有技术相比具有以下有益效果。
本发明通过对滨海软土地基进行第一次、第二次强夯置换加固，实现通过击实功将砂层压密降低其含水率和孔隙率，以消除砂层地震液化可能性，通过碎块石置换浅层淤泥土形成碎石置换桩复合地基以增强地基承载力，同时碎块石置换桩体挤密桩间土体以降低土体的孔隙率和含水率，通过第一次和第二次强夯之间进行排水加速淤泥软土层的排水固结过程，有效提高地基的承载力、消除下部砂层的液化可能性，实现淤泥软土地基的高效强夯置换加固。
本发明加固方法可以高效、快速、经济的加固滨海淤泥软土地基，以提高滨海淤泥软土地基的承载力、控制地基的工后沉降，并消除砂层的液化特性，解决淤泥软土地基承载力低、加固处理难度大、排水固结速度较慢、加固处理费用高等难题，以提高加固处理以后的淤泥软土地基的极限承载力、有效减小上部建筑物的工后沉降、消除下部砂层的液化可能性，达到既经济又安全的目的。
下面结合附图对本发明的具体实施方式作进一步详细的描述。
附图说明
附图作为本申请的一部分，用来提供对本发明的进一步的理解，本发明的示意性实施例及其说明用于解释本发明，但不构成对本发明的不当限定。显然，下面描述中的附图仅仅是一些实施例，对于本领域普通技术人员来说，在不付出创造性劳动的前提下，还可以根据这些附图获得其他附图。在附图中：
图1本发明流程示意图；
图2实施例滨海淤泥软土地基地层剖面图；
图3实施例滨海淤泥软土地基场地平面图；
图4实施例二次强夯置换地基夯点位置平面布置图；
图5实施例孔隙水压力计埋设位置示意图；
图6实施例满夯施工夯点平面布置图；
图7实施例满夯完毕以后实测夯后标高的方格网布置和测点编号示意图；
图8实施例地基置换墩长度测量位置示意图
图9实施例地基置换墩平板载荷试验位置示意图；
图10实施例地基墩间土平板载荷试验位置示意图；
需要说明的是，这些附图和文字描述并不旨在以任何方式限制本发明的构思范围，而是通过参考特定实施例为本领域技术人员说明本发明的概念。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合本发明实施例中的附图，对实施例中的技术方案进行清楚、完整地描述，以下实施例用于说明本发明，但不用来限制本发明的范围。
实施例1
一种滨海淤泥软土地基二次强夯碎石置换加固方法，具体步骤如下(流程如图1所示)：
步骤1、拟定滨海软土地基的基本参数，包括：滨海软土地基土层的数量、每层土的名称、厚度；地下水位信息；滨海软土地基场地的长度、宽度和面积；强夯置换碎石墩的设计墩长。
具体为：实施例滨海软土地基土层的数量为6层；从上自下分别是：第一层为杂填土、厚度0.6m，第二层为淤粉质粘土厚度为3.0m，第三层为淤泥、厚度为2.0m，第四层为粉细砂、厚度4.3m，第五层为中粗砂、厚度为3.0m，第六层为粉质粘土、厚度为8.0m，实施例淤泥软土地基地层剖面如图2所示；地下水位位于地表以下-1.2m；滨海软土地基场地的长度40m、宽度30m、面积1200m 2，实施例淤泥软土地基平面图如图3所示；强夯置换碎石墩的设计墩长12.0m。
步骤2、初步平整施工场地，清除地面表层0.5～1.0m厚的杂填土，测量场地基准高程。
具体为：初步平整实施例地基施工场地，清除处地面表层0.6m厚的杂填土，测量场地基准高程为6.0m。
步骤3、在初平地面上回填1.0～1.5m厚的强风化碎块石，碎块石最大粒径不大于300mm、不均匀系数大于5。
具体为：在实施例初平地面上回填1.0m厚的强风化碎块石，碎块石最大粒径为250mm、不均匀系数取5.5。
步骤4、确定场地强夯置换的夯点位置和数量，夯点按正方形或梅花形布置，夯点间距可取3.0～6.0m，对地基的所有夯点进行编号。
