Ask for help Offshore silty soil layer excavation construction method

The landlord should introduce the stratum of the 6-meter foundation pit, and the 6-meter is silt? What is the soil layer of the foundation pit floor and 10 meters below? Even if there are no buildings around this foundation pit, the foundation pit also needs temporary support, and the silt is not self-stable, and the soil layer will slide frequently; Even in relatively good soils, it is impossible to excavate a vertical slope or a slope that is too steep.

The water table is 1 meter deep, precipitation or water blocking should be considered. What building? Is there a basement?

Yesterday, the field test, take the gravel soil and fill the topsoil, in the foundation pit to build a 10%-15% slope ramp, but in the process of refilling, the soil is unstable, resulting in interruption, according to the situation, experts on the feasibility of the construction of the gravel gravity retaining wall, according to the site situation, is being discussed, no results ......Hey......There is a tricky ......

Cement mixing pile is a better solution. I just read this information and think that steel sheet piles can also be driven to (4) silty clay. Need to calculate the bottom bulge and support problem, the span of 59 meters, I don't know which one has the experience of support?

If there are no buildings around, the terrain is gentle, dig a little bigger, let go of the digging, and finally build the structure. If the conditions are not met, it is necessary to support it.

This belongs to the foundation pit support, the surrounding cast-in-place pile, the middle reinforced mesh concrete wall, with the well point precipitation, while the construction of the slope protection, the construction period can be guaranteed.

Silt excavation construction plan:

According to the actual investigation of the site and the construction conditions formed, it is difficult to dig and transport the silt directly, so it was decided to fill the construction road (pile number K2 + 380 K2 + 710) with ballast along the edge line of both sides outside the road construction red line. The width of the road is 6m, the left side is 290m long (deducting the width of the intersection 40m), the right side is long and deducting the width of the intersection, a total length, the ballast filling according to the construction experience of the previous stage, considering that the settlement on the mud layer is very large, the road is filled deep, and the depth of the filling road can be determined by burying the settlement plate, and the slag is filled. A long-arm excavator with a length of more than 19 meters is used to dig out the mud from the middle to both sides of the construction road, and the mud can be basically dug out within the construction red line.

Transported out of the car to paint the mud. The fluidity of the mud is very large, and the excavation in the construction area, and the mud below the 60m outside the red line are flowing to the excavation face. If the road is deep enough, it can also play a role in blocking the mud outside the red line.

This pavement can also be effectively used when filling the sand cushion in the later stage.

During the construction of the sidewalk, the silt is excavated to the elevation according to the slope of 1:5, and then backfilled with slag, backfilled with slag while excavating, the first layer of slag is filled according to the filling, and the second layer and the third layer are filled in time after settlement until it can meet the heavy vehicle walking. After the soft foundation treatment is completed, the slag backfill is carried out into the preloading period, and the excess material above the elevation of the sidewalk is dug up and transported to the designated place.

The foundation pit drainage is used to reduce the water level, considering the poor bearing capacity of this kind of silt soil and the abundance of groundwater, a temporary drainage ditch is made on both sides of the side line, which is 1m wide and deep. Water is pumped every day to lower the water level.

According to the requirements of the headquarters and the opinions of the design institute, the elevation to which the excavation is carried out first and the thick sand cushion is filled. The sand cushion may be difficult to bear the weight of the drainage sheet pile driver, it is recommended to lay a layer of geotextile under the sand cushion to increase the bearing capacity.

Excavation construction in three sections, excavation in sections, and backfill in sections.

1. Precipitation construction plan.

The top of the foundation pit slope should be slightly higher than the periphery to avoid the peripheral rainwater from flowing into the pit. Foundation pit earthwork construction layered excavation, and each layer of soil first arranged collection well pumping, pumping in place before excavation, excavation depth to do not appear surface water is appropriate. Therefore, before earthwork construction, a ring drainage ditch should be set around the foundation pit, and the longitudinal and transverse drainage ditch should be appropriately set up in the foundation pit according to the water volume situation on the site during construction, with a cross-section of 200mmx300mm, and a layer of pebbles at the bottom of the ditch.

A water collection well is set up every 30m-40m in the annular drainage ditch, with a cross-section of 500mmx800mm, and the water is pumped with a submersible pump.

Second, earthwork excavation.

Earthwork excavation should pay attention to the following matters:

1. When excavating earthwork, it must be strictly in accordance with the principle of "layering, first supporting and then digging", and the depth of each excavation is controlled at about 1 meter to ensure that in the excavation process, there will be no surface water due to local excavation too deep.

