The cement mixing pile is based on the chemical mechanism of cement hydration, and the soft soil and cement are forcedly mixed locally in the deep part of the stratum through a special deep mixing machine to harden the soft soil and increase the strength of the foundation. This method is suitable for the treatment of soft foundations. It has a significant effect on the treatment of soft clay foundations such as silty clay, silty clay and saturated soil. It can be put into use very quickly after treatment and has a fast construction speed; there is no noise and no noise during construction. Vibration, no pollution to the environment; investment province. In areas south of the Yangtze River in China, there is abundant rainfall and abundant groundwater content. The common treatment method for soft foundation treatment of building foundations is cement-soil mixing piles. Here we take a look at cement mixing pile construction quality and supervision and control rules.

Cement mixing pile construction quality and supervision and control rules

First, the type of cement mixing pile

Cement mixing pile is a widely used foundation reinforcement method. According to the chemical mechanism of cement hydration, there are mainly two construction techniques: one is to make cement into cement slurry on the ground first, and then send it to underground and foundation. After the earth is stirred, the physical and mechanical properties of the foundation soil are strengthened after the solidified; and the dry and loose cement powder is directly sent to the underground and the foundation soil by compressed air, and pore water in the foundation soil is used. After the hydration reaction, consolidation is performed again to achieve the purpose of improving the foundation. At present, China's cement mixing pile construction more "spray" process.

Second, the cement mixing pile construction quality control of the key and difficult

The construction quality of the cement mixing pile sealing curtain is directly related to the safety of the foundation pit and the surrounding environment (roads, buildings, etc.). Occurrence of subsidence of the surrounding road or uneven settlement of the building due to leakage of the foundation pit occurs from time to time. How to control the construction quality of cement mixing piles and ensure the safety of foundation pits and surrounding environment under the condition of “invisible and intangible” is the key work of quality control in the construction process.

1, prior control

1.1 Seriously review the construction organization design of the construction unit. According to the requirements of the design drawings and requirements, engineering geological data, JGJ79-2002 "Technical Specifications for Construction Foundation Treatment", carefully review the construction organization design submitted by the construction unit to determine the feasibility of the construction program. Carefully check the integrity of the incoming equipment and the employment permit for the staff. Mainly inspect the length of the pile pipe, the power of the pile driver, the rate of rise of the pile pipe, the computer recorder, the depth measuring device and the supporting equipment. The above conditions must meet the requirements of the construction process.

1.2 The mixing pile construction site should be leveled in advance to remove all obstacles (including large stones, roots, and household garbage) on the ground and underground. When the site is low, it should be backfilled with clay, and no backfills should be allowed.

1.3 Cement mixing piles should use qualified cement. Prior to use, the contractor shall submit samples of cement for inspection before they can be used.

1.4 In order to solve the large amount of cement mixing piles, large monitoring intensity, and the practical problems of on-site monitoring of the side-by-side difficulties in the whole process of pile-by-piling, in order to strengthen the on-site station and strengthen the quantity control of incoming materials, it should be introduced into the computer control system to form " The three-in-one complete supervision system of on-site station, material supervision, and computer monitoring, on the basis of strengthening the site supervision side station, controls cement entering the site according to the determined pile length and cement usage, and requires that all pile drivers be equipped with computers. Recorder and printing equipment to understand and control the amount of cement slurry, drilling speed, construction pile length, pile forming time and other parameters. The supervising engineer collects the computer record sheet every day, and checks the amount of cement entering the site and the pile foundation completed by the site supervision supervisor as a basis for signing the engineering quantity.

1.5 The cement mixing pile construction machinery must have good stability performance. All drilling rigs should be drilled by the supervision engineer and the project management department before inspection.

2. In-process control

Effective monitoring of cement mixing pile construction is the key to ensuring that the project quality meets the design requirements. Therefore, the following monitoring measures should be taken during site construction.