具体为：确定实施例场地强夯置换的夯点位置，夯点的平面布置如图4所示，夯点中数量为70个，夯点按正方形布置，夯点间距取4.0m，实施例地基的所有夯点编号如图4所示，编号从H1至H70。
步骤5、量测强夯开始前地基的孔隙水压力基准值，具体为：在强夯置换地基的夯区中心区域附近埋设孔隙水压力计，孔隙水压力计埋设不少于3个，确定每个孔隙水压力计的高程、每个孔隙水压力计埋设高程间距为2.0～3.0m，埋设好孔隙水压力计以后测定强夯开始前每个测点的孔隙水压力基准值
Figure PCTCN2019123609-appb-000011
其中i＝(1,…,N p)，N p是孔隙水压力计埋设的数量。
具体为：在实施例强夯置换地基的夯区中心区域附近埋设孔隙水压力计，孔隙水压力计为振弦式孔隙水压力计、型号为RC011-KYJ，孔隙水压力计埋设数量为3个，第一个孔隙水压力计的高程是地表下-3.0m、第一个孔隙水压力计的高程是地表下-4.5m、第一个孔隙水压力计的高程是地表下-7.0m，3个孔隙水压力计埋设高程间距分别为1.5m和2.5m，孔隙水压力计埋设位置如图5所示；埋设好孔隙水压力计以后测定强夯开始前每个测点的孔隙水压力 基准值
Figure PCTCN2019123609-appb-000012
其中i＝(1,…,N p)，N p＝3是孔隙水压力计埋设的数量，每个测点的孔隙水压力基准值如表1所示。
表1实施例淤泥软土地基测点的孔隙水压力基准值
Figure PCTCN2019123609-appb-000013
步骤6、对地基强夯置换的所有夯点进行第一次强夯，具体为：
①将强夯墩点分为2序，如图4所示，第1序为编号H1至H10、H21至H30、H41至H50、H61至H70的夯点，第2序为H11至H20、H31至H40、H51至H60的夯点；实施例采用隔空分序跳打的方式完成全部夯点施工，隔空分序跳打的施工顺序为：第一序所有夯点夯击10遍→第二序所有夯点夯击10遍→第一序所有夯点夯击8遍以上→第二序所有夯点夯击8遍以上；
②起重机就位，采用直径1.5m直径的点夯锤，使夯锤对准夯点位置，测量夯前锤顶高程，夯击能采用3000kN·m，根据夯锤重量、夯锤直径和锤顶高程计算夯锤提升的设计高度，第一次强夯的夯锤提升设计高度按下式计算：
Figure PCTCN2019123609-appb-000014
式中：H 1第一次强夯夯锤提升设计高度；
Figure PCTCN2019123609-appb-000015
是第一次强夯的夯击能，取3000kN·m，m 1是一次强夯夯锤的质量，取30吨；g是重力加速度，取10m/s 2；
将
Figure PCTCN2019123609-appb-000016
m 1＝30吨，g＝10m/s 2带入式(1)，计算得到第一次强夯夯锤提升设计高度H 1＝10m。
③使用起重机将夯锤起吊到设计高度10.0m，解除夯锤挂钩使夯锤自由下落完成一遍夯击，测量锤顶高程，计算每遍夯沉量；实施例淤泥软土地基第一次强夯场地中心夯点H35在每一击强夯下锤顶高程、夯沉量统计如表2所示。
表2第一次强夯场地中心夯点H35测量的锤顶高程、夯沉量统计表
夯击次数 夯锤提升设计高度(m) 锤顶高程(m) 夯沉量(m)
1 10.0 1.86 4.14
2 10.0 2.11 3.89
3 10.0 2.44 3.56
4 10.0 2.66 3.34
5 10.0 2.99 3.01
6 10.0 3.30 2.70
7 10.0 3.49 2.51
8 10.0 3.80 2.20
9 10.0 4.00 2.00
10 10.0 4.28 1.72
11 10.0 4.46 1.54
12 10.0 4.70 1.30