When excavating to the base elevation, if there is an over-excavation phenomenon, the earthwork backfill shall not be used, and the gravel must be filled with yellow sand.

2. Safety requirements.

After the excavation begins, protective railings are set around the foundation pit, and the railing structure well meets the safety requirements of edge and hole operation.

Excavation must be carried out in strict accordance with the procedures stipulated in the national code, carefully check the reliability of the pit wall and enclosure before each layer of excavation, and conduct regular testing and inspection throughout the construction process.

Cables should be used for the power, canal and lighting wires entering the pit, and their direction should be arranged according to the requirements of the construction plan, and there should be reliable fixing on the pit wall.

Yes, definitely. Soft soil is a general term for muck and mucky soil. It is mainly composed of natural silt sediments with high water content, high compressibility and low bearing capacity and a small amount of humus.

Soft soil refers to the fine-grained soil with high water content, large porosity ratio, high compressibility and low shear strength deposited in coastal, lake marsh, valley and river beach. It has the characteristics of high natural water content, large natural porosity ratio, high compressibility, low shear strength, small consolidation coefficient, long consolidation time, high sensitivity, large perturbation, poor permeability, complex distribution of soil layers, and large differences in physical and mechanical properties between layers.

The detailed process of earthwork excavation:

1. The basement is excavated in the order of the construction area, and the handover is carried out after the pile foundation bearing capacity test is qualified, and the monomer is fully excavated.

2. The excavation of the basement foundation pit should be carried out only after the supporting structure (net spray, spray anchor, pile) reaches the strength.

Step 1: Level the site, measure the elevation of the site, and place the positioning control line.

The second step: excavate the first layer of supporting slope soil in sections, with an excavation width of about 15m, and then interspersed with sprayed concrete construction on the slope surface by the enclosure construction team, and excavate a layer of support and a layer of circular construction.

Step 3: The excavation of the basement earthwork section is divided into three layers for construction. The last layer is dug to the bottom of the foundation pit, and the manual cleaning and trimming are carried out, and the thickness of the soil is 30cm.

Step 4: Finally, the treatment of the ramp earthwork of the earth-moving vehicle in the foundation pit is relayed by two excavators, and the excavator in the pit concentrates on transferring the soil to the ramp mouth, and the excavator at the top of the pit is loaded with soil and loading the vehicle. Finally, the excavator in the pit is lifted from the bottom of the pit by a truck crane (or excavated to the extra part of the foundation groove, and the excavator is backfilled after it comes out.

The fifth step: bind the foundation floor steel bar and column, shear wall reinforcement and pour the bottom plate concrete.

Step 6: Construction of the negative layer structure.

The seventh step: do the waterproof layer, the protective layer, the basement structure after the completion of the acceptance, after the completion of the second layer of the main body and then carry out the foundation pit outside the earthwork backfill.

3. Foundation pit earthwork bottoming construction method:

1) when the mechanical excavation elevation reaches 30cm from the design height, it must be followed up and trimmed by manual groove cleaning flow, and the control of the elevation at the bottom of the foundation pit should be based on the datum point provided by the owner, and the horizontal height will be measured by the surveying technician to the more stable structure around the foundation pit, and make obvious signs, the elevation point should keep up with the excavation progress, and a point should be measured at 3 5m on the fan-shaped working face.

2) the construction technician will be the level elevation to the surrounding engineering pile near the elevation of the bottom of the foundation pit, and make a mark, or mark with a small wooden pile, painted with red paint, the elevation of the pile top is the elevation of the cushion layer, that is, the excavation depth of the earthwork is 30cm below the pile top.

3) excavation construction personnel adopt fixed measuring tools according to the measurement mark, and the earthwork at the bottom of the pit is repaired and leveled.

To prevent mechanical into the groove or artificial disturbance of the foundation, the elevation of the bottom of the pit should be strictly controlled, and no over-excavation should be allowed.

1. Take precipitation first, bai In general, DU should first understand the underground.

After the precipitation level is calculated, the precipitation well is constructed, and the underground water level is reduced below the basement, and then the foundation groove is excavated.

2. The project is 11 meters deep and belongs to the construction of dangerous projects stipulated in the construction safety construction regulations. A special construction plan should be prepared.

3. The more dangerous project refers to the seven sub-projects referred to in Article 26 of the Regulations on the Administration of Work Safety in Construction Projects, and the special safety construction plan shall be prepared separately before construction.

1) Foundation pit support and dewatering engineering.