2.1 Determine the technical parameters and construction process, and do a good job of test piles. At the site of each test site, in accordance with the design requirements, review the actual geological conditions, to determine the length of the pile, the test piles of not less than 5, 7 days after the formation of piles to take light penetrating method, according to the number of touch probe to determine the strength of the pile, and Core-pulling was performed to observe the uniformity of stirring and shot-spraying, and the construction effects of various cement contents and construction processes were judged. After the test of the test pile is qualified, the important parameters such as the determination of the length of the pile, the stirring time, the descending speed, the lifting speed, and the cement content ratio are summed up, so that the large-area construction can be performed according to the parameters determined in summary.

2.2 Control of pile position and pile elevation

1 position. Before the construction, the construction unit will insert the pile mark at the center of the pile and check it by the surveying supervisor. The pile position deviation is not more than 50cm.

2 pile top, pile bottom elevation. It is required that the height of the pile bottom should be more than 10cm deep, and the height of the pile top must be more than 20cm.

3 deep verticality. During the construction of each pile, the verticality of the agitator shaft was measured with a metre according to the deflection of the guide frame and the verticality of the pile was measured indirectly. The deviation of the verticality of the pile shall not exceed 1.5%.

2.3 Cement Content and Slurry Control

1 pile cement content. The cement content of each pile is one of the key factors to ensure the quality. In order to strengthen the control, the total amount control method can be adopted to calculate and analyze the average cement consumption and the average working efficiency for each linear meter of each work bench. The estimated efficiency of the pile is compared. According to the cement content determined by the experimental pile, check the cement content of each pile.

2 Cement strength. According to the design requirements, it must be inspected before it can be used.

3 Slurry. Through the specific water-cement ratio of the specific barrel water volume, the amount of cement added to each pulp was determined. The prepared slurry must not be isolated and must not be left unattended for longer than 2 hours.

4 Mud mix uniformity. The slurry in the storage tank should be uniform, and the continuity should be ensured during the transportation. When the slurry is stirred, if the slurry transmission pipeline is blocked or burst, it should be organized and processed in time. If it is too long, the slurry should be changed.

2.4 In order to ensure that the mixing amount per meter of the pile and the amount of cement slurry meet the design requirements, the construction unit shall be equipped with a computer recorder in accordance with the requirements of the supervision engineer. At the same time, the site shall be equipped with grout gravimeter to prepare inspection engineers and project quality inspectors to check whether the cement slurry water-cement ratio meets the design requirements at any time.

2.5 Cement stirring pile construction uses "four jets and four stirrings" process. When drilling for the first time, it is strictly forbidden to bring submerged drills in order to avoid plugging the pipe with the slurry. The strict control of the lifting speed during construction shall not exceed 0.8m/min, the working current shall not exceed the rated value, and the spray pressure shall not be less than 0.4MPa. It is not allowed to stir the slurry pile head has not reached the top of the slurry has been mixed with the phenomenon. Once the slurry is stopped for any reason, the depth of interruption should be recorded in time when the spray is interrupted. Within 12 hours, take additional measures to deal with the accident, and fill the situation in the construction record. The additional spray overlap should be greater than 100cm, and more than 12 hours should be taken to make up the pile.

2.6 In order to ensure the quality of the cement mixing pile tip, pile top and pile body, the first time drilling and spraying should stay at the bottom of the pile for 30 seconds to carry out the grind pile end, and during the lift slurry lifting process, all are sprayed into the pile body, and Pile heads were piled at the top of the pile with a dwell time of 30 seconds. In the range of 1-1.5m in the top of the pile, shotcrete stirring is increased once. The elevation of the top surface of the pile formed is higher than the designed elevation by more than 20m.

2.7 In order to ensure that the cement in the pile body is uniform and continuous, front and back office operators are required to be relatively fixed and closely coordinated. When the slurry is stopped in the background, the front desk shall be promptly notified to prevent broken piles and lack of slurry.