13 10.0 4.91 1.09
14 10.0 5.08 0.92
15 10.0 5.29 0.71
16 10.0 5.38 0.62
17 10.0 5.47 0.53
18 10.0 5.50 0.50
④将夯锤从夯坑中取出，当夯坑深度大于50cm时及时向夯坑内填加置换料将夯坑填平，置换料使用中风化至微风化的碎块石，碎块石最大粒径取250mm，最大粒径300mm的碎块石的含量不大于25％，碎块石不均匀系数大于5.5，含泥量为3％；
⑤每个夯点重复步骤②～步骤④18遍，置换墩长为13.5m，达到了设计深度要求，完成每个墩点的第一次强夯施工；
⑥对各序的每个夯点重复步骤②～步骤⑤，连续进行了18次夯击，第1序和第2序之间不设时间间隔连续进行夯击施工，对最后两击的夯沉量也不做限定；
步骤7、进行地基的排水降低孔隙水压力，使用预先埋设的孔隙水压力计测定场地的孔隙水压力值，监测地基孔隙水压力的消散规律，具体为：
①步骤6的第一次夯击完成时地基内的孔隙水压力达到最大值，夯墩由碎块石组成而形成排水通道，淤泥土层内的地下水由夯墩排水汇集在夯坑内；
②使用抽水设备抽排夯坑内的积水；
③使用埋设的孔隙水压力计测定场地的孔隙水压力值，每间隔8小时测量一次，并按下式计算孔隙水压力实测值相对与基准值的变化率：
Figure PCTCN2019123609-appb-000017
式中：其中i＝(1,…,N p)，N p是孔隙水压力计埋设的数量，m＝(1,2,3,…,N)，N是孔隙水压力测量次数，
Figure PCTCN2019123609-appb-000018
是强夯之前地基中第i个测点的孔隙水压力的基准值，
Figure PCTCN2019123609-appb-000019
是第一次夯击完成以后第i个测点第m次测量获得的地基孔隙水压力值，
Figure PCTCN2019123609-appb-000020
是第一次强夯完成以后第i个测点第m次测量获得的地基孔隙水压力值相对于初始基准值的变化率。
具体为：使用埋设的孔隙水压力计测定实施例场地的孔隙水压力值，孔隙水压力计埋设位置如图5所示，每间隔12小时测量一次，共计测量5次历史60个小时，孔隙水压力计埋设的数量N p＝3，孔隙水压力测量次数N＝5，每次测量得到的孔隙水压力值
Figure PCTCN2019123609-appb-000021
和计算得到的孔隙水压力变化率
Figure PCTCN2019123609-appb-000022
如表3所示。
表3实施例淤泥软土地基测点的孔隙水压力变化率
Figure PCTCN2019123609-appb-000023
④当所有测点的
Figure PCTCN2019123609-appb-000024
均小于20％时，孔隙水压力消散完毕，如表3所示：即当测量到第5次时，测点1、测点2、测点3的孔隙水压力变化率分别为13％、14％和8％，三个测点的变化率均小于20％，停止测量孔隙水压力值，进入下一步骤。
步骤8、对地基强夯置换的所有夯点进行第二次强夯，具体为：
①第二次强夯全部夯点，夯击不分序次，施工顺序从最中心的夯点向两侧夯点施工；具体如图4：实施例中心夯点为H35，施工顺序是以夯点H35为中心从内至外的顺序夯击上、下、左、右的所有夯点；
②起重机就位，采用直径2.0m直径的点夯锤，使夯锤对准夯点位置，测量夯前锤顶高程，夯击能采用5000～6000kN·m，根据夯锤重量、夯锤直径和锤顶高程计算夯锤提升的设计高度；第二次强夯的夯锤提升设计高度按下式计算：
Figure PCTCN2019123609-appb-000025
式中：H 2第二次强夯夯锤提升设计高度；