Foundation pit support engineering refers to the excavation depth of more than 5m (including 5m) of the foundation pit (groove) and the use of supporting structure construction; or although the foundation pit does not exceed 5m, the geological conditions and surrounding environment are complex, and the groundwater level is above the bottom of the pit.

2) Earthwork excavation works.

Earthwork excavation refers to the earthwork excavation of foundation pits and grooves with an excavation depth of more than 5m (including 5m).

4. At the same time, the construction enterprise shall organize experts to demonstrate the construction plan.

Article 5 Construction enterprises shall organize an expert group to conduct a demonstration and review of the project.

1) Deep foundation pit engineering.

The excavation depth is more than 5m (including 5m) or the basement is more than three floors (including three floors), or the depth is not more than 5m (including 5m), but the geological conditions, the surrounding environment and the underground pipeline are extremely complex.

5. The support plan is comprehensively considered according to different geological conditions and the surrounding environment, and it should be cautious.

It is strongly recommended that you follow the above procedures for construction, otherwise, if there is a problem, you cannot afford it.

In the specification GB50007-2002, there is such a clause: "Article Silt is a cohesive soil deposited in a still water or slow flowing water environment and formed by biochemical action, with a natural water content greater than the liquid limit and a natural porosity ratio greater than or equal to." When the natural water content is greater than the liquid limit and the natural porosity ratio is less than but greater than or equal to the cohesive soil or silt soil, it is silty soil. ”

The silt texture stratum has flow plasticity, which should not only prevent the diameter shrinkage due to insufficient internal support pressure caused by underbalance, but also prevent the formation softening and shrinking due to overequilibrium, and the pressure of the mud in the hole should be balanced with the in-situ stress in the depth of the hole. Therefore, it is necessary to prepare a reasonable proportion of mud to ensure that the mud in circulation quickly forms a dense mud skin. The pressure of the mud and the strong mud skin are used to balance the pressure of the formation, which can easily cause collapse.

1. Mud specific gravity design.

The specific gravity of mud should be controlled when trenchless pipe laying.

Because the silt stratum is soft, the Poisson's ratio is large, and the necking degree is significantly higher than that of the conventional stratum during reaming, the specific gravity of silty soil should be taken as far as possible. To prepare a large specific gravity slurry, it can be directly aggravated by increasing the amount of bentonite, but excessive bentonite will increase the viscosity and shear force of the mud, resulting in the mud not meeting the requirements in terms of fluidity. Moreover, the gravity of bentonite is not high, and the effect of increasing the specific gravity of mud is not significant.

Therefore, special weighting agents are generally used to aggravate the mud.

Silty soil is not silt or thin mud or the like, as long as the surrounding conditions allow, it is completely possible to slope and excavate. According to the naked eye, silty soil is a consolidated and non-flowing silt, which is theoretically a soil with a natural porosity ratio greater than 1 and less than.

According to the nature of the soil, the biggest difference between silt and silty soil is that the natural porosity ratio is different: the porosity ratio greater than is called silt, and the one greater than 1 and less than is called silty soil, but the natural moisture content is greater than the liquid limit, and the silt belongs to the unconsolidated and flowing soil.

Water content is the ratio of the mass of water in the soil to the mass of the soil particles, expressed as a percentage in units of 1. That is: w = (MW ms) 100% The moisture content of the natural soil layer is an indicator of the humidity of the soil, and its range of variation is very large, it is related to the type of soil, burial conditions, etc., generally dry coarse sand, its value is close to zero, and saturated sand can reach 40%; The water content of hard clay is about less than 30%, while the water content of saturated soft clay can reach more than 100%.

Generally, the same type of soil has a low strength if it has a high water content. Liquid limit wl: The water content of the soil when it changes from a plastic state to a liquid state (flow state).

At this time, in addition to the bound water, there is also free water in the soil. The unit of natural liquid limit and water content are the same thing, and the unit in percentage form is 1.

Silty silty clay is a cohesive soil with a natural moisture content greater than the liquid limit and a natural porosity ratio.

This soil is mainly found in the southeast coastal areas of China and along and around rivers, rivers and lakes in the Chinese mainland. Due to the high compressibility and low strength of the foundation, the settlement of the foundation is large, and most of it is uneven. It is easy to cause cracks in walls and buildings to overturn.

In the construction of the project, we must pay enough attention.

The natural porosity ratio of silty silty clay is greater than or equal to 1 and less than. Peat soil is an organic soil that accumulates in a moist and oxygen-deficient environment without completely decaying plant remains. The organic matter content is WU 60%.

It has a high water content, great compressibility, and unevenness. Generally not suitable for natural foundations and need to be treated.