2.8 Spraying time and stopping time should be strictly controlled during construction. After each pile is drilled, it shall be continuously operated without spraying the slurry. It is strictly forbidden to drill the pipe without spraying. The storage volume in the storage tank shall not be less than the amount of one pile plus 50 kg. If the storage volume is less than the above weight, the construction of the next pile shall not be carried out.

2.9 If the supervision engineer finds that the amount of shotcrete is insufficient during construction, the whole pile will be required to be re-stirred. The shot volume of the double-spray is not less than the designed amount.

3, after the detection

3.1 Quality Inspection during Construction

3.1.1 The supervisor shall check the construction record at any time and compare the construction process with the quality evaluation of cement mixing piles. For unqualified construction piles, measures such as supplementing piles or strengthening nearby construction piles should be taken according to the specific conditions such as location and quantity.

3.1.2 Testing cement mixing pile unit

1 The inspection and inspection of piles shall be selected by the supervisor, and the inspection shall be conducted in accordance with the requirements of the supervision engineer;

2 After the construction of the cement mixing pile unit is completed, 2% of the number of piles shall be taken for quality inspection of the piles. Generally, within 7 days after the piles are piled, the lightweight soil probe is used to drill the pile body soil samples, and the degree of mixing is observed. The strength of the pile body is determined by comparing the number of hitting probes (N10). The number of hits in the pile shall not be less than 35 hits/30cm. The depth of inspection shall generally be less than the height of the designed pile top and not exceed 4.0cm. If the piles are long, the light penetrators are used for detection. The result may not be accurate, and no detection effect can be achieved. The following methods can be used to detect:

a. According to 2% of the total number of roots for pitting, dig deep to 1m below the base surface, check the pile integrity, continuity and mixing uniformity;

b. Pull core testing for 0.5% mixing piles;

c. The test of the bearing capacity of single piles and composite foundations is carried out in locations where the foundations are relatively poor.

3 The contractor shall test the bearing capacity of single pile or composite pile foundation by static load method test according to the drawings or contract requirements. The bearing capacity of the foundation should meet the design requirements.

4 After penetration testing to detect piles with doubts on the strength of piles, according to supervision instructions to take the piles in the original state of soil and soil consolidation, the direct determination of the strength of the pile.

5 For piles with complex geological conditions or problems in construction, the load bearing test method shall be applied according to the supervision instructions to check the bearing capacity of the engineering piles.

6 For the section where the mixing piles are adjacent to each other in a stringent manner, several piles should be excavated to check the appearance quality when the piles are maintained to a certain age.

A. The pile body is even and uniform with no necking and sinking.

B, stirring evenly, no loose body.

C. The pile tops are evenly spaced and evenly spaced.

3.2 Cement mixing pile unit project acceptance

3.2.1 After the construction of the cement mixing pile unit project is completed, the construction unit shall apply for acceptance of the unit project on the basis of self-inspection. The acceptance is joint acceptance. The units participating in the acceptance include construction, design, supervision, owners, and supervision units as organizational units.

3.2.2 The construction unit shall prepare the hole-opening drawings, construction original records, test data of the mixing piles, covert acceptance visas for unit projects, unit project quality assessment forms, etc. for acceptance of the unit project. Before the acceptance, the pile foundation shall be cleaned and the elevation of the pile top shall be cleaned. The following 0.5m soil between piles reveals a complete pile head. After the inspection personnel inspected and approved the site, they signed the unit's covert acceptance visa form and the acceptance passed.

Conclusion: It has been proved by practice that the construction of cement mixing piles adopts a complete supervision system consisting of “stand-by-site station, material supervision, and computer monitoring”. It does a good job of pre-supervising supervision and control. It takes every construction step in the construction process and takes scientific and effective measures. The monitoring means can effectively control the pile quality of cement mixing piles after a good post-construction inspection of piles and achieve a better soft-base treatment effect. The above about cement mixing pile construction quality and supervision and control rules are briefly introduced here, I hope to help you. For more information, please visit this website. Stay tuned.

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