Figure PCTCN2019123609-appb-000026
是第二次强夯的夯击能，可取6000kN·m，m 2是二次强夯夯锤的质量，取40吨；g是重力加速度，取10m/s 2
将
Figure PCTCN2019123609-appb-000027
m 2＝40吨，g＝10m/s 2带入式(1)，计算得到第二次强夯夯锤提升设计高度H 2＝15.0m。
③使用起重机将夯锤起吊到设计高度15.0m，解除夯锤挂钩使夯锤自由下落完成一遍夯击，测量锤顶高程，按计算每遍夯击的夯沉量；实施例淤泥软土地基第二次强夯场地中心夯点在每一击强夯下锤顶高程、夯沉量统计如表4所示。
表4第二次强夯场地中心夯点H35测量的锤顶高程、夯沉量统计表
夯击次数 夯锤提升设计高度(m) 锤顶高程(m) 夯沉量(m)
1 15.0 5.32 0.68
2 15.0 5.45 0.55
3 15.0 5.50 0.50
4 15.0 5.54 0.46
5 15.0 5.60 0.40
6 15.0 5.64 0.36
7 15.0 5.68 0.32
8 15.0 5.72 0.28
9 15.0 5.77 0.23
10 15.0 5.81 0.19
11 15.0 5.86 0.14
12 15.0 5.91 0.09
13 15.0 5.93 0.07
④将夯锤从夯坑中取出，当夯坑深度大于50cm时及时向夯坑内填加置换料将夯坑填平，置换料使用中风化至微风化的碎块石，碎块石最大粒径为250mm，最大粒径250mm的碎块石的含量位20％，碎块石不均匀系数大于5.5，含泥量为3％；
⑤对场地的所有夯点重复步骤②至步骤④10～30遍，每个夯点的夯击遍数不小于10遍，当最后两遍的夯沉量小于10cm时，完成夯点的第二次强夯施工；具体为：对场地的所有夯点重复步骤②至步骤④13遍以上，每个夯点的夯击遍数不小于10遍；地基中心夯点H35的夯沉量如表4所示，第12击夯沉量为9cm、第13击夯沉量为7cm，即第12击、13击的夯沉量均小于10cm，完成夯点的第二次强夯施工。
步骤9、进行地基范围内的满夯施工，具体为：①挖除深度1.0～1.5m深度的浮土，并用强风化碎块石回填整平场地至基准标高，强风化碎块石最大粒径不大于300mm、碎块石的不均匀系数大于5、含泥量不大于5％；②满夯分两序进行，第一序夯击3遍，第二序夯击2遍， 满夯的夯点之间相互搭接不小于1/3锤底直径；③满夯夯击使用直径2.4m、重20吨并带有气孔的夯锤，以夯击能2000kN·m进行所有夯点的满夯施工；
进行实施例地基范围内的满夯施工：
①挖除深度1.0m深度的浮土，并用强风化碎块石回填整平场地至基准标高6.0m，强风化碎块石最大粒径不大于250mm、碎块石的不均匀系数大于5.5、含泥量不大于3％；
②实施例满夯分两序进行，全部夯点第一序夯击3遍，全部夯点第二序夯击2遍，满夯的夯点之间相互搭接不小于1/3锤底直径，满夯施工夯点平面布置图满夯的夯点的布置如图6所示，共计设置450个满夯夯点；
③满夯夯击使用直径2.4m、重20吨并带有气孔的夯锤，以夯击能2000kN·m进行所有夯点的满夯施工；
④满夯完毕以后以10m×10m的方格网实测夯后标高，方格网布置和测点编号如图7所示，各个测点的实测标高如表5所示。
表5地基强夯完成以后实测标高统计表
测点号 高程(m) 测点号 高程(m)
C1 5.97 C6 6.02
C2 6.10 C7 5.98
C3 6.03 C8 6.18
C4 5.89 C9 6.02
C5 6.11    
步骤10、采用地质雷达或地质钻孔的方式检测碎石置换墩的墩长，确定强夯碎石置换墩的墩长，测量置换墩数量不少于5个；
具体为：实施例采用地质钻孔的方式监测碎石置换墩的墩长，选取6个置换墩进行钻孔测量，6个置换墩长度测量位置如图8所示，6个置换墩的墩长测量值如表7所示，实测墩长均大于设计墩长12.0m。
表6置换墩的实测墩长统计表
编号 墩长(m) 编号 墩长(m)
1 12.38 4 13.35
2 13.50 5 12.75
3 12.18 6 13.20
步骤11、进行强夯置换地基的置换墩体的平板载荷试验，确定强夯置换墩体的承载力特征值，可随机选取2～3个置换墩体进行平板载荷试验，置换墩体的平板载荷试验数量不少于2个，置换墩体平板载荷试验的方法参照《建筑地基基础设计规范》GB 50007-2011中的相关规定执行。
具体为：进行强夯置换地基的置换墩体的平板载荷试验，确定强夯置换墩体的承载力特征值，随机选取2个置换墩体进行平板载荷试验，置换墩平板载荷试验位置如图9所示；置换墩体平板载荷试验的方法参照《建筑地基基础设计规范》GB 50007-2011中的相关规定执行；通过试验统计：平板载荷试验置换墩1的的承载力特征值为848.00kPa，平板载荷试验置换墩2的承载力特征值为807.00kPa。
步骤12、进行强夯置换地基的墩间土的平板载荷试验，确定强夯置换墩间土的承载力特征值，墩间土的平板载荷试验在约2～3m的深度处进行，确定墩间土的平板荷载试验的最大荷载和承载力特征值，可随机选取3～4个墩间土的位置进行平板载荷试验，墩间土的平板载荷试验数量不少于3个，置换墩体平板载荷试验的方法参照《建筑地基基础设计规范》GB 50007-2011中的相关规定执行。
具体为：进行实施例地基强夯置换以后墩间土的平板载荷试验，墩间土的平板载荷试验在2.5m的深度处进行，随机选取3个墩间土的位置进行平板载荷试验，墩间土平板载荷试验位置如图10所示；置换墩体平板载荷试验的方法参照《建筑地基基础设计规范》GB 50007-2011中的相关规定执行；通过试验统计：墩间土平板载荷试验1的承载力特征值为423.00kPa，墩间土平板载荷试验2的承载力特征值为386.00kPa，墩间土平板载荷试验3的承载力特征值为406.00kPa。
本发明通过对滨海软土地基进行第一次、第二次强夯置换加固，实现通过击实功将砂层压密降低其含水率和孔隙率，以消除砂层地震液化可能性，通过碎块石置换浅层淤泥土形成碎石置换桩复合地基以增强地基承载力，同时碎块石置换桩体挤密桩间土体以降低土体的孔隙率和含水率，通过第一次和第二次强夯之间进行排水加速淤泥软土层的排水固结过程，有效提高地基的承载力、消除下部砂层的液化可能性，实现淤泥软土地基的高效强夯置换加固。
以上所述仅是本发明的较佳实施例而已，并非对本发明作任何形式上的限制，虽然本发明已以较佳实施例揭露如上，然而并非用以限定本发明，任何熟悉本专利的技术人员在不脱离本发明技术方案范围内，当可利用上述提示的技术内容作出些许更动或修饰为等同变化的等效实施例，但凡是未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所作的任何简单修改、等同变化与修饰，均仍属于本发明方案的范围内。

Claims (6)

  1. 一种滨海淤泥软土地基二次强夯碎石置换加固方法，其特征在于，包括以下步骤：
    步骤1、拟定滨海软土地基的基本参数；滨海软土地基的基本参数包括：滨海软土地基土层的数量、每层土的名称、厚度；地下水位信息；滨海软土地基场地的长度、宽度和面积；强夯置换碎石墩的设计墩长；
    步骤2、初步平整施工场地，清除地面表层0.5～1.0m厚的杂填土，测量场地基准高程；
    步骤3、在初平地面上回填1.0-1.5m厚的强风化碎块石，碎块石最大粒径不大于300mm、不均匀系数大于5；
    步骤4、确定场地强夯置换的夯点位置和数量，夯点按正方形或梅花形布置，夯点间距可取3.0～6.0m，对地基的所有夯点进行编号；
    步骤5、在强夯置换地基的夯区中心区域附近埋设孔隙水压力计，量测强夯开始前地基的孔隙水压力基准值；
    步骤6、起重机就位，确定夯锤提升高度，对地基强夯置换的所有夯点进行第一次强夯，将强夯墩点分为2-3序，采用隔空分序跳打的方式完成全部夯点施工，并及时向夯坑内填加置换料；
    步骤7、进行地基的排水降低孔隙水压力，使用预先埋设的孔隙水压力计测定场地的孔隙水压力值，监测地基孔隙水压力的消散规律，待孔隙水压力消散完毕，停止测量孔隙水压力值，进入下一步骤；
    步骤8、确定夯锤提升高度，对地基强夯置换的所有夯点进行第二次强夯，夯击不分序次，施工顺序从最中心的夯点向两侧施工，并及时向夯坑内填加置换料；
    步骤9、挖除浮土并用强风化碎块石回填整平场地至基准标高，进行地基范围内的满夯施工；
    步骤10、采用地质雷达或地质钻孔的方式检测碎石置换墩的墩长，确定强夯碎石置换墩的墩长，监测置换墩数量不少于5个；
    步骤11、进行强夯置换地基的置换墩体的平板载荷试验，确定强夯置换墩体的承载力特征值；
    步骤12、进行强夯置换地基的墩间土的平板载荷试验，确定强夯置换墩间土的承载力特征值。
  2. 根据权利要求1所述的一种滨海淤泥软土地基二次强夯碎石置换加固方法，其特征在于，所述步骤5具体为：在强夯置换地基的夯区中心区域附近埋设孔隙水压力计，孔隙水压力计埋设不少于3个，确定每个孔隙水压力计的高程、每个孔隙水压力计埋设高程间距为 2.0～3.0m，埋设好孔隙水压力计以后测定强夯开始前每个测点的孔隙水压力基准值
    Figure PCTCN2019123609-appb-100001
    其中i＝(1,…,N p)，N p是孔隙水压力计埋设的数量。
  3. 根据权利要求1所述的一种滨海淤泥软土地基二次强夯碎石置换加固方法，其特征在于，所述步骤6具体为：
    ①将强夯墩点分为2-3序，采用隔空分序跳打的方式完成全部夯点施工；
    ②起重机就位，采用直径1.5m～2.0m直径的点夯锤，使夯锤对准夯点位置，测量夯前锤顶高程，夯击能采用3000～4000kN·m，根据夯锤重量、夯锤直径和锤顶高程计算夯锤提升的设计高度，第一次强夯的夯锤提升设计高度按下式计算：
    Figure PCTCN2019123609-appb-100002
    式中：H 1第一次强夯夯锤提升设计高度；
    Figure PCTCN2019123609-appb-100003
    是第一次强夯的夯击能，可取3000～4000kN·m，m 1是一次强夯夯锤的质量；g是重力加速度；
    ③使用起重机将夯锤起吊到设计高度，解除夯锤挂钩使夯锤自由下落完成一遍夯击，测量锤顶高程，计算每遍夯沉量；
    ④将夯锤从夯坑中取出，当夯坑深度大于50cm时及时向夯坑内填加置换料将夯坑填平，置换料使用中风化至微风化的碎块石，碎块石最大粒径不大于300mm，最大粒径300mm的碎块石的含量不大于30％，碎块石不均匀系数大于5，含泥量小于5％；
    ⑤每个夯点重复步骤②～步骤④15遍以上，使墩长达到设计深度要求，完成每个墩点的第一次强夯施工；
    ⑥对各序的每个夯点重复步骤②～步骤⑤，连续进行夯击，各序之间不设时间间隔连续进行夯击施工，对最后两击的夯沉量也不做限定。
  4. 根据权利要求1所述的一种滨海淤泥软土地基二次强夯碎石置换加固方法，其特征在于，所述步骤7具体为：
    ①步骤6的第一次夯击完成时地基内的孔隙水压力达到最大值，夯墩由碎块石组成而形成排水通道，淤泥土层内的地下水由夯墩排水汇集在夯坑内；
    ②使用抽水设备抽排夯坑内的积水；
    ③使用埋设的孔隙水压力计测定场地的孔隙水压力值，每间隔8～12小时测量一次，并按下式计算孔隙水压力实测值相对与基准值的变化率：
    Figure PCTCN2019123609-appb-100004
    式中：其中i＝(1,…,N p)，N p是孔隙水压力计埋设的数量，m＝(1,2,3,…,N)，m是孔隙水压力测量次数，
    Figure PCTCN2019123609-appb-100005
    是强夯之前地基中第i个测点的孔隙水压力的基准值，
    Figure PCTCN2019123609-appb-100006
    是第一次夯击完成以后第i个测点第m次测量获得的地基孔隙水压力值，
    Figure PCTCN2019123609-appb-100007
    是第一次强夯完成以后第i个测点第m次测量获得的地基孔隙水压力值相对于初始基准值的变化率；
    ④当所有测点的
    Figure PCTCN2019123609-appb-100008
    均小于20％时，孔隙水压力消散完毕，停止测量孔隙水压力值，进入下一步骤。
  5. 根据权利要求1所述的一种滨海淤泥软土地基二次强夯碎石置换加固方法，其特征在于，所述步骤8具体为：
    ①第二次夯击不分序次，施工顺序从最中心的夯点向两侧施工；
    ②起重机就位，采用直径2.0m直径的点夯锤，使夯锤对准夯点位置，测量夯前锤顶高程，夯击能采用5000～6000kN·m，根据夯锤重量、夯锤直径和锤顶高程计算夯锤提升的设计高度；第二次强夯的夯锤提升设计高度按下式计算：
    Figure PCTCN2019123609-appb-100009
    式中：H 2第二次强夯夯锤提升设计高度；
    Figure PCTCN2019123609-appb-100010
    是第二次强夯的夯击能，可取5000～6000kN·m，m 2是二次强夯夯锤的质量；g是重力加速度；
    ③使用起重机将夯锤起吊到设计高度，解除夯锤挂钩使夯锤自由下落完成一遍夯击，测量锤顶高程，计算每遍夯击的夯沉量；
    ④将夯锤从夯坑中取出，当夯坑深度大于50cm时及时向夯坑内填加置换料将夯坑填平，置换料使用中风化至微风化的碎块石，碎块石最大粒径不大于300mm，最大粒径300mm的碎块石的含量不大于30％，碎块石不均匀系数大于5，含泥量小于5％；
    ⑤对场地的所有夯点重复步骤②至步骤④10～30遍，每个夯点的夯击遍数不小于10遍，当最后两遍的夯沉量须小于10cm时，完成夯点的第二次强夯施工。
  6. 根据权利要求1所述的一种滨海淤泥软土地基二次强夯碎石置换加固方法，其特征在于，所述步骤9具体为：
    ①挖除深度1.0～1.5m深度的浮土，并用强风化碎块石回填整平场地至基准标高，强风化碎块石最大粒径不大于300mm、碎块石的不均匀系数大于5、含泥量不大于5％；；
    ③满夯夯击使用直径2.4m、重20吨并带有气孔的夯锤，以夯击能2000kN·m进行所有夯点的满夯施工；
    ②满夯分两序进行，第一序夯击3遍，第二序夯击2遍，满夯的夯点之间相互搭接不小于1/3锤底直径；
    ④满夯完毕以后以10m×10m或20m×20m的方格网实测夯后标高。
PCT/CN2019/123609 2019-10-18 2019-12-06 一种滨海淤泥软土地基二次强夯碎石置换加固方法 WO2021072941A1 (zh)

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